Table of contents

We present the results of a high-cadence spectroscopic and imaging monitoring campaign of the active galactic nucleus (AGN) of NGC 4395. High signal-to-noise-ratio spectra were obtained at the Gemini-N 8 m telescope using the GMOS integral field spectrograph (IFS) on 2019 March 7 and at the Keck I 10 m telescope using the Low-Resolution Imaging Spectrometer with slit masks on 2019 March 3 and April 2. Photometric data were obtained with a number of 1 m-class telescopes during the same nights. The narrow-line region (NLR) is spatially resolved; therefore, its variable contributions to the slit spectra make the standard procedure of relative flux calibration impractical. We demonstrate that spatially resolved data from the IFS can be effectively used to correct the slit-mask spectral light curves. While we obtained no reliable lag owing to the lack of a strong variability pattern in the light curves, we constrain the broad-line time lag to be less than 3 hr, consistent with the photometric lag of ∼80 minutes reported by Woo et al. By exploiting the high-quality spectra, we measure the second moment of the broad component of the Hα emission line to be 586 ± 19 km s⁻¹, superseding the lower value reported by Woo et al. Combining the revised line dispersion and the photometric time lag, we update the black hole mass to (1.7 ± 0.3) × 10⁴M_⊙.

The physical origin of the overionized recombining plasmas (RPs) in supernova remnants (SNRs) has been attracting attention because its understanding provides new insight into SNR evolution. However, the process of the overionization, although it has been discussed in some RP-SNRs, is not yet fully understood. Here, we report on spatially resolved spectroscopy of X-ray emission from IC 443 with XMM-Newton. We find that RPs in regions interacting with dense molecular clouds tend to have lower electron temperature and lower recombination timescale. These tendencies indicate that RPs in these regions are cooler and more strongly overionized, which is naturally interpreted as a result of rapid cooling by the molecular clouds via thermal conduction. Our result on IC 443 is similar to that on W44 showing evidence for thermal conduction as the origin of RPs at least in older remnants. We suggest that evaporation of clumpy gas embedded in a hot plasma rapidly cools the plasma as was also found in the W44 case. We also discuss if ionization by protons accelerated in IC 443 is responsible for RPs. Based on the energetics of particle acceleration, we conclude that the proton bombardment is unlikely to explain the observed properties of RPs.

Warm absorbers (WAs) located approximately in the region of 1–1000 pc are common phenomena in many active galactic nuclei (AGNs). The driving mechanism of WAs is still under debate. Ultra-fast outflows (UFOs) that are launched very close to the central black hole are also frequently observed in AGNs. When UFOs move outward, they collide with the interstellar medium (ISM) gas. In this paper, we study the possibility that WAs can be generated by the interaction between ISM gas and the UFOs. We find that under some ISM gas conditions, WAs can be generated. However, the covering factor of WAs is much smaller than that given by observations. This indicates that other mechanisms should also be at work. We also find that the properties of the WAs mainly depend on the density of the ISM injected into the computational domain from the outer radial boundary (1000 pc). The higher the density of the ISM is, the higher the mass flux and kinetic power of the WAs will be. The kinetic power of the UFO-driven WAs is much less than 1% of the bolometric luminosity of the host AGNs. Therefore, the UFO-driven WAs might not contribute sufficient feedback to the host galaxy.

Radio magnetars are exotic sources noted for their diverse spectrotemporal phenomenology and pulse profile variations over weeks to months. Unusual for radio magnetars, the Galactic Center (GC) magnetar PSR J1745−2900 has been continually active since its discovery in 2013. We monitored the GC magnetar at 4–8 GHz for 6 hr in 2019 August–September using the Robert C. Byrd Green Bank Telescope. During our observations, the GC magnetar emitted a flat fluence spectrum over 5–8 GHz to within 2σ uncertainty. From our data, we estimate a 6.4 GHz period-averaged flux density, ${\overline{S}}_{6.4}\approx (240\pm 5)$μJy. Tracking the temporal evolution of ${\overline{S}}_{6.4}$, we infer a gradual weakening of GC magnetar activity during 2016–2019 relative to that between 2013 and 2015.5. Typical single pulses detected in our study reveal marginally resolved subpulses with opposing spectral indices, a feature characteristic of radio magnetars but unseen in rotation-powered pulsars. However, unlike in fast radio bursts, these subpulses exhibit no perceptible radio frequency drifts. Throughout our observing span, ≃5 ms scattered pulses significantly jitter within two stable emission components of widths 220 ms and 140 ms, respectively, in the average pulse profile.

On 2020 November 30, Parker Solar Probe (PSP) was crossed by a coronal mass ejection (CME)-driven shock, which we suggest was also crossing a convected, isolated magnetic structure (MS) at about the same time. By analyzing PSP/FIELDS magnetic field measurements, we find that the leading edge of the MS coincided with the crossing of the shock, while its trailing edge, identified as a crossing of a current sheet, overtook PSP about 7 minutes later. Prior to the arrival of the shock, the flux of 30 keV–3 MeV ions and electrons, as measured by PSP/Integrated Science Investigation of the Sun (ISOIS)/Energetic Particle Instrument (EPI-Lo), increased gradually, peaking at the time of the shock passage. However, during the crossing of the MS downstream of the shock, the energetic-ion flux dropped dramatically, before recovering at about the time of the crossing of the trailing edge of the MS. Afterwards, the ion fluxes remained approximately constant within the sheath region of the CME shock. We interpret this depletion of energetic ions within the MS as the result of insufficient time to accelerate particles at the shock within the MS, given that the structure moves along the shock surface owing to its advection with the solar wind. We present results from a quantitative numerical model of the interaction of an idealized MS with a shock, which supports this interpretation.

Lyα-emitting galaxies (LAEs) are easily detectable in the high-redshift universe and are potentially efficient tracers of large-scale structure at early epochs, as long as their observed properties do not depend strongly on environment. We investigate the luminosity and equivalent width functions of LAEs in the overdense field of a protocluster at redshift z ≃ 3.78. Using a large sample of LAEs (many spectroscopically confirmed), we find that the Lyα luminosity distribution is well represented by a Schechter function with $\mathrm{log}({L}^{* }/\mathrm{erg}\ {{\rm{s}}}^{-1})={43.26}_{-0.22}^{+0.20}$ and $\mathrm{log}({\phi }^{* }/{\mathrm{Mpc}}^{-3})=-{3.40}_{-0.04}^{+0.03}$ with α = −1.5. Fitting the equivalent width distribution as an exponential, we find a scale factor of $\omega ={79}_{-15}^{+15}$ Å. We also measured the Lyα luminosity and equivalent width functions using the subset of LAEs lying within the densest cores of the protocluster, finding similar values for L* and ω. Hence, despite having a mean overdensity more than 2× that of the general field, the shapes of the Lyα luminosity function and equivalent width distributions in the protocluster region are comparable to those measured in the field LAE population by other studies at similar redshift. While the observed Lyα luminosities and equivalent widths show correlations with the UV continuum luminosity in this LAE sample, we find that these are likely due to selection biases and are consistent with no intrinsic correlations within the sample. This protocluster sample supports the strong evolutionary trend observed in the Lyα escape fraction and suggests that LAEs at lower redshift can be on average significantly more dusty that their counterparts at higher redshift.

Theories of modified gravity generically violate the strong equivalence principle, so that the internal dynamics of a self-gravitating system in freefall depends on the strength of the external gravitational field (the external field effect). We fit rotation curves (RCs) from the SPARC database with a model inspired by Milgromian dynamics (MOND), which relates the outer shape of an RC to the external Newtonian field from the large-scale baryonic matter distribution through a dimensionless parameter e_N. We obtain a > 4σ statistical detection of the external field effect (i.e. e_N > 0 on average), confirming previous results. We then locate the SPARC galaxies in the cosmic web of the nearby universe and find a striking contrast in the fitted e_N values for galaxies in underdense versus overdense regions. Galaxies in an underdense region between 22 and 45 Mpc from the celestial axis in the northern sky have RC fits consistent with e_N ≃ 0, while those in overdense regions adjacent to the CfA2 Great Wall and the Perseus−Pisces Supercluster return e_N that are a factor of two larger than the median for SPARC galaxies. We also calculate independent estimates of e_N from galaxy survey data and find that they agree with the e_N inferred from the RCs within the uncertainties, the chief uncertainty being the spatial distribution of baryons not contained in galaxies or clusters.

We study the response of hot Jupiters to a static tidal perturbation using the concentric MacLaurin spheroid method. For strongly irradiated planets, we first performed radiative transfer calculations to relate the planet's equilibrium temperature, T_eq, to its interior entropy. We then determined the gravity harmonics, shape, moment of inertia, and static Love numbers for a range of two-layer interior models that assume a rocky core plus a homogeneous and isentropic envelope composed of hydrogen, helium, and heavier elements. We identify general trends and then study HAT-P-13b, the WASP planets 4b, 12b, 18b, 103b, and 121b, and Kepler-75b and CoRot-3b. We compute the Love numbers, k_nm, and transit radius correction, ΔR, which we compare with predictions in the literature. We find that the Love number, k₂₂, of tidally locked giant planets cannot exceed a value of 0.6, and that the high T_eq consistent with strongly irradiated hot Jupiters tends to further lower k₂₂. While most tidally locked planets are well described by a linear regime response of k₂₂ = 3J₂/q₀ (where q₀ is the rotation parameter of the gravitational potential), for extreme cases such as WASP-12b, WASP-103b, and WASP-121b, nonlinear effects can account for over 10% of the predicted k₂₂. The k₂₂ values larger than 0.6, as they have been reported for planets WASP-4b and HAT-P13B, cannot result from a static tidal response without extremely rapid rotation and thus are inconsistent with their expected tidally locked state.

The standard picture of galaxy formation motivates the decomposition of the Milky Way into 3–4 stellar populations with distinct kinematic and elemental abundance distributions: the thin disk, thick disk, bulge, and stellar halo. To test this idea, we construct a Gaussian mixture model (GMM) for both simulated and observed stars in the solar neighborhood, using measured velocities and iron abundances (i.e., an augmented Toomre diagram) as the distributions to be decomposed. We compare results for the Gaia−APOGEE DR16 crossmatch catalog of the solar neighborhood with those from a suite of synthetic Gaia−APOGEE crossmatches constructed from FIRE-2 cosmological simulations of Milky Way mass galaxies. We find that in both the synthetic and real data, the best-fit GMM uses five independent components, some of whose properties resemble the standard populations predicted by galaxy formation theory. Two components can be identified unambiguously as the thin disk and another as the halo. However, instead of a single counterpart to the thick disk, there are three intermediate components with different age and alpha abundance distributions (although these data are not used to construct the model). We use decompositions of the synthetic data to show that the classified components indeed correspond to stars with different origins. By analogy with the simulated data, we show that our mixture model of the real Gaia−APOGEE crossmatch distinguishes the following components: (1) a classic thin disk of young stars on circular orbits (46%), (2) thin disk stars heated by interactions with satellites (22%), (3, 4) two components representing the velocity asymmetry of the alpha-enhanced thick disk (27%), and (5) a stellar halo consistent with early, massive accretion (4%).

We measure the central kinematics for the dwarf spheroidal galaxy Leo I using integrated-light measurements and previously published data. We find a steady rise in the velocity dispersion from 300'' into the center. The integrated-light kinematics provide a velocity dispersion of 11.76 ± 0.66 km s⁻¹ inside 75''. After applying appropriate corrections to crowding in the central regions, we achieve consistent velocity dispersion values using velocities from individual stars. Crowding corrections need to be applied when targeting individual stars in high-density stellar environments. From integrated light, we measure the surface brightness profile and find a shallow cusp toward the center. Axisymmetric, orbit-based models measure the stellar mass-to-light ratio, black hole mass, and parameters for a dark matter halo. At large radii it is important to consider possible tidal effects from the Milky Way, so we include a variety of assumptions regarding the tidal radius. For every set of assumptions, models require a central black hole consistent with a mass (3.3 ± 2) × 10⁶M_⊙. The no-black-hole case for any of our assumptions is excluded at over 95% significance, with 6.4 < Δχ² < 14. A black hole of this mass would have significant effects on dwarf galaxy formation and evolution. The dark halo parameters are heavily affected by the assumptions for the tidal radii, with the circular velocity only constrained to be above 30 km s⁻¹. Reasonable assumptions for the tidal radius result in stellar orbits consistent with an isotropic distribution in the velocities. These more realistic models have little need for a dark matter halo.

The high cosmological precision offered by the next generation of galaxy surveys hinges on improved corrections for Galactic dust extinction. We explore the possibility of estimating both the dust extinction and large-scale structure from a single photometric galaxy survey, making use of the predictable manner in which Milky Way dust affects the measured brightness and colors of galaxies in a given sky location in several redshift bins. To test our method, we use a synthetic catalog from a cosmological simulation designed to model the Vera C. Rubin Observatory Legacy Survey of Space and Time. At high Galactic latitude (∣b∣ ≳ 20°) and a resolution of 1° ($7^{\prime}$), we predict the uncertainty in the measurement of dust extinction, E(B − V), to be 0.005 mag (0.015 mag). This is similar to the uncertainty of existing dust maps, illustrating the feasibility of our method. Simultaneous estimation of large-scale structure is predicted to recover the galaxy overdensity δ with a precision of ∼0.01 (∼0.05) at 1° ($7^{\prime}$) resolution. We also introduce a Bayesian formalism that combines prior information from existing dust maps with the likelihood of Galactic dust extinction determined from the excursion of observed galaxy properties.

In this work, a modified force-field approach is established to investigate the long-term solar modulation of galactic cosmic-ray (GCR) protons. In this approach, the solar modulation potential ϕ is assumed to be energy dependent. As ϕ also depends on the local interstellar spectrum (LIS), a new proton LIS model is first presented based on data from Voyager 1 and 2, PAMELA, and AMS-02. Then, a double power-law expression is proposed to model ϕ as a function of proton energy. By fitting to the selected GCR measurements, the solar cycle variation characteristics of parameters in the expression of ϕ are obtained, and these parameters are reconstructed using the sunspot number, the heliospheric current sheet tilt angle, and the polarity of heliospheric magnetic field. Finally, a new analytical predictive model for GCR protons is established. It is shown that the 11 and 22 yr cyclic variations of GCRs are reproduced, and the computed proton intensities are in good agreement with GCR measurements at various energies since 1954.

We present near-infrared K-band spectra for a sample of seven Class 0 protostars in the Perseus and Orion star-forming regions. We detect Brγ, CO overtone, and H₂ emission, features that probe the near-circumstellar environment of the protostar and reveal evidence of magnetospheric accretion, a hot inner disk atmosphere, and outflows, respectively. Comparing the properties of these features with those of Class I sources from the literature, we find that their Brγ emission and CO emission are generally consistent in strength and velocity width. The Brγ line profiles are broad and centrally peaked, with FWHMs of ∼200 km s⁻¹ and wings extending to ∼300 km s⁻¹. The line ratios of our H₂ emission features, which are spatially extended for some sources, are consistent with shock excitation and indicate the presence of strong jets or a disk wind. Within our small sample, the frequency of CO band emission (∼67%) is high relative to that of Class I samples (∼15%), indicating that Class 0 sources have high inner disk accretion rates, similar to those of the most actively accreting Class I sources. Collectively, our results suggest that Class 0 sources have similar accretion mechanisms to the more evolved classes, with strong organized stellar magnetic fields established at the earliest observable stage of evolution.

By directly inverting several neutron star (NS) observables in the three-dimensional parameter space for the equation of state of super-dense neutron-rich nuclear matter, we show that the lower radius limit for PSR J0740+6620 of mass 2.08 ± 0.07 M_⊙ from Neutron Star Interior Composition Explorer (NICER)'s very recent observation sets a much tighter lower boundary than previously known for nuclear symmetry energy in the density range of (1.0 ∼ 3.0) times the saturation density ρ₀ of nuclear matter. The super-soft symmetry energy leading to the formation of proton polarons in this density region of NSs is clearly disfavored by the first radius measurement for the most massive NS observed reliably so far.

We examine the impact of baryonic physics on the halo distribution in hydrodynamic simulations compared to that in dark matter–only (DMO) simulations. We find that, in general, DMO simulations produce halo mass functions (HMFs) that are shifted to higher halo masses than their hydrodynamic counterparts due to the lack of baryonic physics. However, the exact nature of this mass shift is a complex function of mass, halo definition, redshift, and larger-scale environment, and it depends on the specifics of the baryonic physics implemented in the simulation. We present fitting formulae for the corrections one would need to apply to each DMO halo catalog in order to reproduce the HMF found in its hydrodynamic counterpart. Additionally, we explore the dependence on environment of this HMF discrepancy and find that, in most cases, halos in low-density environments are slightly more impacted by baryonic physics than halos in high-density environments. We thus also provide environment-dependent mass correction formulae that can reproduce the conditional, as well as global, HMF. We show that our mass corrections also repair the large-scale clustering of halos, though the environment-dependent corrections are required to achieve an accuracy better than 2%. Finally, we examine the impact of baryonic physics on the halo mass–concentration relation and find that its slope in hydrodynamic simulations is consistent with that in DMO simulations. Ultimately, we recommend that any future work relying on DMO halo catalogs incorporate our mass corrections to test the robustness of their results to baryonic effects.

We present three-dimensional simulations of core-collapse supernovae using the FLASH code that follow the progression of the explosion to the stellar surface, starting from neutrino radiation hydrodynamic simulations of the neutrino-driven phase performed with the Chimera code. We consider a 9.6 M_☉ zero-metallicity progenitor starting from both 2D and 3D Chimera models and a 10 M_☉ solar-metallicity progenitor starting from a 2D Chimera model, all simulated until shock breakout in 3D while tracking 160 nuclear species. The relative velocity difference between the supernova shock and the metal-rich Rayleigh–Taylor (R-T) "bullets" determines how the metal-rich ejecta evolves as it propagates through the density profile of the progenitor and dictates the final morphology of the explosion. We find maximum ⁵⁶Ni velocities of ∼1950 and ∼1750 km s⁻¹ at shock breakout from 2D and 3D 9.6 M_☉Chimera models, respectively, due to the bullets' ability to penetrate the He/H shell. When mapping from 2D, we find that the development of higher-velocity structures is suppressed when the 2D Chimera model and 3D FLASH model meshes are aligned. The development of faster-growing spherical-bubble structures, as opposed to the slower-growing toroidal structure imposed by axisymmetry, allows for interaction of the bullets with the shock and seeds further R-T instabilities at the He/H interface. We see similar effects in the 10 M_☉ model, which achieves maximum ⁵⁶Ni velocities of ∼2500 km s⁻¹ at shock breakout.

At present, 19 double neutron star (DNS) systems are detected by radio timing and two merging DNS systems are detected by kilohertz gravitational waves. Because of selection effects, none of them has an orbital period P_b in the range of a few tens of minutes. In this paper we consider a multimessenger strategy proposed by Kyutoku et al., jointly using the Laser Interferometer Space Antenna and the Square Kilometre Array to detect and study Galactic pulsar-neutron star (PSR-NS) systems with P_b ∼ 10–100 minutes. We assume that we will detect PSR-NS systems by this strategy. We use standard pulsar-timing software to simulate times of arrival of pulse signals from these binary pulsars. We obtain the precision of timing parameters of short-orbital-period PSR-NS systems with orbital period P_b ∈ (8, 120) minutes. We use the simulated uncertainty of the orbital decay, ${\dot{P}}_{b}$, to predict future tests for a variety of alternative theories of gravity. We show quantitatively that highly relativistic PSR-NS systems will significantly improve the constraint on parameters of specific gravity theories in the strong field regime. We also investigate the orbital periastron advance caused by the Lense−Thirring effect in a PSR-NS system with P_b = 8 minutes, and show that the Lense−Thirring effect will be detectable to a good precision.

We report the electron density dependence of extreme ultraviolet line intensity ratios in Ar xiv studied using a well-defined electron beam ion trap plasma. The purpose of this study is to examine the potential of the Ar xiv lines in diagnosing the electron density of solar corona active regions with a temperature higher than 3 MK. The experimentally obtained dependence is in good agreement with collisional-radiative model calculations, which ensures the usability of the Ar xiv lines.

Galactic and extragalactic cosmic rays fully illuminate and trigger several physical and physicochemical changes in molecular clouds (MCs), including gas and grain heating, molecular destruction and formation, and molecular and atomic desorption (sputtering) from dust/ices to gas phase. Besides the major component in cosmic ray inventory (in flux) being electrons, protons, and alphas, particles with larger atomic numbers have a higher rate of energy delivery (due to richer cosmic ray showers) than the lighter particles, and this may add extra energy input into MCs. To understand this issue, we perform complementary calculations to the previous work on MCs, now adding the heavy ions (12 ≤ Z ≤ 29) in the cosmic ray incoming inventory. Once more, the calculations were performed employing the Monte Carlo toolkit GEANT4 code (considering nuclear and hadron physics). We observe that most projectiles in the heavy ion group have lower deposited energies (roughly 10 times less) than iron with the exception of magnesium (Z = 12) and silicon (Z = 14) which are about double. Cobalt presents the lowest deposited energies with respect to iron (only 0.5%). The total energy deposition in the current model was only roughly 10% higher (outer layers) and virtually the same at the center of the cloud when compared with the previous model (with only protons + alphas + electrons sources). The results show that energy deposition by heavy ions is small compared with the values from light particles, and also suggest a very low temperature enhancement due to heavy ions within the MC, being the protons the dominant agent in the energy delivery and also in the cloud's heating.

We present the results of a spectroscopic monitoring program of the Pleiades region aimed at completing the census of spectroscopic binaries in the cluster, extending it to longer periods than previously reachable. We gathered 6104 spectra of 377 stars between 1981 and 2021, and merged our radial velocities with 1151 measurements from an independent survey by others started three years earlier. With the combined data spanning more than 43 yr, we have determined orbits for some 30 new binary and multiple systems, more than doubling the number previously known in the Pleiades. The longest period is 36.5 yr. A dozen additional objects display long-term trends in their velocities, implying even longer periods. We examine the collection of orbital elements for cluster members, and find that the shape of the incompleteness-corrected distribution of periods (up to 10⁴ days) is similar to that of solar-type binaries in the field, while that of the eccentricities is different. The mass-ratio distribution is consistent with being flat. The binary frequency in the Pleiades for periods up to 10⁴ days is 25% ± 3% after corrections for undetected binaries, which is nearly double that of the field up to the same period. The total binary frequency including known astrometric binaries is at least 57%. We estimate the internal radial velocity dispersion in the cluster to be 0.48 ± 0.04 km s⁻¹. We revisit the determination of the tidal circularization period, and confirm its value to be 7.2 ± 1.0 days, with an improved precision compared to an earlier estimate.

Comoving pairs, even at the separations of ${ \mathcal O }({10}^{6})$ au, are a predicted reservoir of conatal stars. We present detailed chemical abundances of 62 stars in 31 comoving pairs with separations of 10²–10⁷ au and 3D velocity differences <2 km s⁻¹. This sample includes both bound comoving pairs/wide binaries and unbound comoving pairs. Observations were taken using the Magellan Inamori Kyocera Echelle (MIKE) spectrograph on board the Magellan/Clay Telescope at high resolution (R ∼ 45,000) with a typical signal-to-noise ratio of 150 pixel⁻¹. With these spectra, we measure surface abundances for 24 elements, including Li, C, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, La, Nd, and Eu. Taking iron as the representative element, our sample of wide binaries is chemically homogeneous at the level of 0.05 dex, which agrees with prior studies on wide binaries. Importantly, even systems at separations 2 × 10⁵–10⁷ au are homogeneous to 0.09 dex, as opposed to the random pairs, which have a dispersion of 0.23 dex. Assuming a mixture model of the wide binaries and random pairs, we find that 73 ± 22% of the comoving pairs at separations 2 × 10⁵–10⁷ au are conatal. Our results imply that a much larger parameter space of phase space may be used to find conatal stars, to study M-dwarfs, star cluster evolution, exoplanets, chemical tagging, and beyond.

We introduce a Bayesian approach coupled with a Markov Chain Monte Carlo method and the maximum-likelihood statistic for fitting the profiles of narrow absorption lines (NALs) in quasar spectra. This method also incorporates the overlap between different absorbers. We illustrate and test this method by fitting models to a "mini-broad" (mini-BAL) and six NAL profiles in four spectra of the quasar UM 675 taken over a rest-frame interval of 4.24 yr. Our fitting results are consistent with past results for the mini-BAL system in this quasar by Hamann et al. We also measure covering factors (C_f) for two narrow components in the C iv and N v mini-BALs and their overlap covering factor with the broad component. We find that C_f (N v) is always larger than C_f (C iv) for the broad component, while the opposite is true for the narrow components in the mini-BAL system. This could be explained if the broad and narrow components originated in gas at different radial distances, but it seems more likely to be due to being produced by gas at the same distance but with different gas densities (i.e., ionization states). The variability detected only in the broad absorption component in the mini-BAL system is probably due to gas motion, since both C_f (C iv) and C_f (N v) vary. We determine for the first time that multiple absorbing clouds (i.e., a broad and two narrow components) overlap along our line of sight. We conclude that the new method improves fitting results considerably compared to previous methods.

We report the discovery of the first radio pulsar associated with NGC 6712, an eclipsing black widow (BW) pulsar, J1853–0842A, found by high-sensitivity searches using the Five-hundred-meter Aperture Spherical radio Telescope. This 2.15 ms pulsar is in a 3.56 hr compact circular orbit with a very low mass companion likely of mass 0.018 to 0.036 M_⊙ and exhibits eclipsing of the pulsar signal. Though the distance to PSR J1853–0842A predicted from its dispersion measure (155.125 ± 0.004 cm⁻³ pc) and Galactic free electron density models are about 30% smaller than that of NGC 6712 obtained from interstellar reddening measurements, this is likely due to limited knowledge about the spiral arms and Scutum stellar cloud in this direction. Follow-up timing observations spanning 445 days allow us to localize the pulsar's position to be 0.14 core radii from the center of NGC 6712 and measure a negative spin-down rate for this pulsar of −2.39(2) × 10⁻²¹ s s⁻¹. The latter cannot be explained without the acceleration of the globular cluster (GC) and decisively supports the association between PSR J1853–0842A and NGC 6712. Considering the maximum GC acceleration, the Galactic acceleration, and the Shklovskii effect, we place an upper limit on the intrinsic spin-down rate to be 1.11 × 10⁻²⁰ s s⁻¹. From an analysis of the eclipsing observations, we estimate the electron density of the eclipse region to be about 1.88 × 10⁶ cm⁻³. We also place an upper limit of the accretion rate from the companion at about 3.05 × 10⁻¹³M_⊙ yr⁻¹, which is comparable with some other BWs.

Cosmic-ray acceleration at non-relativistic shocks relies on scattering by turbulence that the cosmic rays drive upstream of the shock. We explore the rate of energy transfer from cosmic rays to non-resonant Bell modes and the spectral softening it implies. Accounting for the finite time available for turbulence driving at supernova-remnant shocks yields a smaller spectral impact than found earlier with steady-state considerations. Generally, for diffusion scaling with the Bohm rate by a factor η, the change in spectral index is at most η divided by the Alfvénic Mach number of the thermal sub-shock. For M_A ≲ 50 it is well below this limit. Only for very fast shocks and very efficient cosmic-ray acceleration can the change in spectral index reach 0.1. For standard SNR parameters, it is negligible. Independent confirmation is derived by considering the synchrotron energy losses of electrons: if intense nonthermal multi-keV emission is produced, the energy loss, and hence the spectral steepening, is very small for hadronic cosmic rays that produce TeV-band gamma-ray emission.

During the first half of main-sequence lifetimes, the evolution of rotation and magnetic activity in solar-type stars appears to be strongly coupled. Recent observations suggest that rotation rates evolve much more slowly beyond middle age, while stellar activity continues to decline. We aim to characterize this midlife transition by combining archival stellar activity data from the Mount Wilson Observatory with asteroseismology from the Transiting Exoplanet Survey Satellite (TESS). For two stars on opposite sides of the transition (88 Leo and ρ CrB), we independently assess the mean activity levels and rotation periods previously reported in the literature. For the less active star (ρ CrB), we detect solar-like oscillations from TESS photometry, and we obtain precise stellar properties from asteroseismic modeling. We derive updated X-ray luminosities for both stars to estimate their mass-loss rates, and we use previously published constraints on magnetic morphology to model the evolutionary change in magnetic braking torque. We then attempt to match the observations with rotational evolution models, assuming either standard spin-down or weakened magnetic braking. We conclude that the asteroseismic age of ρ CrB is consistent with the expected evolution of its mean activity level and that weakened braking models can more readily explain its relatively fast rotation rate. Future spectropolarimetric observations across a range of spectral types promise to further characterize the shift in magnetic morphology that apparently drives this midlife transition in solar-type stars.

We investigate the possibility of erosion of planetesimals in a protoplanetary disk. We use theory and direct numerical simulations (lattice Boltzmann method) to calculate the erosion of large—much larger than the mean-free path of gas molecules—bodies of different shapes in flows. We find that erosion follows a universal power law in time, at intermediate times, independent of the Reynolds number of the flow and the initial shape of the body. Consequently, we estimate that planetesimals in eccentric orbits, of even very small eccentricity, rapidly (in about 100 yr) erodes away if the semimajor axis of their orbit lies in the inner disk—less than about 10 au. Even planetesimals in circular orbits erode away in approximately 10,000 yr if the semimajor axis of their orbits are ⪅0.6 au.

This work presents an investigation of the stochastic X-ray variability from the 164 Hz accreting millisecond pulsar IGR J17062–6143, based on regular observations collected with the Neutron Star Interior Composition Explorer between 2017 July and 2020 August. Over this period, the power-density spectrum showed a stable morphology, with broad ∼25% rms band-limited noise below 16 Hz. Quasi-periodic oscillations (QPOs) were occasionally observed, with the most notable detections including a low-frequency QPO centered at 2.7 Hz and a sharp QPO centered at 115 Hz that may be a 2:3 resonance with the spin frequency. Further, the energy dependence of the band-limited noise is studied through a spectroscopic analysis of the complex covariance in two frequency intervals. It is found that the power-law continuum is the primary driver for the observed variability, although the thermal (blackbody) emission also appears to be intrinsically variable in area (5% rms) and temperature (1% rms). Notably, the 1 keV emission feature seen in all X-ray spectra of IGR J17062–6143 varies with the same amplitude as the power-law emission, but systematically lags behind that continuum emission. These results appear consistent with a scenario in which a time-variable Compton scattering corona is the primary source for the observed stochastic variability, with the variability observed in the emission feature and at the lowest photon energies being due to the disk reflection of the power-law continuum.

Polytropes have gained renewed interest because they account for several seemingly disconnected observational properties of galaxies. Here we study whether polytropes are also able to explain the stellar mass distribution within galaxies. We develop a code to fit surface density profiles using polytropes projected in the plane of the sky (propols). Sérsic profiles are known to be good proxies for the global shapes of galaxies and we find that, ignoring central cores, propols, and Sérsic profiles are indistinguishable within observational errors (within 5% over five orders of magnitude in surface density). The range of physically meaningful polytropes yields Sérsic indexes between 0.4 and 6. The code has been systematically applied to ∼750 galaxies with carefully measured mass density profiles and including all morphological types and stellar masses ($7\lt {\rm{log}}[{M}_{\star }/{{\rm{M}}}_{\odot }]\lt 12$). The propol fits are systematically better than Sérsic profiles when ${\rm{log}}({M}_{\star }/{{\rm{M}}}_{\odot })\lesssim 9$ and systematically worse when ${\rm{log}}({M}_{\star }/{{\rm{M}}}_{\odot })\gtrsim 10$. Although with large scatter, the observed polytropic indexes increase with increasing mass and tend to cluster around m = 5. For the most massive galaxies, propols are very good at reproducing their central parts, but they do not handle well cores and outskirts overall. Polytropes are self-gravitating systems in thermal meta-equilibrium as defined by the Tsallis entropy. Thus, the above results are compatible with the principle of maximum Tsallis entropy dictating the internal structure in dwarf galaxies and in the central region of massive galaxies.

We present and test an effective model for N-body simulations that aims at mimicking the impact of supernova (SN) feedback on the dark matter (DM) distribution of isolated halos hosting dwarf galaxies. Although the model is physically decoupled from the cosmological history of both the DM halo and the dwarf galaxy, it allows us to study the impact of different macroscopic parameters such as galaxy concentration, feedback energy, and energy injection time in the process of SN-driven core formation in a physically clear way. Using our effective model in a suite of N-body simulations of an isolated halo with different SN feedback parameters, we find that whether or not a DM core forms is determined by the total amount of SN feedback energy that is transferred to the DM particles. At a fixed injected energy, transfer of energy to the DM is more efficient the faster the energy is injected and the more compact the galaxy is, leading to an increased size of the formed DM core as a result. Analyzing the orbital evolution of kinematic tracers, we demonstrate that a core forms through SN feedback only if the energy injection is impulsive relative to the dynamical timescale of particles in the inner halo. However, there is no fundamental link between the total amount of injected energy and the injection rate. Consequently, the presence of signatures of impulsive changes of the gravitational potential is not a sufficient condition for dwarf-sized halos to have cored density profiles.

Dust impact detection by electric field instruments is a well-established technique. On the other hand, not all aspects of signal generation by dust impacts are completely understood. We present a study of events related to dust impacts on the spacecraft body detected by electric field probes operating simultaneously in the monopole (probe-to-spacecraft potential measurement) and dipole (probe-to-probe potential measurement) configurations by the Earth-orbiting Magnetospheric Multiscale mission spacecraft. This unique measurement allows us to investigate connections between monopole and dipole data. Our analysis shows that the signal detected by the electric field instrument in a dipole configuration is generated by an ion cloud expanding along the electric probes. In this case, expanding ions affect not only the potential of the spacecraft body but also one or more electric probes at the end of antenna booms. Electric probes located far from the spacecraft body can be influenced by an ion cloud only when the spacecraft is located in tenuous ambient plasma inside of the Earth's magnetosphere. Derived velocities of the expanding ions on the order of tens of kilometers per second are in the range of values measured experimentally in the laboratory.

The recent availability of high-resolution far-infrared (FIR) polarization observations of galaxies using HAWC+/SOFIA has facilitated studies of extragalactic magnetic fields in the cold and dense molecular disks. We investigate whether any significant structural differences are detectable in the kiloparsec-scale magnetic field of the grand design face-on spiral galaxy M51 when traced within the diffuse (radio) and the dense and cold (FIR) interstellar medium (ISM). Our analysis reveals a complex scenario where radio and FIR polarization observations do not necessarily trace the same magnetic field structure. We find that the magnetic field in the arms is wrapped tighter at 154 μm than at 3 and 6 cm; statistically significant lower values for the magnetic pitch angle are measured at FIR in the outskirts (R ≥ 7 kpc) of the galaxy. This difference is not detected in the interarm region. We find strong correlations of the polarization fraction and total intensity at FIR and radio with the gas column density and ¹²CO(1–0) velocity dispersion. We conclude that the arms show a relative increase of small-scale turbulent B-fields at regions with increasing column density and dispersion velocities of the molecular gas. No correlations are found with H i neutral gas. The star formation rate shows a clear correlation with the radio polarized intensity, which is not found in FIR, pointing to a small-scale dynamo-driven B-field amplification scenario. This work shows that multiwavelength polarization observations are key to disentangling the interlocked relation between star formation, magnetic fields, and gas kinematics in the multiphase ISM.

We report the analysis of the deep (∼270 ks) X-ray Chandra data of one of the most radio-loud, Seyfert 2 galaxies in the nearby universe (z = 0.01135), IC 5063. The alignment of the radio structure with the galactic disk and ionized bicone, enables us to study the effects of both radio jet and nuclear irradiation on the interstellar medium (ISM). The nuclear and bicone spectra suggest a low photoionization phase mixed with a more ionized or thermal gas component, while the cross-cone spectrum is dominated by shocked and collisionally ionized gas emission. The clumpy morphology of the soft (<3 keV) X-ray emission along the jet trails, and the large (≃2.4 kpc) filamentary structure perpendicular to the radio jets at softer energies (<1.5 keV), suggest a large contribution of the jet−ISM interaction to the circumnuclear gas emission. The hard X-ray continuum (>3 keV) and the Fe Kα 6.4 keV emission are both extended to kpc size along the bicone direction, suggesting an interaction of nuclear photons with dense clouds in the galaxy disk, as observed in other Compton Thick (CT) active nuclei. The northwest cone spectrum also exhibits an Fe xxv emission line, which appears spatially extended and spatially correlated with the most intense radio hot-spot, suggesting jet−ISM interaction.

Star-forming dwarf galaxies have properties similar to those expected in high-redshift galaxies. Hence, these local galaxies may provide insights into the evolution of the first galaxies and the physical processes at work. We present a sample of 11 potential local analogs to high-z (LAHz) galaxies. The sample consists of blue compact dwarf galaxies, selected to have spectral energy distributions that fit galaxies at 1.5 < z < 4. We use SOFIA-HAWC+ observations combined with optical and near-infrared data to characterize the dust properties, star formation rate (SFR), and star formation histories (SFHs) of the sample of LAHz galaxies. We employ Bayesian analysis to characterize the dust using two-component blackbody models. Using the Lightning package, we fit the spectral energy distribution of the LAHz galaxies over the far-UV−far-infrared wavelength range and derive the SFH in five time steps up to a look-back time of 13.3 Gyr. Of the 11 LAHz candidates, six galaxies have SFH consistent with no star formation activity at look-back times beyond 1 Gyr. The remaining galaxies show residual levels of star formation at ages ≳1 Gyr, making them less suitable as local analogs. The six young galaxies stand out in our sample by having the lowest gas-phase metallicities. They are characterized by warmer dust, having the highest specific SFR and the highest gas mass fractions. The young age of these six galaxies suggests that merging is less important as a driver of the star formation activity. The six LAHz candidates are promising candidates for studies of the gasdynamics role in driving star formation.

The discovery of gravitational-wave radiation from merging black holes (BHs) also uncovered BHs with masses in the range of ≈20–160 M_⊙. In contrast, the most massive Galactic stellar-mass BH currently known has a mass of ≈21 M_⊙. While low-mass X-ray binaries (LMXBs) will never independently evolve into a binary BH system, and binary evolution effects can play an important role in explaining the different BH masses found through studies of X-ray binaries and gravitational-wave events, (electromagnetic) selection effects may also play a role in this discrepancy. Assuming BH LMXBs originate in the Galactic plane, we show that the spatial distributions of the current samples of confirmed and candidate BH LMXBs are both biased to sources that lie at a large distance from the plane. Specifically, most of the confirmed and candidate BH LMXBs are found at a Galactic height larger than three times the scale height for massive star formation. In addition, the confirmed BH LMXBs are found at larger distances to the Galactic center than the candidate BH LMXBs. Interstellar absorption makes candidate BH LMXBs in the plane and bulge too faint for a dynamical mass measurement using current instrumentation. Given the observed and theoretical evidence for BH natal and/or Blaauw kicks, their relation with BH mass and binary orbital period, and the relation between outburst recurrence time and BH mass, the observational selection effects imply that the current sample of confirmed BH LMXBs is biased against the most massive BHs.

Reaction schema for the formation of the recently detected ethynyl cyclopropenylidene (c-C₃HCCH) molecule are currently lacking in the literature. The present quantum chemical study shows that the reaction of the abundant ethynyl (C₂H) and cyclopropenylidene (c-C₃H₂) molecules proceeds barrierlessly through the formation of a 1 ²A c-HC₃HCCH intermediate at 71.2 kcal mol⁻¹ below the reactants. The uphill exit channel climb for the C−H bond dissociation will compete with a transition state 45.9 kcal mol⁻¹ below the reactants to form another, lower-energy intermediate ($1{\ }^{2}A^{\prime}$ c-C₃H₂CCH) 84.3 kcal mol⁻¹ below the reactants. The direct dissociation from the first intermediate is likely the dominant pathway under astrophysical conditions because the hydrogen leaving group can dissipate the energy kinetically. In either case of direct dissociation or crossing the transition state, the hydrogen atom dissociation to the final products lying 27.2 kcal mol⁻¹ below the starting materials requires a crossover of electronic states with the singly occupied molecular orbital moving from the π cloud of the cyclopropenyl group onto the leaving H atom. As a result, this C₂H + c-C₃H₂ → c-C₃HCCH + H reaction should be as fast as theorized in astrophysical media such as TMC-1, where the titular molecule has now been observed.

We report follow-up spectroscopic observations of the 1.62 day, K-type, detached, active, near-circular, double-lined eclipsing binary EPIC 219511354 in the open cluster Ruprecht 147, identified previously on the basis of photometric observations from the Kepler/K2 mission. This is the fourth eclipsing system analyzed in this cluster. A combined analysis of the light curve and radial velocities yields accurate masses of M_Aa = 0.912 ± 0.013 M_☉ and M_Ab = 0.822 ± 0.010 M_☉ for the primary (star Aa) and secondary (Ab), along with radii of R_Aa = 0.920 ±0.016 R_☉ and R_Ab = 0.851 ± 0.016 R_☉, and effective temperatures of 5035 ± 150 and 4690 ± 130 K, respectively. Comparison with current models of stellar evolution for the known age and metallicity of the cluster reveals that both radii are larger (by 10%–14%) and both temperatures cooler (by ∼6%) than theoretically predicted, as is often seen in M dwarfs. This is likely caused by the significant stellar activity in the system, manifested here by 6% peak-to-peak out-of-eclipse variability, a filled-in Hα line, and its detection as an X-ray source. We also find EPIC 219511354 to be a hierarchical triple system, with a low-mass tertiary in an eccentric 220 day orbit.

Fast radio burst (FRB) dispersion measures (DMs) record the presence of ionized baryons that are otherwise invisible to other techniques enabling resolution of the matter distribution in the cosmic web. In this work, we aim to estimate the contribution to FRB 180924 DM from foreground galactic halos. Localized by ASKAP to a massive galaxy, this sightline is notable for an estimated cosmic web contribution to the DM (DM_cosmic =220 pc cm⁻³), which is less than the average value at the host redshift (z = 0.3216) estimated from the Macquart relation (280 pc cm⁻³). In the favored models of the cosmic web, this suggests few intersections with foreground halos at small impact parameters (≲100 kpc). To test this hypothesis, we carried out spectroscopic observations of the field galaxies within ∼1' of the sightline with VLT/MUSE and Keck/LRIS. Furthermore, we developed a probabilistic methodology that leverages photometric redshifts derived from wide-field DES and WISE imaging. We conclude that there is no galactic halo that closely intersects the sightline and also that the net DM contribution from halos DM_halos < 45 pc cm⁻³ (95% c.l.). This value is lower than the DM_halos estimated from an "average" sightline (121 pc cm⁻³) using the Planck ΛCDM model and the Aemulus halo mass function and reasonably explains its low DM_cosmic value. We conclude that FRB 180924 represents the predicted majority of sightlines in the universe with no proximate foreground galactic halos. Our framework lays the foundation for a comprehensive analysis of FRB fields in the near future.

How charged particles are accelerated efficiently and form a power-law energy spectrum in magnetic reconnection is a problem that is not well understood. In a previous paper, it was shown that the electron Kelvin–Helmholtz instability (EKHI) in force-free magnetic reconnection generates fast-expanding vortices that can accelerate electrons in a few tens of ion gyroperiods (less than 1 ms in the solar corona) to form a power-law energy distribution. In this paper, we present a particle-in-cell (PIC) simulation study of ion acceleration in force-free magnetic reconnection in the presence of the EKHI-induced turbulence. We find that ions are not significantly accelerated by the EKHI-induced stochastic electric field until the magnetic vortices expand to sizes comparable to the ion gyroradius. The Alfvén waves generated by the EKHI couple with the magnetic vortices, leading to resonance between the ions inside the magnetic vortices and Alfvén waves and enhanced ion heating. The induced Alfvén wave resonance results in a broken power-law energy spectrum with a breakpoint at $\sim {m}_{i}{v}_{A}^{2}$, where v_A is the Alfvén velocity. We show that the process that forms the nonthermal tail is a second-order Fermi mechanism and the mean spectral index is α = (1 + 4a²D/R)/2, where D is the spatial scale of the inductive electric field, R is that of vortices, and a = B_g/B₀, with ratio of guide field B_g and asymptotic B₀.

Strong nonlocal thermodynamic equilibrium recombination line emission from the envelope of MWC 349A has been studied observationally and theoretically and has been used to derive information about the physical and kinematic properties of the circumstellar environment around this object. In this paper, we construct a detailed model of radiative transfer of the commonly observed maser lines H26α and H30α in MWC 349A, specifically taking into account the effect of maser saturation. The envelope is modeled as a combination of an ionized Keplerian rotating disk and a disk wind expanding at a velocity of 60 km s⁻¹. Our modeling results show that millimeter-line H26α is significantly affected by the saturation effect. The line intensity is predicted to be greatly reduced in comparison with previous models which ignore the saturation effect. The H30α maser is predicted to be unsaturated. Our model shows that the predicted intensity and line shape are in agreement with observations. The predicted position–velocity diagrams are also consistent with observations and the interpretation that the H26α maser appears at smaller radii in comparison to the H30α maser. We also emphasize that the wind component is important in shaping the line profiles of the recombination masers.

We present a case study using data from multiple spacecraft and statistics from the ACE spacecraft to investigate the relaxation of reconnected magnetic field lines in solar wind magnetic reconnection exhausts, which constitute one of the two outflow regions resulting from magnetic reconnection, and which are often characterized by a plasma jet, magnetic strength depletion, and density and temperature enhancements. The normal magnetic fractions (∣B_n/B∣) of the reconnection exhausts are used to indicate the degrees of relaxation of the magnetic field lines. 97 out of 98 reconnection exhausts have a relatively small ∣B_n/B∣ (<0.3), while only one exhaust associated with a relatively small interplanetary coronal mass ejection has a large ∣B_n/B∣ of 0.85. This result demonstrates the nonrelaxed nature of reconnected magnetic field lines in solar wind, due to the open boundary condition. As a consequence, the magnetic tension of such nonrelaxed magnetic field lines can accelerate the local plasma to produce the observed jet within the reconnection exhaust. Our results support the understanding that most solar wind reconnection exhausts are probably initiated near the Sun, where the plasma beta is low, and that they are not ongoing when they are observed at 1 au, because of the solar wind expansion from near the Sun to 1 au.

We investigate the structure and stability against radial oscillations, pycnonuclear reactions, and inverse β-decay of hot white dwarfs. We consider the fluid matter to be made up of nucleons and electrons confined in a Wigner–Seitz cell surrounded by free photons. It is considered that the temperature depends on the mass density considering the presence of an isothermal core. We find that the temperature produces remarkable effects on the equilibrium and radial stability of white dwarfs. The stable equilibrium configuration results are compared with those for white dwarfs estimated from the Extreme Ultraviolet Explorer survey and the Sloan Digital Sky Survey. We derive masses, radii, and central temperatures for the most massive white dwarfs according to the surface gravity and effective temperature reported by the surveys. We note that these massive stars are in the mass region where general relativity effects are important. These stars are near the threshold of instabilities due to radial oscillations, pycnonuclear reactions, and inverse β-decay. Regarding the radial stability of these stars as a function of the temperature, we find that it decreases with the increment of central temperature. We also find that the maximum-mass point and the zero eigenfrequencies of the fundamental mode are determined at the same central energy density. Regarding low-temperature stars, pycnonuclear reactions occur in similar central energy densities, and the central energy density threshold for inverse β-decay is not modified. For T_c ≥ 1.0 × 10⁸ [K], the onset of radial instability is attained before pycnonuclear reaction and inverse β-decay.

Without the intrinsic magnetic field, the solar wind interaction with Mars can be significantly different from the interaction with Earth and other magnetized planets. In this paper, we investigate how a global configuration of the magnetic structures, consisting of the bow shock, the induced magnetosphere, and the magnetotail, is modulated by the interplanetary magnetic field (IMF) orientation. A 3D multispecies numerical model is established to simulate the interaction of solar wind with Mars under different IMF directions. The results show that the shock size including the subsolar distance and the terminator radius increases with Parker spiral angle, as is the same case with the magnetotail radius. The location and shape of the polarity reversal layer and inverse polarity reversal layer in the induced magnetotail are displaced to the y < 0 sector for a nonzero flow-aligned IMF component, consistent with previous analytical solutions and observations. The responses of the Martian global magnetic configuration to the different IMF directions suggest that the external magnetic field plays an important role in the solar wind interaction with unmagnetized planets.

Through the Backyard Worlds: Planet 9 citizen science project, we have identified a wide-separation (∼10', ∼9900 au projected) substellar companion to the nearby (∼17.5 pc), mid-M dwarf Ross 19. We have developed a new formalism for determining chance alignment probabilities based on the BANYAN Σ tool, and find a 100% probability that this is a physically associated pair. Through a detailed examination of Ross 19A, we find that the system is metal-poor ([Fe/H] = −0.40 ± 0.12) with an age of ${7.2}_{-3.6}^{+3.8}$ Gyr. Combining new and existing photometry and astrometry, we find that Ross 19B is one of the coldest known wide-separation companions, with a spectral type on the T/Y boundary, an effective temperature of ${500}_{-100}^{+115}$ K, and a mass in the range 15–40 M_Jup. This new, extremely cold benchmark companion is a compelling target for detailed characterization with future spectroscopic observations using facilities such as the Hubble Space Telescope or James Webb Space Telescope.

Understanding the inner structure of the clumpy molecular torus surrounding the active galactic nucleus is essential in revealing the forming mechanism. However, spatially resolving the torus is difficult because of its size of a few parsecs. Thus, to probe the clump conditions in the torus, we performed the velocity decomposition of the CO rovibrational absorption lines (Δv = 0 →1, ΔJ = ±1) at λ ∼ 4.67 μm observed toward an ultraluminous infrared galaxy IRAS 08572+3915 NW with the high-resolution spectroscopy (R ∼ 10,000) of Subaru Telescope. Consequently, we found that each transition had two outflowing components, i.e., (a) and (b), both at approximately ∼−160 km s⁻¹, but with broad and narrow widths, and an inflowing component, i.e., (c), at approximately ∼+100 km s⁻¹, which were attributed to the torus. The ratios of the velocity dispersions of each component led to those of the rotating radii around the black hole of R_rot,a: R_rot,b: R_rot,c ≈ 1: 5: 17, indicating the torus where clumps are outflowing in the inner regions and inflowing in the outer regions if a hydrostatic disk with ${\sigma }_{V}\propto {R}_{\mathrm{rot}}^{-0.5}$ is assumed. Based on the kinetic temperature of components (a) and (b) of ∼720 and ∼25 K, respectively, estimated from the level population, the temperature gradient is ${T}_{\mathrm{kin}}\propto {R}_{\mathrm{rot}}^{-2.1}$. Magnetohydrodynamic models with large density fluctuations of two orders of magnitude or more are necessary to reproduce this gradient.

We investigate a repulsion mechanism between two low-mass planets migrating in a protoplanetary disk, for which the relative migration switches from convergent to divergent. This mechanism invokes density waves emitted by one planet transferring angular momentum to the coorbital region of the other and then directly to it through the horseshoe drag. We formulate simple analytical estimates, which indicate when the repulsion mechanism is effective. One condition for a planet to be repelled is that it forms a partial gap in the disk and another is that this should contain enough material to support angular momentum exchange with it. Using two-dimensional hydrodynamical simulations, we obtain divergent migration of two super-Earths embedded in a protoplanetary disk because of repulsion between them and verify these conditions. To investigate the importance of resonant interaction, we study the migration of planet pairs near first-order commensurabilities. It appears that proximity to resonance is significant but not essential. In this context we find repulsion still occurs when the gravitational interaction between the planets is removed, suggesting the importance of angular momentum transfer through waves excited by another planet. This may occur through the scattering of coorbital material (the horseshoe drag), or material orbiting close by. Our results indicate that if conditions favor the repulsion between two planets described above, we expect to observe planet pairs with their period ratios greater, often only slightly greater, than resonant values or possibly rarity of commensurability.

We present bolometric and broadband light curves and spectra for a suite of core-collapse supernova models exploded self-consistently in spherical symmetry within the PUSH framework. We analyze broad trends in these light curves and categorize them based on morphology. We find that these morphological categories relate simply to the progenitor radius and mass of the hydrogen envelope. We present a proof-of-concept sensitive-variable analysis, indicating that an important determining factor in the properties of a light curve within a given category is ⁵⁶Ni mass. We follow spectra from the photospheric to the nebular phase. These spectra show characteristic iron-line blanketing at short wavelengths and Doppler-shifted Fe ii and Ti ii absorption lines. To enable this analysis, we develop a first-of-its-kind pipeline from a massive progenitor model, through a self-consistent explosion in spherical symmetry, to electromagnetic counterparts. This opens the door to more detailed analyses of the collective properties of these observables. We provide a machine-readable database of our light curves and spectra online at go.ncsu.edu/astrodata.

Massive black holes at the centers of galaxies can launch powerful wide-angle winds that, if sustained over time, can unbind the gas from the stellar bulges of galaxies. These winds may be responsible for the observed scaling relation between the masses of the central black holes and the velocity dispersion of stars in galactic bulges. Propagating through the galaxy, the wind should interact with the interstellar medium creating a strong shock, similar to those observed in supernovae explosions, which is able to accelerate charged particles to high energies. In this work we use data from the Fermi Large Area Telescope to search for the γ-ray emission from galaxies with an ultrafast outflow (UFO): a fast (v ∼ 0.1 c), highly ionized outflow, detected in absorption at hard X-rays in several nearby active galactic nuclei (AGN). Adopting a sensitive stacking analysis we are able to detect the average γ-ray emission from these galaxies and exclude that it is due to processes other than UFOs. Moreover, our analysis shows that the γ-ray luminosity scales with the AGN bolometric luminosity and that these outflows transfer ∼0.04% of their mechanical power to γ-rays. Interpreting the observed γ-ray emission as produced by cosmic rays (CRs) accelerated at the shock front, we find that the γ-ray emission may attest to the onset of the wind–host interaction and that these outflows can energize charged particles up to the transition region between galactic and extragalactic CRs.

Angular momentum is a key property regulating star formation and evolution. However, the physics driving the distribution of the stellar rotation rates of early-type main-sequence stars is as yet poorly understood. Using our catalog of 40,034 early-type stars with homogeneous $v\sin i$ parameters, we review the statistical properties of their stellar rotation rates. We discuss the importance of possible contaminants, including binaries and chemically peculiar stars. Upon correction for projection effects and rectification of the error distribution, we derive the distributions of our sample's equatorial rotation velocities, which show a clear dependence on stellar mass. Stars with masses less than 2.5 M_⊙ exhibit a unimodal distribution, with the peak velocity ratio increasing as stellar mass increases. A bimodal rotation distribution, composed of two branches of slowly and rapidly rotating stars, emerges for more massive stars (M > 2.5 M_⊙). For stars more massive than 3.0 M_⊙, the gap between the bifurcated branches becomes prominent. For the first time, we find that metal-poor ([M/H] < −0.2 dex) stars only exhibit a single branch of slow rotators, while metal-rich ([M/H] > 0.2 dex) stars clearly show two branches. The difference could be attributed to unexpectedly high spin-down rates and/or in part strong magnetic fields in the metal-poor subsample.

In this article, we show through a series of rigorous mathematical steps, starting with Liouville's equation and solving it for the case of two protons using the method of characteristics, that a velocity distribution function, f(u), is formed that exhibits a power law, f ∝ u^γ, where γ is −9/2, and an exponential-type rollover at large speeds, providing a potential explanation for the observations of suprathermal ions in the solar wind. The solution is valid for all times and all background conditions, though the power law does at some point merge with the core of the distribution. When it does so, a final distribution is found that agrees with overall energy conservation. Analytical approximations to the solution are discussed, along with explanations for the various phases that the solution undergoes.

A repeating fast radio burst (FRB), FRB 20180916B (hereafter FRB 180916), was reported to have a 16.35-day period. This period might be related to a precession period. In this paper, we investigate two precession models to explain the periodic activity of FRB 180916. In both models, the radio emission of FRB 180916 is produced by a precessing jet. For the first disk-driven jet precession model, an extremely low viscous parameter (i.e., the dimensionless viscosity parameter α ≲ 10⁻⁸) is required to explain the precession of FRB 180916, which implies its implausibility. For the second tidal-force-driven jet precession model, we consider that a compact binary consists of a neutron star/black hole and a white dwarf; the white dwarf fills its Roche lobe, and mass transfer occurs. Due to the misalignment between the disk and orbital plane, the tidal force of the white dwarf can drive jet precession. We show that the relevant precession periods are several days to hundreds of days, depending on the specific accretion rates and component masses. The duration of FRB 180916 generation in the binary with extremely high accretion rate will be several thousand years.

We present an investigation of the quiescent and transient X-ray binaries (XRBs) of the Galactic Center (GC). We extended our Chandra analysis of the non-thermal X-ray sources, located in the central parsec, from Hailey et al. (2018), using an additional 4.6 Msec of ACIS-S data obtained in 2012–2018. The individual Chandra spectra of the 12 sources fit to an absorbed power-law model with a mean photon index Γ ≈ 2 and show no Fe emission lines. Long-term variability was detected from nine of them, confirming that a majority are quiescent XRBs. Frequent X-ray monitoring of the GC revealed that the 12 non-thermal X-ray sources, as well as four X-ray transients have shown at most a single outburst over the last two decades. They are distinct from the six known neutron star LMXBs in the GC, which have all undergone multiple outbursts with ≲ 5 year recurrence time on average. Based on the outburst history data of the broader population of X-ray transients, we conclude that the 16 sources represent a population of ∼240–630 tightly bound BH-LMXBs with ∼4−12 hr orbital periods, consistent with the stellar/binary dynamics modeling in the vicinity of Sgr A*. The distribution of the 16 BH-LMXB candidates is disk-like (at 87% CL) and aligned with the nuclear star cluster. Our results have implications for XRB formation and the rate of gravitational wave events in other galactic nuclei.

With the continuous upgrade of detectors, greater numbers of gravitational wave (GW) events have been captured by the LIGO Scientific Collaboration and Virgo Collaboration (LVC), which offer a new avenue to test general relativity and explore the nature of gravity. Although various model-independent tests have been performed by LVC in previous works, it is still interesting to ask what constraints can be placed on specific models by current GW observations. In this work, we focus on three models of scalar-tensor theories, the Brans–Dicke theory (BD), the theory with scalarization phenomena proposed by Damour and Esposito-Farèse (DEF), and screened modified gravity (SMG). Of the four possible neutron star–black hole events that have occurred so far, we use two of them to place constraints. The other two are excluded in this work because of possible unphysical deviations. We consider the inspiral range with the cutoff frequency at the innermost stable circular orbit and add a modification of dipole radiation into the waveform template. The scalar charges of neutron stars in the dipole term are derived by solving the Tolman–Oppenheimer–Volkoff equations for different equations of state. The constraints are obtained by performing the full Bayesian inference with the help of the open source software Bilby. The results show that the constraints given by GWs are comparable to those given by pulsar timing experiments for DEF theory, but are not competitive with the current solar system constraints for BD and SMG theories.

Star formation can be triggered by compression from shock waves. In this study, we investigated the interaction of hydrodynamic shocks with Bonnor–Ebert spheres using 3D hydrodynamical simulations with self-gravity. Our simulations indicated that the cloud evolution primarily depends on two parameters: shock speed and initial cloud radius. Stronger shocks can compress clouds more efficiently, and when the central region becomes gravitationally unstable, a shock triggers cloud contraction. However, if it is excessively strong, it shreds the cloud more violently and the cloud is destroyed. From simple theoretical considerations, we derived the condition of triggered gravitational collapse, which agreed with the simulation results. Introducing sink particles, we followed the further evolution after star formation. Since stronger shocks tend to shred the cloud material more efficiently, the stronger the shock is, the smaller the final (asymptotic) masses of the stars formed (i.e., sink particles) become. In addition, shocks accelerate clouds, promoting mixing of shock-accelerated interstellar medium gas. As a result, the separation between sink particles and shocked clouds center and their relative speeds increase over time. We also investigated the effect of cloud turbulence on shock–cloud interaction. We observed that cloud turbulence prevents rapid cloud contraction; thus, turbulent clouds are destroyed more rapidly than thermally supported clouds. Therefore, the masses of stars formed become smaller. Our simulations provide a general guide to the evolutionary process of dense cores and Bok globules impacted by shocks.

We present an alternative method for reconstructing a velocity-delay map in reverberation mapping (RM) based on the pixon algorithm initially proposed for image reconstruction by Pina. The pixon algorithm allows for a variable pixon basis to adjust resolution of each image pixel according to the information content in that pixel, which therefore enables the algorithm to make the best possible use of measured data. The final optimal pixon basis functions would be those that minimize the number of pixons while still providing acceptable descriptions to data within the accuracy allowed by noises. We adapt the pixon algorithm to RM analysis and develop a generic framework to implement the algorithm. Simulation tests and comparisons with the widely used maximum entropy method demonstrate the feasibility and high performance of our pixon-based RM analysis. This paper serves as an introduction to the framework and the application to velocity-unresolved RM. An extension to velocity-resolved cases will be presented in a companion paper.

Energy cascade from magnetohydrodynamic to kinetic scales can create many coherent structures in the turbulent astrophysical plasma environment, such as magnetic holes and magnetic peaks. Knowing the properties of each coherent structure is critical to better understand the process of the energy cascade. Recently, electron-scale magnetic peaks (ESMPs) are revealed to exist in the solar wind at 1 au. Here, we investigate the properties of the ESMPs upstream of the terrestrial bow shock based on observations of the Magnetospheric Multiscale spacecraft. We regard an isolated ESMP or a train of ESMPs as an ESMP event, and 204 ESMPs or 32 ESMP events are found. Both the durations and cross-section sizes of the ESMPs obey log-normal distributions. The median duration and cross-section size are ∼0.25 s and ∼0.33 ion gyroradius, respectively. The ESMP event with an average occurrence rate of ∼8.8 events per day tends to occur during the weak interplanetary magnetic field strength or the slow solar wind. We also find that the ion foreshock is an important source of the ESMP events, and a small part of the ESMP events originates from the upstream pristine solar wind. Although only 12 out of 204 ESMPs have bipolar electron velocities, we suggest that the electron vortex is an essential feature for the stable ESMP. The generation mechanism of the ESMPs is unclear; nevertheless, finding out the origin of the electron vortex in the ion foreshock might help to reveal their generation mechanism.

Small-scale magnetic holes (SSMHs) are frequently observed in the solar wind at 1 au, as well as the terrestrial current sheet and magnetosheath. These kinetic-size structures play an important role in energy dissipation and particle transportation. Here, we report the existence of SSMHs in the upstream regime of the Martian bow shock and statistically investigate these SSMHs based on 5 yr observations of the Mars Atmosphere and Volatile EvolutioN spacecraft. A total of 549 SSMHs are found, and their durations and sizes obey the lognormal distribution. The median duration is ∼0.46 s, and the median size is ∼2 ion inertial lengths. We regard an isolated SSMH or a train of SSMHs as a SSMH event. The average occurrence rate of the SSMH events is ∼0.6 event per day. The occurrence rate is much larger in the region belonging to the ion foreshock on average, suggesting that the ion foreshock is an important source of SSMHs. The occurrence of the SSMH events tends to be larger when the ion number density and the interplanetary magnetic field (IMF) strength are larger, indicating that the generation of SSMHs might be associated with ions and the IMF strength. Although their generation mechanism is still unclear, the finding of the link between the occurrence rate of the SSMH events and ion number density, as well as the IMF strength, might provide a clue to further reveal the generation mechanism of SSMHs in the solar wind or planetary foreshock.

When gravitational waves pass near massive astrophysical objects, they can be gravitationally lensed. The lensing can split them into multiple wave fronts, magnify them, or imprint beating patterns on the waves. Here we focus on the multiple images produced by strong lensing. In particular, we investigate strong lensing forecasts, the rate of lensing, and the role of lensing statistics in strong lensing searches. Overall, we find a reasonable rate of lensed detections for double, triple, and quadruple images at the LIGO–Virgo–KAGRA design sensitivity. We also report the rates for A+ and LIGO Voyager and briefly comment on potential improvements due to the inclusion of subthreshold triggers. We find that most galaxy-lensed events originate from redshifts z ∼ 1–4 and report the expected distribution of lensing parameters for the observed events. Besides forecasts, we investigate the role of lensing forecasts in strong lensing searches, which explore repeated event pairs. One problem associated with the searches is the rising number of event pairs, which leads to a rapidly increasing false alarm probability. We show how knowledge of the expected galaxy-lensing time delays in our searches allow us to tackle this problem. Once the time delays are included, the false alarm probability increases linearly (similar to nonlensed searches) instead of quadratically with time, significantly improving the search. For galaxy cluster lenses, the improvement is less significant. The main uncertainty associated with these forecasts are the merger-rate density estimates at high redshift, which may be better resolved in the future.

We present results for the first observed outburst from the transient X-ray binary source MAXI J0637–430. This study is based on eight observations from the Nuclear Spectroscopic Telescope Array (NuSTAR) and six observations from the Neil Gehrels Swift Observatory X-Ray Telescope (Swift/XRT) collected from 2019 November 19 to 2020 April 26 as the 3–79 keV source flux declined from 8.2 × 10⁻¹⁰ to 1.4 × 10⁻¹² erg cm⁻² s⁻¹. We see the source transition from a soft state with a strong disk-blackbody component to a hard state dominated by a power-law or thermal Comptonization component. NuSTAR provides the first reported coverage of MAXI J0637–430 above 10 keV, and these broadband spectra show that a two-component model does not provide an adequate description of the soft-state spectrum. As such, we test whether blackbody emission from the plunging region could explain the excess emission. As an alternative, we test a reflection model that includes a physical Comptonization continuum. Finally, we also test a spectral component based on reflection of a blackbody illumination spectrum, which can be interpreted as a simple approximation to the reflection produced by returning disk radiation due to the bending of light by the strong gravity of the black hole. We discuss the physical implications of each scenario and demonstrate the value of constraining the source distance.

We analyze the tidal disruption probability of potential neutron star–black hole (NSBH) merger gravitational-wave (GW) events, including GW190426_152155, GW190814, GW200105_162426, and GW200115_042309, detected during the third observing run of the LIGO/Virgo Collaboration and the detectability of kilonova emission in connection with these events. The posterior distributions of GW190814 and GW200105_162426 show that they must be plunging events, and hence no kilonova signal is expected from these events. With the stiffest NS equation of state allowed by the constraint of GW170817 taken into account, the probability that GW190426_152155 and GW200115_042309 can make tidal disruption is ∼24% and ∼3%, respectively. However, the predicted kilonova brightness is too faint to be detected for present follow-up search campaigns, which explains the lack of electromagnetic (EM) counterpart detection after triggers of these GW events. Based on the best-constrained population synthesis simulation results, we find that disrupted events account for only ≲20% of cosmological NSBH mergers, since most of the primary BHs could have low spins. The associated kilonovae for those disrupted events will still be difficult for LSST to discover after GW triggers in the future because of their low brightness and larger distances. For future GW-triggered multimessenger observations, potential short-duration gamma-ray bursts and afterglows are more probable EM counterparts of NSBH GW events.

We study the process of panspermia in Milky Way–like galaxies by modeling the probability of successful travel of organic compounds between stars harboring potentially habitable planets. To this end, we apply the modified habitability recipe of Gobat & Hong to a model galaxy from the McMaster Unbiased Galaxy Simulations suite of zoom-in cosmological simulations. We find that, unlike habitability, which only occupies a narrow dynamic range over the entire galaxy, the panspermia probability can vary by orders of magnitude between the inner (R, b = 1–4 kpc) and outer disk. However, only a small fraction of star particles have very large values for the panspermia probability and, consequently, the fraction of star particles where the panspermia process is more effective than prebiotic evolution is much lower than from naïve expectations based on the ratio between the panspermia probability and natural habitability.

Lorentz invariance plays a fundamental role in modern physics. However, tiny violations of the Lorentz invariance may arise in some candidate quantum gravity theories. Prominent signatures of the gravitational Lorentz invariance violation (gLIV) include anisotropy, dispersion, and birefringence in the dispersion relation of gravitational waves (GWs). Using a total of 50 GW events in the GW transient catalogs GWTC-1 and GWTC-2, we perform an analysis on the anisotropic birefringence phenomenon. The use of multiple events allows us to completely break the degeneracy among gLIV coefficients and globally constrain the coefficient space. Compared to previous results at mass dimensions 5 and 6 for the Lorentz-violating operators, we tighten the global limits of 34 coefficients by factors ranging from 2 to 7.

Ancient sunspot records written in classical Chinese provide important information regarding ancient solar activity. The Chinese recorded 14 observations of sunspots that resembled an egg (hereafter, egg record; the word egg is used to represent approximate sunspot sizes) before 1000 CE. However, the egg records in classical Chinese were too short to provide sufficient sunspot details. This study was conducted to decode egg records from 1769 and 1917 through telescopic sunspot observations. The results of our decoding show that egg-like sunspots were generally used by observers in East Asia to represent a very large sunspot group with an approximately elliptical outline. An egg record generally served as a marker of intense solar activity. Three egg records (in 1278, 1769, and 1917) were observed to be close to the solar maxima, with the time difference being smaller than 1 yr. Some egg records could thus be used to identify the solar maxima. The mean time difference between 10 egg records and the nearest solar maxima is 2 yr. Therefore, egg records can provide necessary information for uncovering additional intense solar activity from ancient times.

We report the discovery of SDSS J133725.26+395237.7 (hereafter SDSS J1337+3952), a double-lined white dwarf (WD+WD) binary identified in early data from the fifth-generation Sloan Digital Sky Survey (SDSS-V). The double-lined nature of the system enables us to fully determine its orbital and stellar parameters with follow-up Gemini spectroscopy and Swift UVOT ultraviolet fluxes. The system is nearby (d = 113 pc), and consists of a 0.51 M_⊙ primary and a 0.32 M_⊙ secondary. SDSS J1337+3952 is a powerful source of gravitational waves in the millihertz regime, and will be detectable by future space-based interferometers. Due to this gravitational wave emission, the binary orbit will shrink down to the point of interaction in ≈220 Myr. The inferred stellar masses indicate that SDSS J1337+3952 will likely not explode as a Type Ia supernova (SN Ia). Instead, the system will probably merge and evolve into a rapidly rotating helium star and could produce an underluminous thermonuclear supernova along the way. The continuing search for similar systems in SDSS-V will grow the statistical sample of double-degenerate binaries across parameter space, constraining models of binary evolution and SNe Ia.

We examine the effect of spatial resolution on initial mass ejection in grid-based hydrodynamic simulations of binary neutron star mergers. The subset of the dynamical ejecta with velocities greater than ∼0.6c can generate an ultraviolet precursor to the kilonova on approximately hour timescales and contribute to a years long nonthermal afterglow. Previous work has found differing amounts of this fast ejecta, by one to two orders of magnitude, when using particle-based or grid-based hydrodynamic methods. Here, we carry out a numerical experiment that models the merger as an axisymmetric collision in a corotating frame, accounting for Newtonian self-gravity, inertial forces, and gravitational wave losses. The lower computational cost allows us to reach spatial resolutions as high as 4 m, or ∼3 × 10⁻⁴ of the stellar radius. We find that fast ejecta production converges to within 10% for a cell size of 20 m. This suggests that fast ejecta quantities found in existing grid-based merger simulations are unlikely to increase to the level needed to match particle-based results upon further resolution increases. The resulting neutron-powered precursors are in principle detectable out to distances ≲200 Mpc with upcoming facilities.We also find that head-on collisions at the freefall speed, relevant for eccentric mergers, yield fast and slow ejecta quantities of order 10⁻²M_⊙, with a kilonova signature distinct from that of quasi-circular mergers.

Invariant curves are generally closed curves in Poincaré's surface of section. Here we study an interesting dynamical phenomenon, first discovered by Binney et al. in a rotating Kepler potential, where an invariant curve of the surface of section can split into two disconnected line segments under certain conditions, which is distinctively different from the islands of resonant orbits. We first demonstrate the existence of split invariant curves in the Freeman bar model, where all orbits can be described analytically. We find that the split phenomenon occurs when orbits are nearly tangent to the minor/major axis of the bar potential. Moreover, the split phenomenon seems "necessary" to avoid invariant curves intersecting with each other. Such a phenomenon appears only in rotating potentials, and we demonstrate its universal existence in other general rotating bar potentials. It also implies that actions are no longer proportional to the area bounded by an invariant curve if the split occurs, but they can still be computed by other means.

In the standard scenario of planet formation, terrestrial planets, ice giants, and cores of gas giants are formed by the accumulation of planetesimals. However, there are few N-body simulation studies of planetesimal accretion that correctly take into account the merging condition of planetesimals. In order to investigate a realistic accretion process of planetesimals, it is necessary to clarify the merging criteria of planetesimals at collision. We perform numerical collision experiments using smoothed particle hydrodynamics and obtain the merging criteria as a function of planetesimal mass and impact parameters for undifferentiated rocky and icy planetesimals and differentiated icy planetesimals. We vary the total mass of colliding planetesimals, their mass ratios, and the impact angle and obtain the critical impact velocity as the merging criteria distinguishing merging from hit-and-run collision. We find that the critical impact velocity normalized by the two-body surface escape velocity decreases with increasing impact angle. The critical impact velocity does not depend on the total mass, while it has a weak positive dependence on the mass ratio. These results barely depend on the composition and internal structure of the planetesimals.

Energetic neutral atom (ENA) models typically require post-processing routines to convert the distributions of plasma and H atoms into ENA maps. Here we investigate how two kinetic-MHD models of the heliosphere (the BU and Moscow models) manifest in modeled ENA maps using the same prescription and how they compare with Interstellar Boundary Explorer (IBEX) observations. Both MHD models treat the solar wind as a single-ion plasma for protons, which include thermal solar wind ions, pick-up ions (PUIs), and electrons. Our ENA prescription partitions the plasma into three distinct ion populations (thermal solar wind, PUIs transmitted and ones energized at the termination shock) and models the populations with Maxwellian distributions. Both kinetic-MHD heliospheric models produce a heliotail with heliosheath plasma that is organized by the solar magnetic field into two distinct north and south columns that become lobes of high mass flux flowing down the heliotail; however, in the BU model, the ISM flows between the two lobes at distances in the heliotail larger than 300 au. While our prescription produces similar ENA maps for the two different plasma and H atom solutions at the IBEX-Hi energy range (0.5–6 keV), the modeled ENA maps require a scaling factor of ∼2 to be in agreement with the data. This problem is present in other ENA models with the Maxwellian approximation of multiple ion species and indicates that either a higher neutral density or some acceleration of PUIs in the heliosheath is required.

We present the results from our time-series imaging data taken with the 1.3 m Devasthal fast optical telescope and 0.81 m Tenagara telescope in V, R_c, and I_c bands covering an area of ∼184 × 184 toward the star-forming region Sh 2–190. This photometric data helped us to explore the nature of the variability of pre-main-sequence (PMS) stars. We have identified 85 PMS variables, i.e., 37 Class ii and 48 Class iii sources. Forty-five of the PMS variables show periodicity in their light curves. We show that the stars with thicker disks and envelopes rotate slower and exhibit larger photometric variations compared to their diskless counterparts. This result suggests that rotation of the PMS stars is regulated by the presence of circumstellar disks. We also found that the periods of the stars show a decreasing trend with increasing mass in the range of ∼0.5–2.5 M_⊙. Our result indicates that most of the variability in Class ii sources is ascribed to the presence of a thick disk, while the presence of cool spots on the stellar surface causes the brightness variation in Class iii sources. X-ray activities in the PMS stars were found to be at the saturation level reported for the main-sequence stars. The younger counterparts of the PMS variables show less X-ray activity, hinting at a less significant role of a stellar disk in X-ray generation.

In this study we aim for a deeper understanding of the power-law slope, α, of waiting time distributions. Statistically independent events with linear behavior can be characterized by binomial, Gaussian, exponential, or Poissonian size distribution functions. In contrast, physical processes with nonlinear behavior exhibit spatiotemporal coherence (or memory) and "fat tails" in their size distributions that fit power-law-like functions, as a consequence of the time variability of the mean event rate, as demonstrated by means of Bayesian block decomposition in the work of Wheatland et al. In this study we conduct numerical simulations of waiting time distributions N(τ) in a large parameter space for various (polynomial, sinusoidal, Gaussian) event rate functions λ(t), parameterized with an exponent p that expresses the degree of the polynomial function λ(t) ∝ t^p. We derive an analytical exact solution of the waiting time distribution function in terms of the incomplete gamma function, which is similar to a Pareto type II function and has a power-law slope of α = 2 + 1/p, in the asymptotic limit of large waiting times. Numerically simulated random distributions reproduce this theoretical prediction accurately. Numerical simulations in the nonlinear regime (p ≥ 2) predict power-law slopes in the range of 2.0 ≤ α ≤ 2.5. The self-organized criticality model yields a prediction of α = 2. Observations of solar flares and coronal mass ejections (over at least a half solar cycle) are found in the range of α_obs ≈ 2.1–2.4. Deviations from strict power-law functions are expected due to the variability of the flare event rate λ(t), and deviations from theoretically predicted slope values α occur due to the Poissonian weighting bias of power-law fits.

We use three campaigns of K2 observations to complete the census of rotation in low-mass members of the benchmark, ≈670 Myr old open cluster Praesepe. We measure new rotation periods (P_rot) for 220 ≲1.3 M_⊙ Praesepe members and recovery periods for 97% (793/812) of the stars with a P_rot in the literature. Of the 19 stars for which we do not recover a P_rot, 17 were not observed by K2. As K2's three Praesepe campaigns took place over the course of 3 yr, we test the stability of our measured P_rot for stars observed in more than one campaign. We measure P_rot consistent to within 10% for >95% of the 331 likely single stars with ≥2 high-quality observations; the median difference in P_rot is 0.3%, with a standard deviation of 2%. Nearly all of the exceptions are stars with discrepant P_rot measurements in Campaign 18, K2's last, which was significantly shorter than the earlier two (≈50 days rather than ≈75 days). This suggests that, despite the evident morphological evolution we observe in the light curves of 38% of the stars, P_rot measurements for low-mass stars in Praesepe are stable on timescales of several years. A P_rot can therefore be taken to be representative even if measured only once.

Interstellar objects (ISOs), the parent population of 1i/'Oumuamua and 2i/Borisov, are abundant in the interstellar medium of the Milky Way. This means that the interstellar medium, including molecular-cloud regions, has three components: gas, dust, and ISOs. From observational constraints of the field density of ISOs drifting in the solar neighborhood, we infer that a typical molecular cloud of 10 pc diameter contains some 10¹⁸ ISOs. At typical sizes ranging from hundreds of meters to tens of kilometers, ISOs are entirely decoupled from the gas dynamics in these molecular clouds. Here we address the question of whether ISOs can follow the collapse of molecular clouds. We perform low-resolution simulations of the collapse of molecular clouds containing initially static ISO populations toward the point where stars form. In this proof-of-principle study, we find that the interstellar objects definitely follow the collapse of the gas—and many become bound to the new-forming numerical approximations to future stars (sinks). At minimum, 40% of all sinks have one or more ISO test particles gravitationally bound to them for the initial ISO distributions tested here. This value corresponds to at least 10¹⁰ actual ISOs being bound after three initial freefall times. Thus, ISOs are a relevant component of star formation. We find that more massive sinks bind disproportionately large fractions of the initial ISO population, implying competitive capture of ISOs. Sinks can also be solitary, as their ISOs can become unbound again—particularly if sinks are ejected from the system. Emerging planetary systems will thus develop in remarkably varied environments, ranging from solitary to richly populated with bound ISOs.

Relatively large dust grains (referred to as pebbles) accumulate at the outer edge of the gap induced by a planet in a protoplanetary disk, and a ring structure with a high dust-to-gas ratio can be formed. Such a ring has been thought to be located immediately outside the planetary orbit. We examined the evolution of the dust ring formed by a migrating planet, by performing two-fluid (gas and dust) hydrodynamic simulations. We found that the initial dust ring does not follow the migrating planet and remains at the initial location of the planet in cases with a low viscosity of α ∼ 10⁻⁴. The initial ring is gradually deformed by viscous diffusion, and a new ring is formed in the vicinity of the migrating planet, which develops from the trapping of the dust grains leaking from the initial ring. During this phase, two rings coexist outside the planetary orbit. This phase can continue over ∼1 Myr for a planet migrating from 100 au. After the initial ring disappears, only the later ring remains. This change in the ring morphology can provide clues as to when and where the planet was formed, and is the footprint of the planet. We also carried out simulations with a planet growing in mass. These simulations show more complex asymmetric structures in the dust rings. The observed asymmetric structures in the protoplanetary disks may be related to a migrating and growing planet.

The cosmic black hole accretion density (BHAD) is critical for our understanding of the formation and evolution of supermassive black holes (BHs). However, at high redshifts (z > 3), X-ray observations report BHADs significantly (∼10 times) lower than those predicted by cosmological simulations. It is therefore paramount to constrain the high-z BHAD using independent methods other than direct X-ray detections. The recently established relation between star formation rate and BH accretion rate among bulge-dominated galaxies provides such a chance, as it enables an estimate of the BHAD from the star formation histories (SFHs) of lower-redshift objects. Using the CANDELS Lyα Emission At Reionization (CLEAR) survey, we model the SFHs for a sample of 108 bulge-dominated galaxies at z = 0.7–1.5, and further estimate the BHAD contributed by their high-z progenitors. The predicted BHAD at z ≈ 4–5 is consistent with the simulation-predicted values, but higher than the X-ray measurements (by ≈3–10 times at z = 4–5). Our result suggests that the current X-ray surveys could be missing many heavily obscured Compton-thick active galactic nuclei (AGNs) at high redshifts. However, this BHAD estimation assumes that the high-z progenitors of our z = 0.7–1.5 sample remain bulge-dominated where star formation is correlated with BH cold-gas accretion. Alternatively, our prediction could signify a stark decline in the fraction of bulges in high-z galaxies (with an associated drop in BH accretion). JWST and Origins will resolve the discrepancy between our predicted BHAD and the X-ray results by constraining Compton-thick AGN and bulge evolution at high redshifts.

The detection of star-to-star chemical variations in star clusters older than 2 Gyr has changed the traditional view of star clusters as canonical examples of "simple stellar populations" into the so-called "multiple stellar populations" (MPs). Although the significance of MPs seems to correlate with cluster total mass, it seems that the presence of MPs is determined by cluster age. In this article, we use deep photometry from the Hubble Space Telescope to investigate whether the FG-type dwarfs in the ∼1.7 Gyr old cluster NGC 1846, have helium spread. By comparing the observation with the synthetic stellar populations, we estimate a helium spread of ΔY ∼ 0.01 ± 0.01 among the main-sequence stars in NGC 1846. The maximum helium spread would not exceed ΔY ∼ 0.02, depending on the adopted fraction of helium-enriched stars. To mask the color variation caused by such a helium enrichment, a nitrogen enrichment of at least Δ[N/Fe] = 0.8 dex is required, which is excluded by previous analyses of the red-giant branch in this cluster. We find that our result is consistent with the ΔY–mass relationship for Galactic globular clusters. To examine whether or not NGC 1846 harbors MPs, higher photometric accuracy is required. We conclude that under the adopted photometric quality, there is no extreme helium variation among NGC 1846 dwarfs.

It is widely accepted that coronal magnetic flux ropes are the core structures of large-scale solar eruptive activities, which have a dramatic impact on the solar-terrestrial system. Previous studies have demonstrated that varying magnetic properties of a coronal flux rope system could result in a catastrophe of the rope, which may trigger solar eruptive activities. Since the total mass of a flux rope also plays an important role in stabilizing the rope, we use 2.5 dimensional magnetohydrodynamic numerical simulations in this article to investigate how a flux rope evolves as its total mass varies. It is found that an unloading process that decreases the total mass of the rope could result in an upward (eruptive) catastrophe in the flux rope system, during which the rope jumps upward and the magnetic energy is released. This indicates that mass unloading processes could initiate the eruption of the flux rope. Moreover, when the system is not too diffusive, there is also a downward (confined) catastrophe that could be caused by mass loading processes via which the total mass accumulates. The magnetic energy, however, is increased during the downward catastrophe, indicating that mass loading processes could cause confined activities that may contribute to the storage of energy before the onset of coronal eruptions.

We study the 3 μm scattering feature of water ice detected in the outer disk of HD 142527 by performing radiative transfer simulations. We show that an ice mass abundance at the outer disk surface of HD 142527 is much lower than estimated in a previous study. It is even lower than inferred from far-infrared ice observations, implying ice disruption at the disk surface. Next, we demonstrate that a polarization fraction of disk-scattered light varies across the ice-band wavelengths depending on ice grain properties; hence, polarimetric spectra would be another tool for characterizing water-ice properties. Finally, we argue that the observed reddish disk-scattered light is due to grains a few microns in size. To explain the presence of such grains at the disk surface, we need a mechanism that can efficiently oppose dust settling. If we assume turbulent mixing, our estimate requires α ≳ 2 × 10⁻³, where α is a nondimensional parameter describing the vertical diffusion coefficient of grains. Future observations probing gas kinematics would be helpful to elucidate vertical grain dynamics in the outer disk of HD 142527.

We present a two-dimensional radiative-dynamical model of the combined stratosphere and upper troposphere of Jupiter to understand its temperature distribution and meridional circulation pattern. Our study highlights the importance of radiative and mechanical forcing for driving the middle atmospheric circulation on Jupiter. Our model adopts a state-of-the-art radiative transfer scheme with recent observations of Jovian gas abundances and haze distribution. Assuming local radiative equilibrium, latitudinal variation of hydrocarbon abundances is not able to explain the observed latitudinal temperature variations in the mid-latitudes. With mechanical forcing parameterized as a frictional drag on zonal wind, our model produces ∼2 K latitudinal temperature variations observed in low to mid-latitudes in the troposphere and lower stratosphere, but cannot reproduce the observed 5 K temperature variations in the middle stratosphere. In the high latitudes, temperature and meridional circulation depend strongly on polar haze radiation. The simulated residual mean circulation shows either two broad equator-to-pole cells or multi-cell patterns, depending on the frictional drag timescale and polar haze properties. A more realistic wave parameterization and a better observational characterization of haze distribution and optical properties are needed to better understand latitudinal temperature distributions and circulation patterns in the middle atmosphere of Jupiter.

Using Planck polarization data, we search for and constrain spatial variations of the polarized dust foreground for cosmic microwave background (CMB) observations, specifically in its spectral index, β_d. Failure to account for such variations will cause errors in the foreground cleaning that propagate into errors on cosmological parameter recovery from the cleaned CMB map. It is unclear how robust prior studies of the Planck data that constrained β_d variations are due to challenges with noise modeling, residual systematics, and priors. To clarify constraints on β_d and its variation, we employ two pixel space analyses of the polarized dust foreground at >37 scales on ≈60% of the sky at high Galactic latitudes. A template fitting method, which measures β_d over three regions of ≈20% of the sky, does not find significant deviations from a uniform β_d = 1.55, consistent with prior Planck determinations. An additional analysis in these regions, based on multifrequency fits to a dust and CMB model per pixel, puts limits on ${\sigma }_{{\beta }_{d}}$, the Gaussian spatial variation in β_d. The data support ${\sigma }_{{\beta }_{d}}$ up to 0.45 at the highest latitudes, 0.30 at midlatitudes, and 0.15 at low latitudes. We also demonstrate that care must be taken when interpreting the current Planck constraints, β_d maps, and noise simulations. Due to residual systematics and low dust signal-to-noise ratios at high latitudes, forecasts for ongoing and future missions should include the possibility of large values of ${\sigma }_{{\beta }_{d}}$ as estimated in this paper, based on current polarization data.

We investigate the kinematic properties of Galactic H ii regions using radio recombination line (RRL) emission detected by the Australia Telescope Compact Array at 4–10 GHz and the Jansky Very Large Array at 8–10 GHz. Our H ii region sample consists of 425 independent observations of 374 nebulae that are relatively well isolated from other, potentially confusing sources and have a single RRL component with a high signal-to-noise ratio. We perform Gaussian fits to the RRL emission in position-position–velocity data cubes and discover velocity gradients in 178 (42%) of the nebulae with magnitudes between 5 and 200 ${\rm{m}}\,{{\rm{s}}}^{-1}\,{\mathrm{arcsec}}^{-1}$. About 15% of the sources also have an RRL width spatial distribution that peaks toward the center of the nebula. The velocity gradient position angles appear to be random on the sky with no favored orientation with respect to the Galactic plane. We craft H ii region simulations that include bipolar outflows or solid body rotational motions to explain the observed velocity gradients. The simulations favor solid body rotation since, unlike the bipolar outflow kinematic models, they are able to produce both the large, >40 ${\rm{m}}\,{{\rm{s}}}^{-1}\,{\mathrm{arcsec}}^{-1}$, velocity gradients and also the RRL width structure that we observe in some sources. The bipolar outflow model, however, cannot be ruled out as a possible explanation for the observed velocity gradients for many sources in our sample. We nevertheless suggest that most H ii region complexes are rotating and may have inherited angular momentum from their parent molecular clouds.

As available data sets grow in size and complexity, advanced visualization tools enabling their exploration and analysis become more important. In modern astronomy, integral field spectroscopic galaxy surveys are a clear example of increasing high dimensionality and complex data sets, which challenges the traditional methods used to extract the physical information they contain. We present the use of a novel self-supervised machine-learning method to visualize the multidimensional information on stellar population and kinematics in the MaNGA survey in a 2D plane. Our framework is insensitive to nonphysical properties such as the size of the integral field unit and is therefore able to order galaxies according to their resolved physical properties. Using the extracted representations, we study how galaxies distribute based on their resolved and global physical properties. We show that even when exclusively using information about the internal structure, galaxies naturally cluster into two well-known categories, rotating main-sequence disks and massive slow rotators, from a purely data-driven perspective, hence confirming distinct assembly channels. Low-mass rotation-dominated quenched galaxies appear as a third cluster only if information about the integrated physical properties is preserved, suggesting a mixture of assembly processes for these galaxies without any particular signature in their internal kinematics that distinguishes them from the two main groups. The framework for data exploration is publicly released with this publication, ready to be used with the MaNGA or other integral field data sets.

Pulsar timing array (PTA) experiments are becoming increasingly sensitive to gravitational waves (GWs) in the nanohertz frequency range, where the main astrophysical sources are supermassive black hole binaries (SMBHBs), which are expected to form following galaxy mergers. Some of these individual SMBHBs may power active galactic nuclei, and thus their binary parameters could be obtained electromagnetically, which makes it possible to apply electromagnetic (EM) information to aid the search for a GW signal in PTA data. In this work, we investigate the effects of such an EM-informed search on binary detection and parameter estimation by performing mock data analyses on simulated PTA data sets. We find that by applying EM priors, the Bayes factor of some injected signals with originally marginal or sub-threshold detectability (i.e., Bayes factor ∼1) can increase by a factor of a few to an order of magnitude, and thus an EM-informed targeted search is able to find hints of a signal when an uninformed search fails to find any. Additionally, by combining EM and GW data, one can achieve an overall improvement in parameter estimation, regardless of the source's sky location or GW frequency. We discuss the implications for the multi-messenger studies of SMBHBs with PTAs.

Quasi-periodic pulsations (QPPs), which usually appear as temporal pulsations of the total flux, are frequently detected in the light curves of solar/stellar flares. In this study, we present the investigation of nonstationary QPPs with multiple periods during the impulsive phase of a powerful flare on 2017 September 6, which were simultaneously measured by the Hard X-ray Modulation Telescope (Insight-HXMT), as well as the ground-based BLENSW. The multiple periods, detected by applying a wavelet transform and Lomb–Scargle periodogram to the detrended light curves, are found to be ∼20–55 s in the Lyα and mid-ultraviolet Balmer continuum emissions during the flare impulsive phase. Similar QPPs with multiple periods are also found in the hard X-ray emission and low-frequency radio emission. Our observations suggest that the flare QPPs could be related to nonthermal electrons accelerated by the repeated energy release process, i.e., triggering of repetitive magnetic reconnection, while the multiple periods might be modulated by the sausage oscillation of hot plasma loops. For the multiperiodic pulsations, other generation mechanisms could not be completely ruled out.

Superluminous supernovae (SLSNe) are luminous transients that can be detected to high redshifts with upcoming optical time-domain surveys such as the Vera C. Rubin Observatory Legacy Survey of Space and Time. An interesting open question is whether the properties of SLSNe evolve through cosmic time. To address this question, in this paper we model the multicolor light curves of all 21 Type I SLSNe from the Dark Energy Survey (DES) with a magnetar spin-down engine, implemented in the Modular Open-Source Fitter for Transients (MOSFiT). With redshifts up to z ≈ 2, this sample includes some of the highest-redshift SLSNe. We find that the DES SLSNe span a similar range of ejecta and magnetar engine parameters as previous samples of mostly lower-redshift SLSNe (spin period P ≈ 0.79–13.61 ms, magnetic field B ≈ (0.03–7.33) × 10¹⁴ G, ejecta mass M_ej ≈ 1.54–30.32 M_⊙, and ejecta velocity v_ej ≈ (0.55–1.45) × 10⁴ km s⁻¹). The DES SLSN sample by itself exhibits the previously found negative correlation between M_ej and P, with a pronounced absence of SLSNe with low ejecta mass and rapid spin. Combining our results for the DES SLSNe with 60 previous SLSNe modeled in the same way, we find no evidence for redshift evolution in any of the key physical parameters.

We present an analysis of wind absorption in the C iiλ1335 doublet toward 40 classical T Tauri stars with archival far-ultraviolet (FUV) spectra obtained by the Hubble Space Telescope. Absorption features produced by fast or slow winds are commonly detected (36 out of 40 targets) in our sample. The wind velocity of the fast wind decreases with disk inclination, which is consistent with expectations for a collimated jet. Slow wind absorption is mostly detected in disks with intermediate or high inclination, without a significant dependence of wind velocity on disk inclination. Both the fast and slow wind absorption are preferentially detected in FUV lines of neutral or singly ionized atoms. The Mg iiλλ2796, 2804 lines show wind absorption consistent with the absorption in the C ii lines. We develop simplified semi-analytical disk/wind models to interpret the observational disk wind absorption. Both fast and slow winds are consistent with expectations from a thermal-magnetized disk wind model and are generally inconsistent with a purely thermal wind. Both the models and the observational analysis indicate that wind absorption occurs preferentially from the inner disk, which offers a wind diagnostic in complement to optical forbidden line emission that traces the wind in larger volumes.

We present the largest sample of brown dwarf (BD) protoplanetary disk spectral energy distributions modeled to date. We compile 49 objects with ALMA observations from four star-forming regions: ρ Ophiuchus, Taurus, Lupus, and Upper Scorpius. Studying multiple regions with various ages enables us to probe disk evolution over time. Specifically, from our models, we obtain values for dust grain sizes, dust settling, and disk mass; we compare how each of these parameters vary between the regions. We find that disk mass decreases with age. We also find evidence of disk evolution (i.e., grain growth and significant dust settling) in all four regions, indicating that planet formation and disk evolution may begin to occur at earlier stages. We generally find that these disks contain too little mass to form planetary companions, though we cannot rule out that planet formation may have already occurred. Finally, we examine the disk mass–host mass relationship and find that BD disks are largely consistent with previously determined relationships for disks around T Tauri stars.