Table of contents

Nearly every massive galaxy harbors a supermassive black hole (SMBH) in its nucleus. SMBH masses are millions to billions of solar mass, and they correlate with properties of spheroids of their host galaxies. While the SMBH growth channels, mergers, and gas accretion are well established, their origin remains uncertain: they could have emerged either from massive "seeds" (10⁵–10⁶M_⊙) formed by direct collapse of gas clouds in the early universe or from smaller (100 M_⊙) BHs, end products of first stars. The latter channel would leave behind numerous intermediate-mass BHs (IMBHs, 10²–10⁵M_⊙). Although many IMBH candidates have been identified, none are accepted as definitive; thus, their very existence is still debated. Using data mining in wide-field sky surveys and applying dedicated analysis to archival and follow-up optical spectra, we identified a sample of 305 IMBH candidates having masses $3\times {10}^{4}\,{M}_{\odot }\lt {M}_{\mathrm{BH}}\lt 2\times {10}^{5}\,{M}_{\odot }$, which reside in galaxy centers and are accreting gas that creates characteristic signatures of a type I active galactic nucleus (AGN). We confirmed the AGN nature of 10 sources (including five previously known objects that validate our method) by detecting the X-ray emission from their accretion disks, thus defining the first bona fide sample of IMBHs in galactic nuclei. All IMBH host galaxies possess small bulges and sit on the low-mass extension of the ${M}_{\mathrm{BH}}\mbox{--}{M}_{\mathrm{bulge}}$ scaling relation, suggesting that they must have experienced very few if any major mergers over their lifetime. The very existence of nuclear IMBHs supports the stellar-mass seed scenario of the massive BH formation.

We report the first detections of the repeating fast radio burst source FRB 121102 above 5.2 GHz. Observations were performed using the 4–8 GHz receiver of the Robert C. Byrd Green Bank Telescope with the Breakthrough Listen digital backend. We present the spectral, temporal, and polarization properties of 21 bursts detected within the first 60 minutes of a total of 6 hr of observations. These observations comprise the highest burst density yet reported in the literature, with 18 bursts being detected in the first 30 minutes. A few bursts clearly show temporal sub-structure with distinct spectral properties. These sub-structures superimpose to provide an enhanced peak signal-to-noise ratio at higher trial dispersion measures. Broad features occur in ∼1 GHz wide subbands that typically differ in peak frequency between bursts within the band. Finer-scale structures (∼10–50 MHz) within these bursts are consistent with the structure expected from Galactic diffractive interstellar scintillation. The bursts exhibit nearly 100% linear polarization, and a large average rotation measure of 9.359 ± 0.012 × 10⁴ rad m⁻² (in the observer's frame). No circular polarization was found for any burst. We measure an approximately constant polarization position angle in the 13 brightest bursts. The peak flux densities of the reported bursts have average values (0.2 ± 0.1 Jy) similar to those seen at lower frequencies (<3 GHz), while the average burst widths (0.64 ± 0.46 ms) are relatively narrower.

The imidogen radical is an important molecule of the chemistry of nitrogen in the interstellar medium and is thought to be a key intermediate in the gas-phase synthesis of ammonia. The full fine structure of the $N=1\leftarrow 0$ rotational transition of ${}^{15}\mathrm{NH}$ has been observed for the first time by pure rotational spectroscopy around 1 THz. The radical has been produced by means of low-pressure glow discharge of H₂ and ${}^{15}{\rm{N}}$-enriched nitrogen. A number of hyperfine components have been observed and accurately measured. The analysis of the data provided very precise spectroscopic constants, which include rotational, centrifugal distortion, electron spin–spin interaction, and electron spin–rotation terms in addition to the hyperfine parameters relative to the isotropic and anisotropic electron spin–nuclear spin interactions for ¹⁵N and H and to the nuclear spin–rotation for ¹⁵N. The efficiency of the discharge system allowed us to observe several components of the same rotational transition in the excited vibrational state v = 1, for which a set of spectroscopic constants has also been determined.

We present chemical abundances of 15 stars in the γ Leo moving group based on high-resolution spectra with the Subaru High Dispersion Spectrograph. The sample was picked up by applying wavelet transform to UVW velocity components of stars in the solar neighborhood. Both photometric and spectroscopic method have been used to determine the stellar parameters of stars. Abundances of 11 elements including Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Y, and Ba are measured. Our results show that the member stars display a wide metallicity distribution with abundance ratios similar to Milky Way disk stars. We presume that the γ Leo moving group originated from dynamical effects that are probably related to the Galactic spiral arms.

Luminous red nova transients, presumably from stellar coalescence, exhibit long-term precursor emission over hundreds of binary orbits, leading to impulsive outbursts with durations similar to a single orbital period. In an effort to understand these signatures, we present and analyze a hydrodynamic model of unstable mass transfer from a giant-star donor onto a more compact accretor in a binary system. Our simulation begins with mass transfer at the Roche limit separation and traces a phase of runaway decay leading to the plunge of the accretor within the envelope of the donor. We characterize the fluxes of mass and angular momentum through the system and show that the orbital evolution can be reconstructed from measurements of these quantities. The morphology of outflow from the binary changes significantly as the binary orbit tightens. At wide separations, a thin stream of relatively high-entropy gas trails from the outer Lagrange points. As the orbit tightens, the orbital motion desynchronizes from the donor's rotation, and low-entropy ejecta trace a broad fan of largely ballistic trajectories. An order-of-magnitude increase in mass ejection rate accompanies the plunge of the accretor with the envelope of the donor. We argue that this transition marks the precursor-to-outburst transition observed in stellar coalescence transients.

With the recent discoveries of terrestrial planets around active M-dwarfs, destruction processes masking the possible presence of life are receiving increased attention in the exoplanet community. We investigate potential biosignatures of planets having Earth-like (N₂–O₂) atmospheres orbiting in the habitable zone of the M-dwarf star AD Leo. These are bombarded by high energetic particles that can create showers of secondary particles at the surface. We apply our cloud-free 1D climate-chemistry model to study the influence of key particle shower parameters and chemical efficiencies of NOx and HOx production from cosmic rays. We determine the effect of stellar radiation and cosmic rays upon atmospheric composition, temperature, and spectral appearance. Despite strong stratospheric O₃ destruction by cosmic rays, smog O₃ can significantly build up in the lower atmosphere of our modeled planet around AD Leo related to low stellar UVB. The abundance of N₂O decreases with increasing flaring energies but a sink reaction for N₂O with excited oxygen becomes weaker, stabilizing its abundance. CH₄ is removed mainly by Cl in the upper atmosphere for the strong flaring cases and not via hydroxyl as is otherwise usually the case. Cosmic rays weaken the role of CH₄ in heating the middle atmosphere so that H₂O absorption becomes more important. We additionally underline the importance of HNO₃ as a possible marker for strong stellar particle showers. In a nutshell, uncertainty in NOx and HOx production from cosmic rays significantly influences the abundance of biosignatures and spectral appearance.

We explore the masses, merger rates, eccentricities, and spins for field binary black holes (BHs) driven to merger by a third companion through the Lidov–Kozai mechanism. Using a population synthesis approach, we model the creation of stellar-mass BH triples across a range of different initial conditions and stellar metallicities. We find that the production of triple-mediated mergers is enhanced at low metallicities by a factor of ∼100 due to the lower BH natal kicks and reduced stellar mass loss. These triples naturally yield heavy binary BHs with near-zero effective spins, consistent with most of the mergers observed to date. This process produces a merger rate of between 2 and 25 Gpc⁻³ yr⁻¹ in the local universe, suggesting that the Lidov–Kozai mechanism can potentially explain all of the low-spin, heavy BH mergers observed by Advanced LIGO/Virgo. Finally, we show that triples admit a unique eccentricity and spin distribution that will allow this model to be tested in the near future.

Ray tracing is a central tool for constructing mock observations of compact object emission and for comparing physical emission models with observations. We present Arcmancer, a publicly available general ray-tracing and tensor algebra library, written in C++ and providing a Python interface. Arcmancer supports Riemannian and semi-Riemannian spaces of any dimension and metric, and has novel features such as support for multiple simultaneous coordinate charts, embedded geometric shapes, local coordinate systems, and automatic parallel propagation. The Arcmancer interface is extensively documented and user friendly. While these capabilities make the library well suited for a large variety of problems in numerical geometry, the main focus of this paper is in general relativistic polarized radiative transfer. The accuracy of the code is demonstrated in several code tests and in a comparison with grtrans, an existing ray-tracing code. We then use the library in several scenarios as a way to showcase the wide applicability of the code. We study a thin variable-geometry accretion disk model and find that polarization carries information of the inner disk opening angle. Next, we study rotating neutron stars and determine that to obtain polarized light curves at better than a $\sim 1 \%$ level of accuracy, the rotation needs to be taken into account both in the spacetime metric and in the shape of the star. Finally, we investigate the observational signatures of an accreting black hole lensed by an orbiting black hole. We find that these systems exhibit a characteristic asymmetric twin-peak profile both in flux and polarization properties.

Swift J0243.6+6124 is a newly discovered Galactic Be/X-ray binary, revealed in late 2017 September in a giant outburst with a peak luminosity of 2 × 10³⁹(d/7 kpc)² erg s⁻¹ (0.1–10 keV), with no formerly reported activity. At this luminosity, Swift J0243.6+6124 is the first known galactic ultraluminous X-ray pulsar. We describe Neutron star Interior Composition Explorer (NICER) and Fermi Gamma-ray Burst Monitor (GBM) timing and spectral analyses for this source. A new orbital ephemeris is obtained for the binary system using spin frequencies measured with GBM and 15–50 keV fluxes measured with the Neil Gehrels Swift Observatory Burst Alert Telescope to model the system's intrinsic spin-up. Power spectra measured with NICER show considerable evolution with luminosity, including a quasi-periodic oscillation near 50 mHz that is omnipresent at low luminosity and has an evolving central frequency. Pulse profiles measured over the combined 0.2–100 keV range show complex evolution that is both luminosity and energy dependent. Near the critical luminosity of L ∼ 10³⁸ erg s⁻¹, the pulse profiles transition from single peaked to double peaked, the pulsed fraction reaches a minimum in all energy bands, and the hardness ratios in both NICER and GBM show a turnover to softening as the intensity increases. This behavior repeats as the outburst rises and fades, indicating two distinct accretion regimes. These two regimes are suggestive of the accretion structure on the neutron star surface transitioning from a Coulomb collisional stopping mechanism at lower luminosities to a radiation-dominated stopping mechanism at higher luminosities. This is the highest observed (to date) value of the critical luminosity, suggesting a magnetic field of B ∼ 10¹³ G.

X-ray lines of helium-like calcium (Ca xix) between 3.17 and 3.21 Å and associated Ca xviii dielectronic satellites have previously been observed in solar flare spectra, and their excitation mechanisms are well established. Dielectronic satellites of lower-ionization stages (Ca xvii–Ca xv) are not as well characterized. Several spectra during a large solar flare in 2001 by the DIOGENESS X-ray spectrometer on the CORONAS-F spacecraft show the Ca xvii and Ca xvi satellites, as well as lines of ionized argon (Ar xvii, Ar xvi), including dielectronic satellites. The DIOGENESS spectra are compared with spectra from a synthesis code developed here based on an isothermal assumption with various atomic sources including dielectronic satellite data from the Cowan Hartree–Fock code. Best-fit comparisons are made by varying the temperature as the code's input (Ar/Ca abundance ratio fixed at 0.33); close agreement is achieved, although with adjustments to some ion fractions. The derived temperature is close to that derived from the two GOES X-ray channels, T_GOES. Some lines are identified for the first time. Similar spectra from the P78-1 spacecraft and the Alcator C-Mod tokamak have also been analyzed and similar agreements were obtained. The importance of blends of calcium and argon lines is emphasized, affecting line ratios used for temperature diagnostics. This analysis will be applied to the Solar Maximum Mission Bent Crystal Spectrometer archive and to X-ray spectra expected from the ChemiX instrument on the Sun-orbiting Interhelioprobe spacecraft, while the relevance to X-ray spectra from non-solar sources is indicated.

We use the sky-average spectrum measured by EDGES High-band (90–190 MHz) to constrain parameters of early galaxies independent of the absorption feature at 78 MHz reported by Bowman et al. These parameters represent traditional models of cosmic dawn and the epoch of reionization produced with the 21cmFAST simulation code. The parameters considered are (1) the UV ionizing efficiency (ζ); (2) minimum halo virial temperature hosting efficient star-forming galaxies (${T}_{\mathrm{vir}}^{\min }$); (3) integrated soft-band X-ray luminosity (${L}_{{\rm{X}}\lt 2\mathrm{keV}}/\mathrm{SFR}$); and (4) minimum X-ray energy escaping the first galaxies (E₀), corresponding to a typical H i column density for attenuation through the interstellar medium. The High-band spectrum disfavors high values of ${T}_{\mathrm{vir}}^{\min }$ and ζ, which correspond to signals with late absorption troughs and sharp reionization transitions. It also disfavors intermediate values of ${L}_{{\rm{X}}\lt 2\mathrm{keV}}/\mathrm{SFR}$, which produce relatively deep and narrow troughs within the band. Specifically, we rule out $39.4\lt {\mathrm{log}}_{10}({L}_{{\rm{X}}\lt 2\mathrm{keV}}/\mathrm{SFR})\lt 39.8$ (95% C.L.). We then combine the EDGES High-band data with constraints on the electron-scattering optical depth from Planck and the hydrogen neutral fraction from high-z quasars. This produces a lower degeneracy between ζ and ${T}_{\mathrm{vir}}^{\min }$ than that reported by Greig & Mesinger using the Planck and quasar constraints alone. Our main result in this combined analysis is the estimate $4.5\leqslant {\mathrm{log}}_{10}({T}_{\mathrm{vir}}^{\min }/{\rm{K}})\leqslant 5.7$ (95% C.L.). We leave the evaluation of 21 cm models using simultaneously data from EDGES Low- and High-band for future work.

Mixing in the convective core is quite uncertain in core helium-burning stars. To explore the overshooting mixing beyond the convective core, we incorporated the k–ω proposed by Li into the Modules of Experiments in Stellar Astrophysics (MESA), and investigated the overshooting mixing in evolution of subdwarf B (sdB) models. We found that the development of the convective core can be divided into three stages. When the radiative temperature gradient, ${{\rm{\nabla }}}_{\mathrm{rad}}$, monotonically decreases outwardly, the overshooting mixing presents exponential decay similar with Herwig, and the overshooting distance is to make ${{\rm{\nabla }}}_{\mathrm{rad}}\simeq {{\rm{\nabla }}}_{\mathrm{ad}}$ at the boundary of the convective core, in agreement with the prediction of the self-driving mechanism Castellani et al. When the radiative temperature gradient, ${{\rm{\nabla }}}_{\mathrm{rad}}$, shows a minimum value near the convective boundary, the convective core may be divided into two if the minimum value of ${{\rm{\nabla }}}_{\mathrm{rad}}$ is smaller than the adiabatic temperature gradient ${{\rm{\nabla }}}_{\mathrm{ad}}$. For the single-zone case, the overshooting mixing shows exponential decay, but the overshooting distance is much smaller than in the initial stage. For the double-zone case, the overshooting mixing is similar to that of the single case beyond the convective core, while it almost stops on both sides of the above convective shell. Our overshooting mixing scheme is similar to the maximal overshoot scheme of Constantino et al. In the final stage, helium injections into the convective core by the overshooting mixing happens, similar to the "core breathing pulses."

We analyze Herschel Space Observatory observations of 104 young stellar objects with protoplanetary disks in the ∼1.5 Myr star-forming region Lynds 1641 (L1641) within the Orion A Molecular Cloud. We present spectral energy distributions from the optical to the far-infrared including new photometry from the Herschel Photodetector Array Camera and Spectrometer at 70 μm. Our sample, taken as part of the Herschel Orion Protostar Survey, contains 24 transitional disks, 8 of which we identify for the first time in this work. We analyze the full disks (FDs) with irradiated accretion disk models to infer dust settling properties. Using forward modeling to reproduce the observed ${n}_{{K}_{S}-[70]}$ index for the FD sample, we find the observed disk indices are consistent with models that have depletion of dust in the upper layers of the disk relative to the midplane, indicating significant dust settling. We perform the same analysis on FDs in Taurus with Herschel data and find that Taurus is slightly more evolved, although both samples show signs of dust settling. These results add to the growing literature that significant dust evolution can occur in disks by ∼1.5 Myr.

There is a long history of using optical emission and absorption lines to constrain the metallicity and ionization parameters of gas in galaxies. However, comparable diagnostics are less well developed for the ultraviolet (UV). Here, we assess the diagnostic potential of both absorption and emission features in the UV and evaluate the diagnostics against observations of local and high-redshift galaxies. We use the Flexible Stellar Population Synthesis (FSPS) nebular emission model of Byler et al., extended to include emission predictions in the UV, to evaluate the metallicity sensitivity of established UV stellar absorption indices and to identify those that include a significant contribution from nebular emission. We present model UV emission-line fluxes as a function of metallicity and ionization parameter, assuming both instantaneous bursts and constant star formation rates. We identify combinations of strong emission lines that constrain metallicity and ionization parameters, including [C iii] λ1907, C iii] λ1909, O iii] λ1661,1666, Si iii] λ1883,1892, C ivλ1548,1551, N ii] λ1750,1752, and Mg iiλ2796, and we develop UV versions of the canonical "Baldwin Phillips Terlevich" diagram. We quantify the relative contribution from stellar wind emission and nebular line emission to diagnostic line ratios that include the C ivλ1548,1551 lines, and we also develop an observationally motivated relationship for N and C enrichment that improves the performance of photoionization models. We summarize the best diagnostic choices and the associated redshift range for low-, mid-, and high-resolution rest-UV spectroscopy in preparation for the launch of the James Webb Space Telescope.

Sagittarius A* (Sgr A*) is the variable radio, near-infrared (NIR), and X-ray source associated with accretion onto the Galactic center black hole. We present an analysis of the most comprehensive NIR variability data set of Sgr A* to date: eight 24 hr epochs of continuous monitoring of Sgr A* at 4.5 μm with the IRAC instrument on the Spitzer Space Telescope, 93 epochs of 2.18 μm data from Naos Conica at the Very Large Telescope, and 30 epochs of 2.12 μm data from the NIRC2 camera at the Keck Observatory, in total 94,929 measurements. A new approximate Bayesian computation method for fitting the first-order structure function extracts information beyond current fast Fourier transformation (FFT) methods of power spectral density (PSD) estimation. With a combined fit of the data of all three observatories, the characteristic coherence timescale of Sgr A* is ${\tau }_{b}={243}_{-57}^{+82}$ minutes (90% credible interval). The PSD has no detectable features on timescales down to 8.5 minutes (95% credible level), which is the ISCO orbital frequency for a dimensionless spin parameter a = 0.92. One light curve measured simultaneously at 2.12 and 4.5 μm during a low flux-density phase gave a spectral index α_s = 1.6 ± 0.1 (${F}_{\nu }\propto {\nu }^{-{\alpha }_{s}}$). This value implies that the Sgr A* NIR color becomes bluer during higher flux-density phases. The probability densities of flux densities of the combined data sets are best fit by log-normal distributions. Based on these distributions, the Sgr A* spectral energy distribution is consistent with synchrotron radiation from a non-thermal electron population from below 20 GHz through the NIR.

The Hubble Space Telescope/WFC3 multiband photometry spanning from the UV to the near-IR of four fields in the Galactic bulge, together with that for six template globular and open clusters, are used to photometrically tag the metallicity [Fe/H] of stars in these fields after proper-motion rejecting most foreground disk contaminants. Color–magnitude diagrams and luminosity functions (LF) are then constructed, in particular for the most metal-rich and most metal-poor stars in each field. We do not find any significant difference between the I-band and H-band LFs, hence turnoff luminosity and age of the metal-rich and metal-poor components therefore appear essentially coeval. In particular, we find that no more than ∼3% of the metal-rich component can be ∼5 Gyr old, or younger. Conversely, theoretical LFs match well to the observed ones for an age of ∼10 Gyr. Assuming this age is representative for the bulk of bulge stars, we then recall the observed properties of star-forming galaxies at 10 Gyr lookback time, i.e., at z ∼ 2, and speculate about bulge formation in that context. We argue that bar formation and buckling instabilities leading to the observed boxy/peanut, X-shaped bulge may have arisen late in the history of the Milky Way Galaxy, once its gas fraction had decreased compared to the high values typical of high-redshift galaxies. This paper follows the public release of the photometric and astrometric catalogs of the measured stars in the four fields.

By a method of population synthesis we construct a model of dark matter (DM) accretion onto binary black holes (BHs) and investigate the merger rate of the binary BHs. We find that the merger rate can weakly increase (less than 10%). However, the DM accretion can efficiently enhance the masses of binary BHs. In our model, the result for Z = 0.01 without the DM accretion cannot explain GW170104, GW170814, and GW150914, while with the DM accretion it can cover all observations well. For the higher metallicity (Z = 0.02), our model cannot explain the mergers of high-mass binary BHs like GW170104, GW170814, and GW150914. We estimate that the merger rate of binary BHs lies between 55 and 197 Gpc⁻³ yr⁻¹.

We study particle acceleration at the termination shock of a striped pulsar wind by integrating trajectories in a prescribed model of the magnetic field and flow pattern. Drift motion on the shock surface maintains either electrons or positrons on "Speiser" orbits in a ring-shaped region close to the equatorial plane of the pulsar, enabling them to be accelerated to very high energy by the first-order Fermi mechanism. A power-law spectrum results: ${{dN}}_{{\rm{e}}}/d\gamma \propto {\gamma }^{{\alpha }_{{\rm{e}}}}$, where α_e lies in the range −1.8 to −2.4 and depends on the downstream turbulence level. For sufficiently strong turbulence, we find α_e ≃ −2.2, and both the photon index and the flux of 1–100 keV X-rays from the Crab Nebula, as measured by NuSTAR, can be reproduced. The particle spectrum hardens to α_e ≃ −1.8 at lower turbulence levels, which may explain the hard photon index observed by the Chandra X-ray Observatory in the central regions of the Nebula.

We have observed the submillimeter continuum condensation SMM4 in Serpens Main using the Atacama Large Millimeter/submillimeter Array during its Cycle 3 in 1.3 mm continuum, ¹²CO J = 2–1, SO J_N = 6₅–5₄, and C¹⁸O J = 2–1 lines at angular resolutions of ∼055 (240 au). The 1.3 mm continuum emission shows that SMM4 is spatially resolved into two protostars embedded in the same core: SMM4A showing a high brightness temperature, 18 K, with little extended structure and SMM4B showing a low brightness temperature, 2 K, with compact and extended structures. Their separation is ∼2100 au. Analysis of the continuum visibilities reveals a disk-like structure with a sharp edge at r ∼ 240 au in SMM4A, and a compact component with a radius of 56 au in SMM4B. The ¹²CO emission traces fan-shaped and collimated outflows associated with SMM4A and SMM4B, respectively. The blue and red lobes of the SMM4B outflow have different position angles by ∼30°. Their inclination and bending angles in the 3D space are estimated at i_b ∼ 36°, i_r ∼ 70°, and α ∼ 40°, respectively. The SO emission traces shocked regions, such as cavity walls of outflows and the vicinity of SMM4B. The C¹⁸O emission mainly traces an infalling and rotating envelope around SMM4B. The C¹⁸O fractional abundance in SMM4B is ∼50 times smaller than that of the interstellar medium. These results suggest that SMM4A is more evolved than SMM4B. Our studies in Serpens Main demonstrate that continuum and line observations at millimeter wavelengths allow us to differentiate evolutionary phases of protostars within the Class 0 phase.

We present the discovery by the SPitzer InfraRed Intensive Transients Survey (SPIRITS) of a likely supernova (SN) in NGC 3556 (M108) at only 8.8 Mpc that was not detected by optical searches. A luminous infrared (IR) transient at M_[4.5] = −16.7 mag (Vega), SPIRITS 16tn is coincident with a dust lane in the inclined, star-forming disk of the host. Using observations in the IR, optical, and radio, we attempt to determine the nature of this event. We estimate A_V ≈ 8–9 mag of extinction, placing it among the three most highly obscured IR-discovered SNe. The [4.5] light curve declined at a rate of 0.013 mag day⁻¹, and the [3.6]–[4.5] color increased from 0.7 to ≳1.0 mag by 184.7 days post discovery. Optical/IR spectroscopy shows a red continuum but no clearly discernible features, preventing a definitive spectroscopic classification. Radio observations constrain the radio luminosity of SPIRITS 16tn to L_ν ≲ 10²⁴ erg s⁻¹ Hz⁻¹ between 3 and 15 GHz, excluding many varieties of core-collapse SNe. An SN Ia is ruled out by the observed IR color and lack of spectroscopic features from Fe-peak elements. SPIRITS 16tn was fainter at [4.5] than typical stripped-envelope SNe by ≈1 mag. Comparison of the spectral energy distribution to SNe II suggests that SPIRITS 16tn was both highly obscured and intrinsically dim, possibly akin to the low-luminosity SN 2005cs. We infer the presence of an IR dust echo powered by an initial peak luminosity of the transient of 5 × 10⁴⁰ erg s⁻¹ ≲ L_peak ≲ 4 × 10⁴³ erg s⁻¹, consistent with the observed range for SNe II. This discovery illustrates the power of IR surveys to overcome the compounding effects of visible extinction and optically subluminous events in completing the inventory of nearby SNe.

We present the rest-frame UV and optical photometry and morphology of low-redshift broad-line quasar host galaxies from the Sloan Digital Sky Survey Reverberation Mapping project. Our sample consists of 103 quasars at z < 0.8, spanning a luminosity range of −25 ≤ M_g ≤ −17 mag. We stack the multi-epoch images in the g and i bands taken by the Canada–France–Hawaii Telescope. The combined g-band (i-band) images reach a 5σ depth of 26.2 (25.2) mag, with a typical point-spread function (PSF) size of 07 (06). Each quasar is decomposed into a PSF and a Sérsic profile, representing the components of the central active galactic nucleus (AGN) and the host galaxy, respectively. The systematic errors of the measured host galaxy flux in the two bands are 0.23 and 0.18 mag. The relative errors of the measured galaxy half-light radii (R_e) are about 13%. We estimate the rest-frame u- and g-band flux of the host galaxies, and find that the AGN-to-galaxy flux ratios in the g band are between 0.9 and 4.4 (68.3% confidence). These galaxies have high stellar masses ${M}_{\ast }={10}^{10}\mbox{--}{10}^{11}\,{M}_{\odot }$. They have similar colors to star-forming galaxies at similar redshifts, which is consistent with AGN positive feedback in these quasars. We find that the ${M}_{* }\mbox{--}{M}_{\mathrm{BH}}$ relation in our sample is shallower than the local M_Bulge–M_BH relation. The Sérsic indices and the M_*–R_e relation indicate that the majority of the host galaxies are disk-like.

We present an analysis of the binary-lens microlensing event OGLE-2017-BLG-0537. The light curve of the event exhibits two strong caustic-crossing spikes among which the second caustic crossing was resolved by high-cadence surveys. It is found that the lens components with a mass ratio ∼0.5 are separated in projection by $\sim 1.3{\theta }_{{\rm{E}}}$, where θ_E is the angular Einstein radius. Analysis of the caustic-crossing part yields ${\theta }_{{\rm{E}}}=1.77\pm 0.16$ mas and a lens-source relative proper motion of μ = 12.4 ± 1.1 mas yr⁻¹. The measured μ is the third highest value among the events with measured proper motions and is ∼3 times higher than the value of typical Galactic bulge events, making the event a strong candidate for follow-up observations to directly image the lens by separating it from the source. From the angular Einstein radius combined with the microlens parallax, it is estimated that the lens is composed of two main-sequence stars with masses M₁ ∼ 0.4 M_⊙ and M₂ ∼ 0.2 M_⊙ located at a distance of D_L ∼ 1.2 kpc. However, the physical lens parameters are not very secure due to the weak microlens-parallax signal, thus we cross-check the parameters by conducting a Bayesian analysis based on the measured Einstein radius and event timescale, combined with the blending constraint. From this, we find that the physical parameters estimated from the Bayesian analysis are consistent with those based on the measured microlens parallax. Resolving the lens from the source can be done in about 5 years from high-resolution follow-up observations and this will provide a rare opportunity to test and refine the microlensing model.

Microlensing is a powerful and unique technique to probe isolated objects in the Galaxy. To study the characteristics of these interesting objects based on the microlensing method, measurement of the microlens parallax is required to determine the properties of the lens. Of the various methods to measure microlens parallax, the most routine way is to make simultaneous ground- and space-based observations, i.e., by measuring the space-based microlens parallax. However, space-based campaigns usually require "expensive" resources. Gould & Yee (2012) proposed an idea called the "cheap space-based microlens parallax" that can measure the lens-parallax using only two or three space-based observations of high-magnification events (as seen from Earth). This cost-effective observation strategy to measure microlens parallaxes could be used by space-borne telescopes to build a complete sample for studying isolated objects. This would enable a direct measurement of the mass function including both extremely low-mass objects and high-mass stellar remnants. However, to adopt this idea requires a test to check how it would work in actual situations. Thus, we present the first practical test of this idea using the high-magnification microlensing event OGLE-2016-BLG-1045, for which a subset of Spitzer observations fortuitously duplicates the prescription of Gould & Yee (2012). From the test, we confirm that the measurement of the lens-parallax adopting this idea has sufficient accuracy to determine the physical properties of the isolated lens.

We present nebular phase optical and near-infrared spectroscopy of the Type Ia supernova (SN) 2017cbv. The early light curves of SN 2017cbv showed a prominent blue bump in the U, B, and g bands lasting for ∼5 days. One interpretation of the early light curve is that the excess blue light is due to shocking of the SN ejecta against a nondegenerate companion star—a signature of the single degenerate scenario. If this is the correct interpretation, the interaction between the SN ejecta and the companion star could result in significant Hα (or helium) emission at late times, possibly along with other species, depending on the companion star and its orbital separation. A search for Hα emission in our +302 d spectrum yields a nondetection, with a L_Hα < 8.0 × 10³⁵ erg s⁻¹ (given an assumed distance of D = 12.3 Mpc), which we verified by implanting simulated Hα emission into our data. We make a quantitative comparison to models of swept-up material stripped from a nondegenerate companion star and limit the mass of hydrogen that might remain undetected to M_H < 1 × 10⁻⁴M_⊙. A similar analysis of helium star related lines yields a M_He < 5 × 10⁻⁴M_⊙. Taken at face value, these results argue against a nondegenerate H- or He-rich companion in Roche lobe overflow as the progenitor of SN 2017cbv. Alternatively, there could be weaknesses in the envelope-stripping and radiative transfer models necessary to interpret the strong H and He flux limits.

We present deep Magellan/Megacam stellar photometry of four recently discovered faint Milky Way satellites: Sagittarius II (Sgr II), Reticulum II (Ret II), Phoenix II (Phe II), and Tucana III (Tuc III). Our photometry reaches ∼2–3 magnitudes deeper than the discovery data, allowing us to revisit the properties of these new objects (e.g., distance, structural properties, luminosity measurements, and signs of tidal disturbance). The satellite color-magnitude diagrams show that they are all old (∼13.5 Gyr) and metal poor ([Fe/H] ≲ −2.2). Sgr II is particularly interesting, as it sits in an intermediate position between the loci of dwarf galaxies and globular clusters in the size–luminosity plane. The ensemble of its structural parameters is more consistent with a globular cluster classification, indicating that Sgr II is the most extended globular cluster in its luminosity range. The other three satellites land directly on the locus defined by Milky Way ultra-faint dwarf galaxies of similar luminosity. Ret II is the most elongated nearby dwarf galaxy currently known for its luminosity range. Our structural parameters for Phe II and Tuc III suggest that they are both dwarf galaxies. Tuc III is known to be associated with a stellar stream, which is clearly visible in our matched-filter stellar density map. The other satellites do not show any clear evidence of tidal stripping in the form of extensions or distortions. Finally, we also use archival H i data to place limits on the gas content of each object.

We develop a new method, Stars' Galactic Origin (StarGO), to identify the galactic origins of halo stars using their kinematics. Our method is based on a self-organizing map (SOM), which is one of the most popular unsupervised learning algorithms. StarGO combines SOM with a novel adaptive group identification algorithm with essentially no free parameters. To evaluate our model, we build a synthetic stellar halo from mergers of nine satellites in the Milky Way. We construct the mock catalog by extracting a heliocentric volume of 10 kpc from our simulations and assigning expected observational uncertainties corresponding to bright stars from Gaia DR2 and LAMOST DR5. We compare the results from StarGO against those from a friends-of-friends-based method in the space of orbital energy and angular momentum. We show that StarGO is able to systematically identify more satellites and achieve higher number fraction of identified stars for most of the satellites within the extracted heliocentric volume. When applied to data from Gaia DR2, StarGO will enable us to reveal the origins of the inner stellar halo in unprecedented detail.

Three periastron passages of the PSR B1259−63/LS 2883 binary system, consisting of a 48 ms rotation-powered pulsar and a Be star, have been observed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope, in 2010, 2014, and 2017. During the most recent periastron passage, sustained low-level gamma-ray emission was observed over a ∼3-week-long interval immediately after periastron, which was followed by an interval of no emission. Sporadic flares were detected starting 40 days post-periastron and lasted approximately 50 days, during which the emission displayed significant spectral curvature, variability on timescales as short as 1.5 minutes, and peak flux levels well in excess of the pulsar spin-down power. By contrast, during the 2010 and 2014 periastron passages, significant gamma-ray emission was not observed with the LAT until 30 and 32 days post-periastron, respectively. The previous flares did not exhibit spectral curvature, showed no short term variability, and did not exceed the pulsar spin-down power. The high flux and short timescales observed in 2017 suggest significant beaming of the emission is required and constrain the size of the emission region. The flares occur long enough after periastron that the neutron star should already have passed through the extended disk-like outflow, thus constraining options for target material and seed photon sources for inverse Compton models.

The Shocked POststarburst Galaxy Survey (SPOGS) aims to identify galaxies in the transitional phase between actively star-forming and quiescence with nebular lines that are excited from shocks rather than star formation processes. We explored the ultraviolet (UV) properties of objects with near-ultraviolet (NUV) and far-ultraviolet (FUV) photometry from archival GALEX data; 444 objects were detected in both bands, 365 in only the NUV, and 24 in only the FUV, for a total of 833 observed objects. We compared SPOGs to samples of star-forming galaxies (SFs), quiescent galaxies (Qs), classical E+A post-starburst galaxies, active galactic nuclei (AGN) host galaxies, and interacting galaxies. We found that SPOGs have a larger range in their FUV–NUV and NUV–r colors compared with most of the other samples, although all of our comparison samples occupied color space inside of the SPOGs region. On the basis of their UV colors, SPOGs are a heterogeneous group, possibly made up of a mixture of SFs, Qs, and/or AGN. Using Gaussian mixture models, we are able to recreate the distribution of FUV–NUV colors of SPOGs and E + A galaxies with different combinations of SFs, Qs, and AGN. We find that the UV colors of SPOGs require a >60% contribution from SFs, with either Qs or AGN representing the remaining contribution, while UV colors of E + A galaxies required a significantly lower fraction of SFs, supporting the idea that SPOGs are at an earlier point in their transition from quiescent to star-forming than E + A galaxies.

We investigate the magnetic characteristics of a persistent coronal hole (CH) extracted from EUV imagery using Heliospheric and Magnetic Imager filtergrams over the period 2012 February–October. The magnetic field, its distribution, and the magnetic fine structure in the form of flux tubes (FTs) are analyzed in different evolutionary states of the CH. We find a strong linear correlation between the magnetic properties (e.g., signed/unsigned magnetic field strength) and the area of the CH. As such, the evolutionary pattern in the magnetic field clearly follows a three-phase evolution (growing, maximum, and decaying) as found from EUV data (Part I). This evolutionary process is most likely driven by strong FTs with a mean magnetic field strength exceeding 50 G. During the maximum phase they entail up to 72% of the total signed magnetic flux of the CH, but only cover up to 3.9% of the total CH area, whereas during the growing and decaying phases, strong FTs entail 54%–60% of the signed magnetic flux and cover around 1%–2% of the CH's total area. We conclude that small-scale structures of strong unipolar magnetic field are the fundamental building blocks of a CH and govern its evolution.

The recent HAWC observations of a very-high-energy γ-ray halo around Geminga and Monogem indicate a very slow diffusion of cosmic rays that results in a tiny contribution of positrons from these two pulsars to the local flux. This makes the cosmic positron excess anomaly observed by PAMELA and AMS-02 even more puzzling. However, from the boron-to-carbon ratio data one can infer that the average diffusion coefficient in the Galaxy should be much larger. In this work we propose a two-zone diffusion model in which the diffusion is slow only in a small region around the source, outside of which the propagation is as fast as usual. We find that this scenario can naturally explain the positron excess data with parameters even more reasonable than those in the conventional one-zone diffusion model. The reason is that during the lifetime of Geminga (∼300 kyr), the electrons/positrons have propagated too far away with a fast diffusion and led to a low local flux. The slow-diffusion region in the two-zone model helps to confine the electrons/positrons for a long time and lead to an enhancement of the local flux. So under the constraint of the HAWC observations, pulsars are still the probable origin of the cosmic-ray positron excess.

To characterize the meteoroid environment around Mercury and its contribution to the planet's exosphere, we combined four distinctive sources of meteoroids in the solar system: main-belt asteroids, Jupiter-family comets, Halley-type comets, and Oort Cloud comets. All meteoroid populations are described by currently available dynamical models. We used a recent calibration of the meteoroid influx onto Earth as a constraint for the combined population model on Mercury. We predict vastly different distributions of orbital elements, impact velocities, and directions of arrival for all four meteoroid populations at Mercury. We demonstrate that the most likely model of Mercury's meteoroid environment—in the sense of agreement with Earth—provides good agreement with previously reported observations of Mercury's exosphere by the MESSENGER spacecraft and is not highly sensitive to variations of uncertain parameters such as the ratio of these populations at Earth, the size–frequency distribution, and the collisional lifetime of meteoroids. Finally, we provide a fully calibrated model consisting of high-resolution maps of mass influx and surface vaporization rates for different values of Mercury's true anomaly angle.

Relativistic supernovae constitute a subclass of Type Ic supernovae (SNe). Their nonthermal, radio emission differs notably from that of regular Type Ic supernovae as they have a fast expansion speed (with velocities ∼0.6–0.8 c) which cannot be explained by a "standard" spherical SN explosion, but advocates for a quickly evolving, mildly relativistic ejecta associated with the SN. In this paper, we compute the synchrotron radiation emitted by the cocoon of a long gamma-ray burst jet (GRB). We show that the energy and velocity of the expanding cocoon, and the radio nonthermal light curves and spectra are consistent with those observed in relativistic SNe. Thus, the radio emission from this events is not coming from the SN shock front, but from the mildly relativistic cocoon produced by the passage of a GRB jet through the progenitor star. We also show that the cocoon radio emission dominates the GRB emission at early times for GRBs seen off-axis, and the flux can be larger at late times compared with on-axis GRBs if the cocoon energy is at least comparable with respect to the GRB energy.

We present an analytical model to investigate the production of pebbles and their radial transport through a protoplanetary disk (PPD) with magnetically driven winds. While most of the previous analytical studies in this context assumed that the radial turbulent coefficient is equal to the vertical dust diffusion coefficient, in the light of the results of recent numerical simulations, we relax this assumption by adopting effective parameterizations of the turbulent coefficients involved, in terms of the strength of the magnetic fields driving the wind. Theoretical studies have already pointed out that even in the absence of winds, these coefficients are not necessarily equal, though how this absence affects pebble production has not been explored. In this paper, we investigate the evolution of the pebble production line, the radial mass flux of the pebbles, and their corresponding surface density as a function of the plasma parameter at the disk midplane. Our analysis explicitly demonstrates that the presence of magnetically driven winds in a PPD leads to considerable reduction of the rate and duration of the pebble delivery. We show that when the wind is strong, the core growth in mass due to the pebble accretion is so slow that it is unlikely that a core could reach a pebble isolation mass during a PPD lifetime. When the mass of a core reaches this critical value, pebble accretion is halted due to core-driven perturbations in the gas. With decreasing wind strength, however, pebble accretion may, in a shorter time, increase the mass of a core to the pebble isolation mass.

Here, we use synthetic data to explore the performance of forward models and inverse methods for helioseismic holography. Specifically, this work presents the first comprehensive test of inverse modeling for flows using lateral-vantage (deep-focus) holography. We derive sensitivity functions in the Born approximation. We then use these sensitivity functions in a series of forward models and inversions of flows from a publicly available magnetohydrodynamic quiet-Sun simulation. The forward travel times computed using the kernels generally compare favorably with measurements obtained by applying holography, in a lateral-vantage configuration, on a 15 hr time series of artificial Dopplergrams extracted from the simulation. Inversions for the horizontal flow components are able to reproduce the flows in the upper 3 Mm of the domain, but are compromised by noise at greater depths.

The periods of magnetic activity cycles in the Sun and solar-type stars do not exhibit a simple or even single trend with respect to rotation rate or luminosity. Dynamo models can be used to interpret this diversity and can ultimately help us understand why some solar-like stars do not exhibit a magnetic cycle, whereas some do, and for the latter what physical mechanisms set their magnetic cycle period. Three-dimensional nonlinear MHD simulations present the advantage of having only a small number of tunable parameters, and produce in a dynamically self-consistent manner the flows and the dynamo magnetic fields pervading stellar interiors. We conduct a series of such simulations within the EULAG-MHD framework, varying the rotation rate and luminosity of the modeled solar-like convective envelopes. We find decadal magnetic cycles when the Rossby number near the base of the convection zone is moderate (typically between 0.25 and 1). Secondary, shorter cycles located at the top of the convective envelope close to the equator are also observed in our numerical experiments, when the local Rossby number is lower than 1. The deep-seated dynamo sustained in these numerical experiments is fundamentally nonlinear, in that it is the feedback of the large-scale magnetic field on the large-scale differential rotation that sets the magnetic cycle period. The cycle period is found to decrease with the Rossby number, which offers an alternative theoretical explanation to the variety of activity cycles observed in solar-like stars.

Recent limitations in the TiO line list used in cross-correlation detection schemes have made the detection and quantification of TiO in exoplanetary atmospheres challenging. The quality of the line list appears to degrade at wavelengths shorter than 630 nm. The C${}^{3}{\rm{\Delta }}$–X${}^{3}{\rm{\Delta }}$ electronic transition has strong rovibronic bands near 500 nm. In an effort to improve the line list, a spectrum of TiO in a furnace at 1950 K is analyzed, and the assigned lines of the C${}^{3}{\rm{\Delta }}$–X${}^{3}{\rm{\Delta }}$ transition are fit with the ${\hat{N}}^{2}$ Hamiltonian in the molecular spectrum fitting software, PGOPHER. Several newly determined molecular constants are reported and the average error in fitting the line positions is 0.017 cm⁻¹ or ∼1 ppm relative error. The new line positions are expected to resolve any problems with cross-correlation templates near 500 nm.

Observations and numerical simulations have shown that the relation between the mass scaled with the critical density of the universe and the X-ray temperature of galaxy clusters is approximately represented by ${M}_{{\rm{\Delta }}}\propto {T}_{X}^{3/2}$ (e.g., ${\rm{\Delta }}=500$). This relation is often interpreted as evidence that clusters are in virial equilibrium. However, the recently discovered fundamental plane (FP) of clusters indicates that the temperature of clusters primarily depends on a combination of the characteristic mass M_s and radius r_s of the Navarro–Frenk–White profile rather than M_Δ. Moreover, the angle of the FP revealed that clusters are not in virial equilibrium because of continuous mass accretion from the surrounding matter. By considering both the FP and the mass dependence of the cluster concentration parameter, we show that this paradox can be solved and the relation ${M}_{{\rm{\Delta }}}\propto {T}_{X}^{3/2}$ actually reflects the central structure of clusters. We also find that the intrinsic scatter in the halo concentration–mass relation can largely account for the spread of clusters on the FP. We also show that X-ray data alone form the FP and the angle and the position are consistent with those of the FP constructed from gravitational lensing data. We demonstrate that a possible shift between the two FPs can be used to calibrate cluster masses obtained via X-ray observations.

We use deep Hubble Space Telescope (HST) WFC3/IR imaging to study the initial mass function (IMF) of the ultra-faint dwarf galaxy Coma Berenices (Com Ber). Our observations reach the lowest stellar mass ever probed in a resolved galaxy, with 50% completeness at ∼0.17 M_⊙. Unresolved background galaxies, however, limit our purity below ∼0.23 M_⊙. If modeled with a single power law, we find that the IMF slope is $-{1.45}_{-0.3}^{+0.29}$ (68% credible intervals), compared to a Milky Way value of −2.3. For a broken power law, we obtain a low-mass slope of $-{1.18}_{-0.33}^{+0.49}$, a high-mass slope of $-{1.88}_{-0.49}^{+0.43}$, and a break mass of ${0.57}_{-0.08}^{+0.12}$M_⊙, compared to −1.3, −2.3, and 0.5 M_⊙ for a Kroupa IMF, and for a log-normal IMF model, we obtain values of ${0.33}_{-0.16}^{+0.15}$M_⊙ for the location parameter and of ${0.68}_{-0.12}^{+0.17}$ for σ (0.22 M_⊙ and 0.57 for the Chabrier system IMF). All three parameterizations produce similar agreement with the data. Our results agree with previous analyses of shallower optical HST data. However, an analysis of similar optical data of other dwarfs finds IMFs significantly more bottom-light than in the Milky Way. These results suggest two, non-mutually exclusive possibilities: that the discrepancy of the dwarf galaxies' IMF with respect to the Milky Way is at least partly an artifact of using a single-power-law model, and that there is real variance in the IMF at low masses between the currently studied nearby dwarfs, with Com Ber being similar to the Milky Way, but other dwarfs differing significantly.

Accurate inferences of solar meridional flow are crucial for understanding solar dynamo processes. Wave travel times, as measured on the surface, will change if the waves encounter perturbations, e.g., in the sound speed or flows, as they propagate through the solar interior. Using functions called sensitivity kernels, we can image the underlying anomalies that cause measured shifts in travel times. The inference of large-scale structures, e.g., meridional circulation, requires computing sensitivity kernels in spherical geometry. Mandal et al. have computed such spherical kernels in the limit of the first-Born approximation. In this work, we perform an inversion for meridional circulation using travel-time measurements obtained from 6 years of Solar Dynamics Observatory/Helioseismic and Magnetic Imager data and those sensitivity kernels. We enforce mass conservation by inverting for a stream function. The number of free parameters is reduced by projecting the solution onto cubic B-splines in radius and derivatives of the Legendre-polynomial basis in latitude, thereby improving the condition number of the inverse problem. We validate our approach for synthetic observations before performing the actual inversion. The inversion suggests a single-cell profile with a return flow occurring at depths below 0.78 R_⊙.

We investigate the dynamical evolution of galaxies in groups with different formation epochs. Galaxy groups have been selected to be in different dynamical states, namely dynamically old and dynamically young, which reflect their early and late formation times, respectively, based on their halo mass assembly. The brightest galaxies in dynamically young groups have suffered their last major galaxy merger typically ∼2 Gyr more recently than their counterparts in dynamically old groups. Furthermore, we study the evolution of velocity dispersion in these two classes and compare them with the analytic models of isolated halos. The velocity dispersion of dwarf galaxies in high-mass, dynamically young groups increases slowly in time, while the analogous dispersion in dynamically old, high-mass groups is constant. In contrast, the velocity dispersion of giant galaxies in low-mass groups decreases rapidly at late times. This increasing velocity bias is caused by dynamical friction, and starts much earlier in the dynamically old groups. The recent Radio-SAGE model of galaxy formation suggests that radio luminosities of central galaxies, considered to be tracers of AGN activity, are enhanced in halos that assembled more recently, independent of the time since the last major merger.

The relative magnetic helicity is a quantity that is often used to describe the level of entanglement of non-isolated magnetic fields, such as the magnetic field of solar active regions. The aim of this paper is to investigate how different kinds of photospheric boundary flows accumulate relative magnetic helicity in the corona and if and how well magnetic-helicity-related quantities identify the onset of an eruption. We use a series of three-dimensional, parametric magnetohydrodynamic simulations of the formation and eruption of magnetic flux ropes. All the simulations are performed on the same grid, using the same parameters, but they are characterized by different driving photospheric flows, i.e., shearing, convergence, stretching, and peripheral- and central- dispersion flows. For each of the simulations, the instant of the onset of the eruption is carefully identified by using a series of relaxation runs. We find that magnetic energy and total relative helicity are mostly injected when shearing flows are applied at the boundary, while the magnetic energy and helicity associated with the coronal electric currents increase regardless of the kind of photospheric flows. We also find that, at the onset of the eruptions, the ratio between the non-potential magnetic helicity and the total relative magnetic helicity has the same value for all the simulations, suggesting the existence of a threshold in this quantity. Such a threshold is not observed for other quantities as, for example, those related to the magnetic energy.

We use a hybrid observational/theoretical approach to study the relation between galaxy kinematics and the derived stellar and halo masses of galaxies up to z = 3 as a function of stellar mass, redshift, and morphology. Our observational sample consists of a concatenation of 1125 galaxies with kinematic measurements at 0.4 < z < 3 from long-slit and integral field studies. We investigate several ways to measure halo masses from observations based on results from semi-analytical models, showing that galaxy halo masses can be retrieved with a scatter of ∼0.4 dex by using only stellar masses. We discover a third parameter, relating to the time of the formation of the halo, that reduces the scatter in the relation between the stellar and halo masses such that systems forming earlier have a higher stellar mass–to–halo mass ratio, which we also find observationally. We find that this scatter correlates with morphology such that early-type or older stellar systems have higher M_*/M_halo ratios. We furthermore show, using this approach and through weak lensing and abundance matching, that the ratio of stellar to halo mass does not significantly evolve with redshift at 1 < z < 3. This is evidence for the regulated hierarchical assembly of galaxies such that the ratio of stellar to dark matter mass remains approximately constant since z = 2. We use these results to show that the dark matter accretion rate evolves from dM_halo/dt ∼ 4000 ${M}_{\odot }$ yr⁻¹ at z ∼ 2.5 to a few 100 ${M}_{\odot }$ yr⁻¹ by z ∼ 0.5.

Ring galaxies are fascinating laboratories: a catastrophic impact between two galaxies (one not much smaller than the other) has produced fireworks, especially in the larger one, when hit roughly perpendicularly to the plane. We analyze the point sources produced by the starburst episode following the impact in the rings of seven galaxies and determine their X-ray luminosity function (XLF). In total, we detect 63 sources, of which 50 have luminosity L_X ≥ 10³⁹ erg s⁻¹, classifying them as ultraluminous X-ray sources (ULXs). We find that the total XLF is not significantly different from XLFs derived for other kinds of galaxies, with a tendency of having a larger fraction of high X-ray luminosity objects. Both the total number of ULXs and the number of ULXs per unit star formation rate are found in the upper envelope of the more normal galaxies distribution. Further analysis would be needed to address the issue of the nature of the compact component in the binary system.

We present the first part of our Disks ARound T Tauri Stars with SPHERE (DARTTS-S) survey: observations of eight T Tauri stars that were selected based on their strong (sub)millimeter excesses using SPHERE/IRDIS polarimetric differential imaging in the J and H bands. All observations successfully detect the disks, which appear vastly different in size, from ≈80 au in scattered light to >400 au, and display total polarized disk fluxes between 0.06% and 0.89% of the stellar flux. For five of these disks, we are able to determine the three-dimensional structure and the flaring of the disk surface, which appears to be relatively consistent across the different disks, with flaring exponents α between ≈1.1 and ≈1.6. We also confirm literature results with regard to the inclination and position angle of several of our disks and are able to determine which side is the near side of the disk in most cases. While there is a clear trend of disk mass with stellar ages (≈1 to >10 Myr), no correlations of disk structures with age were found. There are also no correlations with either stellar mass or submillimeter flux. We do not detect significant differences between the J and H bands. However, we note that while a high fraction (7/8) of the disks in our sample show ring-shaped substructures, none of them display spirals, in contrast to the disks around more massive Herbig Ae/Be stars, where spiral features are common.

The planets of our solar system formed from a gas-dust disk. However, there are some properties of the solar system that are peculiar in this context. First, the cumulative mass of all objects beyond Neptune (trans-Neptunian objects [TNOs]) is only a fraction of what one would expect. Second, unlike the planets themselves, the TNOs do not orbit on coplanar, circular orbits around the Sun, but move mostly on inclined, eccentric orbits and are distributed in a complex way. This implies that some process restructured the outer solar system after its formation. However, some of the TNOs, referred to as Sednoids, move outside the zone of influence of the planets. Thus, external forces must have played an important part in the restructuring of the outer solar system. The study presented here shows that a close fly-by of a neighboring star can simultaneously lead to the observed lower mass density outside 30 au and excite the TNOs onto eccentric, inclined orbits, including the family of Sednoids. In the past it was estimated that such close fly-bys are rare during the relevant development stage. However, our numerical simulations show that such a scenario is much more likely than previously anticipated. A fly-by also naturally explains the puzzling fact that Neptune has a higher mass than Uranus. Our simulations suggest that many additional Sednoids at high inclinations still await discovery, perhaps including bodies like the postulated planet X.

Zonal flows in rotating systems have been previously shown to be suppressed by the imposition of a background magnetic field aligned with the direction of rotation. Understanding the physics behind the suppression may be important in systems found in astrophysical fluid dynamics, such as stellar interiors. However, the mechanism of suppression has not yet been explained. In the idealized setting of a magnetized beta plane, we provide a theoretical explanation that shows how magnetic fluctuations directly counteract the growth of weak zonal flows. Two distinct calculations yield consistent conclusions. The first, which is simpler and more physically transparent, extends the Kelvin–Orr shearing wave to include magnetic fields and shows that a weak, long-wavelength shear flow organizes magnetic fluctuations to absorb energy from the mean flow. The second calculation, based on the quasilinear, statistical CE2 framework, is valid for arbitrary wavelength zonal flow and predicts a self-consistent growth rate of the zonal flow. We find that a background magnetic field suppresses zonal flow if the bare Alfvén frequency is comparable to or larger than the bare Rossby frequency. However, suppression can occur for even smaller magnetic fields if the resistivity is sufficiently small enough to allow sizable magnetic fluctuations. Our calculations reproduce the $\eta /{B}_{0}^{2}=\mathrm{const}.$ scaling that describes the boundary of zonation, as found in previous work, and we explicitly link this scaling to the amplitude of magnetic fluctuations.

We present a long-term light curve of the precataclysmic variable (CV) V1082 Sgr obtained by the K2 mission over the course of 81 days. We analyze the entire complex light curve as well as explore several sections in detail with a sliding periodogram. The long data set allows the first detection of the orbital period in the light curve, as well as the confirmation of cyclical variability on a longer timescale of about a month. A portion of the light curve in deep minimum reveals a clean, near-sinusoidal variability attributed to the rotation of the spotted surface of the donor star. We model that portion of the light curve assuming that the donor star grossly under-fills its Roche lobe, has cool spots similar to a chromospherically active, slightly evolved early K-star, and might be irradiated by the X-ray beam from the magnetically accreting white dwarf. The fast variability of the object in the active phases resembles the light curves of magnetic CVs (polars).

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a novel transit radio telescope operating across the 400–800 MHz band. CHIME is composed of four 20 m × 100 m semicylindrical paraboloid reflectors, each of which has 256 dual-polarization feeds suspended along its axis, giving it a ≳200 deg² field of view. This, combined with wide bandwidth, high sensitivity, and a powerful correlator, makes CHIME an excellent instrument for the detection of fast radio bursts (FRBs). The CHIME Fast Radio Burst Project (CHIME/FRB) will search beam-formed, high time and frequency resolution data in real time for FRBs in the CHIME field of view. Here we describe the CHIME/FRB back end, including the real-time FRB search and detection software pipeline, as well as the planned offline analyses. We estimate a CHIME/FRB detection rate of 2–42 FRBs sky^–1 day^–1 normalizing to the rate estimated at 1.4 GHz by Vander Wiel et al. Likely science outcomes of CHIME/FRB are also discussed. CHIME/FRB is currently operational in a commissioning phase, with science operations expected to commence in the latter half of 2018.

Galactic winds and fountains driven by supernova-heated gas play an integral role in redistributing gas in galaxies, depositing metals in the circumgalactic medium, and quenching star formation. The interplay between these outflows and ram-pressure stripping (RPS) due to the galaxy's motion through an ambient medium may enhance these effects by converting fountain flows into expelled gas. In this paper, we present controlled, 3D simulations of RPS combined with thermally driven, local outflows from clustered supernovae in an isolated disk galaxy modeled on the Large Magellanic Cloud (LMC), a dwarf satellite of the Milky Way on its first infall. Observational evidence of local outflows emanating from supergiant shells in the LMC and a trailing filament of H i gas originating from these regions—with no obvious Leading Arm counterpart—may represent a perfect example of this process. Our simulations present a proof of concept that ram pressure can convert fountain flows into expelled gas. We find that fountains launched near the peak star formation time of the LMC can comprise part of the LMC filament in the Trailing Stream but with lower column densities than observed. Larger, more numerous outflows from the LMC may be possible and may contribute more mass, but higher-inertia gas will lengthen the timescale for this gas to be swept away by ram pressure. Given the high-resolution observations, increased knowledge of star formation histories, and growing evidence of multiphase ionized outflows, the LMC is an ideal test bed for future wind models.

Well-sampled optical light curves of 50 gamma-ray bursts (GRBs) with plateau features are compiled from the literature. By empirical fitting, we obtained the parameters of the optical plateaus, such as the decay slopes (α₁ and α₂), the break times (T_b), and the corresponding optical fluxes (F_b) at the break times. The break time of optical plateaus ranges from tens of seconds to 10⁶ s, with a typical value of about 10⁴ s. We have calculated the break luminosity, and it mainly ranges from 10⁴⁴ erg s⁻¹ to 10⁴⁷ erg s⁻¹, which is generally two or three orders of magnitude less than the corresponding break luminosity of the X-ray afterglow plateaus. We reanalyzed the optical plateaus and also found that a significantly tighter correlation exists when we added the isotropic equivalent energy of GRBs E_γ,iso into the L_b,z–T_b,z relation. The best-fit correlation is obtained to be ${L}_{{\rm{b}},{\rm{z}}}\propto \,{T}_{{\rm{b}},{\rm{z}}}^{-0.9}\,{E}_{\gamma ,\mathrm{iso}}^{0.4}$. We next explored the possible correlations among L_b,z, T_b,z and E_p,i, and found there is also a tight correlation between them, which takes the form of ${L}_{{\rm{b}},{\rm{z}}}\propto \,{T}_{{\rm{b}},{\rm{z}}}^{-0.9}\,{E}_{{\rm{p}},{\rm{i}}}^{0.5}$. We argue that these two tight L_b,z–T_b,z–E_γ,iso and L_b,z–T_b,z–E_p,i correlations are more physical, and it may be directly related to the radiation physics of GRBs. The tight correlations can possibly be used as standard candles.

The study of the chemical evolution of glycine in the interstellar medium is one of the challenging topics in astrochemistry. Here we present the chemical modeling of glycine in hot cores using the state-of-the-art three-phase chemical model NAUTILUS, which is focused on the latest glycine chemistry. For the formation process of glycine on the grain surface, we obtained consistent results with previous studies that glycine would be formed via the reactions of COOH with CH₂NH₂. However, we will report three important findings regarding the chemical evolution and the detectability of interstellar glycine. First, with the experimentally obtained binding energy from the temperature-programmed desorption (TPD) experiment, a large proportion of glycine was destroyed through the grain surface reactions with NH or CH₃O radicals before it fully evaporated. As a result, the formation process in the gas phase is more important than thermal evaporation from grains. If this is the case, NH₂OH and CH₃COOH rather than CH₃NH₂ and CH₂NH would be the essential precursors to the gas-phase glycine. Second, since the gas-phase glycine will be quickly destroyed by positive ions or radicals, the early evolutionary phase of the hot cores would be the preferable target for the future glycine surveys. Third, we suggest the possibility that the suprathermal hydrogen atoms can strongly accelerate the formation of COOH radicals from CO₂, resulting in the dramatic increase of formation rate of glycine on grains. The efficiency of this process should be investigated in detail by theoretical and experimental studies in the future.

The radial distance to the corotation radius ${R}_{\mathrm{coro}}$ (where the angular speed of the gas and stars, ${{\rm{\Omega }}}_{\mathrm{gas}}$, in orbit around the Galactic center (GC) is equal to the angular speed of the spiral arm pattern, ${{\rm{\Omega }}}_{\mathrm{sp}}$) has often been predicted (at various places), but not measured with high precision. Here we test the locations of masers with respect to the Perseus arm (Table 1). Our analysis of the masers and H ii regions near the Perseus arm (mostly located on the inner arm side, by about 0.4 ± 0.1 kpc from the cold CO mid-arm) shows that the corotation ${R}_{\mathrm{coro}}$ must be >10.8 kpc from the GC (Figure 1). This implies that the angular rotation speed of the spiral pattern ${{\rm{\Omega }}}_{\mathrm{sp}}$< 21.3 km s⁻¹ kpc⁻¹. Another test in Galactic quadrant II shows that the radial velocity of the masers is generally more negative than that of the CO mid-arm (Figure 2), indicating a deceleration with respect to the CO mid-arm, by about 9 ± 3 km s⁻¹. This implies that ${{\rm{\Omega }}}_{\mathrm{sp}}$ < 20.7 km s⁻¹ kpc⁻¹, and thus ${R}_{\mathrm{coro}}$ > 11.1 kpc. Finally, comparing our results with other published results (Table 2), we find a statistical mean corotation radius ${R}_{\mathrm{coro}}$ predicted to be near 12 ± 1 kpc from the GC (beyond the Perseus arm; before the Cygnus arm), and a mean angular spiral pattern speed, ${{\rm{\Omega }}}_{\mathrm{sp}}$, predicted to be near 19 ± 2 km s⁻¹ kpc⁻¹.

We present hydrodynamic simulations of spherically symmetric super-Eddington winds from radius-expansion type I X-ray bursts. Previous studies assumed a steady-state wind and treated the mass-loss rate as a free parameter. Using MESA, we follow the multi-zone time-dependent burning, the convective and radiative heating of the atmosphere during the burst rise, and the launch and evolution of the optically thick radiation-driven wind as the photosphere expands outward to radii r_ph ≳ 100 km. We focus on neutron stars (NSs) accreting pure helium and study bursts over a range of ignition depths. We find that the wind ejects ≈0.2% of the accreted layer, nearly independent of ignition depth. This implies that ≈30% of the nuclear energy release is used to unbind matter from the NS surface. We show that ashes of nuclear burning are ejected in the wind and dominate the wind composition for bursts that ignite at column depths ≳10⁹ g cm⁻². The ejecta are composed primarily of elements with mass numbers A > 40, which we find should imprint photoionization edges on the burst spectra. Evidence of heavy-element edges has been reported in the spectra of strong radius-expansion bursts. We find that after ≈1 s, the wind composition transitions from mostly light elements (⁴He and ¹²C), which sit at the top of the atmosphere, to mostly heavy elements (A > 40), which sit deeper down. This may explain why the photospheric radii of all superexpansion bursts show a transition after ≈1 s from a superexpansion (${r}_{\mathrm{ph}}\gt {10}^{3}\,\mathrm{km}$) to a moderate expansion (${r}_{\mathrm{ph}}\sim 50\,\mathrm{km}$).

Chondrules are a major component of chondritic meteorites and potentially populated the entire protoplanetary disk before planet formation. Chondrules provide insights into the physical and chemical evolution of the protoplanetary disk. An important constraint for the protoplanetary disk is whether chondrules in individual chondrite groups formed in spatially separate reservoirs and were then transported and mixed throughout the disk, finally accreting in chondrites, or did chondrules in individual chondrite groups form and then accrete in the same reservoir and locality, without large-scale transport and mixing involved. Both scenarios have been proposed. Here we use bulk chondrule compositional data from the recently published ChondriteDB database in combination with a mixing model we developed to test whether the compositional distributions of chondrule populations in individual chondrites (1) are the result of mixing chondrules from multiple parental reservoirs or (2) originated from single parental reservoirs. We thereby provide a fundamental framework that each mixing model needs to obey. Although one mixing model is principally possible, this particular model is unlikely, and it therefore appears more reasonable that chondrules in individual chondrites originated from single, although different, parental reservoirs. Significant disk-wide transport or mixing of chondrules seems unlikely, while chondrule-forming models that produce chondrules from single reservoirs seem more likely. Anomalous minor element and nucleosynthetic isotope chondrule compositions are possibly best explained by admixing tiny nuggets such as refractory or presolar grains with distinct elemental or isotopic compositions into chondrules.

N49 (LHA 120-N49) is a bright X-ray supernova remnant (SNR) in the Large Magellanic Cloud. We present new ¹²CO (J = 1–0, 3–2), H i, and 1.4 GHz radio continuum observations of the SNR N49 using Mopra, ASTE, ALMA, and ATCA. We have newly identified three H i clouds using ATCA with an angular resolution of ∼20'': one associated with the SNR and the others located in front of the SNR. Both the CO and H i clouds in the velocity range from 281 to 291 km s⁻¹ are spatially correlated with both the soft X-rays (0.2–1.2 keV) and the hard X-rays (2.0–7.0 keV) of N49 on a ∼10 pc scale. CO 3–2/1–0 intensity ratios indicate higher values of the CO cloud toward the SNR shell with an angular resolution of ∼45'', and thus a strong interaction was suggested. Using the ALMA, we have spatially resolved CO clumps embedded within or along the southeastern rim of N49 with an angular resolution of ∼3''. Three of the CO clumps are rim brightened on a 0.7–2 pc scale in both hard X-rays and the radio continuum: this provides further evidence for dynamical interactions between the CO clumps and the SNR shock wave. The enhancement of the radio synchrotron radiation can be understood in terms of magnetic field amplification around the CO clumps via a shock–cloud interaction. We also present a possible scenario in which the recombining plasma that dominates the hard X-rays from N49 was formed via thermal conduction between the SNR shock waves and the cold/dense molecular clumps.

We use Atacama Large Millimeter Array (ALMA) observations of four submillimeter galaxies (SMGs) at z ∼ 2–3 to investigate the spatially resolved properties of the interstellar medium (ISM) at scales of 1–5 kpc (01–06). The velocity fields of our sources, traced by the ¹²CO(J = 3–2) emission, are consistent with disk rotation to the first order, implying average dynamical masses of ∼3 × 10¹¹${M}_{\odot }$ within two half-light radii. Through a Bayesian approach we investigate the uncertainties inherent to dynamically constraining total gas masses. We explore the covariance between the stellar mass-to-light ratio and CO-to-H₂ conversion factor, α_CO, finding values of ${\alpha }_{\mathrm{CO}}={1.1}_{-0.7}^{+0.8}$ for dark matter fractions of 15%. We show that the resolved spatial distribution of the gas and dust continuum can be uncorrelated to the stellar emission, challenging energy balance assumptions in global SED fitting. Through a stacking analysis of the resolved radial profiles of the CO(3–2), stellar, and dust continuum emission in SMG samples, we find that the cool molecular gas emission in these sources (radii ∼5–14 kpc) is clearly more extended than the rest-frame ∼250 μm dust continuum by a factor >2. We propose that assuming a constant dust-to-gas ratio, this apparent difference in sizes can be explained by temperature and optical depth gradients alone. Our results suggest that caution must be exercised when extrapolating morphological properties of dust continuum observations to conclusions about the molecular gas phase of the interstellar medium (ISM).

We present an analysis of widths and kinematic properties of coronal mass ejections (CMEs) obtained via a supervised image segmentation algorithm, the CORonal SEgmentation Technique (CORSET), on simultaneous observations from the two COR2 telescopes on the Solar Terrestrial Relations Observatory (STEREO) mission, from 2007 May to 2014 September. The sample of 460 events with measurements from two vantage points offers the opportunity to test the accuracy and constraints of single-viewpoint properties that underlie the bulk of CME research to date. In addition, we examine the dependence of the properties on the morphology of the events. The main findings are as follows. (1) The radial speeds derived from different perspectives are in good agreement with a relatively low intrinsic uncertainty of 39%. (2) Projection effects are more important for determination of CME width rather than for speed. (3) The expansion speeds depend on CME morphology, with loop-type CMEs expanding twice as fast as flux-rope CMEs, possibly underpinning the more explosive nature. (4) Triangulations of CME speed and propagation direction are optimal from viewpoints separated by 60°–90°; e.g., between the Lagrangian points L₁ and L₅ (or L₄). (5) The projected speeds are underestimated, on average, by at least 20% when compared to their deprojected (triangulated) values. We also discuss in detail the lessons learned from the application of the CORSET algorithm to event tracking. Our findings should hopefully be a useful guide in the use of (semi)automated algorithms for extraction of CME physical parameters and in the interpretation of single-viewpoint observations (likely to be the norm after the end of the STEREO mission).

We present numerical simulations of energetic flows propagating through the debris cloud of a binary neutron star (BNS) merger. Starting from the scale of the central engine, we use a moving-mesh hydrodynamics code to simulate the complete dynamical evolution of the relativistic jets produced. We compute synchrotron emission directly from the simulations and present multiband light curves of the early (subday) through late (weeks to years) afterglow stages. Our work systematically compares two distinct models for the central engine, referred to as the narrow- and wide-engine scenarios, respectively associated with a successful structured jet and quasi-isotropic explosion. Both engine models naturally evolve angular and radial structures through hydrodynamical interaction with the merger debris cloud. They both also result in a relativistic blast wave capable of producing the observed multiband afterglow data. However, we find that the narrow- and wide-engine scenarios might be differentiated by a new emission component that we refer to as a merger flash. This component is a consequence of applying the synchrotron radiation model to the shocked optically thin merger cloud. Such modeling is appropriate if injection of nonthermal electrons is sustained in the breakout relativistic shell, for example by internal shocks or magnetic reconnection. The rapidly declining signature may be detectable for future BNS mergers during the first minutes to the day following the gravitational wave chirp. Furthermore, its nondetection for the GRB170817A event may disfavor the wide, quasi-isotropic explosion model.

Spitzer Space Telescope Infrared Array Camera (IRAC) images of M100 show numerous long filaments with regularly spaced clumps, suggesting the associated cloud complexes formed by large-scale gravitational instabilities in shocked and accumulated gas. Optical images give no hint of this underlying regularity. The typical spacing between near-infrared clumps is ∼410 pc, which is ∼3 times the clump diameter, consistent with the fastest growing mode in a filament of critical line density. The IRAC magnitudes and colors of several hundred clumps are measured in the most obvious 27 filaments and elsewhere. The clump colors suggest that the dust is associated with diffuse gas, polycyclic aromatic hydrocarbon emission, and local heating from star formation. Neighboring clumps on the same filament have similar magnitudes. The existence of many clumps all along the filament lengths suggests that the ages of the filaments are uniform. The observations support a model where interstellar gas is systematically accumulated over lengths exceeding several kpc, forming spiral-like filaments that spontaneously collapse into giant clouds and stellar complexes. Optical wavelengths show primarily the irregular dust debris, H ii regions, and lingering star formation downstream from these primal formation sites.

Galaxy clusters can act as gravitational lenses and magnify the universe behind them, allowing us to see deep into the early universe. The Hubble Space Telescope Frontier Fields program uses six galaxy clusters imaged by Hubble to discover and study galaxies at z ∼ 5–10. Seven independent teams developed lens models and derived magnifications for each galaxy cluster, based on positional and redshift constraints from the best available data at the time. In this work we evaluate 10 models for MACS J0416.1-2403 that were made public in 2015 by contrasting them with new spectroscopic redshifts that were measured in 2016. We developed an independent comparison method that uses the source plane root-mean-square as a metric of lensing model performance. Our analysis quantifies the ability of models to predict unknown multiple images. We examine the source plane scatter of multiply imaged systems and explore the dependence of the scatter on the location and the redshift of the background sources. The analysis we present evaluates the performance of the different algorithms in the specific case of the MACS J0416.1-2403 models.

ALMA surveys of nearby star-forming regions have shown that the dust mass in the disk is correlated with the stellar mass, but with a large scatter. This scatter could indicate either different evolutionary paths of disks or different initial conditions within a single cluster. We present ALMA Cycle 3 follow-up observations for 14 Class II disks that were low signal-to-noise (S/N) detections or non-detections in our Cycle 2 survey of the ∼2 Myr old Chamaeleon I star-forming region. With five times better sensitivity, we detect millimeter dust continuum emission from six more sources and increase the detection rate to 94% (51/54) for Chamaeleon I disks around stars earlier than M3. The stellar-disk mass scaling relation reported in Pascucci et al. is confirmed with these updated measurements. Faint outliers in the F_mm–M_* plane include three non-detections (CHXR71, CHXR30A, and T54) with dust mass upper limits of 0.2 M_⊕ and three very faint disks (CHXR20, ISO91, and T51) with dust masses ∼0.5 M_⊕. By investigating the SED morphology, accretion property and stellar multiplicity, we suggest for the three millimeter non-detections that tidal interaction by a close companion (≲100 au) and internal photoevaporation may play a role in hastening the overall disk evolution. The presence of a disk around only the secondary star in a binary system may explain the observed stellar SEDs and low disk masses for some systems.

Recent observations of cool cluster cores that include the BCG gravity claim that the observed threshold in min(t_cool/t_ff) (cooling time to free-fall time ratio) lies at a somewhat higher value, close to 10–30, compared with the threshold seen in numerical simulations. There are only a few clusters in which this ratio falls much below 10. In this paper, we compare 3D hydrodynamic simulations of feedback active galactic nuclei (AGNs) jets interacting with the intracluster medium, with and without a BCG potential. We find that, for a fixed feedback efficiency, the presence of a BCG does not significantly affect the temperature, but increases (decreases) the core density (entropy) on average. Most importantly, min(t_cool/t_ff) is only affected slightly by the inclusion of the BCG gravity. Also notable is that the lowest value of min(t_cool/t_ff) in the NFW+BCG runs is about twice as large as in the NFW runs. We also look at the role of depletion of cold gas due to star formation, and show that it only affects the rotationally dominant component, while the radially dominant component remains largely unaffected. Stellar gas depletion also increases the repetition rate of AGN jets. The distribution of metals due to AGN jets in our simulations is predominantly along the jet direction, and the equatorial spread of metals is less compared with the observations. We also show that the turbulence in cool-core clusters is weak, which is consistent with recent Hitomi results on the Perseus cluster.

We present a joint analysis of the rest-frame ultraviolet (UV) luminosity functions of continuum-selected star-forming galaxies and galaxies dominated by active galactic nuclei (AGNs) at z ∼ 4. These 3740 z ∼ 4 galaxies are selected from broadband imaging in nine photometric bands over 18 deg² in the Spitzer/HETDEX Exploratory Large Area Survey field. The large area and moderate depth of our survey provide a unique view of the intersection between the bright end of the galaxy UV luminosity function (M_AB < −22) and the faint end of the AGN UV luminosity function. We do not separate AGN-dominated galaxies from star-formation-dominated galaxies, but rather fit both luminosity functions simultaneously. These functions are best fit with a double power law for both the galaxy and AGN components, where the galaxy bright-end slope has a power-law index of −3.80 ± 0.10 and the corresponding AGN faint-end slope is ${\alpha }_{\mathrm{AGN}}=-{1.49}_{-0.21}^{+0.30}$. We cannot rule out a Schechter-like exponential decline for the galaxy UV luminosity function, and in this scenario the AGN luminosity function has a steeper faint-end slope of $-{2.08}_{-0.11}^{+0.18}$. Comparison of our galaxy luminosity function results with a representative cosmological model of galaxy formation suggests that the molecular gas depletion time must be shorter, implying that star formation is more efficient in bright galaxies at z = 4 than at the present day. If the galaxy luminosity function does indeed have a power-law shape at the bright end, the implied ionizing emissivity from AGNs is not inconsistent with previous observations. However, if the underlying galaxy distribution is Schechter, it implies a significantly higher ionizing emissivity from AGNs at this epoch.

We present results of an archival coincidence analysis between Fermi Large Area Telescope (LAT) gamma-ray data and public neutrino data from the IceCube neutrino observatory's 40-string (IC 40) and 59-string (IC 59) observing runs. Our analysis has the potential to detect either a statistical excess of neutrino + gamma-ray (ν + γ) emitting transients or, alternatively, individual high gamma-multiplicity events, as might be produced by a neutrino observed by IceCube coinciding with a LAT-detected gamma-ray burst. Dividing the neutrino data into three data sets by hemisphere (IC 40, IC 59-North, and IC 59-South), we construct uncorrelated null distributions by Monte Carlo scrambling of the neutrino data sets. We carry out signal-injection studies against these null distributions, demonstrating sensitivity to individual ν + γ events of sufficient gamma-ray multiplicity, and to ν + γ transient populations responsible for >13% (IC 40), >9% (IC 59-North), or >8% (IC 59-South) of the gamma-coincident neutrinos observed in these data sets, respectively. Analyzing the unscrambled neutrino data, we identify no individual high-significance neutrino + high gamma-multiplicity events and no significant deviations from the test statistic null distributions. However, we observe a similar and unexpected pattern in the IC 59-North and IC 59-South residual distributions that we conclude reflects a possible correlation (p = 7.0%) between IC 59 neutrino positions and persistently bright portions of the Fermi gamma-ray sky. This possible correlation should be readily testable using eight years of further data already collected by IceCube. We are currently working with Astrophysical Multimessenger Observatory Network (AMON) partner facilities to generate low-latency ν + γ alerts from Fermi-LAT gamma-ray and IceCube and ANTARES neutrino data and distribute these in real time to AMON follow-up partners.

We use the framework developed as part of the MESA Isochrones and Stellar Tracks (MIST) project to assess the utility of several types of observables in jointly measuring the age and 1D stellar model parameters in star clusters. We begin with a pedagogical overview summarizing the effects of stellar model parameters, such as the helium abundance, mass-loss efficiency, and mixing-length parameter, on observational diagnostics such as the color–magnitude diagram, mass–radius relation, and surface abundances, among others. We find that these parameters and the stellar age influence observables in qualitatively distinctive, degeneracy-breaking ways. To assess the current state of affairs, we use the recent Gaia Data Release 2 (DR2) along with data from the literature to investigate three well-studied old open clusters—NGC 6819, M67, NGC 6791—as case studies. Although there is no obvious tension between the existing observations and the MIST models for NGC 6819, there are interesting discrepancies in the cases of M67 and NGC 6791. At this time, parallax zero-point uncertainties in Gaia DR2 remain one of the limiting factors in the analysis of these clusters. With a combination of exquisite photometry, parallax distances, and cluster memberships from Gaia at the end of its mission, we anticipate precise and accurate ages for these and other star clusters in the Galaxy.

Observations of several gravitationally microlensed quasars in X-rays revealed variations in the profile of the iron Kα line in the course of microlensing events. We explore the effect by simulating a microlensing caustic crossing a spatially resolved model of emission from a thin accretion disk around a Kerr black hole. We demonstrate the sequence of spectral changes during the event, in particular the appearance of additional peaks and edges in the line profile due to microlensing. We trace the origin of these features to points on the disk, at which the total energy shift (g-factor) contours are tangent to the caustic. Contours tangent from the inner side of the caustic generate peaks, while those tangent from its outer side generate edges. We derive analytical shapes of the generated features and map the peak strength as a function of position of the tangent point on the disk. Since the features are determined by the positional geometry of the caustic relative to the g-factor contours, the same type of behavior can be expected in a much broader range of emission models. The sequence of line profile changes thus serves as a sensitive probe of the geometry and physics of the innermost region of the quasar accretion disk.

The Hyades, Praesepe, and Pleiades are well-studied stellar clusters that anchor important secondary stellar age indicators. Recent studies have shown that main sequence turn off based ages for these clusters may depend on the degree of rotation in the underlying stellar models. Rotation induces structural instabilities that can enhance the chemical mixing of a star, extending its fuel supply. In addition, rotation introduces a modulation of the star's observed magnitude and color due to the effects of gravity darkening. We aim to investigate the extent to which stellar rotation affects the age determination of star clusters. We utilize the MESA stellar evolution code to create models that cover a range of rotation rates corresponding to Ω/Ω_c = 0.0–0.6 in 0.1 dex steps, allowing the assessment of variations in this dimension. The statistical analysis package, MATCH, is employed to derive ages and metallicities by fitting our MESA models to Tycho B_T, V_T, and 2MASS J, K_s color–magnitude diagrams. We find that the derived ages are relatively insensitive to the effects of rotation. For the Hyades, Praesepe, and Pleiades clusters, we derive ages based on synthetic populations that model a distribution of rotation rates or a fixed rate. Across each case, the derived ages tend to agree roughly within errors, near 680, 590, and 110–160 Myr for the Hyades, Praesepe, and Pleiades clusters, respectively. These ages are in agreement with Li depletion boundary-based ages and previous analyses that used nonrotating isochrones. Our methods do not provide a strong constraint on the metallicities of these clusters.

Black hole (BH) mergers driven by gravitational perturbations of external companions constitute an important class of formation channels for merging BH binaries detected by LIGO. We have studied the orbital and spin evolution of binary BHs in triple systems, where the tertiary companion excites large eccentricity in the inner binary through Lidov–Kozai oscillations, causing the binary to merge via gravitational radiation. Using the single-averaged and double-averaged secular dynamics of triples (where the equations of motion are averaged over the inner orbit and both orbits, respectively), we perform a large set of numerical integrations to determine the merger window (the range of companion inclinations that allows the inner binary to merge within ∼10 Gyr) and the merger fraction as a function of various system parameters (e.g., the binary masses m₁, m₂ and initial semimajor axis a₀, the mass, semimajor axis, and eccentricity ${e}_{\mathrm{out}}$ of the outer companion). For typical BH binaries (${m}_{\mathrm{1,2}}\simeq 20\,{M}_{\odot }\mbox{--}30\,{M}_{\odot }$ and a₀ ≳ 10 au), the merger fraction increases rapidly with e_out because of the octupole perturbation, ranging from ∼1% at ${e}_{\mathrm{out}}=0$ to 10%–20% at e_out = 0.9. We derive analytical expressions and approximate scaling relations for the merger window and merger fraction for systems with negligible octupole effect, and apply them to neutron star binary mergers in triples. We also follow the spin evolution of the BHs during the companion-induced orbital decay, where de Sitter spin precession competes with Lidov–Kozai orbital precession/nutation. Starting from aligned spin axes (relative to the orbital angular momentum axis), a wide range of final spin–orbit misalignment angle θ_sl^f can be generated when the binary enters the LIGO sensitivity band. For systems where the octupole effect is small (such as those with m₁ ≃ m₂ or e_out ∼ 0), the distribution of ${\theta }_{\mathrm{sl}}^{{\rm{f}}}$ peaks around 90°. As the octupole effect increases, a more isotropic distribution of final spin axis is produced. Overall, merging BH binaries produced by Lidov–Kozai oscillations in triples exhibit a unique distribution of the effective (mass-weighted) spin parameter χ_eff; this may be used to distinguish this formation channel from other dynamical channels.

Recent research on the exoplanets caused a particular focus on the protoplanetary disks (PPDs). The time evolution of a PPD gives us new insight on the planetary system around the central objects. Although the time dependency of a quasi-spherical disk has been considered in detail by many theoretical works, the time dependency of a PPD has not yet been fully understood. In this study, we consider the time evolution of the inner regions of a polytropic PPD with a toroidal magnetic field in the non-ideal magnetohydrodynamic regime. In this regime, we consider a magnetic Prandtl number for this disk that is the ratio of magnetic diffusivity to the viscosity. Also, we use a self-similar formalism to study the dynamical behavior of a PPD. Two variables, i.e., the independent self-similar variable (x) and dimensionless polytropic index (a), are mainly considered in the formulation of the problem. Therefore, we are able to consider both polytropic and isothermal cases in a unit formulation. The problem is solvable for small x in the isothermal case, where we obtain a new perspective on the dynamics of a PPD. Furthermore, we investigate the magnetic dissipation originated from the magnetic diffusivity, which is dependent on the magnetic Prandtl number, in the PPDs. The importance of this study is in the angular momentum transport and formation of planetesimal in a PPD.

Stars of spectral type Oe are very rare. To date, only 13 Oe stars have been identified within our Galaxy. In this paper, we present six new Oe stars and four new B0e stars found in LAMOST DR5. Repeated spectral observations of the same Oe stars show some emission-line variability. The Hβ emission of TYC 4801-17-1 shows rapid V/R variation. Phase lags in the V/R ratio of TYC 4801-17-1 spectra are also seen. We found that the unusual O4.5 star RL 128 is an Oe star with variable Hα intensity and its Ca ii triplet emission appears when Hα emission reaches maximum intensity. These newly identified early-type Oe and B0e stars significantly increase the known sample.

The variation in the high-energy cutoff, E_c, in active galactic nuclei (AGNs) uniquely probes the corona physics. In this work, we show that the ratio of two NuSTAR spectra (analogous to the difference-imaging technique widely used in astronomy) is uniquely useful in studying E_c variations. The spectra ratio could directly illustrate potential E_c variation between two spectra. By comparing with the ratio of two spectral-fitting models, it also examines the reliability of the spectral fitting measured E_c variation. Assisted with this technique, we revisit the five AGNs in the literature (MCG-5-23-16, 3C 382, NGC 4593, NGC 5548, and Mrk 335), for which E_c (kT_e) variations have been claimed with NuSTAR observations. We show that the claimed E_c variations appear inconsistent with the spectra ratios in three of them, thus they need to be revised, demonstrating the striking usefulness of spectra ratio. We present thereby improved spectral-fitting results and E_c variations. We also report a new source with E_c variations based on NuSTAR observations (radio galaxy 4C+74.26). We find the corona tends to be hotter when it brightens (hotter-when-brighter) in 3C 382, NGC 5548, Mrk 335, and 4C+74.27, but MCG-5-23-16 and NGC 4593 show no evidence of significant E_c variations. Meanwhile, all six sources in this small sample appear softer when brighter. Changes in corona geometry are required to explain the observed hotter-when-brighter trends.

The bipolar outflow associated with the Class 0 low-mass protostellar source (IRAS 18148–0440) in L483 has been studied in the CCH and CS line emission at 245 and 262 GHz, respectively. Sub-arcsecond resolution observations of these lines have been conducted with ALMA. Structures and kinematics of the outflow cavity wall are investigated in the CS line, and are analyzed by using a parabolic model of an outflow. We constrain the inclination angle of the outflow to be from 75° to 90°, i.e., the outflow is blowing almost perpendicular to the line of sight. Comparing the outflow parameters derived from the model analysis with those of other sources, we confirm that the opening angle of the outflow and the gas velocity on its cavity wall correlate with the dynamical timescale of the outflows. Moreover, a hint of a rotating motion of the outflow cavity wall is found. Although the rotation motion is marginal, the specific angular momentum of the gas on the outflow cavity wall is evaluated to be comparable to or twice that of the infalling-rotating envelope of L483.

With recent Lyα forest data from BOSS and XQ-100, some studies suggested that the lower mass limit on the fuzzy dark matter (FDM) particles is lifted up to ${10}^{-21}\,\mathrm{eV}$. However, such a limit was obtained by ΛCDM simulations with the FDM initial condition and the quantum pressure (QP) was not taken into account, which could have generated non-trivial effects in large-scale structures. We investigate the QP effects in cosmological simulations systematically, and find that the QP leads to further suppression of the matter power spectrum at small scales, as well as the halo mass function in the low-mass end. We estimate the suppressing effect of QP in the 1D flux power spectrum of Lyα forest and compare it with data from BOSS and XQ-100. The rough uncertainties of thermal gas properties in the flux power spectrum model calculation were discussed. We conclude that more systematic studies, especially with QP taken into account, are necessary to constrain FDM particle mass using Lyα forest.

We present a parsec-scale molecular hydrogen (H₂ 1–0 S(1) at 2.12 μm) outflow discovered from the UKIRT Widefield Infrared Survey for H₂. The outflow is located in the infrared dark cloud core MSXDC G053.11+00.05 MM1 at 1.7 kpc and is likely associated with two young stellar objects (YSOs) at the center. Although the overall morphology of the outflow is bipolar along the NE–SW direction with a brighter lobe to the southwest, the detailed structure consists of several flows and knots. With a total length of ∼1 pc, the outflow luminosity is fairly high with ${L}_{{{\rm{H}}}_{2}}\gt 6\,{L}_{\odot }$, implying a massive outflow-driving YSO if the entire outflow is driven by a single source. The two putative driving sources that are located at the outflow center show photometric variability of ≳1 mag in H- and K-bands. Together with their early evolutionary stage from spectral energy distribution (SED) fitting, this indicates that both are capable of ejecting outflows and may be eruptive variable YSOs. The YSO masses inferred from SED fitting are ∼10 M_⊙ and ∼5 M_⊙, which suggests the association of the outflow with massive YSOs. The geometrical morphology of the outflow is well-explained by the lower-mass YSO by assuming a single-source origin; however, without kinematic information, the contribution from the higher mass YSO cannot be ruled out. Considering star formation process by fragmentation of a high-mass core into several lower-mass stars, we also suggest the possible presence of another, yet-undetected driving source that is deeply embedded in the core.

We have surveyed the Voyager magnetic field data from launch through 1990 in search of low-frequency waves that are excited by newborn interstellar pickup ions (PUIs). During this time the Voyager 1 and 2 spacecraft reached 43.5 and 33.6 au, respectively. The use of daily spectrograms permits us to perform a thorough search of the data. We have identified 637 different data intervals that show evidence of waves excited by either pickup He⁺, H⁺, or both, and these intervals extend to the furthest distances in the years studied. To compare wave features against more typical interplanetary observations, we also employ 1675 data intervals spanning the same years that do not contain wave signatures and use these as control intervals. While the majority of wave events display the classic spectral characteristics of waves due to PUIs, including left-hand polarization in the spacecraft frame, a significant number of the events are right-hand polarized in the spacecraft frame. We have no complete explanation for this result, but we do show that right-handed waves are seen when the local magnetic field is nonradial.

In this companion paper, we describe low-frequency magnetic waves observed in 637 intervals of Voyager 1 and 2 data from launch late in 1977 through 1990. By the end of 1990 the Voyager 1 spacecraft reached 43.5 au, while the Voyager 2 spacecraft reaches 33.6 au. The waves are attributed to newborn interstellar pickup He⁺ and H⁺. In this analysis we follow the idea put forward by Cannon et al. and followed by Fisher et al. and Aggarwal et al. wherein the necessary condition for the observation of the waves is that the wave growth rate exceeds the background turbulence rate. We explore this idea and build on the conclusion in our companion paper that the waves are typically observed in rarefaction regions where the turbulence level is low and noise-dominated signals sometimes distort the computed background turbulence spectra.

We demonstrate that the "smoke" of limited instrumental sensitivity smears out structure in gamma-ray burst (GRB) pulse light curves, giving each a triple-peaked appearance at moderate signal-to-noise ratio (S/N) and a simple monotonic appearance at low S/N. We minimize this effect by studying six very bright GRB pulses (S/N generally >100), discovering surprisingly that each exhibits complex time-reversible wavelike residual structures. These "mirrored" wavelike structures can have large amplitudes, occur on short timescales, begin/end long before/after the onset of the monotonic pulse component, and have pulse spectra that generally evolve hard to soft, rehardening at the time of each structural peak. Among other insights, these observations help explain the existence of negative pulse spectral lags and allow us to conclude that GRB pulses are less common, more complex, and have longer durations than previously thought. Because structured emission mechanisms that can operate forward and backward in time seem unlikely, we look to kinematic behaviors to explain the time-reversed light-curve structures. We conclude that each GRB pulse involves a single impactor interacting with an independent medium. Either the material is distributed in a bilaterally symmetric fashion, the impactor is structured in a bilaterally symmetric fashion, or the impactor's motion is reversed such that it returns along its original path of motion. The wavelike structure of the time-reversible component suggests that radiation is being both produced and absorbed/deflected dramatically, repeatedly, and abruptly relative to the emission of the monotonic component.

We use deep, multi-epoch near-IR images of the VISTA Variables in the Vía Láctea (VVV) Survey to measure proper motions (PMs) of stars in the Milky Way globular cluster (GC) FSR1716 = VVV-GC05. The color-magnitude diagram of this object, made by using PM-selected members, shows an extended horizontal branch, nine confirmed RR Lyrae (RRL) members in the instability strip, and possibly several hotter stars extending to the blue. Based on the fundamental-mode (ab-type) RRL stars that move coherently with the cluster, we confirmed that FSR1716 is an Oosterhoff I GC with a mean period $\langle {P}_{{ab}}\rangle$ = 0.574 days. Intriguingly, we detect tidal extensions to both sides of this cluster in the spatial distribution of PM-selected member stars. Also, one of the confirmed RRabs is located ∼11 arcmin in projection from the cluster center, suggesting that FSR1716 may be losing stars due to the gravitational interaction with the Galaxy. We also measure radial velocities (RVs) for five cluster red giants selected using the PMs. The combination of RVs and PMs allow us to compute for the first time the orbit of this GC, using an updated Galactic potential. The orbit results to be confined within $| {Z}_{\max }| \lt 2.0$ kpc, and has eccentricity 0.4 < e < 0.6, with perigalactic distance $1.5\lt {R}_{\mathrm{peri}}(\mathrm{kpc})\lt 2.3$, and apogalactic distance $5.3\lt {R}_{\mathrm{apo}}(\mathrm{kpc})\lt 6.4$. We conclude that, in agreement with its relatively low metallicity ([Fe/H] = −1.4 dex), this is an inner-halo GC plunging into the disk of the Galaxy. As such, this is a unique object with which to test the dynamical processes that contribute to the disruption of Galactic GCs.

Deep near-IR images from the VISTA Variables in the Vía Láctea (VVV) Survey were used to search for RR Lyrae stars within 100 arcmin from the Galactic Center. A large sample of 960 RR Lyrae of type ab (RRab) stars were discovered. A catalog is presented featuring the positions, magnitudes, colors, periods, and amplitudes for the sample, in addition to estimated reddenings, distances, and metallicities, and measured individual relative proper motions. We use the reddening-corrected Wesenheit magnitudes, defined as ${W}_{{K}_{s}}={K}_{s}-0.428\times (J-{K}_{s})$, in order to isolate bona fide RRL belonging to the Galaxy Center, finding that 30 RRab are foreground/background objects. We measure a range of extinctions from ${A}_{{K}_{s}}=0.19$ to 1.75 mag for the RRab in this region, finding that large extinction is the main cause of the sample incompleteness. The mean period is P = 0.5446 ± 0.0025 days, yielding a mean metallicity of [Fe/H] = −1.30 ± 0.01 (σ = 0.33) dex for the RRab sample in the Galactic Center region. The median distance for the sample is D = 8.05 ± 0.02 kpc. We measure the RRab surface density using the less reddened region sampled here, finding a density of 1000 RRab/sq deg at a projected Galactocentric distance R_G = 1.6 deg. Under simple assumptions, this implies a large total mass (M > 10⁹M_⊙) for the old and metal-poor population contained inside R_G. We also measure accurate relative proper motions, from which we derive tangential velocity dispersions of σV_l = 125.0 and σV_b = 124.1 km s⁻¹ along the Galactic longitude and latitude coordinates, respectively. The fact that these quantities are similar indicate that the bulk rotation of the RRab population is negligible, and implies that this population is supported by velocity dispersion. In summary, there are two main conclusions of this study. First, the population as a whole is no different from the outer bulge RRab, predominantly a metal-poor component that is shifted with respect to the Oosterhoff type I population defined by the globular clusters in the halo. Second, the RRab sample, as representative of the old and metal-poor stellar population in the region, has high velocity dispersions and zero rotation, suggesting a formation via dissipational collapse.

Energetic particles from Earth's bow shock can frequently access the lunar orbit. These energetic particles are mainly ions. Since they are mostly field-aligned, they have much greater impacts on the lunar near side than on its far side. We present a statistical study of these upstream energetic ions at the lunar orbit using ARTEMIS observations. During the five-year time interval from 2012 to 2016, 496 energetic ion events with time durations ≥30 minutes were identified. The average duration of an event is about 1.93 hr. Most events occurred at the dawn-looking quadrants of Earth, showing an asymmetric dawn–dusk distribution in space. In 490 of the 496 events, the magnetic field lines directly extend to the bow shock. This is very important in order for energetic ions to arrive at the lunar orbit along field lines. The highest energies of these upstream energetic ions range from 101.5 to 658.5 keV based on the energy channels of ARTEMIS. The spatial distribution of the events depends on the highest energy. Events with higher energies tend to occur near the subsolar region and are related to greater AE indices, indicating stronger disturbances of the geomagnetosphere. By taking into account upstream energetic ions, in addition to galactic cosmic rays and solar energetic particles, our results provide a more comprehensive understanding of the energetic particle environment of the lunar near side.

We report the observations of a moderate but relatively intense geoeffective solar eruption on 2015 November 4 from the peripheral diffusive polarities of active region 12443. We use space-borne Solar Dynamics Observatory and ACE observations. EUV images identified a helical pattern along a filament channel, and we regard this channel as flux-rope structure. Flow velocity derived from tracked magnetograms infers converging motion along the polarity inversion line beneath the filament channel. An associated magnetic cancellation process was detected in the converging region. Further, the pre-eruptive EUV brightening was observed in the converging region, the most intense part of which appeared in the magnetic cancellation region. These observations imply that the converging and canceling flux probably contributed to the formation of the helical magnetic fields associated with the flux rope. A filament-height estimation method suggests that the middle part of the filament probably lies at a low altitude and was consistent with the initial place of the eruption. A thick current channel associated with the flux rope is also determined. For an expanding thick current channel, the critical height of the decay index for torus instability lies in the range of 37–47 Mm. Southward magnetic fields in the sheath and the ejecta induced a geomagnetic storm with a D_st global minimum of ∼−90 nT.

As established by photometric surveys, white dwarfs with hydrogen atmospheres and surface gravity, log(g) ≈ 8.0 pulsate as they cool across the temperature range of 12,500 K ≳ T_eff ≳ 10,800 K. Known as DAVs or ZZ Ceti stars, their oscillations are attributed to gravity modes excited by convective driving. Overstability requires convective driving to exceed radiative damping. Previous works have demonstrated that ω ≳ max(τ_c⁻¹, L_ℓ,b) is a necessary and sufficient condition for overstability. Here τ_c and L_ℓ,b are the effective thermal timescale and Lamb frequency at the base of the surface convection zone. Below the observational red edge, L_ℓ,b ≫ τ_c⁻¹, so overstable modes all have ωτ_c ≫ 1. Consequently, their photometric amplitudes are reduced by that large factor rendering them difficult to detect. Although proposed previously, the condition ω ≳ L_ℓ,b has not been clearly interpreted. We show that modes with ω < L_ℓ,b suffer enhanced radiative damping that exceeds convective driving rendering them damped. A quasi-adiabatic analysis is adequate to account for this enhancement. Although this approximation is only marginally valid at the red edge, it becomes increasingly accurate toward both higher and lower ${T}_{\mathrm{eff}}$. Recently, Kepler discovered a number of cool DAVs that exhibit sporadic flux outbursts. Typical outbursts last several hours, are separated by days, and release ∼10³³–10³⁴ erg. We attribute outbursts to limit cycles arising from sufficiently resonant 3-mode couplings between overstable parent modes and pairs of radiatively damped daughter modes. Limit cycles account for the durations and energies of outbursts and their prevalence near the red edge of the DAV instability strip.

We report the first science results from the newly completed Expanded Owens Valley Solar Array (EOVSA), which obtained excellent microwave (MW) imaging spectroscopy observations of SOL2017-09-10, a classic partially occulted solar limb flare associated with an erupting flux rope. This event is also well-covered by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) in hard X-rays (HXRs). We present an overview of this event focusing on MW and HXR data, both associated with high-energy nonthermal electrons, and we discuss them within the context of the flare geometry and evolution revealed by extreme ultraviolet observations from the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory. The EOVSA and RHESSI data reveal the evolving spatial and energy distribution of high-energy electrons throughout the entire flaring region. The results suggest that the MW and HXR sources largely arise from a common nonthermal electron population, although the MW imaging spectroscopy provides information over a much larger volume of the corona.

Magnetic reconnection is prevalent in the solar wind and is usually associated with interplanetary coronal mass ejections. We examined a Petschek-like reconnection exhaust (RE) in the front boundary of a magnetic cloud observed by the WIND spacecraft on 1998 June 2 and presented the first observation of a slow shock pair bounding the Petschek-like outflow jet in the interplanetary space. The whole structure contained an Alfvénic accelerated outflow and a pair of reverse slow shocks. The Alfvénic accelerated outflow was identified by Walén analysis. Rankine–Hugoniot relations were applied to confirm the slow shocks bounding the RE. Both shocks strictly satisfied the characteristics of slow shocks: (1) the intermediate Alfvén Mach numbers were both below unit in the up/downstream region; (2) the slow Mach number was above unit in the upstream side but below unit in the downstream side. Plasma was compressed and heated across the trailing slow shock, especially in the shock jump layer that has a temperature 2.4 times that of the upstream.

Molecular gas in the Arches cloud located near the Arches cluster is one of the emitters of the K-α line of neutral iron and the X-ray continuum in the Galactic center (GC). Similarly to the cloud Sgr B2, another well-known emitter of the iron line in the GC, the Arches cloud demonstrates a temporal decline of the X-ray emission. The most natural origin of this emission is irradiation of primary photons of an X-ray flare from a distant source, most likely Sgr A*. However, recent observations of the Arches cloud discovered variations of equivalent width of the 6.4 keV iron line, which indicated that the X-ray emission from the cloud is a combination of two components with different origins and different equivalent widths, one of which is time variable, while the other is stationary during the period of observations. We considered two different scenarios: (a) this emission is formed by reflection from two clouds, which are at some distance from each other, when they are irradiated by two different flares; and (b) the other scenario assumes a combination of X-ray fluxes produced in the same cloud by reflection of primary photons and by subrelativistic cosmic rays. We present restrictions for both the model and conditions at which these scenarios can be realized. Although none of the models can be completely ruled out, we find that the X-ray reflection model requires fewer assumptions and therefore is the most viable.

We have previously focused on studying the electron-capture isotopes within the dynamic spiral-arms cosmic-rays propagation model and empirically derived the energy dependence of the electron attachment rate using the observation of ⁴⁹Ti/⁴⁹V and ⁵¹V/⁵¹Cr ratios in cosmic rays. We have also shown how this relation recovers the energy dependence seen in the lab measurements. In this work, we use this relation to construct the ⁴⁴Ti/⁴⁴Ca ratio and place a lower limit on the amount of ⁴⁴Ti that is required for it to be nucleosynthesized at the source. The results also imply that the acceleration process of the radioisotopes cannot be much longer than a century timescale (or else the required nucleosynthesized amount has to be correspondingly larger). We also provide a similar lower limit on the source ⁶⁰Fe by comparing to the recently observed ⁶⁰Fe/⁵⁶Fe.

Based on the first Gaia data release and spectroscopy from the LAMOST Data Release 4, we study the kinematics and chemistry of the local halo stars. The halo stars are identified kinematically with a relative speed of at least 220 km s⁻¹ with respect to the local standard of rest. In total, 436 halo stars are identified. From this halo sample, 16 high-velocity (HiVel) stars are identified. We studied the metallicity and [α/Fe] distribution of these HiVel stars. Though most HiVel stars are metal-poor, there are several stars that have metallicities above −0.5 dex. To understand the origin of high-velocity stars, we evolve the trajectory of the star backward along the orbit in our adopted Galaxy potential model to determine the orbital parameters and assess whether the star could have originated in the Galactic center (GC). We found that some high-velocity stars could have originated from the GC, but other stars were probably kicked up from the Galactic disk.

Carbon chain molecules may be an important reservoir of reactive organics during star and planet formation. Carbon chains have been observed toward several low-mass young stellar objects (YSOs), but their typical abundances and chemical relationships in such sources are largely unconstrained. We present a carbon chain survey toward 16 deeply embedded (Class 0/I) low-mass protostars made with the IRAM 30 m telescope. Carbon chains are found to be common at this stage of protostellar evolution. We detect CCS, CCCS, HC₃N, HC₅N, l-C₃H, and C₄H toward 88%, 38%, 75%, 31%, 81%, and 88% of sources, respectively. Derived column densities for each molecule vary by one to two orders of magnitude across the sample. As derived from survival analysis, median column densities range between 1.2 × 10¹¹ cm⁻² (CCCS) and 1.5 × 10¹³ cm⁻² (C₄H), and estimated fractional abundances with respect to hydrogen range between 2 × 10⁻¹³ (CCCS) and 5 × 10⁻¹¹ (C₄H), which are low compared to cold cloud cores, warm carbon chain chemistry (WCCC) sources, and protostellar model predictions. We find significant correlations between molecules of the same carbon chain families, as well as between the cyanopolyynes (HC_nN) and the pure hydrocarbon chains (C_nH). This latter correlation is explained by a closely related production chemistry of C_nH and cyanopolyynes during low-mass star formation.

The second data release from the Gaia mission (DR2) provides a comprehensive and unprecedented picture of the motions of astronomical sources in the plane of the sky, extending from the solar neighborhood to the outer reaches of the Milky Way. I present proper-motion measurements based on Gaia DR2 for 17 ultra-faint dwarf galaxies within 100 kpc of the Milky Way. I compile the spectroscopically confirmed member stars in each dwarf bright enough for Gaia astrometry from the literature, producing member samples ranging from two stars in Triangulum II to 68 stars in Boötes I. From the spectroscopic member catalogs, I estimate the proper motion of each system. I find good agreement with the proper motions derived by the Gaia collaboration for Boötes I and Leo I. The tangential velocities for 14 of the 17 dwarfs are determined to better than 50 km s⁻¹, more than doubling the sample of such measurements for Milky Way satellite galaxies. The orbital pericenters are well constrained, with a mean value of 38 kpc. Only one satellite, Tucana III, is on an orbit passing within 15 kpc of the Galactic center, suggesting that the remaining ultra-faint dwarfs are unlikely to have experienced severe tidal stripping. As a group, the ultra-faint dwarfs are on high-velocity, eccentric, retrograde trajectories, with nearly all of them having space motions exceeding 370 km s⁻¹. A large majority of the objects are currently close to the pericenters of their orbits. In a low-mass (M_vir = 0.9 × 10¹²M_⊙) Milky Way potential, eight out of the 17 galaxies lack well-defined apocenters and appear likely to be on their first infall, indicating that the Milky Way mass may be larger than previously estimated or that many of the ultra-faint dwarfs are associated with the Magellanic Clouds. The median eccentricity of the ultra-faint dwarf orbits is 0.79, similar to the values seen in numerical simulations but distinct from the rounder orbits of the more luminous dwarf spheroidals.

On 2017 March 11, the DLT40 Transient Discovery Survey discovered SN 2017cbv in NGC 5643, a Type 2 Seyfert Galaxy in the Lupus Constellation. SN 2017cbv went on to become a bright Type Ia supernova, with a V_max of 11.51 ± 0.05 mag. We present early time optical and infrared photometry of SN 2017cbv covering the rise and fall of over 68 days. We find that SN 2017cbv has a broad light curve Δm₁₅(B) = 0.88 ± 0.07, a B-band maximum at 2457,840.97 ± 0.43, a negligible host galaxy reddening where E(B − V)_host ≈ 0, and a distance modulus of 30.49 ± 0.32 to the SN, corresponding to a distance of ${12.58}_{-1.71}^{+1.98}$ Mpc. We also present the results of two different numerical models we used for analysis in this paper: SALT2, an empirical model for Type Ia supernova optical light curves that accounts for variability components; and SNooPy, the CSP-II light-curve model that covers both optical and near-infrared wavelengths and is used for distance estimates.

We present a reorganization of the Oh et al. wide, comoving catalog of 4555 groups of stars (10,606 individual objects) identified in the Tycho Gaia Astrometric Survey (TGAS) into new and known coevolving groups of stars in the Milky Way. We use the BANYAN Σ kinematic analysis tool to identify 1015 individual stars in the Oh et al. catalog that yielded a >80% probability in 1 of 27 known associations (e.g., the AB Doradus moving group, Columba, Upper Scorpius) in the vicinity of the Sun. Among the 27 groups uncovered by Oh et al. that had >10 connected components, we find that 4 are newly discovered. We use a combination of Tycho, Gaia, Two micron All Sky catalog, Wide Field Infrared Survey Explorer Mission, Galaxy Evolution Explorer, and Rontgen Satellite photometry as well as Gaia parallaxes to determine that these new groups are likely older than the Pleiades but younger than ∼1 Gyr. Using isochrone fitting, we find that the majority of these new groups have solar-type stars and solar-type metallicity. Among the 35 Oh et al. groups with five to nine members, we find that 19 also appear new and comoving, with Oh et al. Group 30 is particularly exciting as it is well within 100 pc (range of 77–90 pc) and also appears to be older than the Pleiades. For known star-forming regions, open clusters, and moving groups identified by Oh et al., we find that the majority were broken up into pieces over several Oh et al. groups (e.g., Lower Centaurus Crux members are spread over 26 Oh et al. groups); however, we found no correlation with positions of the groups on color–magnitude diagrams, and therefore no substructure of the association correlated with the Oh et al. designated group. We find that across the 27 groups tested by BANYAN Σ there were 400 new members to 20 different associations uncovered by Oh et al. that require further vetting.

The observed scatter in intergalactic Lyα opacity at z ≲ 6 requires large-scale fluctuations in the neutral fraction of the intergalactic medium (IGM) after the expected end of reionization. Post-reionization models that explain this scatter invoke fluctuations in either the ionizing ultraviolet background (UVB) or IGM temperature. These models make very different predictions, however, for the relationship between Lyα opacity and local density. Here, we test these models using Lyα-emitting galaxies (LAEs) to trace the density field surrounding the longest and most opaque known Lyα trough at z < 6. Using deep Subaru Hyper Suprime-Cam narrowband imaging, we find a highly significant deficit of z ≃ 5.7 LAEs within 20 ${{\rm{h}}}^{-1}\,\mathrm{Mpc}$ of the trough. The results are consistent with a model in which the scatter in Lyα opacity near z ∼ 6 is driven by large-scale UVB fluctuations, and disfavor a scenario in which the scatter is primarily driven by variations in IGM temperature. UVB fluctuations at this epoch present a boundary condition for reionization models, and may help shed light on the nature of the ionizing sources.

We study the radial metallicity gradient Δ[M/H]/ΔR_g as a function of [Mg/Fe] and $| Z|$ with the help of a guiding radius based on the Apache Point Observatory Galactic Evolution Experiment and Gaia and then analyze the radial migration effect on the radial metallicity gradient and metallicity-rotation gradient between the Galactic thin and thick disks. The derived trend of gradient Δ[M/H]/ΔR_g versus [Mg/Fe] shows a transition at [Mg/Fe] ∼0.18 dex, below which the gradient is negative and varies a little as [Mg/Fe] increases; however, it changes sharply in [Mg/Fe] ranges of 0.16–0.18, above which the gradient increases linearly with increasing [Mg/Fe], being a positive value at [Mg/Fe] ≳ 0.22 dex. These positive gradients in the high-[Mg/Fe] populations are found at $| Z| \lt 0.8$ kpc, and there are nearly no gradients toward higher $| Z|$. By comparing the metallicity distributions, the radial metallicity gradients Δ[M/H]/ΔR, and the metallicity-rotation gradients between the total sample and $| R-{R}_{g}| \lt 2\,\mathrm{kpc}$ subsample (or $| R-{R}_{g}| \gt 2\,\mathrm{kpc}$ subsample), we find that, for the thick disk, blurring flattens the gradient Δ[M/H]/ΔR and favors metal-poor high-eccentricity stars. These stars are responsible for the measured positive metallicity-rotation gradient of the thick disk.

HH 211-mms is one of the youngest Class 0 protostellar systems in Perseus, at a distance of ∼235 pc. We have mapped its central region at up to ∼7 au (003) resolution. A dusty disk is seen deeply embedded in a flattened envelope, with an intensity jump in the dust continuum at ∼350 GHz. It is nearly edge-on and is almost exactly perpendicular to the jet axis. It has a size of ∼30 au along the major axis. It is geometrically thick, indicating that the (sub)millimeter light-emitting grains have yet to settle to the midplane. Its inner part is expected to have transformed into a Keplerian rotating disk with a radius of ∼10 au. A rotating disk atmosphere and a compact rotating bipolar outflow are detected in SO N_J = 8₉ − 7₈. The outflow fans out from the inner disk surfaces and is rotating in the same direction as the flattened envelope, and hence could trace a disk wind carrying away angular momentum from the inner disk. From the rotation of the disk atmosphere, the protostellar mass is estimated to be ≲50 M_Jup. Together with results from the literature, our result favors a model where the disk radius grows linearly with the protostellar mass, as predicted by models of pre-stellar dense core evolution that asymptotes to an r⁻¹ radial profile for both the column density and angular velocity.

Theoretically long gamma-ray bursts (GRBs) are expected to happen in low-metallicity environments, because in a single massive star scenario, low iron abundance prevents loss of angular momentum through stellar wind, resulting in ultra-relativistic jets and the burst. In this sense, not just a simple metallicity measurement but also low iron abundance ([Fe/H] ≲ −1.0) is essentially important. Observationally, however, oxygen abundance has been measured more often due to stronger emission. In terms of oxygen abundance, some GRBs have been reported to be hosted by high-metallicity star-forming galaxies, in tension with theoretical predictions. Here we compare iron and oxygen abundances for the first time for GRB host galaxies (GRB 980425 and 080517) based on the emission-line diagnostics. The estimated total iron abundances, including iron in both gas and dust, are well below the solar value. The total iron abundances can be explained by the typical value of theoretical predictions ([Fe/H] ≲ −1.0), despite high oxygen abundance in one of them. According to our iron abundance measurements, the single massive star scenario still survives even if the oxygen abundance of the host is very high, such as the solar value. Relying only on oxygen abundance could mislead us on the origin of the GRBs. The measured oxygen-to-iron ratios, [O/Fe], can be comparable to the highest values among the iron-measured galaxies in the Sloan Digital Sky Survey. Possible theoretical explanations of such high [O/Fe] include the young age of the hosts, top-heavy initial mass function, and fallback mechanism of the iron element in supernova explosions.

We report the results of the Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of the solar chromosphere on the southern polar limb. Coordinated observations with the Interface Region Imaging Spectrograph (IRIS) are also conducted. ALMA provided unprecedented high spatial resolution in the millimeter band (≈20) at 100 GHz frequency with a moderate cadence (20 s). The results are as follows. (1) The ALMA 100 GHz images show saw-tooth patterns on the limb, and a comparison with Solar Dynamics Observatory/Atmospheric Imaging Assembly 171 Å images shows a good correspondence of the limbs with each other. (2) The ALMA animation shows a dynamic thorn-like structure elongating from the saw-tooth patterns on the limb, with lengths reaching at least 8'', thus suggesting jet-like activity in the ALMA microwave range. These ALMA jets are in good correspondence with the IRIS jet clusters. (3) A blob-ejection event is observed. By comparing with the IRIS Mg ii slit-jaw images, the trajectory of the blob is located along the spicular patterns.

We present the first 2D hydrodynamical finite-volume simulations in which dust is fully coupled with the gas, including its back-reaction onto it, and at the same time the dust size is evolving according to coagulation and fragmentation based on a subgrid model. The aim of this analysis is to present the differences occurring when dust evolution is included relative to simulations with fixed dust size, with and without an embedded Jupiter-mass planet that triggers gap formation. We use the two-fluid polar Godunov-type code RoSSBi developed by Surville et al. combined with a new local subgrid method for dust evolution based on the model by Birnstiel et al. We find striking differences between simulations with variable and fixed dust sizes. The timescales for dust depletion differ significantly and yield a completely different evolution of the dust surface density. In general, sharp features such as pileups of dust in the inner disk and near gap edges, when a massive planet is present, become much weaker. This has important implications for the interpretation of observed substructure in disks, suggesting that the presence of a massive planet does not necessarily cause sharp gaps and rings in the dust component. Also, particles with different dust sizes show a different distribution, pointing to the importance of multiwavelength synthetic observations in order to compare with observations by ALMA and other instruments. We also find that simulations adopting fixed intermediate particle sizes, in the range of 10⁻² to 10⁻¹ cm, best approximate the surface density evolution seen in simulations with dust evolution.

We present the results of a study of the time-averaged spectral energy distributions (SEDs) of eight flat spectrum radio quasars (FSRQs) present in the second catalog of high energy sources detected beyond 50 GeV by the Fermi Large Area Telescope (2FHL). Both leptonic and hadronic scenarios are adopted to explain the multiwavelength SEDs and we find them to be marginally consistent with the 2FHL spectra above 50 GeV. We derive the expected degree of X-ray and γ-ray polarizations both for the average and elevated activity states and note that (i) a hadronic radiative model consistently predicts a higher degree of high energy polarization compared to leptonic ones and (ii) the X-ray polarization degree is higher than the γ-ray polarization in the leptonic scenario, but similar to the γ-ray polarization if the observed radiation is powered by hadronic processes. From the leptonic modeling, the location of the γ-ray emitting region is found to be at the outer edge of the broad line region (BLR) and is consistent with the γγ opacity estimates for the γ-ray absorption by the BLR. We conclude that a majority of the FSRQs could be detected by the upcoming Cherenkov Telescope Array, though future high energy polarimeters will be able to detect them only during elevated activity states, which could provide supportive evidence for the hadronic origin of the X-ray and γ-ray emission.

Detailed observations of globular clusters (GCs) have revealed evidence of self-enrichment: some of the heavy elements that we see in stars today were produced by cluster stars themselves. Moreover, GCs have internal subpopulations with different elemental abundances, including, in some cases, in elements such as iron that are produced by supernovae. This paper presents a theoretical model for GC formation motivated by observations of Milky Way star-forming regions and simulations of star formation, where giant molecular clouds fragment into multiple clumps that undergo star formation at slightly different times. Core collapse supernovae from earlier-forming clumps can enrich later-forming clumps to the degree that the ejecta can be retained within the gravitational potential well, resulting in subpopulations with different total metallicities once the clumps merge to form the final cluster. The model matches the mass–metallicity relation seen in GC populations around massive elliptical galaxies, and predicts metallicity spreads within clusters in excellent agreement with those seen in Milky Way GCs, even for those whose internal abundance spreads are so large that their entire identity as a GC is in question. The internal metallicity spread serves as an excellent measurement of how much self-enrichment has occurred in a cluster, a result that is very robust to variation in the model parameters.

Chondrites are some of the most primitive objects in the solar system, and they maintain a record of the degree of thermal metamorphism experienced in their parent bodies. This thermal history can be classified by the petrologic type. We investigate the thermal evolution of planetesimals to account for the current abundances (known as the fall statistics) of petrologic types 3–6 of ordinary chondrites. We carry out a number of numerical calculations in which formation times and sizes of planetesimals are taken as parameters. We find that planetesimals that form within 2.0 Myr after the formation of Ca-Al-rich inclusions (CAIs) can contain all petrologic types of ordinary chondrites. Our results also indicate that plausible scenarios of planetesimal formation, which are consistent with the fall statistics, are that planetesimals with radii larger than 60 km start to form around 2.0 Myr after CAIs and/or that ones with radii less than 50 km should be formed within 1.5 Myr after CAIs. Thus, thermal modeling of planetesimals is important for revealing the occurrence and amount of metamorphosed chondrites and for providing invaluable insights into planetesimal formation.

In this paper, we present the observations of two successive fast-mode extreme ultraviolet (EUV) wave events observed on 2016 July 23. Both fast-mode waves were observed by the Atmospheric Imaging Assembly instrument on board the Solar Dynamics Observatory satellite, with a traveling speed of ≈675 and 640 km s⁻¹, respectively. These two wave events were associated with two filament eruptions and two GOES M-class solar flares from the NOAA active region 12565, which was located near the western limb. The EUV waves mainly move toward the south direction. We observed the interaction of the EUV waves with a helmet streamer further away to the south. When either or one of the EUV waves penetrates into the helmet streamer, a slowly propagating wave with a traveling speed of ≈150 km s⁻¹ is observed along the streamer. We suggest that the slowly moving waves are slow-mode waves, and interpret this phenomenon as the magnetohydrodynamic wave-mode conversion from the fast mode to the slow mode. Furthermore, we observed several stationary fronts to the north and south of the source region.

To investigate the dynamics of the galaxy cluster A2142, we compile an extended catalog of 2239 spectroscopic redshifts of sources, including 237 newly measured redshifts, within 30 arcmin from the cluster center. With the σ-plateau algorithm from the caustic method, we identify 868 members and a number of substructures in the galaxy distribution both in the outskirts, out to ∼3.5 Mpc from the cluster center, and in the central region. In the outskirts, one substructure overlaps a falling clump of gas previously identified in the X-ray band. These substructures suggest the presence of multiple minor mergers, which are responsible for the complex dynamics of A2142, and the absence of recent or ongoing major mergers. We show that the distribution of the galaxies in the cluster core and in several substructures is consistent with the mass distribution inferred from the weak-lensing signal. Moreover, we use spatially resolved X-ray spectroscopy to measure the redshift of different regions of the intracluster medium within ∼3 arcmin from the cluster center. We find a ring of gas near the two X-ray cold fronts identified in previous analyses and measure a velocity of this ring of 810 ± 330 km s⁻¹ larger than the cluster mean velocity. Our analysis suggests the presence of another ring surrounding the core, whose velocity is 660 ± 300 km s⁻¹ larger than the cluster velocity. These X-ray features are not associated with any optical substructures, and support the core-sloshing scenario suggested in previous work.

With new high-resolution CO and H i data, we revisited the large-scale interstellar medium (ISM) environment toward the SS 433/W50 system. We find that two interesting molecular cloud (MC) concentrations, G39.315−1.155 and G40.331−4.302, are well aligned along the precession cone of SS 433 within a smaller opening angle of ∼±7°. The kinematic features of the two MCs at ∼73–84 km s⁻¹, as well as those of the corresponding atomic-gas counterparts, are consistent with the kinematic characteristics of SS 433. That is, the receding gas from SS 433 jet is probably responsible for the redshifted feature of G39.315−1.155 near the Galactic plane, and the approaching one may power the blueshifted gas of G40.331−4.302 toward the observer. Moreover, the H i emission at V_LSR ∼ 70–90 km s⁻¹ displays the morphological resemblance with the radio nebula W50. We suggest that the V_LSR = 77 ± 5 km s⁻¹ gas is physically associated with SS 433/W50, leading to a near kinematic distance of 4.9 ± 0.4 kpc for the system. The observed gas features, which are located outside the current radio boundaries of W50, are probably the fossil record of jet–ISM interactions at ∼10⁵ years ago. The energetic jets of the unique microquasar have profound effects on its ISM environment, which may facilitate the formation of molecular gas on the timescale of ≲0.1 Myr for the ram pressure of ∼2 × 10⁶ K cm⁻³.

We perform cooling simulations for isolated neutron stars using recently developed equations of state for their core. The equations of state are obtained from new parametrizations of the FSU2 relativistic mean-field functional that reproduce the properties of nuclear matter and finite nuclei, while fulfilling the restrictions on high-density matter deduced from heavy-ion collisions, measurements of massive 2 M_⊙ neutron stars, and neutron star radii below 13 km. We find that two of the models studied, FSU2R (with nucleons) and in particular FSU2H (with nucleons and hyperons), show very good agreement with cooling observations, even without including extensive nucleon pairing. This suggests that the cooling observations are more compatible with an equation of state that produces a soft nuclear symmetry energy, hence it generates small neutron star radii. However, both models favor large stellar masses, above 1.8 M_⊙, to explain the colder isolated neutron stars that have been observed, even if nucleon pairing is present.

Supernova iPTF14hls maintained a bright, variable luminosity for more than 600 days, while lines of hydrogen and iron in its spectrum had different speeds but showed little evolution. Here, several varieties of models are explored for iPTF14hls-like events. They are based upon circumstellar medium (CSM) interaction in an ordinary supernova, pulsational pair-instability supernovae (PPISN), and magnetar formation. Each is able to explain the enduring emission and brightness of iPTF14hls but each has shortcomings when confronted with other observed characteristics. The PPISN model can, in some cases, produce a presupernova transient like the one observed at the site of iPTF14hls in 1954. It also offers a clear path to providing the necessary half solar mass of material at ∼5 × 10¹⁶ cm for CSM interaction to work and it can give an irregular light curve without invoking additional assumptions. It explains the 4000 km s⁻¹ seen in the iron lines but without additional energy input it strains to explain the nearly constant 8000 km s⁻¹ velocity seen in H_α. Magnetar models can also explain most of the observed features but they give a smooth light curve and may be difficult to reconcile with the observation of slow-moving hydrogen at late times. The various models predict different spectral characteristics and a remnant that, today, could be a black hole, magnetar, or even a star. Further observations and calculations of radiation transport will narrow the range of possibilities.

We present a suite of Atacama Large Millimeter Array (ALMA) interferometric molecular line and continuum images that elucidate, on linear size scales of ∼30–40 au, the chemical structure of the nearby, evolved, protoplanetary disk orbiting the close binary system V4046 Sgr. The observations were undertaken in the 1.1–1.4 mm wavelength range (ALMA Bands 6 and 7) with antenna configurations involving maximum baselines of several hundred meters, yielding subarcsecond-resolution images in more than a dozen molecular species and isotopologues. Isotopologues of CO and HCN display centrally peaked morphologies of integrated emission-line intensity, whereas the line emission from complex nitrile group molecules (HC₃N, CH₃CN), deuterated molecules (DCN, DCO⁺), hydrocarbons (as traced by C₂H), and potential CO ice line tracers (N₂H⁺, and H₂CO) appears as a sequence of sharp and diffuse rings. The dimensions and morphologies of HC₃N and CH₃CN emission are suggestive of photodesorption of organic ices from the surfaces of dust grains, while the sequence of increasing radius of peak intensity represented by DCN (smallest), DCO⁺, N₂H⁺, and H₂CO (largest) is qualitatively consistent with the expected decline of midplane gas temperature with increasing disk radius. Empirical modeling indicates that the sharp-edged C₂H emission ring lies at relatively deep disk layers, leaving open the question of the origin of C₂H abundance enhancements in evolved disks. This study of the "molecular anatomy" of V4046 Sgr should serve as motivation for additional subarcsecond ALMA molecular line imaging surveys of nearby, evolved protoplanetary disks aimed at addressing major uncertainties in protoplanetary disk physical and chemical structure and molecular production pathways.

Pressure-supported systems modeled under Modified Newtonian dynamics (MOND)ian extended gravity are expected to show an outer flattening in their velocity dispersion profiles. A characteristic scaling between the amplitude of the asymptotic velocity dispersion and the radius at which the flattening occurs is also expected. By comprehensively analyzing the dynamical behavior of ∼300 extremely low-rotating elliptical galaxies from the Mapping Nearby Galaxies at APO (MaNGA) survey, we show this type of pressure-supported system to be consistent with MONDian expectations, for a range of central velocity dispersion values of 60 km s⁻¹ < σ_central < 280 km s⁻¹ and asymptotic velocity dispersion values of $28\,\mathrm{km}\,{{\rm{s}}}^{-1}\lt {\sigma }_{\infty }\lt 250\,\mathrm{km}\,{{\rm{s}}}^{-1}$. We find that a universal velocity dispersion profile accurately describes the studied systems; the predicted kinematics of extended gravity are verified for all well-observed galaxies.

We present a study of the origin of one interplanetary coronal mass ejection (ICME) that lacked an easily identifiable signature of an associated progenitor coronal mass ejection (CME) near the Sun in the observations of SOHO/LASCO at the L1 point. We consider these kinds of ICMEs as problematic, as they pose the difficulty of understanding the Sun–Earth connection and providing space weather warnings; understanding the causes of problematic ICMEs is important for space weather forecasting. This study presents the first detailed analysis of a geoeffective problematic ICME that occurred on 2011 May 28, whose progenitor CMEs are difficult to identify in LASCO images, but fortunately they were captured by SECCHI on board the STEREO spacecraft in the quadrature configuration. There are two progenitor CMEs launching from the Sun in succession of 8 hours. We apply the graduated cylindrical shell model to reconstruct the 3D geometry, propagating direction, velocity, and brightness of the two CMEs. The main cause of the first CME (CME-1) invisible in SOHO/LASCO is due to its low mass; that is, when the CME emerges above the occulter, its brightness is as faint as the noise. The second CME (CME-2) is small, including a narrow angular width and a small cross-section of the magnetic flux rope. Even though propagating toward the Earth, CME-2 appeared as a narrow CME instead of as a halo or partial halo CME in the LASCO field of view. We also show that CME-2 propagates faster than CME-1, and that they might have interacted in the interplanetary space.

We present optical spectroscopic and photometric observations of the nearby type Ic supernova (SN Ic) SN 2014L. This SN was discovered by the Tsinghua-NAOC Transient Survey (TNTS) in the nearby type-Sc spiral galaxy M99 (NGC 4254). Fitting to the early-time light curve indicates that SN 2014L was detected at only a few hours after the shock breakout, and it reached a peak brightness of M_V = −17.73 ± 0.28 mag (L = [2.06 ± 0.50] ×10⁴² erg s⁻¹) approximately 13 days later. SN 2014L shows a close resemblance to SN 2007gr in the photometric evolution, while it shows stronger absorption features of intermediate-mass elements (especially Ca ii) in the early-time spectra. Based on simple modeling of the observed light curves, we derived the mass of synthesized ⁵⁶Ni as M_Ni = 0.075 ± 0.025 M_⊙, and the mass and total energy of the ejecta as M_ej = 1.00 ± 0.20M_⊙ and E_ej = 1.45 ±0.25 foe, respectively. Given these typical explosion parameters, the early detection, and the extensive observations, we suggest that SN 2014L could be a template sample for the investigation of SNe Ic.

The extended Baryon Oscillation Spectroscopic Survey (eBOSS) Data Release 14 sample includes 80,118 luminous red galaxies (LRGs). By combining these galaxies with the high-redshift tail of the BOSS galaxy sample, we form a sample of LRGs at an effective redshift z = 0.72, covering an effective volume of 0.9 Gpc³. We account for spurious fluctuations caused by targeting and by redshift failures, which were validated on a set of mock catalogs. This analysis is sufficient to provide a 2.5% measurement of spherically averaged baryon acoustic oscillations (BAO), ${D}_{V}(z=0.72)={2377}_{-59}^{+61}({r}_{d}/{r}_{d,\mathrm{fid}})$ Mpc, at 2.8σ of significance. Together with the recent quasar-based BAO measurement at z = 1.5 and forthcoming emission line galaxy–based measurements, this measurement demonstrates that eBOSS is fulfilling its remit of extending the range of redshifts covered by such measurements, laying the groundwork for forthcoming surveys such as the Dark Energy Spectroscopic Survey and Euclid.