Table of contents

Remote observation of spectroscopic emissions is a potential tool for the identification and quantification of various species in comets. The CO Cameron band (to trace CO₂) and atomic oxygen emissions (to trace H₂O and/or CO₂, CO) have been used to probe neutral composition in the cometary coma. Using a coupled-chemistry-emission model, various excitation processes controlling the CO Cameron band and different atomic oxygen and atomic carbon emissions have been modeled in comet 67P/Churyumov–Gerasimenko at 1.29 AU (perihelion) and at 3 AU heliocentric distances, which is being explored by ESA's Rosetta mission. The intensities of the CO Cameron band, atomic oxygen, and atomic carbon emission lines as a function of projected distance are calculated for different CO and CO₂ volume mixing ratios relative to water. Contributions of different excitation processes controlling these emissions are quantified. We assess how CO₂ and/or CO volume mixing ratios with respect to H₂O can be derived based on the observed intensities of the CO Cameron band, atomic oxygen, and atomic carbon emission lines. The results presented in this work serve as baseline calculations to understand the behavior of low out-gassing cometary coma and compare them with the higher gas production rate cases (e.g., comet Halley). Quantitative analysis of different excitation processes governing the spectroscopic emissions is essential to study the chemistry of inner coma and to derive neutral gas composition.

We use radiation hydrodynamics with direct particle integration to explore the feasibility of chondrule formation in planetary embryo bow shocks. The calculations presented here are used to explore the consequences of a Mars-size planetary embryo traveling on a moderately excited orbit through the dusty, early environment of the solar system. The embryo's eccentric orbit produces a range of supersonic relative velocities between the embryo and the circularly orbiting gas and dust, prompting the formation of bow shocks. Temporary atmospheres around these embryos, which can be created via volatile outgassing and gas capture from the surrounding nebula, can non-trivially affect thermal profiles of solids entering the shock. We explore the thermal environment of solids that traverse the bow shock at different impact radii, the effects that planetoid atmospheres have on shock morphologies, and the stripping efficiency of planetoidal atmospheres in the presence of high relative winds. Simulations are run using adiabatic and radiative conditions, with multiple treatments for the local opacities. Shock speeds of 5, 6, and 7 km s⁻¹ are explored. We find that a high-mass atmosphere and inefficient radiative conditions can produce peak temperatures and cooling rates that are consistent with the constraints set by chondrule furnace studies. For most conditions, the derived cooling rates are potentially too high to be consistent with chondrule formation.

A macronova (or kilonova) was observed as an infrared excess several days after the short gamma-ray burst GRB 130603B. Although the r-process radioactivity is widely discussed as an energy source, it requires a huge mass of ejecta from a neutron star (NS) binary merger. We propose a new model in which the X-ray excess gives rise to the simultaneously observed infrared excess via thermal re-emission, and explore what constraints this would place on the mass and velocity of the ejecta. This X-ray-powered model explains both the X-ray and infrared excesses with a single energy source such as the central engine like a black hole, and allows for a broader parameter region than the previous models, in particular a smaller ejecta mass $\sim {10}^{-3}\mbox{--}{10}^{-2}{M}_{\odot }$ and higher iron abundance mixed as suggested by general relativistic simulations for typical NS–NS mergers. We also discuss the other macronova candidates in GRB 060614 and GRB 080503, and the implications for the search of electromagnetic counterparts to gravitational waves.

We have commenced a multiyear program, the Caltech-NRAO Stripe 82 Survey (CNSS), to search for radio transients with the Jansky VLA in the Sloan Digital Sky Survey Stripe 82 region. The CNSS will deliver five epochs over the entire ∼270 deg² of Stripe 82, an eventual deep combined map with an rms noise of ∼40 μJy and catalogs at a frequency of 3 GHz, and having a spatial resolution of 3''. This first paper presents the results from an initial pilot survey of a 50 deg² region of Stripe 82, involving four epochs spanning logarithmic timescales between 1 week and 1.5 yr, with the combined map having a median rms noise of 35 μJy. This pilot survey enabled the development of the hardware and software for rapid data processing, as well as transient detection and follow-up, necessary for the full 270 deg² survey. Data editing, calibration, imaging, source extraction, cataloging, and transient identification were completed in a semi-automated fashion within 6 hr of completion of each epoch of observations, using dedicated computational hardware at the NRAO in Socorro and custom-developed data reduction and transient detection pipelines. Classification of variable and transient sources relied heavily on the wealth of multiwavelength legacy survey data in the Stripe 82 region, supplemented by repeated mapping of the region by the Palomar Transient Factory. A total of ${3.9}_{-0.9}^{+0.5}$% of the few thousand detected point sources were found to vary by greater than 30%, consistent with similar studies at 1.4 and 5 GHz. Multiwavelength photometric data and light curves suggest that the variability is mostly due to shock-induced flaring in the jets of active galactic nuclei (AGNs). Although this was only a pilot survey, we detected two bona fide transients, associated with an RS CVn binary and a dKe star. Comparison with existing legacy survey data (FIRST, VLA-Stripe 82) revealed additional highly variable and transient sources on timescales between 5 and 20 yr, largely associated with renewed AGN activity. The rates of such AGNs possibly imply episodes of enhanced accretion and jet activity occurring once every ∼40,000 yr in these galaxies. We compile the revised radio transient rates and make recommendations for future transient surveys and joint radio-optical experiments.

We present high-contrast Magellan adaptive optics images of HD 7449, a Sun-like star with one planet and a long-term radial velocity (RV) trend. We unambiguously detect the source of the long-term trend from 0.6–2.15 μm at a separation of ∼054. We use the object's colors and spectral energy distribution to show that it is most likely an M4–M5 dwarf (mass ∼0.1–0.2 ${M}_{\odot }$) at the same distance as the primary and is therefore likely bound. We also present new RVs measured with the Magellan/MIKE and Planet Finder Spectrograph spectrometers and compile these with archival data from CORALIE and HARPS. We use a new Markov chain Monte Carlo procedure to constrain both the mass ($\gt 0.17$${M}_{\odot }$ at 99% confidence) and semimajor axis (∼18 AU) of the M dwarf companion (HD 7449B). We also refine the parameters of the known massive planet (HD 7449Ab), finding that its minimum mass is ${1.09}_{-0.19}^{+0.52}$M_J, its semimajor axis is ${2.33}_{-0.02}^{+0.01}$ AU, and its eccentricity is ${0.8}_{-0.06}^{+0.08}$. We use N-body simulations to constrain the eccentricity of HD 7449B to ≲0.5. The M dwarf may be inducing Kozai oscillations on the planet, explaining its high eccentricity. If this is the case and its orbit was initially circular, the mass of the planet would need to be ≲1.5 M_J. This demonstrates that strong constraints on known planets can be made using direct observations of otherwise undetectable long-period companions.

By varying the profiles of stellar extreme ultraviolet (EUV) spectral energy distributions (SEDs), we tested the influences of stellar EUV SEDs on the physical and chemical properties of an escaping atmosphere. We apply our model to study four exoplanets: HD 189733b, HD 209458b, GJ 436b, and Kepler-11b. We find that the total mass loss rates of an exoplanet, which are determined mainly by the integrated fluxes, are moderately affected by the profiles of the EUV SED, but the composition and species distributions in the atmosphere can be dramatically modified by the different profiles of the EUV SED. For exoplanets with a high hydrodynamic escape parameter (λ), the amount of atomic hydrogen produced by photoionization at different altitudes can vary by one to two orders of magnitude with the variation of stellar EUV SEDs. The effect of photoionization of H is prominent when the EUV SED is dominated by the low-energy spectral region (400–900 Å), which pushes the transition of H/H⁺ to low altitudes. In contrast, the transition of H/H⁺ moves to higher altitudes when most photons are concentrated in the high-energy spectral region (50–400 Å). For exoplanets with a low λ, the lower temperatures of the atmosphere make many chemical reactions so important that photoionization alone can no longer determine the composition of the escaping atmosphere. For HD 189733b, it is possible to explain the time variability of Lyα between 2010 and 2011 by a change in the EUV SED of the host K-type star, yet invoking only thermal H i in the atmosphere.

We combine Kepler photometry with ground-based spectra to present a comprehensive dynamical model of the double red giant eclipsing binary KIC 9246715. While the two stars are very similar in mass (${M}_{1}={2.171}_{-0.008}^{+0.006}\ {M}_{\odot }$, ${M}_{2}={2.149}_{-0.008}^{+0.006}\ {M}_{\odot }$) and radius (${R}_{1}={8.37}_{-0.07}^{+0.03}\ {R}_{\odot }$, ${R}_{2}={8.30}_{-0.03}^{+0.04}\ {R}_{\odot }$), an asteroseismic analysis finds one main set of solar-like oscillations with unusually low-amplitude, wide modes. A second set of oscillations from the other star may exist, but this marginal detection is extremely faint. Because the two stars are nearly twins, KIC 9246715 is a difficult target for a precise test of the asteroseismic scaling relations, which yield M = 2.17 ± 0.14 M_⊙ and R = 8.26 ± 0.18 R_⊙. Both stars are consistent with the inferred asteroseismic properties, but we suspect the main oscillator is Star 2 because it is less active than Star 1. We find evidence for stellar activity and modest tidal forces acting over the 171 day eccentric orbit, which are likely responsible for the essential lack of solar-like oscillations in one star and weak oscillations in the other. Mixed modes indicate the main oscillating star is on the secondary red clump (a core-He-burning star), and stellar evolution modeling supports this with a coeval history for a pair of red clump stars. This system is a useful case study and paves the way for a detailed analysis of more red giants in eclipsing binaries, an important benchmark for asteroseismology.

From pulsating stars to transiting exoplanets, the search for periodic signals in K2 data, Kepler's two-wheeled extension, is relevant to a long list of scientific goals. Systematics affecting K2 light curves due to the decreased spacecraft pointing precision inhibit the easy extraction of periodic signals from the data. We here develop a method for producing periodograms of K2 light curves that are insensitive to pointing-induced systematics; the Systematics-insensitive Periodogram (SIP). Traditional sine-fitting periodograms use a generative model to find the frequency of a sinusoid that best describes the data. We extend this principle by including systematic trends, based on a set of "eigen light curves," following Foreman-Mackey et al., in our generative model as well as a sum of sine and cosine functions over a grid of frequencies. Using this method we are able to produce periodograms with vastly reduced systematic features. The quality of the resulting periodograms are such that we can recover acoustic oscillations in giant stars and measure stellar rotation periods without the need for any detrending. The algorithm is also applicable to the detection of other periodic phenomena such as variable stars, eclipsing binaries and short-period exoplanet candidates. The SIP code is available at https://github.com/RuthAngus/SIPK2.

Compact binary system mergers are expected to generate gravitational radiation detectable by ground-based interferometers. A subset of these, the merger of a neutron star with another neutron star or a black hole, are also the most popular model for the production of short gamma-ray bursts (GRBs). The Swift Burst Alert Telescope (BAT) and the Fermi Gamma-ray Burst Monitor (GBM) trigger on short GRBs (SGRBs) at rates that reflect their relative sky exposures, with the BAT detecting 10 per year compared to about 45 for GBM. We examine the SGRB populations detected by Swift BAT and Fermi GBM. We find that the Swift BAT triggers on weaker SGRBs than Fermi GBM, providing they occur close to the center of the BAT field of view, and that the Fermi GBM SGRB detection threshold remains flatter across its field of view. Overall, these effects combine to give the instruments the same average sensitivity, and account for the SGRBs that trigger one instrument but not the other. We do not find any evidence that the BAT and GBM are detecting significantly different populations of SGRBs. Both instruments can detect untriggered SGRBs using ground searches seeded with time and position. The detection of SGRBs below the on-board triggering sensitivities of Swift BAT and Fermi GBM increases the possibility of detecting and localizing the electromagnetic counterparts of gravitational wave (GW) events seen by the new generation of GW detectors.

We present radio and X-ray observations of the nearby SN IIb 2013df in NGC 4414 from 10 to 250 days after the explosion. The radio emission showed a peculiar steep-to-shallow spectral evolution. We present a model in which inverse Compton cooling of synchrotron emitting electrons can account for the observed spectral and light curve evolution. A significant mass-loss rate, $\dot{M}\approx 8\times {10}^{-5}\;{M}_{\odot }$ yr⁻¹ for a wind velocity of 10 km s⁻¹, is estimated from the detailed modeling of radio and X-ray emission, which are primarily due to synchrotron and bremsstrahlung, respectively. We show that SN 2013df is similar to SN 1993J in various ways. The shock wave speed of SN 2013df was found to be average among the radio supernovae; ${v}_{\mathrm{sh}}/c\sim 0.07$. We did not find any significant deviation from smooth decline in the light curve of SN 2013df. One of the main results of our self-consistent multiband modeling is the significant deviation from energy equipartition between magnetic fields and relativistic electrons behind the shock. We estimate ${\epsilon }_{e}=200{\epsilon }_{B}$. In general for SNe IIb, we find that the presence of bright optical cooling envelope emission is linked with free–free radio absorption and bright thermal X-ray emission. This finding suggests that more extended progenitors, similar to that of SN 2013df, suffer from substantial mass loss in the years before the supernova.

Detections of $z\;\approx \;$ 0 oxygen absorption and emission lines indicate the Milky Way hosts a hot ($\sim {10}^{6}$ K), low-density plasma extending $\gtrsim 50\;{\rm{kpc}}$ into the Mily Way's halo. Current X-ray telescopes cannot resolve the line profiles, but the variation of their strengths on the sky constrains the radial gas distribution. Interpreting the O vii Kα absorption line strengths has several complications, including optical depth and line of sight velocity effects. Here, we present model absorption line profiles accounting for both of these effects to show the lines can exhibit asymmetric structures and be broader than the intrinsic Doppler width. The line profiles encode the hot gas rotation curve, the net inflow or outflow of hot gas, and the hot gas angular momentum profile. We show how line of sight velocity effects impact the conversion between equivalent width and the column density, and provide modified curves of growth accounting for these effects. As an example, we analyze the LMC sight line pulsar dispersion measure and O vii equivalent width to show the average gas metallicity is $\gtrsim 0.6{Z}_{\odot }$ and b$\;\gtrsim \;100$ km s⁻¹. Determining these properties offers valuable insights into the dynamical state of the Milky Way's hot gas, and improves the line strength interpretation. We discuss future strategies to observe these effects with an instrument that has a spectral resolution of about 3000, a goal that is technically possible today.

We use the Hubble Space Telescope (HST) archive of ultraviolet (UV) quasar spectroscopy to conduct the first blind survey for damped Lyα absorbers (DLAs) at low redshift ($z\lt 1.6$). Our statistical sample includes 463 quasars with spectral coverage spanning a total redshift path ${\rm{\Delta }}z=123.3$ or an absorption path ${\rm{\Delta }}X=229.7$. Within this survey path, we identify 4 DLAs defined as absorbers with H i column density ${N}_{{\rm{H}}{\rm{I}}}$$\geqslant \;{10}^{20.3}$ cm⁻², which implies an incidence per absorption length ${{\ell }}_{{\rm{DLA}}}(X)$$=\;{0.017}_{-0.008}^{+0.014}$ at a median survey path redshift of z = 0.623. While our estimate of ${{\ell }}_{{\rm{DLA}}}(X)$ is lower than earlier estimates at $z\approx 0$ from H i 21 cm emission studies, the results are consistent within the measurement uncertainties. Our data set is too small to properly sample the ${N}_{{\rm{H}}{\rm{I}}}$ frequency distribution function $f({N}_{{\rm{H}}{\rm{I}}},X)$, but the observed distribution agrees with previous estimates at $z\gt 2$. Adopting the $z\gt 2$ shape of $f({N}_{{\rm{H}}{\rm{I}}},X)$, we infer an H i mass density at $z\sim 0.6$ of ${\rho }_{{\rm{H}}\;{\rm{I}}}^{{\rm{DLA}}}$$=\;{0.25}_{-0.12}^{+0.20}\times {10}^{8}{M}_{\odot }\;{{\rm{Mpc}}}^{-3}$. This is significantly lower than previous estimates from targeted DLA surveys with the HST, but consistent with results from low-z H i 21 cm observations, and suggests that the neutral gas density of the universe has been decreasing over the past 10 Gyr.

We report the discovery of extended gamma-ray emission measured by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the region of the supernova remnant (SNR) HB 3 (G132.7+1.3) and the W3 II complex adjacent to the southeast of the remnant. W3 is spatially associated with bright ¹²CO (J = 1–0) emission. The gamma-ray emission is spatially correlated with this gas and the SNR. We discuss the possibility that gamma rays originate in interactions between particles accelerated in the SNR and interstellar gas or radiation fields. The decay of neutral pions produced in nucleon–nucleon interactions between accelerated hadrons and interstellar gas provides a reasonable explanation for the gamma-ray emission. The emission from W3 is consistent with irradiation of the CO clouds by the cosmic rays accelerated in HB 3.

Most modern astrophysical data sets are multi-dimensional; a characteristic that can nowadays generally be conserved and exploited scientifically during the data reduction/simulation and analysis cascades. However, the same multi-dimensional data sets are systematically cropped, sliced, and/or projected to printable two-dimensional diagrams at the publication stage. In this article, we introduce the concept of the "X3D pathway" as a mean of simplifying and easing the access to data visualization and publication via three-dimensional (3D) diagrams. The X3D pathway exploits the facts that (1) the X3D 3D file format lies at the center of a product tree that includes interactive HTML documents, 3D printing, and high-end animations, and (2) all high-impact-factor and peer-reviewed journals in astrophysics are now published (some exclusively) online. We argue that the X3D standard is an ideal vector for sharing multi-dimensional data sets because it provides direct access to a range of different data visualization techniques, is fully open source, and is a well-defined standard from the International Organization for Standardization. Unlike other earlier propositions to publish multi-dimensional data sets via 3D diagrams, the X3D pathway is not tied to specific software (prone to rapid and unexpected evolution), but instead is compatible with a range of open-source software already in use by our community. The interactive HTML branch of the X3D pathway is also actively supported by leading peer-reviewed journals in the field of astrophysics. Finally, this article provides interested readers with a detailed set of practical astrophysical examples designed to act as a stepping stone toward the implementation of the X3D pathway for any other data set.

We present multiepoch, large-scale (∼2000 arcmin²), fairly deep (∼16 μJy), high-resolution (∼1'') radio observations of the Perseus star-forming complex obtained with the Karl G. Jansky Very Large Array at frequencies of 4.5 and 7.5 GHz. These observations were mainly focused on the clouds NGC 1333 and IC 348, although we also observed several fields in other parts of the Perseus complex. We detect a total of 206 sources, 42 of which are associated with young stellar objects (YSOs). The radio properties of about 60% of the YSOs are compatible with a nonthermal radio emission origin. Based on our sample, we find a fairly clear relation between the prevalence of nonthermal radio emission and evolutionary status of the YSOs. By comparing our results with previously reported X-ray observations, we show that YSOs in Perseus follow a Güdel–Benz relation with κ = 0.03, consistent with other regions of star formation. We argue that most of the sources detected in our observations but not associated with known YSOs are extragalactic, but provide a list of 20 unidentified radio sources whose radio properties are consistent with being YSO candidates. Finally, we also detect five sources with extended emission features that can clearly be associated with radio galaxies.

Massive, evolved stars play a crucial role in the metal enrichment, dust budget, and energetics of the interstellar medium; however, the details of their evolution are uncertain because of their rarity and short lifetimes before exploding as supernovae. Discrepancies between theoretical predictions from single-star evolutionary models and observations of massive stars have evoked a shifting paradigm that implicates the importance of binary interaction. We present mid- to far-infrared observations from the Stratospheric Observatory for Infrared Astronomy of a conical "helix" of warm dust (∼180 K) that appears to extend from the Wolf–Rayet star WR102c. Our interpretation of the helix is a precessing, collimated outflow that emerged from WR102c during a previous evolutionary phase as a rapidly rotating luminous blue variable. We attribute the precession of WR102c to gravitational interactions with an unseen compact binary companion whose orbital period can be constrained to 800 days < P < 1400 days from the inferred precession period, τ_p ∼ 1.4 × 10⁴ yr, and limits imposed on the stellar and orbital parameters of the system. Our results concur with the range of orbital periods (P ≲ 1500 days) where spin-up via mass exchange is expected to occur for massive binary systems.

In this work we investigate the sensitivity of principal component analysis (PCA) to the velocity power spectrum in high-opacity regimes of the interstellar medium (ISM). For our analysis we use synthetic position–position–velocity (PPV) cubes of fractional Brownian motion and magnetohydrodynamics (MHD) simulations, post-processed to include radiative transfer effects from CO. We find that PCA analysis is very different from the tools based on the traditional power spectrum of PPV data cubes. Our major finding is that PCA is also sensitive to the phase information of PPV cubes and this allows PCA to detect the changes of the underlying velocity and density spectra at high opacities, where the spectral analysis of the maps provides the universal −3 spectrum in accordance with the predictions of the Lazarian & Pogosyan theory. This makes PCA a potentially valuable tool for studies of turbulence at high opacities, provided that proper gauging of the PCA index is made. However, we found the latter to not be easy, as the PCA results change in an irregular way for data with high sonic Mach numbers. This is in contrast to synthetic Brownian noise data used for velocity and density fields that show monotonic PCA behavior. We attribute this difference to the PCA's sensitivity to Fourier phase information.

The Ertel theorem on the vorticity along the flow of adiabatic fluids is generalized for non-adiabatic flows. Several limiting cases are analyzed and the results are applied to flows behind different hydrodynamics fronts, particularly to thermal fronts (heat and cooling fronts). An important conclusion of the present analysis is that vorticity is inherent in the condensation's (or hot spots) formation by thermal instabilities in plasma flows. Implications for several astrophysical plasmas are outlined.

Electron-impact excitation of H₂ triplet states plays an important role in the heating of outer planet upper thermospheres. The ${d}^{3}{{\rm{\Pi }}}_{u}$ state is the third ungerade triplet state, and the ${d}^{3}{{\rm{\Pi }}}_{u}$–$a{}^{3}{{\rm{\Sigma }}}_{g}^{+}$ emission is the largest cascade channel for the $a{}^{3}{{\rm{\Sigma }}}_{g}^{+}$ state. Accurate energies of the $d{}^{3}{{\rm{\Pi }}}_{u}^{-}$(v, J) levels are calculated from an ab initio potential energy curve. Radiative lifetimes of the ${d}^{3}{{\rm{\Pi }}}_{u}$(v, J) levels are obtained by an accurate evaluation of the ${d}^{3}{{\rm{\Pi }}}_{u}$–$a{}^{3}{{\rm{\Sigma }}}_{g}^{+}$ transition probabilities. The emission yields are determined from experimental lifetimes and calculated radiative lifetimes and are further verified by comparing experimental and synthetic ${d}^{3}{{\rm{\Pi }}}_{u}$–$a{}^{3}{{\rm{\Sigma }}}_{g}^{+}$ spectra at 20 eV impact energy. Spectral analysis revealed that multipolar components beyond the dipolar term are required to model the ${X}^{1}{{\rm{\Sigma }}}_{g}^{+}$–${d}^{3}{{\rm{\Pi }}}_{u}$ excitation, and significant cascade excitation occurs at the ${d}^{3}{{\rm{\Pi }}}_{u}$(v = 0,1) levels. Kinetic energy (E_k) distributions of H atoms produced via predissociation of the ${d}^{3}{{\rm{\Pi }}}_{u}$ state and the ${d}^{3}{{\rm{\Pi }}}_{u}$−$a{}^{3}{{\rm{\Sigma }}}_{g}^{+}$−$b{}^{3}{{\rm{\Sigma }}}_{u}^{+}$ cascade dissociative emission are obtained. Predissociation of the ${d}^{3}{{\rm{\Pi }}}_{u}$ state produces H atoms with an average E_k of 2.3 ± 0.4 eV/atom, while the E_k distribution of the ${d}^{3}{{\rm{\Pi }}}_{u}$−$a{}^{3}{{\rm{\Sigma }}}_{g}^{+}$−$b{}^{3}{{\rm{\Sigma }}}_{u}^{+}$ channel is similar to that of the ${X}^{1}{{\rm{\Sigma }}}_{g}^{+}$–$a{}^{3}{{\rm{\Sigma }}}_{g}^{+}$−$b{}^{3}{{\rm{\Sigma }}}_{u}^{+}$ channel and produces H(1s) atoms with an average E_k of 1.15 ± 0.05 eV/atom. On average, each H₂ excited to the ${d}^{3}{{\rm{\Pi }}}_{u}$ state in an H₂-dominated atmosphere deposits 3.3 ± 0.4 eV into the atmosphere, while each H₂ directly excited to the $a{}^{3}{{\rm{\Sigma }}}_{g}^{+}$ state gives 2.2–2.3 eV to the atmosphere. The spectral distribution of the calculated $a{}^{3}{{\rm{\Sigma }}}_{g}^{+}$ –$b{}^{3}{{\rm{\Sigma }}}_{u}^{+}$ continuum emission due to the ${X}^{1}{{\rm{\Sigma }}}_{g}^{+}$–${d}^{3}{{\rm{\Pi }}}_{u}$ excitation is significantly different from that of direct $a{}^{3}{{\rm{\Sigma }}}_{g}^{+}$ excitation.

The black hole in the center of the Milky Way, Sgr A*, has the largest mass-to-distance ratio among all known black holes in the universe. This property makes Sgr A* the optimal target for testing the gravitational no-hair theorem. In the near future, major developments in instrumentation will provide the tools for high-precision studies of its spacetime via observations of relativistic effects in stellar orbits, in the timing of pulsars, and in horizon-scale images of its accretion flow. We explore here the prospect of measuring the properties of the black hole spacetime using all of these three types of observations. We show that the correlated uncertainties in the measurements of the black hole spin and quadrupole moment using the orbits of stars and pulsars are nearly orthogonal to those obtained from measuring the shape and size of the shadow the black hole casts on the surrounding emission. Combining these three types of observations will therefore allow us to assess and quantify systematic biases and uncertainties in each measurement and lead to a highly accurate, quantitative test of the gravitational no-hair theorem.

We report on X-ray observations of the 5.54 s transient magnetar XTE J1810–197 using the XMM-Newton and Chandra observatories, analyzing new data from 2008 through 2014, and re-analyzing data from 2003 through 2007 with the benefit of these six years of new data. From the discovery of XTE J1810–197 during its 2003 outburst to the most recent 2014 observations, its 0.3–10 keV X-ray flux has declined by a factor of about 50 from 4.1 × 10⁻¹¹ to 8.1 × 10⁻¹³ erg cm⁻² s⁻¹. Its X-ray spectrum has now reached a steady state. Pulsations continue to be detected from a 0.3 keV thermal hot spot that remains on the neutron star (NS) surface. The luminosity of this hot spot exceeds XTE J1810–197's spin-down luminosity, indicating continuing magnetar activity. We find that XTE J1810–197's X-ray spectrum is best described by a multiple component blackbody model in which the coldest 0.14 keV component likely originates from the entire NS surface, and the thermal hot-spot is, at different epochs, well described by an either one- or two-component blackbody model. A 1.2 keV absorption line, possibly due to resonant proton scattering, is detected at all epochs. The X-ray flux of the hot spot decreased by $\approx 20\%$ between 2008 and 2009 March, the same period during which XTE J1810–197 became radio quiet.

We present four ab initio axisymmetric core-collapse supernova simulations initiated from 12, 15, 20, and 25 ${M}_{\odot }$ zero-age main sequence progenitors. All of the simulations yield explosions and have been evolved for at least 1.2 s after core bounce and 1 s after material first becomes unbound. These simulations were computed with our Chimera code employing RbR spectral neutrino transport, special and general relativistic transport effects, and state-of-the-art neutrino interactions. Continuing the evolution beyond 1 s after core bounce allows the explosions to develop more fully and the processes involved in powering the explosions to become more clearly evident. We compute explosion energy estimates, including the negative gravitational binding energy of the stellar envelope outside the expanding shock, of 0.34, 0.88, 0.38, and 0.70 Bethe (B ≡ ${10}^{51}$ erg) and increasing at 0.03, 0.15, 0.19, and 0.52 ${\text{B s}}^{-1}$, respectively, for the 12, 15, 20, and 25 ${M}_{\odot }$ models at the endpoint of this report. We examine the growth of the explosion energy in our models through detailed analyses of the energy sources and flows. We discuss how the explosion energies may be subject to stochastic variations as exemplfied by the effect of the explosion geometry of the 20 ${M}_{\odot }$ model in reducing its explosion energy. We compute the proto-neutron star masses and kick velocities. We compare our results for the explosion energies and ejected ${}^{56}\mathrm{Ni}$ masses against some observational standards despite the large error bars in both models and observations.

Thus far, judging the fate of a massive star (either a neutron star [NS] or a black hole) solely by its structure prior to core collapse has been ambiguous. Our work and previous attempts find a nonmonotonic variation of successful and failed supernovae with zero-age main-sequence mass, for which no single structural parameter can serve as a good predictive measure. However, we identify two parameters computed from the pre-collapse structure of the progenitor, which in combination allow for a clear separation of exploding and nonexploding cases with only a few exceptions (∼1%–2.5%) in our set of 621 investigated stellar models. One parameter is M₄, defining the normalized enclosed mass for a dimensionless entropy per nucleon of s = 4, and the other is ${\mu }_{4}\equiv ({dm}/{M}_{\odot })/({dr}/1000\;\mathrm{km}){| }_{s=4}$, being the normalized mass derivative at this location. The two parameters μ₄ and M₄μ₄ can be directly linked to the mass-infall rate, $\dot{M}$, of the collapsing star and the electron-type neutrino luminosity of the accreting proto-NS, ${L}_{{\nu }_{e}}\propto {M}_{\mathrm{ns}}\dot{M}$, which play a crucial role in the "critical luminosity" concept for the theoretical description of neutrino-driven explosions as runaway phenomena of the stalled accretion shock. All models were evolved employing the approach of Ugliano et al. for simulating neutrino-driven explosions in spherical symmetry. The neutrino emission of the accretion layer is approximated by a gray transport solver, while the uncertain neutrino emission of the 1.1 M_⊙ proto-NS core is parameterized by an analytic model. The free parameters connected to the core-boundary prescription are calibrated to reproduce the observables of SN 1987A for five different progenitor models.

Slow neutron captures are responsible for the production of about 50% of elements heavier than iron, mainly occurring during the asymptotic giant branch phase of low-mass stars (1 ≲ M/M_⊙ ≲ 3), where the main neutron source is the ¹³C(α, n)¹⁶O reaction. This last reaction is activated from locally produced ¹³C, formed by partial mixing of hydrogen into the He-rich layers. We present here the first attempt to describe a physical mechanism for the formation of the ¹³C reservoir, studying the mass circulation induced by magnetic buoyancy without adding new free parameters to those already involved in stellar modeling. Our approach represents the application to the stellar layers relevant for s-processing of recent exact analytical 2D and 3D models for magneto-hydrodynamic processes at the base of convective envelopes in evolved stars in order to promote downflows of envelope material for mass conservation during the occurrence of a dredge-up phenomenon. We find that the proton penetration is characterized by small concentrations, but is extended over a large fractional mass of the He-layers, thus producing ¹³C reservoirs of several 10⁻³M_⊙. The ensuing ¹³C-enriched zone has an almost flat profile, while only a limited production of ¹⁴N occurs. In order to verify the effects of our new findings we show how the abundances of the main s-component nuclei can be accounted for in solar proportions and how our large ¹³C-reservoir allows us to solve a few so far unexplained features in the abundance distribution of post-AGB objects.

Recent high-resolution Atmospheric Imaging Assembly/Solar Dynamics Observatory images show evidence of the development of the Kelvin–Helmholtz (KH) instability, as coronal mass ejections (CMEs) expand in the ambient corona. A large-scale magnetic field mostly tangential to the interface is inferred, both on the CME and on the background sides. However, the magnetic field component along the shear flow is not strong enough to quench the instability. There is also observational evidence that the ambient corona is in a turbulent regime, and therefore the criteria for the development of the instability are a priori expected to differ from the laminar case. To study the evolution of the KH instability with a turbulent background, we perform three-dimensional simulations of the incompressible magnetohydrodynamic equations. The instability is driven by a velocity profile tangential to the CME–corona interface, which we simulate through a hyperbolic tangent profile. The turbulent background is generated by the application of a stationary stirring force. We compute the instability growth rate for different values of the turbulence intensity, and find that the role of turbulence is to attenuate the growth. The fact that KH instability is observed sets an upper limit on the correlation length of the coronal background turbulence.

The aim of the present work is to specify the spatio-temporal characteristics of flare activity observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Geostationary Operational Environmental Satellite (GOES) in connection with the behavior of the longitudinal domain of enhanced sunspot activity known as active longitude (AL). By using our method developed for this purpose, we identified the AL in every Carrington Rotation provided by the Debrecen Photoheliographic Data. The spatial probability of flare occurrence has been estimated depending on the longitudinal distance from AL in the northern and southern hemispheres separately. We have found that more than 60% of the RHESSI and GOES flares is located within $\pm 36^\circ$ from the AL. Hence, the most flare-productive active regions tend to be located in or close to the active longitudinal belt. This observed feature may allow for the prediction of the geo-effective position of the domain of enhanced flaring probability. Furthermore, we studied the temporal properties of flare occurrence near the AL and several significant fluctuations were found. More precisely, the results of the method are the following fluctuations: 0.8, 1.3, and 1.8 years. These temporal and spatial properties of the solar flare occurrence within the active longitudinal belts could provide us with an enhanced solar flare forecasting opportunity.

Coronal rain clumps and prominence knots are dense condensations with chromospheric to transition region temperatures that fall down in the much hotter corona. Their typical speeds are in the range 30–150 km s⁻¹ and of the order of 10–30 km s⁻¹, respectively, i.e., they are considerably smaller than free-fall velocities. These cold blobs contain a mixture of ionized and neutral material that must be dynamically coupled in order to fall together, as observed. We investigate this coupling by means of hydrodynamic simulations in which the coupling arises from the friction between ions and neutrals. The numerical simulations presented here are an extension of those of Oliver et al. to the partially ionized case. We find that, although the relative drift speed between the two species is smaller than 1 m s⁻¹ at the blob center, it is sufficient to produce the forces required to strongly couple charged particles and neutrals. The ionization degree has no discernible effect on the main results of our previous work for a fully ionized plasma: the condensation has an initial acceleration phase followed by a period with roughly constant velocity, and, in addition, the maximum descending speed is clearly correlated with the ratio of initial blob to environment density.

The light curves of solar coronal loops often peak first in channels associated with higher temperatures and then in those associated with lower temperatures. The delay times between the different narrowband EUV channels have been measured for many individual loops and recently for every pixel of an active region observation. The time delays between channels for an active region exhibit a wide range of values. The maximum time delay in each channel pair can be quite large, i.e., >5000 s. These large time delays make-up 3%–26% (depending on the channel pair) of the pixels where a trustworthy, positive time delay is measured. It has been suggested that these time delays can be explained by simple impulsive heating, i.e., a short burst of energy that heats the plasma to a high temperature, after which the plasma is allowed to cool through radiation and conduction back to its original state. In this paper, we investigate whether the largest observed time delays can be explained by this hypothesis by simulating a series of coronal loops with different heating rates, loop lengths, abundances, and geometries to determine the range of expected time delays between a set of four EUV channels. We find that impulsive heating cannot address the largest time delays observed in two of the channel pairs and that the majority of the large time delays can only be explained by long, expanding loops with photospheric abundances. Additional observations may rule out these simulations as an explanation for the long time delays. We suggest that either the time delays found in this manner may not be representative of real loop evolution, or that the impulsive heating and cooling scenario may be too simple to explain the observations, and other potential heating scenarios must be explored.

Inferences about the spatial density or phase-space structure of stellar populations in the Milky Way require a precise determination of the effective survey volume. The volume observed by surveys such as Gaia or near-infrared spectroscopic surveys, which have good coverage of the Galactic midplane region, is highly complex because of the abundant small-scale structure in the three-dimensional interstellar dust extinction. We introduce a novel framework for analyzing the importance of small-scale structure in the extinction. This formalism demonstrates that the spatially complex effect of extinction on the selection function of a pencil-beam or contiguous sky survey is equivalent to a low-pass filtering of the extinction-affected selection function with the smooth density field. We find that the angular resolution of current 3D extinction maps is sufficient for analyzing Gaia sub-samples of millions of stars. However, the current distance resolution is inadequate and needs to be improved by an order of magnitude, especially in the inner Galaxy. We also present a practical and efficient method for properly taking the effect of extinction into account in analyses of Galactic structure through an effective selection function. We illustrate its use with the selection function of red-clump stars in APOGEE using and comparing a variety of current 3D extinction maps.

We present results from recent Suzaku and Chandra X-ray and Multiple Mirrior Telescope optical observations of the strongly merging "double cluster" A1750 out to its virial radius, both along and perpendicular to a putative large-scale structure filament. Some previous studies of individual clusters have found evidence for ICM entropy profiles that flatten at large cluster radii, as compared with the self-similar prediction based on purely gravitational models of hierarchical cluster formation, and gas fractions that rise above the mean cosmic value. Weakening accretion shocks and the presence of unresolved cool gas clumps, both of which are expected to correlate with large-scale structure filaments, have been invoked to explain these results. In the outskirts of A1750, we find entropy profiles that are consistent with self-similar expectations, and gas fractions that are consistent with the mean cosmic value, both along and perpendicular to the putative large-scale filament. Thus, we find no evidence for gas clumping in the outskirts of A1750, in either direction. This may indicate that gas clumping is less common in lower temperature (kT ≈ 4 keV), less massive systems, consistent with some (but not all) previous studies of low-mass clusters and groups. Cluster mass may, therefore, play a more important role in gas clumping than dynamical state. Finally, we find evidence for diffuse, cool (<1 keV) gas at large cluster radii (R₂₀₀) along the filament, which is consistent with the expected properties of the denser, hotter phase of the warm–hot intergalactic medium.

We examine the internal consistency of the Planck 2015 cosmic microwave background (CMB) temperature anisotropy power spectrum. We show that tension exists between cosmological constant cold dark matter (${\rm{\Lambda }}\mathrm{CDM}$) model parameters inferred from multipoles ${\ell }\lt 1000$ (roughly those accessible to Wilkinson Microwave Anisotropy Probe), and from ${\ell }\geqslant 1000$, particularly the CDM density, ${{\rm{\Omega }}}_{c}{h}^{2}$, which is discrepant at $2.5\sigma$ for a Planck -motivated prior on the optical depth, $\tau =0.07\pm 0.02$. We find some parameter tensions to be larger than previously reported because of inaccuracy in the code used by the Planck Collaboration to generate model spectra. The Planck${\ell }\geqslant 1000$ constraints are also in tension with low-redshift data sets, including Planck 's own measurement of the CMB lensing power spectrum ($2.4\sigma$), and the most precise baryon acoustic oscillation scale determination ($2.5\sigma$). The Hubble constant predicted by Planck from ${\ell }\geqslant 1000$, ${H}_{0}=64.1\pm 1.7$ km s${}^{-1}$ Mpc⁻¹, disagrees with the most precise local distance ladder measurement of $73.0\pm 2.4$ km s${}^{-1}$ Mpc⁻¹ at the $3.0\sigma$ level, while the Planck value from ${\ell }\lt 1000$, $69.7\pm 1.7$ km s${}^{-1}$ Mpc⁻¹, is consistent within $1\sigma$. A discrepancy between the Planck and South Pole Telescope high-multipole CMB spectra disfavors interpreting these tensions as evidence for new physics. We conclude that the parameters from the Planck high-multipole spectrum probably differ from the underlying values due to either an unlikely statistical fluctuation or unaccounted-for systematics persisting in the Planck data.

We investigate the claim that the ratio β of radiation pressure force to gravitational force on a dust grain in our solar system can substantially exceed unity for some grain sizes, provided that grain porosity is high enough. For model grains consisting of random aggregates of silicate spherules, we find that the maximum value of β is almost independent of grain porosity, but for small ($\lt 0.3\;\mu {\rm{m}}$) grains, β actually decreases with increasing porosity. We also investigate the effect of metallic iron and amorphous carbon inclusions in the dust grains and find that while these inclusions do increase the radiation pressure cross-section, β remains below unity for grains with 3 pg of silicate material. These results affect the interpretation of the grain trajectories estimated from the Stardust mission, which were modeled assuming β values exceeding one. We find that radiation pressure effects are not large enough for particles Orion and Hylabrook captured by Stardust to be of interstellar origin given their reported impact velocities. We also consider the effects of solar radiation on transverse velocities and grain spin, and show that radiation pressure introduces both transverse velocities and equatorial spin velocities of several hundred meters per second for incoming interstellar grains at 2 au. These transverse velocities are not important for modeling trajectories, but such spin rates may result in centrifugal disruption of aggregates.

The linear instability of an ultrarelativistic hadron beam in the unmagnetized intergalactic medium (IGM) is investigated with respect to the excitation of parallel electrostatic and electromagnetic fluctuations. This analysis is important for the propagation of extragalactic ultrarelativistic cosmic rays from their distant sources to Earth. As opposed to the previous paper, we calculate the minimum instability growth time for Lorentz-distributed cosmic rays which traverse the hot IGM. The growth times are orders of magnitude higher than the cosmic-ray propagation time in the IGM. Since the backreaction of the generated plasma fluctuations (plateauing) lasts longer than the propagation time, the cosmic-ray hadron beam can propagate to the Earth without losing a significant amount of energy to electrostatic turbulence.

We report on NuSTAR and Swift observations of a soft state of the neutron star low-mass X-ray binary GS 1826–24, commonly known as the "clocked" burster. The transition to the soft state was recorded in 2014 June through an increase of the 2–20 keV source intensity measured by MAXI, simultaneous with a decrease of the 15–50 keV intensity measured by Swift/BAT. The episode lasted approximately two months, after which the source returned to its usual hard state. We analyze the broadband spectrum measured by Swift/XRT and NuSTAR and estimate the accretion rate during the soft episode to be $\approx 13\%\;{\dot{m}}_{{\rm{Edd}}}$, within the range of previous observations. However, the best-fit spectral model, adopting the double Comptonization used previously, exhibits significantly softer components. We detect seven type-I X-ray bursts, all significantly weaker (and with shorter rise and decay times) than observed previously. The burst profiles and recurrence times vary significantly, ruling out the regular bursts that are typical for this source. One burst exhibited photospheric radius expansion and we estimate the source distance as $(5.7\pm 0.2)\;{\xi }_{b}^{-1/2}$ kpc, where ξ_b parameterizes the possible anisotropy of the burst emission. The observed soft state may most likely be interpreted as a change in accretion geometry at about similar bolometric luminosity as in the hard state. The different burst behavior can therefore be attributed to this change in accretion flow geometry, but the fundamental cause and process for this effect remain unclear.

The properties of the Galactic Ridge X-ray Emission (GRXE) observed in the 2–10 keV band place fundamental constraints on various types of X-ray sources in the Milky Way. Although the primarily discrete origin of the emission is now well established, the responsible populations of these sources remain uncertain, especially at relatively low fluxes. To provide insights into this issue, we systematically characterize the Fe emission line properties of the candidate types of the sources in the solar neighborhood and compare them with those measured for the GRXE. Our source sample includes 6 symbiotic stars, 16 intermediate polars (IPs), 3 polars, 16 quiescent dwarf novae, and 4 active binaries (ABs); they are all observed with the Suzaku X-ray Observatory. The data of about one-fourth of these sources are analyzed for the first time. We find that the mean equivalent width (EW_6.7) of the 6.7 keV line and the mean 7.0/6.7 keV line ratio are 107 ± 16.0 eV and 0.71 ± 0.04 for IPs and 221 ± 135 eV and 0.44 ± 0.14 for polars, respectively, which are all substantially different from those (490 ± 15 eV and 0.2 ± 0.08) for the GRXE. Instead, the GRXE values are better agreed by the EW_6.7 (438 ± 84.6 eV) and the ratio (0.27 ± 0.06) observed for the DNe. We further find that the EW_6.7 is strongly correlated with the 2–10 keV luminosity of the DNe, which can be characterized by the relation ${\mathrm{EW}}_{6.7}={(438\pm 95{\rm{eV}})(L/{10}^{31}\mathrm{erg}{{\rm{s}}}^{-1})}^{(-0.31\pm 0.15)}$. Accounting for this correlation, the agreement can be improved further, especially when the contributions from other class sources to the GRXE are considered, which all have low EW_6.7 values. We conclude that the GRXE mostly consists of typically faint but numerous DNe, plus ABs, while magnetic cataclysmic variables are probably mainly the high-flux representatives of the responsible populations and dominate the GRXE only in harder energy bands.

We present a reverberation mapping (RM) experiment that combines broad- and intermediate-band photometry; it is the first such attempt targeting 13 quasars at 0.2 < z < 0.9. The quasars were selected to have strong Hα or Hβ emission lines that are located in one of three intermediate bands (with FWHM around 200 Å) centered at 8045, 8505, and 9171 Å. The imaging observations were carried out in the intermediate bands and the broad i and z bands using the prime-focus imager 90Prime on the 2.3 m Bok telescope. Because of the large (∼1 deg²) field of view (FOV) of 90Prime, we included the 13 quasars within only five telescope pointings or fields. The five fields were repeatedly observed over 20–30 epochs that were unevenly distributed over a duration of 5–6 months. The combination of the broad- and intermediate-band photometry allows us to derive accurate light curves for both optical continuum emission (from the accretion disk) and line emission (from the broad-line region, or BLR). We detect Hα time lags between the continuum and line emission in six quasars. These quasars are at relatively low redshifts 0.2 < z < 0.4. The measured lags are consistent with the current BLR size–luminosity relation for Hβ at z < 0.3. While this experiment appears successful in detecting lags of the bright Hα line, further investigation is required to see if it can also be applied to the fainter Hβ line for quasars at higher redshifts. Finally we demonstrate that, by using a small telescope with a large FOV, intermediate-band photometric RM can be efficiently executed for a large sample of quasars at z > 0.2.

We present a follow-up study to the imaging polarimetry performed by Hayes et al. on LAB1 in the SSA22 protocluster region. Arguably the most well-known Lyα "blob," this radio-quiet emission-line nebula likely hosts a galaxy that either is undergoing significant star formation or hosts an active galactic nucleus, or both. We obtain deep, spatially resolved spectropolarimetry of the Lyα emission and detect integrated linear polarization of 9%–13% ± 2%–3% at a distance of approximately 15 kpc north and south of the peak of the Lyα surface brightness with polarization vectors lying tangential to the galactic central source. In these same regions, we also detect a wavelength dependence in the polarization that is low at the center of the Lyα line profile and rises substantially in the wings of the profile. These polarization signatures are easily explained by a weak outflowing shell model. The spectral dependence of the polarization presented here provides a framework for future observations and interpretations of the southern portion of LAB1 in that any model for this system must be able to reproduce this particular spectral dependence. However, questions still remain for the northernmost spur of LAB1. In this region we detect total linear polarization of between 3% and 20% at the 5% significance level. Simulations predict that polarization should increase with radius for a symmetric geometry. That the northern spur does not suggests either that this region is not symmetric (which is likely) and exhibits variations in columns density or that it is kinematically distinct from the rest of LAB1 and powered by another mechanism altogether.

Detection of the cosmological neutral hydrogen signal from the Epoch of Reionization (EoR) and estimation of its basic physical parameters are principal scientific aims of many current low-frequency radio telescopes. Here we describe the Cosmological H i Power Spectrum Estimator (CHIPS), an algorithm developed and implemented with data from the Murchison Widefield Array, to compute the two-dimensional and spherically-averaged power spectrum of brightness temperature fluctuations. The principal motivations for CHIPS are the application of realistic instrumental and foreground models to form the optimal estimator, thereby maximizing the likelihood of unbiased signal estimation, and allowing a full covariant understanding of the outputs. CHIPS employs an inverse-covariance weighting of the data through the maximum likelihood estimator, thereby allowing use of the full parameter space for signal estimation ("foreground suppression"). We describe the motivation for the algorithm, implementation, application to real and simulated data, and early outputs. Upon application to a set of 3 hr of data, we set a 2σ upper limit on the EoR dimensionless power at $k=0.05\;{\rm{h}}$ Mpc⁻¹ of ${{\rm{\Delta }}}_{k}^{2}\lt 7.6\times {10}^{4}$ mK² in the redshift range z = [6.2–6.6], consistent with previous estimates.

We have studied high-mass X-ray binary (HMXB) populations within two low-metallicity, starburst galaxies, Haro 11 and VV 114. These galaxies serve as analogs to high-redshift ($z\gt 2$) Lyman break galaxies and, within the larger sample of Lyman break analogs (LBAs), they are sufficiently nearby (<87 Mpc) to be spatially resolved by Chandra. Previous studies of the X-ray emission in LBAs have found that the 2–10 keV luminosity per star formation rate (SFR) in these galaxies is elevated, potentially because of their low metallicities ($12+\mathrm{log}[{\rm{O}}/{\rm{H}}]=8.3\mbox{--}8.4$). Theoretically, the progenitors of XRBs forming in lower metallicity environments lose less mass from stellar winds over their lifetimes, producing more massive compact objects (i.e., neutron stars and black holes), and thus resulting in more numerous and luminous HMXBs per SFR. In this paper, we have performed an in-depth study of the only two LBAs that have spatially resolved 2–10 keV emission with Chandra to present the bright end of the X-ray luminosity distribution of HMXBs (${L}_{{\rm{X}}}$ ≳ 10³⁹ erg s⁻¹; ultraluminous X-ray sources, ULXs) in these low-metallicity galaxies, based on eight detected ULXs. Compared with the star-forming galaxy X-ray luminosity function (XLF) presented by Mineo et al., Haro 11 and VV 114 host $\approx 4$ times more ${L}_{{\rm{X}}}$$\gt \;{10}^{40}$ erg s⁻¹ sources than expected given their SFRs. We simulate the effects of source blending from crowded lower-luminosity HMXBs using the star-forming galaxy XLF and then vary the XLF normalizations and bright-end slopes until we reproduce the observed point source luminosity distributions. We find that these LBAs have a shallower bright-end slope (${\gamma }_{2}=1.90$) than the standard XLF (${\gamma }_{2}=2.73$). If we conservatively assume that the brightest X-ray source from each galaxy is powered by an accreting supermassive black hole rather than an HMXB and eliminate these sources from consideration, the luminosity distribution becomes poorly constrained but does appear to be consistent with a standard XLF.

We examine a large random sample of orbits in two self-consistent simulations of N-body bars. Orbits in these bars are classified both visually and with a new automated orbit classification method based on frequency analysis. The well-known prograde x1 orbit family originates from the same parent orbit as the box orbits in stationary and rotating triaxial ellipsoids. However, only a small fraction of bar orbits (∼4%) have predominately prograde motion like their periodic parent orbit. Most bar orbits arising from the x1 orbit have little net angular momentum in the bar frame, making them equivalent to box orbits in rotating triaxial potentials. In these simulations a small fraction of bar orbits (∼7%) are long-axis tubes that behave exactly like those in triaxial ellipsoids: they are tipped about the intermediate axis owing to the Coriolis force, with the sense of tipping determined by the sign of their angular momentum about the long axis. No orbits parented by prograde periodic x2 orbits are found in the pure bar model, but a tiny population (∼2%) of short-axis tube orbits parented by retrograde x4 orbits are found. When a central point mass representing a supermassive black hole (SMBH) is grown adiabatically at the center of the bar, those orbits that lie in the immediate vicinity of the SMBH are transformed into precessing Keplerian orbits that belong to the same major families (short-axis tubes, long-axis tubes and boxes) occupying the bar at larger radii. During the growth of an SMBH, the inflow of mass and outward transport of angular momentum transform some x1 and long-axis tube orbits into prograde short-axis tubes. This study has important implications for future attempts to constrain the masses of SMBHs in barred galaxies using orbit-based methods like the Schwarzschild orbit superposition scheme and for understanding the observed features in barred galaxies.

We discuss integral field spectra of the compact star-forming complex that is the brightest near-infrared (NIR) source in the central regions of the starburst galaxy NGC 253. The spectra cover the H and K passbands and were recorded with the Gemini NIR Spectrograph during subarcsecond seeing conditions. Absorption features in the spectrum of the star-forming complex are weaker than in the surroundings. An absorption feature is found near 1.78 μm that coincides with the location of a C₂ bandhead. If this feature is due to C₂ then the star-forming complex has been in place for at least a few hundred Myr. Emission lines of Brγ, [Fe ii], and He i 2.06 μm do not track the NIR continuum light. Pockets of star-forming activity that do not have associated concentrations of red supergiants, and so likely have ages <8 Myr, are found along the western edge of the complex, and there is evidence that one such pocket contains a rich population of Wolf–Rayet stars. Unless the star-forming complex is significantly more metal-poor than the surroundings, then a significant fraction of its total mass is in stars with ages <8 Myr. If the present-day star formation rate is maintained then the timescale to double its stellar mass ranges from a few Myr to a few tens of Myr, depending on the contribution made by stars older than ∼8 Myr. If—as suggested by some studies—the star-forming complex is centered on the galaxy's nucleus, which presumably contains a large population of old and intermediate-age stars, then the nucleus of NGC 253 is currently experiencing a phase of rapid growth in its stellar mass.

Interstellar extinction includes both absorption and scattering of photons from interstellar gas and dust grains, and it has the effect of altering a source's spectrum and its total observed intensity. However, while multiple absorption models exist, there are no useful scattering models in standard X-ray spectrum fitting tools, such as XSPEC. Nonetheless, X-ray halos, created by scattering from dust grains, are detected around even moderately absorbed sources, and the impact on an observed source spectrum can be significant, if modest, compared to direct absorption. By convolving the scattering cross section with dust models, we have created a spectral model as a function of energy, type of dust, and extraction region that can be used with models of direct absorption. This will ensure that the extinction model is consistent and enable direct connections to be made between a source's X-ray spectral fits and its UV/optical extinction.

Emission from carbon monoxide (CO) is ubiquitously used as a tracer of dense star-forming molecular clouds. There is, however, growing evidence that a significant fraction of CO emission originates from diffuse molecular gas. Quantifying the contribution of diffuse CO-emitting gas is vital for understanding the relation between molecular gas and star formation. We examine the Galactic distribution of two CO-emitting gas components, a high column density component detected in ¹³CO and ¹²CO, and a low column density component detected in ¹²CO, but not in ¹³CO. The "diffuse" and "dense" components are identified using a combination of smoothing, masking, and erosion/dilation procedures, making use of three large-scale ¹²CO and ¹³CO surveys of the inner and outer Milky Way. The diffuse component, which globally represents 25% (1.5 × 10⁸M_⊙) of the total molecular gas mass (6.5 $\;\times \;{10}^{8}$M_⊙), is more extended perpendicular to the Galactic plane. The fraction of diffuse gas increases from ∼10%–20% at a galactocentric radius of 3–4 kpc to 50% at 15 kpc, and increases with decreasing surface density. In the inner Galaxy, a yet denser component traced by CS emission represents 14% of the total molecular gas mass traced by ¹²CO emission. Only 14% of the molecular gas mass traced by ¹²CO emission is identified as part of molecular clouds in ¹³CO surveys by cloud identification algorithms. This study indicates that CO emission not only traces star-forming clouds, but also a significant diffuse molecular ISM component.

Nova LMC 2009a is confirmed as a recurrent nova (RN) from positional coincidence with nova LMC 1971b. The observational data set is one of the most comprehensive for any Galactic or extragalactic RN: optical and near-IR photometry from outburst until over 6 years later; optical spectra for the first 6 months, and Swift satellite ultraviolet (UV) and X-ray observations from 9 days to almost 1 year post-outburst. We find M_V = −8.4 ± 0.8_r ± 0.7_s and expansion velocities between 1000 and 4000 km s⁻¹. Coronal line emission before day 9 indicates shocks in the ejecta. Strengthening of He iiλ4686 preceded the emergence of the super-soft source (SSS) in X-rays at ∼63–70 days, which was initially very variable. Periodic modulations, P = 1.2 days, most probably orbital in nature, were evident in the UV and optical from day 43. Subsequently, the SSS shows an oscillation with the same period but with a delay of 0.28P. The progenitor system has been identified; the secondary is most likely a sub-giant feeding a luminous accretion disk. Properties of the SSS infer a white dwarf (WD) mass 1.1 M_⊙ ≲ M_WD ≲ 1.3 M_⊙. If the accretion occurs at a constant rate, ${\dot{M}}_{{\rm{acc}}}\simeq {3.6}_{-2.5}^{+4.7}\times {10}^{-7}\;{M}_{\odot }$ yr⁻¹ is needed, consistent with nova models for an inter-eruption interval of 38 years, low outburst amplitude, progenitor position in the color–magnitude diagram, and spectral energy distribution at quiescence. We note striking similarities between LMC 2009a and the Galactic nova KT Eri, suggesting that KT Eri is a candidate RN.

Classical "ballistic" overshoot models show some contradictions and are not consistent with numerical simulations and asteroseismic studies. Asteroseismic studies imply that overshoot is a weak mixing process. A diffusion model is suitable to deal with it. The form of diffusion coefficient in a diffusion model is crucial. Because overshoot mixing is related to convective heat transport (i.e., entropy mixing), there should be some similarity between them. A recent overshoot mixing model shows consistency between composition mixing and entropy mixing in the overshoot region. A prerequisite to apply the model is to know the dissipation rate of turbulent kinetic energy. The dissipation rate can be worked out by solving turbulent convection models (TCMs). But it is difficult to apply TCMs because of some numerical problems and the enormous time cost. In order to find a convenient way, we have used the asymptotic solution and simplified the TCM to a single linear equation for turbulent kinetic energy. This linear model is easy to implement in calculations of stellar evolution with negligible extra time cost. We have tested the linear model in stellar evolution, and have found that it can well reproduce the turbulent kinetic energy profile of the full TCM, as well as the diffusion coefficient, abundance profile, and stellar evolutionary tracks. We have also studied the effects of different values of the model parameters and have found that the effect due to the modification of temperature gradient in the overshoot region is slight.

We discuss magnetic field and plasma observations of the heliosheath made by Voyager 2 (V2) during 2012, when V2 was observing the effects of increasing solar activity following the solar minimum in 2009. The average magnetic field strength B was 0.14 nT and B reached 0.29 nT on day 249. V2 was in a unipolar region in which the magnetic polarity was directed away from the Sun along the Parker spiral 88% of the time, indicating that V2 was poleward of the heliospheric current sheet throughout most of 2012. The magnetic flux at V2 during 2012 was constant. A merged interaction region (MIR) was observed, and the flow speed increased as the MIR moved past V2. The MIR caused a decrease in the >70 MeV nuc⁻¹ cosmic-ray intensity. The increments of B can be described by a q-Gaussian distribution with q = 1.2 ± 0.1 for daily averages and q = 1.82 ± 0.03 for hour averages. Eight isolated current sheets ("PBLs") and four closely spaced pairs of current sheets were observed. The average change of B across the current sheets was a factor of ≈2, and B increased or decreased with equal probability. Magnetic holes and magnetic humps were also observed. The characteristic size of the PBLs was ≈6 R_L, where R_L is the Larmor radius of protons, and the characteristic sizes of the magnetic holes and humps were ≈38 R_L and ≈11 R_L, respectively.

We investigate the evolution of NOAA Active Region (AR) 11817 during 2013 August 10–12, when it developed a complex field configuration and produced four confined, followed by two eruptive, flares. These C-and-above flares are all associated with a magnetic flux rope (MFR) located along the major polarity inversion line, where shearing and converging photospheric flows are present. Aided by the nonlinear force-free field modeling, we identify the MFR through mapping magnetic connectivities and computing the twist number ${{ \mathcal T }}_{w}$ for each individual field line. The MFR is moderately twisted ($| {{ \mathcal T }}_{w}| \lt 2$) and has a well-defined boundary of high squashing factor Q. We found that the field line with the extremum $| {{ \mathcal T }}_{w}|$ is a reliable proxy of the rope axis, and that the MFR's peak $| {{ \mathcal T }}_{w}|$ temporarily increases within half an hour before each flare while it decreases after the flare peak for both confined and eruptive flares. This pre-flare increase in $| {{ \mathcal T }}_{w}|$ has little effect on the AR's free magnetic energy or any other parameters derived for the whole region, due to its moderate amount and the MFR's relatively small volume, while its decrease after flares is clearly associated with the stepwise decrease in the whole region's free magnetic energy due to the flare. We suggest that ${{ \mathcal T }}_{w}$ may serve as a useful parameter in forewarning the onset of eruption, and therefore, the consequent space weather effects. The helical kink instability is identified as the prime candidate onset mechanism for the considered flares.

Inner-shell ionization of a 1s electron by either photons or electrons is important for X-ray photoionized objects such as active galactic nuclei and electron-ionized sources such as supernova remnants. Modeling and interpreting observations of such objects requires accurate predictions for the charge state distribution (CSD), which results as the 1s-hole system stabilizes. Due to the complexity of the complete stabilization process, few modern calculations exist and the community currently relies on 40-year-old atomic data. Here, we present a combined experimental and theoretical study for inner-shell photoionization of neutral atomic nitrogen for photon energies of 403–475 eV. Results are reported for the total ion yield cross section, for the branching ratios for formation of N⁺, ${{\rm{N}}}^{2+}$, and ${{\rm{N}}}^{3+}$, and for the average charge state. We find significant differences when comparing to the data currently available to the astrophysics community. For example, while the branching ratio to ${{\rm{N}}}^{2+}$ is somewhat reduced, that for N⁺ is greatly increased, and that to ${{\rm{N}}}^{3+}$, which was predicted to be zero, grows to $\approx 10\%$ at the higher photon energies studied. This work demonstrates some of the shortcomings in the theoretical CSD data base for inner-shell ionization and points the way for the improvements needed to more reliably model the role of inner-shell ionization of cosmic plasmas.

Some circumstellar disks, called transitional or hybrid disks, present characteristics of both protoplanetary disks (significant amount of gas) and debris disks (evolved structures around young main-sequence stars, composed of second generation dust, from collisions between planetesimals). Therefore, they are ideal astrophysical laboratories to witness the last stages of planet formation. The circumstellar disk around HD 141569A was intensively observed and resolved in the past from space, but also from the ground. However, the recent implementation of high contrast imaging systems has opened up new opportunities to re-analyze this object. We analyzed Gemini archival data from the Near-infrared Coronagraphic Imager obtained in 2011 in the H band, using several angular differential imaging techniques (classical ADI, LOCI, KLIP). These images reveal the complex structures of this disk with an unprecedented resolution. We also include archival Hubble Space Telescope images as an independent data set to confirm these findings. Using an analysis of the inner edge of the disk, we show that the inner disk is almost axisymmetrical. The measurement of an offset toward the east observed by previous authors is likely due to the fact that the eastern part of this disk is wider and more complex in substructure. Our precise reanalysis of the eastern side shows several structures, including a splitting of the disk and a small finger detached from the inner edge to the southeast. Finally, we find that the arc at 250 AU is unlikely to be a spiral, at least not at the inclination derived from the first ring, but instead could be interpreted as a third belt at a different inclination. If the very symmetrical inner disk edge is carved by a companion, the data presented here put additional constraints on its position. The observed very complex structures will be confirmed by the new generation of coronagraphic instrument (GPI, SPHERE). However, a full understanding of this system will require gas observations at millimetric wavelengths.

Variable-delay Polarization Modulators (VPMs) are currently being implemented in experiments designed to measure the polarization of the cosmic microwave background on large angular scales because of their capability for providing rapid, front-end polarization modulation and control over systematic errors. Despite the advantages provided by the VPM, it is important to identify and mitigate any time-varying effects that leak into the synchronously modulated component of the signal. In this paper, the effect of emission from a 300 K VPM on the system performance is considered and addressed. Though instrument design can greatly reduce the influence of modulated VPM emission, some residual modulated signal is expected. VPM emission is treated in the presence of rotational misalignments and temperature variation. Simulations of time-ordered data are used to evaluate the effect of these residual errors on the power spectrum. The analysis and modeling in this paper guides experimentalists on the critical aspects of observations using VPMs as front-end modulators. By implementing the characterizations and controls as described, front-end VPM modulation can be very powerful for mitigating 1/f noise in large angular scale polarimetric surveys. None of the systematic errors studied fundamentally limit the detection and characterization of B-modes on large scales for a tensor-to-scalar ratio of r = 0.01. Indeed, r < 0.01 is achievable with commensurately improved characterizations and controls.

The global evolution and dispersal of protoplanetary disks (PPDs) are governed by disk angular-momentum transport and mass-loss processes. Recent numerical studies suggest that angular-momentum transport in the inner region of PPDs is largely driven by magnetized disk wind, yet the wind mass-loss rate remains unconstrained. On the other hand, disk mass loss has conventionally been attributed to photoevaporation, where external heating on the disk surface drives a thermal wind. We unify the two scenarios by developing a one-dimensional model of magnetized disk winds with a simple treatment of thermodynamics as a proxy for external heating. The wind properties largely depend on (1) the magnetic field strength at the wind base, characterized by the poloidal Alfvén speed v_Ap, (2) the sound speed c_s near the wind base, and (3) how rapidly poloidal field lines diverge (achieve ${R}^{-2}$ scaling). When ${v}_{\mathrm{Ap}}\gg {c}_{{\rm{s}}}$, corotation is enforced near the wind base, resulting in centrifugal acceleration. Otherwise, the wind is accelerated mainly by the pressure of the toroidal magnetic field. In both cases, the dominant role played by magnetic forces likely yields wind outflow rates that exceed purely hydrodynamical mechanisms. For typical PPD accretion-rate and wind-launching conditions, we expect v_Ap to be comparable to c_s at the wind base. The resulting wind is heavily loaded, with a total wind mass-loss rate likely reaching a considerable fraction of the wind-driven accretion rate. Implications for modeling global disk evolution and planet formation are also discussed.

The MEarth Project is a photometric survey systematically searching the smallest stars near the Sun for transiting rocky planets. Since 2008, MEarth has taken approximately two million images of 1844 stars suspected to be mid-to-late M dwarfs. We have augmented this survey by taking nightly exposures of photometric standard stars and have utilized this data to photometrically calibrate the MEarth system, identify photometric nights, and obtain an optical magnitude with 1.5% precision for each M dwarf system. Each optical magnitude is an average over many years of data, and therefore should be largely immune to stellar variability and flaring. We combine this with trigonometric distance measurements, spectroscopic metallicity measurements, and 2MASS infrared magnitude measurements in order to derive a color–magnitude–metallicity relation across the mid-to-late M dwarf spectral sequence that can reproduce spectroscopic metallicity determinations to a precision of 0.1 dex. We release optical magnitudes and metallicity estimates for 1567 M dwarfs, many of which did not have an accurate determination of either prior to this work. For an additional 277 stars without a trigonometric parallax, we provide an estimate of the distance, assuming solar neighborhood metallicity. We find that the median metallicity for a volume-limited sample of stars within 20 pc of the Sun is [Fe/H] = −0.03 ± 0.008, and that 29/565 of these stars have a metallicity of [Fe/H] = −0.5 or lower, similar to the low-metallicity distribution of nearby G dwarfs. When combined with the results of ongoing and future planet surveys targeting these objects, the metallicity estimates presented here will be important for assessing the significance of any putative planet–metallicity correlation.

Empirically, the X-ray luminosity L_X from M dwarfs has been found to have an upper limit of about 0.2% of the bolometric flux L_bol. In the limit where magnetic fields in M dwarfs are generated in equipartition with convective motions, we use stellar models to calculate the energy flux of Alfvén waves F_A as a function of depth in the sub-surface convection zone. Since Alfvén waves have the optimal opportunity for wave modes to reach the corona, we suggest that F_A sets an upper limit on the mechanical flux F_mech which causes coronal heating. This suggestion accounts quantitatively for the "saturated" values of L_X/L_bol which have been reported empirically for M dwarfs.

We present the discovery of 15 extremely low-mass ($5\lt \mathrm{log}g\lt 7$) white dwarf (WD) candidates, 9 of which are in ultra-compact double-degenerate binaries. Our targeted extremely low-mass Survey sample now includes 76 binaries. The sample has a lognormal distribution of orbital periods with a median period of 5.4 hr. The velocity amplitudes imply that the binary companions have a normal distribution of mass with 0.76 M_⊙ mean and 0.25 M_⊙ dispersion. Thus extremely low-mass WDs are found in binaries with a typical mass ratio of 1:4. Statistically speaking, 95% of the WD binaries have a total mass below the Chandrasekhar mass, and thus are not type Ia supernova progenitors. Yet half of the observed binaries will merge in less than 6 Gyr due to gravitational wave radiation; probable outcomes include single massive WDs and stable mass transfer AM CVn binaries.

We present new Atacama Large Millimeter/Submillimeter Array (ALMA) observations of CO J = 2−1 line emission from the DQ Tau circumbinary disk. These data are used to tomographically reconstruct the Keplerian disk velocity field in a forward-modeling inference framework, and thereby provide a dynamical constraint on the mass of the DQ Tau binary of ${M}_{*}={1.27}_{-0.27}^{+0.46}\;{M}_{\odot }$. Those results are compared with an updated and improved orbital solution for this double-lined system based on long-term monitoring of its stellar radial velocities. Both of these independent dynamical constraints on the binary mass are in excellent agreement: taken together, they demonstrate that the DQ Tau system mass is 1.21 ± 0.26 M_⊙ and that the disk and binary orbital planes are aligned within 3° (at 3σ confidence). The predictions of various theoretical models for pre-main-sequence stellar evolution are also consistent with these masses, though more detailed comparisons are difficult due to lingering uncertainties regarding the photospheric properties of the individual components. DQ Tau is the third, nearly equal-mass, double-lined spectroscopic binary with a circumbinary disk that has been dynamically "weighed" with these two independent techniques: all show consistent results, validating the overall accuracy of the disk-based approach and demonstrating that it can be robustly applied to large samples of young, single stars as ALMA ramps up to operations at full capacity.

We revisit secular stability against quasi-radial collapse for rigidly rotating supermassive stars (SMSs) in general relativity. We suppose that the SMSs are in a nuclear-burning phase and can be modeled by polytropic equations of state with the polytropic index n_p slightly smaller than 3. The stability is determined in terms of the turning point method. We find a fitting formula of the stability condition for the plausible range of n_p ($2.95\lesssim {n}_{{\rm{p}}}\lesssim 3$) for SMSs. This condition reconfirms that while non-rotating SMSs with a mass of $\sim {10}^{5}{M}_{\odot }$–${10}^{6}{M}_{\odot }$ may undergo a general relativistically induced quasi-radial collapse, rigidly rotating SMSs with a ratio of rotational to gravitational potential energy (β) of $\sim {10}^{-2}$ are likely to be stable against collapse unless they are able to accrete ∼5 times more mass during the (relatively brief) hydrogen-burning phase of their evolution. We discuss the implications of our results.

We reprocess the Atacama Large Millimeter/Submillimeter Array (ALMA) long-baseline science verification data taken toward HL Tauri. Assuming the observed gaps are opened up by currently forming, unseen bodies, we estimate the mass of such hypothetical bodies based on the following two approaches: the Hill radius analysis and a more elaborate approach developed from the angular momentum transfer analysis in gas disks. For the former, the measured gap widths are used for estimating the mass of the bodies, while for the latter, the measured gap depths are utilized. We show that their masses are comparable to or less than the mass of Jovian planets. By evaluating Toomre's gravitational instability (GI) condition and cooling effect, we find that the GI might be a mechanism to form the bodies in the outer region of the disk. As the disk might be gravitationally unstable only in the outer region of the disk, inward planetary migration would be needed to construct the current architecture of the observed disk. We estimate the gap-opening mass and show that type II migration might be able to play such a role. Combining GIs with inward migration, we conjecture that all of the observed gaps may be a consequence of bodies that might have originally formed at the outer part of the disk, and have subsequently migrated to the current locations. While ALMA's unprecedented high spatial resolution observations can revolutionize our picture of planet formation, more dedicated observational and theoretical studies are needed to fully understand the HL Tauri images.

The gravitational influence of a planet on a nearby disk provides a powerful tool for detecting and studying extrasolar planetary systems. Here we demonstrate that gaps can be opened in dynamically cold debris disks at the mean-motion resonances of an orbiting planet. The gaps are opened away from the orbit of the planet itself, revealing that not all disk gaps need contain a planetary body. These gaps are large and deep enough to be detectable in resolved disk images for a wide range of reasonable disk-planet parameters, though we are not aware of any such gaps detected to date. The gap shape and size are diagnostic of the planet location, eccentricity and mass, and allow one to infer the existence of unseen planets, as well as many important parameters of both seen and unseen planets in these systems. We present expressions to allow the planetary mass and semimajor axis to be calculated from observed gap width and location.

The discovery of many planets using the Kepler telescope includes 10 planets orbiting eight binary stars. Three binaries, Kepler-16, Kepler-47, and Kepler-453, have at least one planet in the circumbinary habitable zone (BHZ). We constrain the level of high-energy radiation and the plasma environment in the BHZ of these systems. With this aim, BHZ limits in these Kepler binaries are calculated as a function of time, and the habitability lifetimes are estimated for hypothetical terrestrial planets and/or moons within the BHZ. With the time-dependent BHZ limits established, a self-consistent model is developed describing the evolution of stellar activity and radiation properties as proxies for stellar aggression toward planetary atmospheres. Modeling binary stellar rotation evolution, including the effect of tidal interaction between stars in binaries, is key to establishing the environment around these systems. We find that Kepler-16 and its binary analogs provide a plasma environment favorable for the survival of atmospheres of putative Mars-sized planets and exomoons. Tides have modified the rotation of the stars in Kepler-47, making its radiation environment less harsh in comparison to the solar system. This is a good example of the mechanism first proposed by Mason et al. Kepler-453 has an environment similar to that of the solar system with slightly better than Earth radiation conditions at the inner edge of the BHZ. These results can be reproduced and even reparameterized as stellar evolution and binary tidal models progress, using our online tool http://bhmcalc.net.

Spectral line survey observations of seven molecular clouds in the Large Magellanic Cloud (LMC) have been conducted in the 3 mm band with the Mopra 22 m telescope to reveal chemical compositions in low metallicity conditions. Spectral lines of fundamental species such as CS, SO, CCH, HCN, HCO⁺, and HNC are detected in addition to those of CO and ¹³CO, while CH₃OH is not detected in any source and N₂H⁺ is marginally detected in two sources. The molecular-cloud scale (10 pc scale) chemical composition is found to be similar among the seven sources regardless of different star formation activities, and hence, it represents the chemical composition characteristic of the LMC without influences by star formation activities. In comparison with chemical compositions of Galactic sources, the characteristic features are (1) deficient N-bearing molecules, (2) abundant CCH, and (3) deficient CH₃OH. Feature (1) is due to a lower elemental abundance of nitrogen in the LMC, whereas features (2) and (3) seem to originate from extended photodissociation regions and warmer temperature in cloud peripheries due to a lower abundance of dust grains in the low metallicity condition. In spite of general resemblance of chemical abundances among the seven sources, the CS/HCO⁺ and SO/HCO⁺ ratios are found to be slightly higher in a quiescent molecular cloud. An origin of this trend is discussed in relation to possible depletion of sulfur along the molecular cloud formation.

We develop a numerical scheme for solving the equations of fully special relativistic, radiation magnetohydrodynamics (MHDs), in which the frequency-integrated, time-dependent radiation transfer equation is solved to calculate the specific intensity. The radiation energy density, the radiation flux, and the radiation stress tensor are obtained by the angular quadrature of the intensity. In the present method, conservation of total mass, momentum, and energy of the radiation magnetofluids is guaranteed. We treat not only the isotropic scattering but also the Thomson scattering. The numerical method of MHDs is the same as that of our previous work. The advection terms are explicitly solved, and the source terms, which describe the gas–radiation interaction, are implicitly integrated. Our code is suitable for massive parallel computing. We present that our code shows reasonable results in some numerical tests for propagating radiation and radiation hydrodynamics. Particularly, the correct solution is given even in the optically very thin or moderately thin regimes, and the special relativistic effects are nicely reproduced.

We introduce a new class of solutions for Apodized Pupil Lyot Coronagraphs (APLC) with segmented aperture telescopes to remove broadband diffracted light from a star with a contrast level of 10¹⁰. These new coronagraphs provide a key advance to enabling direct imaging and spectroscopy of Earth twins with future large space missions. Building on shaped pupil (SP) apodization optimizations, our approach enables two-dimensional optimizations of the system to address any aperture features such as central obstruction, support structures, or segment gaps. We illustrate the technique with a design that could reach a 10¹⁰ contrast level at 34 mas for a 12 m segmented telescope over a 10% bandpass centered at a wavelength of ${\lambda }_{0}\;=$ 500 nm. These designs can be optimized specifically for the presence of a resolved star and, in our example, for stellar angular size up to 1.1 mas. This would allow one to probe the vicinity of Sun-like stars located beyond 4.4 pc, therefore, fully retiring this concern. If the fraction of stars with Earth-like planets is ${\eta }_{\oplus }=0.1$, with 18% throughput, assuming a perfect, stable wavefront and considering photon noise only, 12.5 exo-Earth candidates could be detected around nearby stars with this design and a 12 m space telescope during a five-year mission with two years dedicated to exo-Earth detection (one total year of exposure time and another year of overheads). Our new hybrid APLC/SP solutions represent the first numerical solution of a coronagraph based on existing mask technologies and compatible with segmented apertures, and that can provide contrast compatible with detecting and studying Earth-like planets around nearby stars. They represent an important step forward toward enabling these science goals with future large space missions.

We construct an X-ray spectral model of reprocessing by a torus in an active galactic nucleus (AGN) with the Monte Carlo simulation framework MONACO. Two torus geometries of smooth and clumpy cases are considered and compared. In order to reproduce a Compton shoulder accurately, MONACO includes not only free electron scattering but also bound electron scattering. Raman and Rayleigh scattering are also treated, and scattering cross sections dependent on chemical states of hydrogen and helium are included. Doppler broadening by turbulence velocity can be implemented. Our model gives results consistent with other available models, such as MYTorus, except for differences due to different physical parameters and assumptions. We studied the dependence on torus parameters for a Compton shoulder, and found that a intensity ratio of a Compton shoulder to the line core mainly depends on column density, inclination angle, and metal abundance. For instance, an increase of metal abundance makes a Compton shoulder relatively weak. Also, the shape of a Compton shoulder depends on the column density. Furthermore, these dependences become different between smooth and clumpy cases. Then, we discuss the possibility of ASTRO-H/SXS spectroscopy of Compton shoulders in AGN reflection spectra.

We conducted one-dimensional and two-dimensional hydrodynamic simulations of post-shock revival evolutions in core-collapse supernovae, employing the simple neutrino light bulb approximation to produce explosions rather easily. In order to estimate the explosion energy, we took into proper account nuclear recombinations and fusions consistently with the equation of state for matter not in statistical equilibrium in general. The methodology is similar to our previous work, but is somehow improved. In this paper, we studied the influence of the progenitor structure on the dynamics systematically. In order to expedite our understanding of the systematics, we constructed six parametric progenitor models, which are different in masses of Fe iron core and Si+S layer, instead of employing realistic models provided by stellar evolution calculations, which are sometimes of stochastic nature as a function of stellar mass on the main sequence. We found that the explosion energy is tightly correlated with the mass accretion rate at shock revival irrespective of dimension and the progenitors with light iron cores but with rather high entropies, which have yet to be produced by realistic stellar evolution calculations, may reproduce the canonical values of explosion energy and nickel mass. The mass of the Si+S layer is also important in the mass accretion history after bounce, on the other hand; the higher mass accretion rates and resultant heavier cores tend to hamper strong explosions.

We report on an effort to extract and monitor interstellar scintillation parameters in regular timing observations collected for the North American Nanohertz Observatory for Gravitational Waves pulsar timing array. Scattering delays are measured by creating dynamic spectra for each pulsar and observing epoch of wide-band observations centered near 1500 MHz and carried out at the Green Bank Telescope and the Arecibo Observatory. The ∼800 MHz wide frequency bands imply dramatic changes in scintillation bandwidth across the bandpass, and a stretching routine has been included to account for this scaling. For most of the 10 pulsars for which the scaling has been measured, the bandwidths scale with frequency less steeply than expected for a Kolmogorov medium. We find estimated scattering delay values that vary with time by up to an order of magnitude. The mean measured scattering delays are similar to previously published values and are slightly higher than predicted by interstellar medium models. We investigate the possibility of increasing the timing precision by mitigating timing errors introduced by the scattering delays. For most of the pulsars, the uncertainty in the time of arrival of a single timing point is much larger than the maximum variation of the scattering delay, suggesting that diffractive scintillation remains as only a negligible part of their noise budget.

Strong spectral softening has been revealed in the late X-ray afterglows of some gamma-ray bursts (GRBs). The scenario of X-ray scattering around the circumburst dusty medium has been supported by previous works due to its overall successful prediction of both the temporal and spectral evolution of some X-ray afterglows. To further investigate the observed feature of spectral softening we now systematically search the X-ray afterglows detected by the X-ray telescope aboard Swift and collect 12 GRBs with significant late-time spectral softening. We find that dust scattering could be the dominant radiative mechanism for these X-ray afterglows regarding their temporal and spectral features. For some well-observed bursts with high-quality data, the time-resolved spectra could be well-produced within the scattering scenario by taking into account the X-ray absorption from the circumburst medium. We also find that during spectral softening the power-law index in the high-energy end of the spectra does not vary much. The spectral softening is mainly manifested by the spectral peak energy continually moving to the soft end.

We analyze a three-dimensional (3D) magnetic structure and its stability in large solar active region (AR) 12192, using the 3D coronal magnetic field constructed under a nonlinear force-free field (NLFFF) approximation. In particular, we focus on the magnetic structure that produced an X3.1-class flare, which is one of the X-class flares observed in AR 12192. According to our analysis, the AR contains a multiple-flux-tube system, e.g., a large flux tube, with footpoints that are anchored to the large bipole field, under which other tubes exist close to a polarity inversion line (PIL). These various flux tubes of different sizes and shapes coexist there. In particular, the latter are embedded along the PIL, which produces a favorable shape for the tether-cutting reconnection and is related to the X-class solar flare. We further found that most of magnetic twists are not released even after the flare, which is consistent with the fact that no observational evidence for major eruptions was found. On the other hand, the upper part of the flux tube is beyond a critical decay index, essential for the excitation of torus instability before the flare, even though no coronal mass ejections were observed. We discuss the stability of the complicated flux tube system and suggest the reason for the existence of the stable flux tube. In addition, we further point out a possibility for tracing the shape of flare ribbons, on the basis of a detailed structural analysis of the NLFFF before a flare.

We examine ion release times in the solar vicinity for the 2012 May 17 Ground Level Enhancement event using the velocity dispersion analysis method. In situ energetic proton data from Solar and Heliospheric Observatory (SOHO)/Energetic and Relativistic Nuclei and Electron and Geostationary Operational Environmental Satellite are used. We find two distinct releases of Solar Energetic Particles (SEPs) near the Sun, separated by ∼40 minutes. From soft X-ray observations, we find that the first release coincides with the solar flare eruption: the release starts from the flare onset and ends near the peak of the soft X-ray; type-III radio bursts also occur when the release starts. A type II radio burst may also start at the begining of the release. However, the associated Coronal Mass Ejection (CME) only has a height of 0.08R_s from extrapolation of SOHO/LASCO data. At the start of the second release, the CME propagates to more than 8.4R_s in height, and there are signatures of an enhanced type II radio burst. The time-integrated spectra for the two releases differ. The spectrum for the second release shows the common double-power-law feature of gradual SEP events. The spectrum for the first release does not resemble power laws because there is considerable modulation at lower energies. Based on our analysis, we suggest that SEPs of the first release were dominated by particles accelerated at the flare, and those of the second release were dominated by particles accelerated at the associated CME-driven shock. Our study may be important to understand certain extreme SEP events.

We solve the nongeostrophic baroclinic instability problem for the tachocline for a continuous model with a constant vertical rotation gradient (the Eady problem), using power series generated by the Frobenius method. The results confirm and greatly extend those from a previous two-layer model. For effective gravity G independent of height, growth rates and ranges of unstable longitudinal wavenumbers m and latitudes increase with decreasing G. As with the two-layer model, the overshoot tachocline is much more unstable than the radiative tachocline. The e-folding growth times range from as short as 10 days to as long as several years, depending on latitude, G, and wavenumber. For a more realistic effective gravity that decreases linearly from the radiative interior to near zero at the top of the tachocline, we find that only m = 1, 2 modes are unstable, with growth rates somewhat larger than for constant G, with the same value as at the bottom of the tachocline. All results are the same whether we assume that the vertical velocity or the perturbation pressure is zero at the top of the layer; this is a direct consquence of not employing the geostrophic assumption for perturbations. We explain most of the properties of the instability in terms of the Rossby deformation radius. We discuss further improvements in the realism of the model, particularly adding toroidal fields that vary in height, and including latitudinal gradients of both rotation and toroidal fields.

The equivalent widths of ${\rm{Mg}}\;{\rm{II}}$ absorption in the circumgalactic medium (CGM) trace the global star formation rate up to z < 6, are larger for star-forming galaxies than passively evolving galaxies, and decrease with increasing distance from the galaxy. We delve further into the physics involved by investigating gas kinematics and cloud column density distributions as a function of galaxy color, redshift, and projected distance from the galaxy (normalized by galaxy virial radius, D/R_vir). For 39 isolated galaxies at 0.3 < z_gal < 1.0, we have detected ${\rm{Mg}}\;{\rm{II}}$ absorption in high-resolution (Δv ≃ 6.6 km s⁻¹) spectra of background quasars within a projected distance of 7 < D < 190 kpc. We characterize the absorption velocity spread using pixel-velocity two-point correlation functions. Velocity dispersions and cloud column densities for blue galaxies do not differ with redshift nor with D/R_vir. This suggests that outflows continually replenish the CGM of blue galaxies with high velocity dispersion, large column density gas out to large distances. Conversely, absorption hosted by red galaxies evolves with redshift where the velocity dispersions (column densities) are smaller (larger) at z_gal < 0.656. After taking into account larger possible velocities in more massive galaxies, we find that there is no difference in the velocity dispersions or column densities for absorption hosted by red galaxies with D/R_vir. Thus, a lack of outflows in red galaxies causes the CGM to become more quiescent over time, with lower velocity dispersions and larger column densities toward lower z_gal. The quenching of star formation appears to affect the CGM out to D/R_vir = 0.75.

The mass scaling relation between supermassive black holes and their host spheroids has previously been described by a quadratic or steeper relation at low masses (10⁵ < M_bh/M_⊙ ≲ 10⁷). How this extends into the realm of intermediate-mass black holes (10² < M_bh/M_⊙ < 10⁵) is not yet clear, although for the barred Sm galaxy LEDA 87300, Baldassare et al. recently reported a nominal virial mass of M_bh = 5 × 10⁴ M_⊙ residing in a "spheroid" of stellar mass equal to 6.3 × 10⁸ M_⊙. We point out, for the first time, that LEDA 87300 therefore appears to reside on the near-quadratic M_bh–M_sph,* relation. However, Baldassare et al. modeled the bulge and bar as the single spheroidal component of this galaxy. Here we perform a 3-component bulge+bar+disk decomposition and find a bulge luminosity which is 7.7 times fainter than the published "bulge" luminosity. After correcting for dust, we find that M_bulge = 0.9 × 10⁸ M_⊙ and M_bulge/M_disk = 0.04—which is now in accord with ratios typically found in Scd–Sm galaxies. We go on to discuss slight revisions to the stellar velocity dispersion (40 ± 11 km s⁻¹) and black hole mass (${M}_{{\rm{bh}}}={2.9}_{-2.3}^{+6.7}\times {10}^{4}\;{f}_{2.3}\;{M}_{\odot }$) and show that LEDA 87300 remains consistent with the M_bh–σ relation, and also the near-quadratic M_bh–M_sph,* relation when using the reduced bulge mass. LEDA 87300 therefore offers the first support for the rapid but regulated (near-quadratic) growth of black holes, relative to their host bulge/spheroid, extending into the domain of intermediate-mass black holes.

HectoMAP is a dense redshift survey of red galaxies covering a 53 deg² strip of the northern sky. HectoMAP is 97% complete for galaxies with r < 20.5, (g− r) > 1.0, and (r − i) > 0.5. The survey enables tests of the physical properties of large-scale structure at intermediate redshift against cosmological models. We use the Horizon Run 4, one of the densest and largest cosmological simulations based on the standard Λ Cold Dark Matter (ΛCDM) model, to compare the physical properties of observed large-scale structures with simulated ones in a volume-limited sample covering 8 × 10⁶h⁻³ Mpc³ in the redshift range 0.22 < z < 0.44. We apply the same criteria to the observations and simulations to identify over- and under-dense large-scale features of the galaxy distribution. The richness and size distributions of observed over-dense structures agree well with the simulated ones. Observations and simulations also agree for the volume and size distributions of under-dense structures, voids. The properties of the largest over-dense structure and the largest void in HectoMAP are well within the distributions for the largest structures drawn from 300 Horizon Run 4 mock surveys. Overall the size, richness and volume distributions of observed large-scale structures in the redshift range 0.22 < z < 0.44 are remarkably consistent with predictions of the standard ΛCDM model.

We study the clustering of galaxies as a function of spectral type and redshift in the range 0.35 < z < 1.1 using data from the Advanced Large Homogeneous Area Medium Band Redshift Astronomical (ALHAMBRA) survey. The data cover 2.381 deg² in 7 fields, after applying a detailed angular selection mask, with accurate photometric redshifts ${\rm{[}}{\sigma }_{z}\lt 0.014(1+z){\rm{]}}$ down to I_AB < 24. From this catalog we draw five fixed number density redshift-limited bins. We estimate the clustering evolution for two different spectral populations selected using the ALHAMBRA-based photometric templates: quiescent and star-forming galaxies. For each sample we measure the real-space clustering using the projected correlation function. Our calculations are performed over the range [0.03, 10.0] h⁻¹ Mpc, allowing us to find a steeper trend for ${r}_{p}\lesssim 0.2\;{h}^{-1}$ Mpc, which is especially clear for star-forming galaxies. Our analysis also shows a clear early differentiation in the clustering properties of both populations: star-forming galaxies show weaker clustering with evolution in the correlation length over the analyzed redshift range, while quiescent galaxies show stronger clustering already at high redshifts and no appreciable evolution. We also perform the bias calculation where similar segregation is found, but now it is among the quiescent galaxies where a growing evolution with redshift is clearer (abrigatted). These findings clearly corroborate the well-known color–density relation, confirming that quiescent galaxies are mainly located in dark matter halos that are more massive than those typically populated by star-forming galaxies.

Large Kuiper Belt objects are conventionally thought to have formed out of a massive planetesimal belt that is a few thousand times its current mass. Such a picture, however, is incompatible with multiple lines of evidence. Here, we present a new model for the conglomeration of Cold Classical Kuiper Belt objects, out of a solid belt only a few times its current mass, or a few per cent of the solid density in a Minimum Mass Solar Nebula. This is made possible by depositing most of the primordial mass in grains of centimeter size or smaller. These grains collide frequently and maintain a dynamically cold belt out of which large bodies grow efficiently: an order-unity fraction of the solid mass can be converted into large bodies, in contrast to the $\sim {10}^{-3}$ efficiency in conventional models. Such a light belt may represent the true outer edge of the solar system, and it may have effectively halted the outward migration of Neptune. In addition to the high efficiency, our model can also produce a mass spectrum that peaks at an intermediate size, similar to the observed Cold Classicals, if one includes the effect of cratering collisions. In particular, the observed power-law break observed at $\sim 30\;\mathrm{km}$ for Cold Classicals, one that has been interpreted as a result of collisional erosion, may be primordial in origin.

Rotational modulations of brown dwarfs have recently provided powerful constraints on the properties of ultra-cool atmospheres, including longitudinal and vertical cloud structures and cloud evolution. Furthermore, periodic light curves directly probe the rotational periods of ultra-cool objects. We present here, for the first time, time-resolved high-precision photometric measurements of a planetary-mass companion, 2M1207b. We observed the binary system with Hubble Space Telescope/Wide Field Camera 3 in two bands and with two spacecraft roll angles. Using point-spread function-based photometry, we reach a nearly photon-noise limited accuracy for both the primary and the secondary. While the primary is consistent with a flat light curve, the secondary shows modulations that are clearly detected in the combined light curve as well as in different subsets of the data. The amplitudes are 1.36% in the F125W and 0.78% in the F160W filters, respectively. By fitting sine waves to the light curves, we find a consistent period of ${10.7}_{-0.6}^{+1.2}$ hr and similar phases in both bands. The J- and H-band amplitude ratio of 2M1207b is very similar to a field brown dwarf that has identical spectral type but different J–H color. Importantly, our study also measures, for the first time, the rotation period for a directly imaged extra-solar planetary-mass companion.

Characterization of transiting planets with transit timing variations (TTVs) requires understanding how to translate the observed TTVs into masses and orbital elements of the planets. This can be challenging in multi-planet transiting systems, but fortunately these systems tend to be nearly plane-parallel and low eccentricity. Here we present a novel derivation of analytic formulae for TTVs that are accurate to first order in the planet–star mass ratios and in the orbital eccentricities. These formulae are accurate in proximity to first-order resonances, as well as away from resonance, and compare well with more computationally expensive N-body integrations in the low-eccentricity, low mass-ratio regime when applied to simulated and to actual multi-transiting Kepler planet systems. We make code available for implementing these formulae.

We consider turbulent synchrotron-emitting media that also exhibit Faraday rotation and provide a statistical description of synchrotron polarization fluctuations. In particular, we consider these fluctuations as a function of the spatial separation of the direction of the measurements and as a function of wavelength for the same line of sight. On the basis of our general analytical approach, we introduce several measures that can be used to obtain the spectral slopes and correlation scales of both the underlying magnetic turbulence responsible for emission and the spectrum of the Faraday rotation fluctuations. We show the synergetic nature of these measures and discuss how the study can be performed using sparsely sampled interferometric data. We also discuss how additional characteristics of turbulence can be obtained, including the turbulence anisotropy and the three-dimensional direction of the mean magnetic field. In addition, we consider the cases when the synchrotron emission and Faraday rotation regions are spatially separated. Appealing to our earlier study, we explain that our new results are applicable to a wide range of spectral indexes of relativistic electrons responsible for synchrotron emission. We expect wide application of our techniques, both with existing synchrotron data sets and with big forthcoming data sets from LOFAR and SKA.

We explore the environmental dependence of star formation timescales in low-mass galaxies using the [α/Fe] abundance ratio as an evolutionary clock. We present integrated [α/Fe] measurements for 11 low-mass (${M}_{\star }\sim {10}^{9}\;{M}_{\odot }$) early-type galaxies (ETGs) with a large range of cluster-centric distance in the Virgo Cluster. We find a gradient in [α/Fe], where the galaxies closest to the cluster center (the cD galaxy, M87) have the highest values. This trend is driven by galaxies within a projected radius of 0.4 Mpc (0.26 times the virial radius of Virgo A), all of which have super-solar [α/Fe]. Galaxies in this mass range exhibit a large scatter in the [α/Fe]–σ diagram, and do not obviously lie on an extension of the relation defined by massive ETGs. In addition, we find a correlation between [α/Fe] and globular cluster specific frequency (S_N), suggesting that low-mass ETGs that formed their stars over a short period of time were also efficient at forming massive star clusters. The innermost low-mass ETGs in our sample have [α/Fe] values comparable to that of M87, implying that environment is the controlling factor for star formation timescales in dense regions. These low-mass galaxies could be the surviving counterparts of the objects that have already been accreted into the halo of M87, and may be the link between present-day low-mass galaxies and the old, metal-poor, high-[α/Fe], high-S_N stellar populations seen in the outer halos of massive ETGs.

We use the low-redshift Zurich Environmental Study (ZENS) catalog to study the dependence of the quenched satellite fraction at ${10}^{10.0}\;{M}_{\odot }\to {10}^{11.5}\;{M}_{\odot }$, and of the morphological mix of these quenched satellites, on three different environmental parameters: group halo mass, halo-centric distance, and large-scale structure (LSS) overdensity. Within the two mass bins into which we divide our galaxy sample, the fraction of quenched satellites is more or less independent of halo mass and the surrounding LSS overdensity, but it increases toward the centers of the halos, as found in previous studies. The morphological mix of these quenched satellites is, however, constant with radial position in the halo, indicating that the well-known morphology–density relation results from the increasing fraction of quenched galaxies toward the centers of halos. If the radial variation in the quenched fraction reflects the action of two quenching processes, one related to mass and the other to environment, then the constancy with radius of the morphological outcome suggests that both have the same effect on the morphologies of the galaxies. Alternatively, mass and environment quenching may be two reflections of a single physical mechanism. The quenched satellites have larger bulge-to-total ratios (B/T) and smaller half-light radii than the star-forming satellites. The bulges in quenched satellites have very similar luminosities and surface brightness profiles, and any mass growth of the bulges associated with quenching cannot greatly change these quantities. The differences in the light-defined B/T and in the galaxy half-light radii are mostly due to differences in the disks, which have lower luminosities in the quenched galaxies. The difference in galaxy half-light radii between quenched and star-forming satellites is however larger than can be explained by uniformly fading the disks following quenching, and the quenched disks have smaller scale lengths than in star-forming satellites. This can be explained either by a differential fading of the disks with galaxy radius or the disks being generally smaller in the past, both of which would be expected in an inside-out disk growth scenario. The overall conclusion is that, at least at low redshifts, the structure of massive quenched satellites at these masses is produced by processes that operate before the quenching takes place. A comparison of our results with semianalytic models argues for a reduction in the efficiency of group halos in quenching their disk satellites and for mechanisms to increase the B/T of low-mass quenched satellites.

Feedback from the active galactic nuclei (AGNs) is one of the most promising heating mechanisms to circumvent the cooling-flow problem in galaxy clusters. However, the role of thermal conduction remains unclear. Previous studies have shown that anisotropic thermal conduction in cluster cool cores (CCs) could drive the heat-flux-driven buoyancy instabilities (HBIs) that reorient the field lines in the azimuthal directions and isolate the cores from conductive heating from the outskirts. However, how the AGN interacts with the HBI is still unknown. To understand these interwined processes, we perform the first 3D magnetohydrodynamic simulations of isolated CC clusters that include anisotropic conduction, radiative cooling, and AGN feedback. We find the following: (1) For realistic magnetic field strengths in clusters, magnetic tension can suppress a significant portion of HBI-unstable modes, and thus the HBI is either completely inhibited or significantly impaired, depending on the unknown magnetic field coherence length. (2) Turbulence driven by AGN jets can effectively randomize magnetic field lines and sustain conductivity at ∼1/3 of the Spitzer value; however, the AGN-driven turbulence is not volume filling. (3) Conductive heating within the cores could contribute to ∼10% of the radiative losses in Perseus-like clusters and up to ∼50% for clusters twice the mass of Perseus. (4) Thermal conduction has various impacts on the AGN activity and intracluster medium properties for the hottest clusters, which may be searched by future observations to constrain the level of conductivity in clusters. The distribution of cold gas and the implications are also discussed.

We address the relation between star formation and active galactic nucleus (AGN) activity in a sample of 231 nearby (0.0002 < z < 0.0358) early-type galaxies by carrying out a multi-wavelength study using archival observations in the UV, IR, and radio. Our results indicate that early-type galaxies in the current epoch are rarely powerful AGNs, with $P\lt {10}^{22}\;{\mathrm{WHz}}^{-1}$ for a majority of the galaxies. Only massive galaxies are capable of hosting powerful radio sources while less massive galaxies are hosts to lower radio power sources. Evidence of ongoing star formation is seen in approximately 7% of the sample. The star formation rate (SFR) of these galaxies is less than 0.1 M_⊙ yr⁻¹. They also tend to be radio faint ($P\lt {10}^{22}\;{\mathrm{WHz}}^{-1}$). There is a nearly equal fraction of star-forming galaxies in radio faint ($P\lt {10}^{22}\;{\mathrm{WHz}}^{-1}$) and radio bright galaxies ($P\geqslant {10}^{22}\;{\mathrm{WHz}}^{-1}$) suggesting that both star formation and radio mode feedback are constrained to be very low in our sample. We notice that our galaxy sample and the Brightest Cluster Galaxies follow similar trends in radio power versus SFR. This may be produced if both radio power and SFR are related to stellar mass.

A systematic search for multicomponent crystal structures is carried out for five different ternary systems of nuclei in a polarizable background of electrons, representative of accreted neutron star crusts and some white dwarfs. Candidate structures are "bred" by a genetic algorithm and optimized at constant pressure under the assumption of linear response (Thomas–Fermi) charge screening. Subsequent phase equilibria calculations reveal eight distinct crystal structures in the T = 0 bulk phase diagrams, five of which are complicated multinary structures not previously predicted in the context of compact object astrophysics. Frequent instances of geometrically similar but compositionally distinct phases give insight into structural preferences of systems with pairwise Yukawa interactions, including and extending to the regime of low-density colloidal suspensions made in a laboratory. As an application of these main results, we self-consistently couple the phase stability problem to the equations for a self-gravitating, hydrostatically stable white dwarf, with fixed overall composition. To our knowledge, this is the first attempt to incorporate complex multinary phases into the equilibrium phase-layering diagram and mass–radius-composition dependence, both of which are reported for He–C–O and C–O–Ne white dwarfs. Finite thickness interfacial phases ("interphases") show up at the boundaries between single-component body-centered cubic (bcc) crystalline regions, some of which have lower lattice symmetry than cubic. A second application—quasi-static settling of heavy nuclei in white dwarfs—builds on our equilibrium phase-layering method. Tests of this nonequilibrium method reveal extra phases that play the role of transient host phases for the settling species.

We examine radiation-regulated accretion onto intermediate-mass and massive black holes (BHs) embedded in a bulge component. Using spherically symmetric one-dimensional radiation-hydrodynamics simulations, we track the growth of BHs accreting from a cold, neutral gas reservoir with temperature ${T}_{\infty }={10}^{4}$ K. We find that the accretion rate of BHs embedded in bulges is proportional to ${r}_{{\rm{B,eff}}}/{r}_{{\rm{B}}}$, where r_B,eff is the increased effective Bondi radius that includes the gravitational potential of the bulge, and r_B is the Bondi radius of the BH. The radiative feedback from the BH suppresses the cold accretion rate to ∼1% of the Bondi rate when a bulge is not considered. However, we find that the BH fueling rate increases rapidly when the bulge mass M_bulge is greater than the critical value of ∼10⁶M_☉ and is proportional to ${r}_{{\rm{B,eff}}}/{r}_{{\rm{B}}}\simeq {M}_{{\rm{bulge}}}/{M}_{{\rm{BH}}}$, where ${M}_{{\rm{BH}}}$ is the BH mass. Since the critical bulge mass is independent of the central BH mass, the growth rate of BHs with masses ${M}_{{\rm{BH}}}={10}^{2}$, 10⁴, and 10⁶M_☉ exhibits distinct dependencies on the bulge-to-BH mass ratio. Our results imply that light seed BHs (≲10²M_☉), which might be the remnants of the Pop III stars, cannot grow through accretion coevally with the early assembly of the bulge of the host galaxies until the bulge reaches the critical mass. However, massive BH seeds (≳10⁵M_☉), which may form via direct collapse, are more likely to be embedded in a supercritical bulge, and thus can grow efficiently coupling to the host galaxies and driving the early evolution of the M_BH–σ relationship.

We find that the young radio sources (gigahertz-peaked spectrum and compact steep spectrum radio sources) follow in the radio/X-ray correlation with $b=0.61\pm 0.07$ (${L}_{R}\propto {L}_{X}^{b}$), and the fundamental plane of black hole activity with the form $\mathrm{log}{L}_{R}={0.58}_{-0.03}^{+0.03}\mathrm{log}{L}_{X}+{0.42}_{-0.07}^{+0.09}\mathrm{log}{M}_{\mathrm{BH}}+{13.83}_{-0.97}^{+0.91}$ and the intrinsic scatter $\sigma =0.29$. The flatter coefficient between radio and X-ray bands denies the jet origin of the X-ray emission in these types of sources. Meanwhile, the higher ratio of X-ray luminosity to Eddington luminosity (${L}_{X}/{L}_{\mathrm{Edd}}$) suggests that the X-ray emission is produced by the hot corona coupling with the standard thin disk. The deviation with the radiative efficient fundamental plane proposed by Dong et al. is mainly due to the extended radio emission in young radio sources. This fundamental plane manifests that even the kiloparsec-scaled radio emission has a tight connection with the accretion process, and could be suitable for the radio-loud active galactic nuclei whose radio and X-ray emission are dominated by the extended jets and the radiative efficient accretion flow, respectively. Otherwise, the high-excitation galaxies and low-excitation galaxies do not have obvious distinctions in the radio/X-ray correlation and the fundamental plane.

In this work, we introduce two models of the hybrid metric-Palatini theory of gravitation. We explore their background evolution, showing explicitly that one recovers standard General Relativity with an effective cosmological constant at late times. This happens because the Palatini Ricci scalar evolves toward and asymptotically settles at the minimum of its effective potential during cosmological evolution. We then use a combination of cosmic microwave background, supernovae, and baryonic accoustic oscillations background data to constrain the models' free parameters. For both models, we are able to constrain the maximum deviation from the gravitational constant G one can have at early times to be around 1%.

The Fermi gamma-ray space telescope has revolutionized our understanding of the cosmic gamma-ray background radiation in the GeV band. However, investigation on the cosmic TeV gamma-ray background radiation still remains sparse. Here, we report the lower bound on the cosmic TeV gamma-ray background spectrum placed by the cumulative flux of individual detected extragalactic TeV sources including blazars, radio galaxies, and starburst galaxies. The current limit on the cosmic TeV gamma-ray background above 0.1 TeV is obtained as 2.8 × 10⁻⁸(E/100 GeV)^−0.55 exp(−E/2100GeV)[GeV cm⁻² s⁻¹ sr⁻¹] < E²dN/dE < 1.1 × 10⁻⁷(E/100 GeV)^−0.49 [GeV cm⁻² s⁻¹ sr⁻¹], where the upper bound is set by requirement that the cascade flux from the cosmic TeV gamma-ray background radiation can not exceed the measured cosmic GeV gamma-ray background spectrum. Two nearby blazars, Mrk 421 and Mrk 501, explain ∼70% of the cumulative background flux at 0.8–4 TeV, while extreme blazars start to dominate at higher energies. We also provide the cumulative background flux from each population, i.e., blazars, radio galaxies, and starburst galaxies which will be the minimum requirement for their contribution to the cosmic TeV gamma-ray background radiation.

We explore the possibility of measuring the mass accretion rate (MAR) of galaxy clusters from their mass profiles beyond the virial radius R₂₀₀. We derive the accretion rate from the mass of a spherical shell whose inner radius is 2R₂₀₀, whose thickness changes with redshift, and whose infall velocity is assumed to be equal to the mean infall velocity of the spherical shells of dark matter halos extracted from N-body simulations. This approximation is rather crude in hierarchical clustering scenarios where both smooth accretion and aggregation of smaller dark matter halos contribute to the mass accretion of clusters. Nevertheless, in the redshift range z = [0, 2], our prescription returns an average MAR within 20%–40% of the average rate derived from the merger trees of dark matter halos extracted from N-body simulations. The MAR of galaxy clusters has been the topic of numerous detailed numerical and theoretical investigations, but so far it has remained inaccessible to measurements in the real universe. Since the measurement of the mass profile of clusters beyond their virial radius can be performed with the caustic technique applied to dense redshift surveys of the cluster outer regions, our result suggests that measuring the mean MAR of a sample of galaxy clusters is actually feasible. We thus provide a new potential observational test of the cosmological and structure formation models.

Observations have suggested that some low-mass stars have larger radii than predicted by 1D structure models. Some theoretical models have invoked very strong interior magnetic fields (of order 1 MG or more) as a possible cause of such large radii. Whether fields of that strength could in principle be generated by dynamo action in these objects is unclear, and we do not address the matter directly. Instead, we examine whether such fields could remain in the interior of a low-mass object for a significant amount of time, and whether they would have any other obvious signatures. First, we estimate the timescales for the loss of strong fields by magnetic buoyancy instabilities. We consider a range of field strengths and simple morphologies, including both idealized flux tubes and smooth layers of field. We confirm some of our analytical estimates using thin flux tube magnetohydrodynamic simulations of the rise of buoyant fields in a fully convective M-dwarf. Separately, we consider the Ohmic dissipation of such fields. We find that dissipation provides a complementary constraint to buoyancy: while small-scale, fibril fields might be regenerated faster than they rise, the dissipative heating associated with such fields would in some cases greatly exceed the luminosity of the star. We show how these constraints combine to yield limits on the internal field strength and morphology in low-mass stars. In particular, we find that for stars of 0.3 solar masses, no fields in flux tubes stronger than about 800 kG are simultaneously consistent with both constraints.

One of the most powerful gamma-ray bursts, GRB 130427A was swiftly detected from GeV γ-rays to optical wavelengths. In the GeV band, the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope observed the highest-energy photon ever recorded of 95 GeV and a bright peak in the early phase followed by emission temporally extended for more than 20 hr. In the optical band, a bright flash with a magnitude of 7.03 ± 0.03 in the time interval from 9.31 to 19.31 s after the trigger was reported by RAPTOR in r band. We study the origin of the GeV γ-ray emission, using the multiwavelength observation detected in X-ray and optical bands. The origin of the temporally extended LAT, X-ray, and optical flux is naturally interpreted as synchrotron radiation, and the 95 GeV photon and the integral flux upper limits placed by the high-altitude water Cerenkov observatory are consistent with synchrotron self-Compton from an adiabatic forward shock propagating into the stellar wind of its progenitor. The extreme LAT peak and the bright optical flash are explained through synchrotron self-Compton and synchrotron emission from the reverse shock, respectively, when the ejecta evolves in the thick-shell regime and carries a significant magnetic field.

We report spectroscopic observations of the resonance lines of singly ionized ⁷Be in the blueshifted absorption line systems found in the post-outburst spectra of two classical novae—V5668 Sgr (Nova Sagittarii 2015 No. 2) and V2944 Oph (Nova Ophiuchi 2015). The unstable isotope ⁷Be should have been created during the thermonuclear runaway (TNR) of these novae and decayed to form ⁷Li within a short period (a half-life of 53.22 days). These confirmations of ⁷Be are the second and the third ones following the first case found in V339 Del by Tajitsu et al. The blueshifted absorption line systems in both novae are clearly divided into two velocity components, both of which contain ⁷Be. This means that the absorbing gases in both velocity components consist of products of TNR. We estimated the amounts of ⁷Be produced during the outbursts of both novae and concluded that significant ⁷Li should have been created. These findings strongly suggest that the explosive production of ⁷Li via the reaction ³He(α,γ)⁷Be and its  subsequent decay to ⁷Li occurs frequently among classical novae and contributes to the process of Galactic Li enrichment.

The Atacama Large Millimeter/submillimeter Array is allowing us to study the innermost regions of the circumstellar envelopes of evolved stars with unprecedented precision and sensitivity. Key processes in the ejection of matter and dust from these objects occur in their inner zones. In this work, we present sub-arcsecond interferometric maps of transitions of metal-bearing molecules toward the prototypical C-rich evolved star IRC +10216. While Al-bearing molecules seem to be present as a roughly spherical shell, the molecular emission from the salts NaCl and KCl presents an elongation in the inner regions with a central minimum. In order to accurately analyze the emission from the NaCl rotational lines, we present new calculations of the collisional rates for this molecule based on new spectroscopic constants. The most plausible interpretation for the spatial distribution of the salts is a spiral with a NaCl mass of 0.08 $\;{M}_{\odot }$. Alternatively, a torus of gas and dust would result in structures similar to those observed. From the torus scenario we derive a mass of ∼1.1 × 10⁻⁴$\;{M}_{\odot }$. In both cases, the spiral and the torus, the NaCl structure presents an inner minimum of 27 AU. In the case of the torus, the outer radius is 73 AU. The kinematics of both the spiral and the torus suggests that they are slowly expanding and rotating. Alternative explanations for the presence of the elongation are explored. The presence of these features only in KCl and NaCl might be a result of their comparatively high dipole moment with respect to the Al-bearing species.

We present the first simulations of tidal stirring of dwarf galaxies in the Local Group carried out in a fully cosmological context. We use the ErisDARK cosmological simulation of a Milky Way (MW)-sized galaxy to identify some of the most massive subhalos (M_vir > 10⁸M_⊙) that fall into the main host before z = 2. Subhalos are replaced before infall with extremely high-resolution models of dwarf galaxies comprising a faint stellar disk embedded in a dark matter halo. The set of models contains cuspy halos as well as halos with "cored" profiles (with the cusp coefficient γ = 0.6) consistent with recent results of hydrodynamical simulations of dwarf galaxy formation. The simulations are then run to z = 0 with as many as 54 million particles and resolutions as small as ∼4 pc using the new parallel N-body code ChaNGa. The stellar components of all satellites are significantly affected by tidal stirring, losing stellar mass, and undergoing a morphological transformation toward a pressure supported spheroidal system. However, while some remnants with cuspy halos maintain significant rotational flattening and disk-like features, all the shallow halo models achieve v_rot/σ_⋆ < 0.5 and round shapes typical of dSph satellites of the MW and M31. Mass loss is also enhanced in the latter, and remnants can reach luminosities and velocity dispersions as low as those of ultra-faint dwarfs.

We simulate the tidal disruption of a collisionless N-body globular star cluster in a total of 300 different orbits selected to have galactocentric radii between 10 and 30 kpc in four dark matter halos: (a) a spherical halo with no subhalos, (b) a spherical halo with subhalos, (c) a realistic halo with no subhalos, and (d) a realistic halo with subhalos. This allows us to isolate and study how the halo's (lack of) dynamical symmetry and substructures affect the dispersal of tidal debris. The realistic halos are constructed from the snapshot of the Via Lactea II simulation at redshift zero. We find that the overall halo's symmetry disperses tidal debris to make the streams fluffier, consistent with previous studies of tidal debris of dwarf galaxies in larger orbits than ours in this study. On the other hand, subhalos in realistic potentials can locally enhance the densities along streams, making streams denser than their counterparts in smooth potentials. We show that many long and thin streams can survive in a realistic and lumpy halo for a Hubble time. This suggests that upcoming stellar surveys will likely uncover more thin streams which may contain density gaps that have been shown to be promising probes for dark matter substructures.

The radio galaxy 3C 273 hosts one of the nearest and best-studied powerful quasar jets. Having been imaged repeatedly by the Hubble Space Telescope (HST) over the past twenty years, it was chosen for an HST program to measure proper motions in the kiloparsec-scale resolved jets of nearby radio-loud active galaxies. The jet in 3C 273 is highly relativistic on sub-parsec scales, with apparent proper motions up to 15c observed by very long baseline interferometry. In contrast, we find that the kiloparsec-scale knots are compatible with being stationary, with a mean speed of −0.2 ± 0.5c over the whole jet. Assuming the knots are packets of moving plasma, an upper limit of 1c implies a bulk Lorentz factor Γ < 2.9. This suggests that the jet has either decelerated significantly by the time it reaches the kiloparsec scale, or that the knots in the jet are standing shock features. The second scenario is incompatible with the inverse Compton off the Cosmic Microwave Background (IC/CMB) model for the X-ray emission of these knots, which requires the knots to be in motion, but IC/CMB is also disfavored in the first scenario due to energetic considerations, in agreement with the recent finding of Meyer & Georganopoulos which ruled out the IC/CMB model for the X-ray emission of 3C 273 via gamma-ray upper limits.

We report the detection of CO(J = 3 $\to$ 2) line emission in the strongly lensed submillimeter galaxy (SMG) SMM J0939+8315 at z = 2.221, using the Combined Array for Research in Millimeter-wave Astronomy. SMM J0939+8315 hosts a type-2 quasar, and is gravitationally lensed by the radio galaxy 3C220.3 and its companion galaxy at z = 0.685. The 104 GHz continuum emission underlying the CO line is detected toward 3C220.3 with an integrated flux density of S_cont = 7.4 ± 1.4 mJy. Using the CO(J = 3 $\to$ 2) line intensity of I_CO(3-2) = (12.6 ± 2.0) Jy km s⁻¹, we derive a lensing- and excitation-corrected CO line luminosity of ${L}_{{\rm{CO(1-0)}}}^{\prime }$ = (3.4 ± 0.7) × 10¹⁰ (10.1/μ_L) K km s⁻¹ pc² for the SMG, where μ_L is the lensing magnification factor inferred from our lens modeling. This translates to a molecular gas mass of M_gas = (2.7 ± 0.6) × 10¹⁰ (10.1/μ_L) M_⊙. Fitting spectral energy distribution models to the (sub)-millimeter data of this SMG yields a dust temperature of T = 63.1${}_{-1.3}^{+1.1}$ K, a dust mass of M_dust = (5.2 ± 2.1) × 10⁸ (10.1/μ_L) M_⊙, and a total infrared luminosity of L_IR = (9.1 ± 1.2) ×10¹² (10.1/μ_L) L_⊙. We find that the properties of the interstellar medium of SMM J0939+8315 overlap with both SMGs and type-2 quasars. Hence, SMM J0939+8315 may be transitioning from a starbursting phase to an unobscured quasar phase as described by the "evolutionary link" model, according to which this system may represent an intermediate stage in the evolution of present-day galaxies at an earlier epoch.

Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs) characterized primarily by a smooth rotation in the magnetic field direction indicative of the presence of a magnetic flux rope. Energetic particle signatures suggest MC flux ropes remain magnetically connected to the Sun at both ends, leading to widely used model of global MC structure as an extended flux rope, with a loop-like axis stretching out from the Sun into the heliosphere and back to the Sun. The time of flight of energetic particles, however, suggests shorter magnetic field line lengths than such a continuous twisted flux rope would produce. In this study, two simple models are compared with observed flux rope axis orientations of 196 MCs to show that the flux rope structure is confined to the MC leading edge. The MC "legs," which magnetically connect the flux rope to the Sun, are not recognizable as MCs and thus are unlikely to contain twisted flux rope fields. Spacecraft encounters with these non-flux rope legs may provide an explanation for the frequent observation of non-MC ICMEs.

We carry out direct numerical simulations of turbulent astrophysical media exposed to the redshift zero metagalactic background. The simulations assume solar composition and explicitly track ionizations, recombinations, and ion-by-ion radiative cooling for hydrogen, helium, carbon, nitrogen, oxygen, neon, sodium, magnesium, silicon, sulfur, calcium, and iron. Each run reaches a global steady state that depends not only on the ionization parameter, $U,$ and mass-weighted average temperature, ${T}_{{\rm{MW}}},$ but also on the one-dimensional turbulent velocity dispersion, ${\sigma }_{{\rm{1D}}}$. We carry out runs that span a grid of models with U ranging from 0 to 10⁻¹ and ${\sigma }_{{\rm{1D}}}$ ranging from 3.5 to 58 km s⁻¹, and we vary the product of the mean density and the driving scale of the turbulence, ${nL},$ which determines the average temperature of the medium, from ${nL}={10}^{16}$ to ${nL}={10}^{20}$ cm⁻². The turbulent Mach numbers of our simulations vary from $M\approx 0.5$ for the lowest velocity dispersion cases to $M\approx 20$ for the largest velocity dispersion cases. When $M\lesssim 1,$ turbulent effects are minimal, and the species abundances are reasonably described as those of a uniform photoionized medium at a fixed temperature. On the other hand, when $M\gtrsim 1,$ dynamical simulations such as the ones carried out here are required to accurately predict the species abundances. We gather our results into a set of tables to allow future redshift zero studies of the intergalactic medium to account for turbulent effects.

We present our results on the Chandra X-ray Observatory Advanced CCD Imaging Spectrometer (ACIS) observations of the bright Oort Cloud comets C/2012 S1 (ISON) and C/2011 L4 (PanSTARRS). ISON was observed between 2013 October 31–November 06 during variable speed solar wind (SW), and PanSTARRS was observed between 2013 April 17–23 during fast SW. ISON produced an extended parabolic X-ray morphology consistent with a collisionally thick coma, while PanSTARRS demonstrated only a diffuse X-ray-emitting region. We consider these emissions to be from charge exchange (CX) and model each comet's emission spectrum from first principles accordingly. Our model agrees with the observational spectra and also generates composition ratios for heavy, highly charged SW ions interacting with the cometary atmosphere. We compare our derived SW ion compositions to observational data and find a strong agreement between them. These results further demonstrate the utility of CX emissions as a remote diagnostics tool of both astrophysical plasma interaction and SW composition. In addition, we observe potential soft X-ray emissions via ACIS around 0.2 keV from both comets that are correlated in intensity to the hard X-ray emissions between 0.4–1.0 keV. We fit our CX model to these emissions, but our lack of a unique solution at low energies makes it impossible to conclude if they are cometary CX in origin. Finally, we discuss probable emission mechanism sources for the soft X-rays and explore new opportunities these findings present in understanding cometary emission processes via Chandra.

We model particle growth in a turbulent, viscously evolving protoplanetary nebula, incorporating sticking, bouncing, fragmentation, and mass transfer at high speeds. We treat small particles using a moments method and large particles using a traditional histogram binning, including a probability distribution function of collisional velocities. The fragmentation strength of the particles depends on their composition (icy aggregates are stronger than silicate aggregates). The particle opacity, which controls the nebula thermal structure, evolves as particles grow and mass redistributes. While growing, particles drift radially due to nebula headwind drag. Particles of different compositions evaporate at "evaporation fronts" (EFs) where the midplane temperature exceeds their respective evaporation temperatures. We track the vapor and solid phases of each component, accounting for advection and radial and vertical diffusion. We present characteristic results in evolutions lasting 2 × 10⁵ years. In general, (1) mass is transferred from the outer to the inner nebula in significant amounts, creating radial concentrations of solids at EFs; (2) particle sizes are limited by a combination of fragmentation, bouncing, and drift; (3) "lucky" large particles never represent a significant amount of mass; and (4) restricted radial zones just outside each EF become compositionally enriched in the associated volatiles. We point out implications for millimeter to submillimeter SEDs and the inference of nebula mass, radial banding, the role of opacity on new mechanisms for generating turbulence, the enrichment of meteorites in heavy oxygen isotopes, variable and nonsolar redox conditions, the primary accretion of silicate and icy planetesimals, and the makeup of Jupiter's core.

The metallicity distribution function of globular clusters (GCs) in galaxies is a key to understanding galactic formation and evolution. The calcium II triplet (CaT) index has recently become a popular metal abundance indicator thanks to its sensitivity to GC metallicity. Here we revisit and assess the reliability of CaT as a metallicity indicator using our new stellar population synthesis simulations based on empirical high-resolution fluxes. The model shows that the CaT strength of old (>10 Gyr) GCs is proportional to [Fe/H] below −0.5. In the modest metal-rich regime, however, CaT does not increase anymore with [Fe/H] due to the little contribution from coolest red giant stars to the CaT absorption. The nonlinear nature of the color–CaT relation is confirmed by the observations of GCs in nearby early-type galaxies. This indicates that the CaT should be used carefully when deriving metallicities of metal-rich stellar populations. Our results offer an explanation for the observed sharp difference between the color and CaT distributions of GCs in the same galaxies. We take this as an analogy to the view that metallicity–color and metallicity–Lick index nonlinearity of GCs is primarily responsible for their observed "bimodal" distributions of colors and absorption indices.

We present a catalog of 166 spectroscopically identified hot subdwarf stars from LAMOST DR1, 44 of which show the characteristics of cool companions in their optical spectra. Atmospheric parameters of 122 subdwarf stars with non-composite spectra were measured by fitting the profiles of hydrogen (H) and helium (He) lines with synthetic spectra from non-LTE model atmospheres. Most of the sdB stars scatter near the Extreme Horizontal Branch in the T_eff–$\mathrm{log}g$ diagram and two well defined groups can be outlined. A clustering of He-enriched sdO stars appears near T_eff = 45,000 K and log g = 5.8. The sdB population separates into several nearly parallel sequences in the T_eff–He abundance diagram with clumps corresponding to those in the T_eff–$\mathrm{log}\;g$ diagram. Over 38,000 K (sdO) stars show abundance extremes; they are either He-rich or He-deficient and we observe only a few stars in the abundance range $-1\lt \mathrm{log}\;y\lt 0$. With increasing temperature these extremes become less prominent and the He abundance approaches log y ∼ −0.5. A unique property of our sample is that it covers a large range in apparent magnitude and galactic latitude, therefore it contains a mix of stars from different populations and galactic environments. Our results are consistent with the findings of Hirsch and we conclude that He-rich and He-deficient sdB stars (log y < 1) probably originate from different populations. We also find that most sdO and sdB stars lie in a narrow strip in the plane of luminosity and helium abundance, which suggests that these atmospheric parameters are correlated.

Earlier studies have suggested that coronal plumes are energized by magnetic reconnection between unipolar flux concentrations and nearby bipoles, even though magnetograms sometimes show very little minority-polarity flux near the footpoints of plumes. Here we use high-resolution extreme-ultraviolet (EUV) images and magnetograms from the Solar Dynamics Observatory (SDO) to clarify the relationship between plume emission and the underlying photospheric field. We find that plumes form where unipolar network elements inside coronal holes converge to form dense clumps, and fade as the clumps disperse again. The converging flows also carry internetwork fields of both polarities. Although the minority-polarity flux is sometimes barely visible in the magnetograms, the corresponding EUV images almost invariably show loop-like features in the core of the plumes, with the fine structure changing on timescales of minutes or less. We conclude that the SDO observations are consistent with a model in which plume emission originates from interchange reconnection in converging flows, with the plume lifetime being determined by the ∼1 day evolutionary timescale of the supergranular network. Furthermore, the presence of large EUV bright points and/or ephemeral regions is not a necessary precondition for the formation of plumes, which can be energized even by the weak, mixed-polarity internetwork fields swept up by converging flows.

We present deep LOFAR observations between 120 and 181 MHz of the "Toothbrush" (RX J0603.3+4214), a cluster that contains one of the brightest radio relic sources known. Our LOFAR observations exploit a new and novel calibration scheme to probe 10 times deeper than any previous study in this relatively unexplored part of the spectrum. The LOFAR observations, when combined with VLA, GMRT, and Chandra X-ray data, provide new information about the nature of cluster merger shocks and their role in re-accelerating relativistic particles. We derive a spectral index of $\alpha =-0.8\pm 0.1$ at the northern edge of the main radio relic, steepening toward the south to $\alpha \approx -2$. The spectral index of the radio halo is remarkably uniform ($\alpha =-1.16$, with an intrinsic scatter of $\;\leqslant 0.04$). The observed radio relic spectral index gives a Mach number of ${ \mathcal M }={2.8}_{-0.3}^{+0.5}$, assuming diffusive shock acceleration. However, the gas density jump at the northern edge of the large radio relic implies a much weaker shock (${ \mathcal M }\approx 1.2$, with an upper limit of ${ \mathcal M }\approx 1.5$). The discrepancy between the Mach numbers calculated from the radio and X-rays can be explained if either (i) the relic traces a complex shock surface along the line of sight, or (ii) if the radio relic emission is produced by a re-accelerated population of fossil particles from a radio galaxy. Our results highlight the need for additional theoretical work and numerical simulations of particle acceleration and re-acceleration at cluster merger shocks.