adsabs/SciX_UAT_keywords huggingface dataset:
Light-curve Model for Luminous Red Novae and Inferences about the Ejecta of Stellar Mergers

The process of unstable mass transfer in a stellar binary can result in either a complete merger of the stars or successful removal of the donor envelope leaving a surviving more compact binary. Luminous red novae (LRNe) are the class of optical transients believed to accompany such merger/common envelope events. Past works typically model LRNe using analytic formulae for supernova light curves that make assumptions (e.g., radiation-dominated ejecta, neglect of hydrogen recombination energy) not justified in stellar mergers due to the lower velocities and specific thermal energy of the ejecta. We present a one-dimensional model of LRN light curves that accounts for these effects. Consistent with observations, we find that LRNe typically possess two light-curve peaks, an early phase powered by initial thermal energy of the hot, fastest ejecta layers and a later peak powered by hydrogen recombination from the bulk of the ejecta. We apply our model to a sample of LRNe to infer their ejecta properties (mass, velocity, and launching radius) and compare them to the progenitor donor star properties from pretransient imaging. We define the maximum luminosity achievable for a given donor star in the limit that the entire envelope is ejected, finding that several LRNe violate this limit. Shock interaction between the ejecta and predynamical mass loss may provide an additional luminosity source to alleviate this tension. Our model can also be applied to the merger of planets with stars or stars with compact objects.

Keywords: common envelope binary stars; stellar mergers; transient sources; time domain astronomy
The Subaru HSC Galaxy Clustering with Photometric Redshift. I. Dark Halo Masses versus Baryonic Properties of Galaxies at 0.3 ≤ z ≤ 1.4

We present the clustering properties of low-z (z ≤ 1.4) galaxies selected by the Hyper Suprime-Cam Subaru Strategic Program Wide layer over 145 deg2. The wide-field and multiwavelength observation yields 5,064,770 galaxies at 0.3 ≤ z ≤ 1.4 with photometric redshifts and physical properties. This enables the accurate measurement of angular correlation functions, and the subsequent halo occupation distribution (HOD) analysis allows us to identify the connection between baryonic and dark halo properties. The fraction of less-massive satellite galaxies at z ≲ 1 is found to be almost constant at ∼20%, but it gradually decreases beyond ${M}_{\star }\sim {10}^{10.4}{h}^{-2}{M}_{\odot }$ . However, the abundance of satellite galaxies at z > 1 is quite small even for less-massive galaxies due to the rarity of massive centrals at high-z. This decreasing trend is connected to the small satellite fraction of Lyman break galaxies at z > 3. The stellar-to-halo mass ratios at 0.3 ≤ z ≤ 1.4 are almost consistent with the predictions obtained using the latest empirical model; however, we identify small excesses from the theoretical model at the massive end. The pivot halo mass is found to be unchanged at ${10}^{12.0\mbox{--}12.2}{h}^{-1}{M}_{\odot }$ at 0.3 ≤ z ≤ 1.4, and we systematically show that ${10}^{12}{h}^{-1}{M}_{\odot }$ is a universal pivot halo mass up to z ∼ 5 that is derived using only the clustering/HOD analyses. Nevertheless, halo masses with peaked instantaneous baryon conversion efficiencies are much smaller than the pivot halo mass regardless of redshift, and the most efficient stellar-mass assembly is thought to be in progress in ${10}^{11.0\mbox{--}11.5}{h}^{-1}{M}_{\odot }$ dark halos.

Keywords: observational cosmology; large-scale structure of the universe; dark matter; galaxy dark matter halos; dark matter distribution; galaxy formation; galaxy evolution
X-Ray and Optical Observations of the Young M Dwarf Dipper Star TIC 234284556

We observed TIC 234284556 in X-rays and in the optical with XMM-Newton to study the recurring dip previously seen in TESS observations. The dip did not appear during our observation. We detect X-ray flares and anti-correlated rotational modulation in X-rays and in the optical.

Keywords: m dwarf stars; stellar coronae; stellar flares; starspots; x-ray stars
Chiral Radiation Transport Theory of Neutrinos

We construct the chiral radiation transport equation for left-handed neutrinos in the context of radiation hydrodynamics for core-collapse supernovae. Based on the chiral kinetic theory incorporating quantum corrections due to the chirality of fermions, we derive a general relativistic form of the chiral transfer equation with collisions. We show that such quantum corrections explicitly break the spherical symmetry and axisymmetry of the system. In the inertial frame, in particular, we find that the so-called side jump leads to quantum corrections in the collisions between neutrinos and matter. We also derive analytic forms of such corrections in the emission and absorption rates for the neutrino absorption process. These corrections result in the generation of kinetic helicity and cross helicity of matter, which should then modify the subsequent evolution of matter. This theoretical framework can be applied to investigate the impacts of the chirality of neutrinos on the evolution of core-collapse supernovae.

Keywords: supernova neutrinos; core-collapse supernovae; radiative transfer equation
Radiative Turbulent Flares in Magnetically Dominated Plasmas

We perform 2D and 3D kinetic simulations of reconnection-mediated turbulent flares in a magnetized electron-positron plasma, with weak and strong radiative cooling. Such flares can be generated around neutron stars and accreting black holes. We focus on the magnetically dominated regime where tension of the background magnetic field lines exceeds the plasma rest-mass density by a factor σ0 > 1. In the simulations, turbulence is excited on a macroscopic scale l0, and we observe that it develops by forming thin, dynamic current sheets on various scales. The deposited macroscopic energy dissipates by energizing thermal and nonthermal particles. The particle energy distribution is shaped by impulsive acceleration in reconnecting current sheets, gradual stochastic acceleration, and radiative losses. We parameterize radiative cooling by the ratio ${ \mathcal A }$ of light-crossing time l0/c to a cooling timescale, and study the effect of increasing ${ \mathcal A }$ on the flare. When radiative losses are sufficiently weak, ${ \mathcal A }\lt {\sigma }_{0}^{-1}$ , the produced emission is dominated by stochastically accelerated particles, and the radiative power depends logarithmically on ${ \mathcal A }$ . The resulting radiation spectrum of the flare is broad and anisotropic. In the strong-cooling regime, ${ \mathcal A }\gt {\sigma }_{0}^{-1}$ , stochastic acceleration is suppressed, while impulsive acceleration in the current sheets continues to operate. As ${ \mathcal A }$ increases further, the emission becomes dominated by thermal particles. Our simulations offer a new tool to study particle acceleration by turbulence, especially at high energies, where cooling competes with acceleration. We find that the particle distribution is influenced by strong intermittency of dissipation, and stochastic acceleration cannot be described by a universal diffusion coefficient.

Keywords: plasma astrophysics; high energy astrophysics; astrophysical magnetism; computational astronomy; compact objects
Conditions for Superwind Classes of Super Star Clusters

Mechanical feedback from young massive stars in super star clusters contributes to the formation of superwinds and superbubbles in star-forming regions. We conduct hydrodynamic simulations using the non-equilibrium ionization package MAIHEM to explore how outflow velocity, mass-loading, metallicity, and ambient density can affect the occurrence of catastrophic cooling. To predict optical and UV emission lines, we apply the photoionization code CLOUDY to the physical conditions predicted by our hydrodynamic simulations. Our results could be useful for characterizing catastrophic cooling in starburst regions like the nearby Green Peas and distant star-forming galaxies.

Keywords: starburst galaxies; cooling flows; hydrodynamics; superbubbles
Exploring the Mass Segregation Effect of X-Ray Sources in Globular Clusters. III. Signs of Binary Disruption in M28

Using archival Chandra observations with a total effective exposure of 323 ks, we derive an updated catalog of point sources in the bulge globular cluster M28. The catalog contains 502 X-ray sources within an area of ∼475 arcmin2, and more than 90% of these sources are first detected in this cluster. We find significant dips in the radial distribution profiles of X-ray sources in M28, and the projected distance and width of the distribution dip for bright (LX ≳ 4.5 × 1030 erg s-1) X-ray sources are larger than for faint (LX ≲ 4.5 × 1030 erg s-1) sources. Fitting with the "generalized King model" gives a slightly larger average mass for the bright sources (1.30 ± 0.15 M⊙) than for the faint ones (1.09 ± 0.14 M⊙), which supports a universal delay in mass segregation between heavy objects in globular clusters. We show that the dynamical age of M28 is comparable to that of Terzan 5 and much smaller than that of 47 Tuc, but M28 is evolving faster (I.e., with a shorter two-body relaxation timescale) than 47 Tuc. These features may suggest an acceleration effect of cluster dynamical evolution by tidal shock in M28. Besides, we find an abnormal deficiency of X-ray sources in the central region (R ≲ 1'5) of M28 compared with its outskirts, which indicates that M28 may have suffered an early phase of primordial binary disruption within its central region, and the mass segregation effect will erase such a phenomenon as clusters evolve to an older dynamical age.

Keywords: globular star clusters; x-ray binary stars; stellar dynamics; dynamical friction; tidal disruption
The Effect of Circumstellar Matter on the Double-peaked Type Ic Supernovae and Implications for LSQ14efd, iPTF15dtg, and SN 2020bvc

Double-peaked light curves are observed for some Type Ic supernovae (SNe Ic), including LSQ14efd, iPTF15dtg, and SN 2020bvc. One possible explanation of the first peak would be shock-cooling emission from massive extended material around the progenitor, which is produced by mass eruption or rapid expansion of the outermost layers of the progenitor shortly before the supernova explosion. We investigate the effects of such circumstellar matter (CSM) on the multiband optical light curves of SNe Ic using the radiation hydrodynamics code STELLA. Two different SNe Ic progenitor masses at the pre-SN stage (3.93 M⊙ and 8.26 M⊙) are considered in the SN models. The adopted parameter space consists of the CSM mass of MCSM = 0.05-0.3M⊙, the CSM radius of RCSM = 1013-1015 cm, and the explosion energy of Eburst = (1.0-12.0) × 1051 erg. We also investigate the effects of the radioactive nickel distribution on the overall shape of the light curve and the color evolution. Comparison of our SN models with the double-peaked SNe Ic LSQ14efd, iPTF15dtg, and SN 2020bvc indicates that these three SNe Ic had a similar CSM structure (i.e., MCSM ≈ 0.1-0.2M⊙ and RCSM = 1013-1014 cm), which might imply a common mechanism for their CSM formation. The implied mass-loss rate of $\dot{M}\gtrsim 1.0\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ is too high to be explained by the previously suggested scenarios for pre-SN eruption, which calls for a novel mechanism.

Keywords: supernovae; type ic supernovae
Searches for Neutrinos from Gamma-Ray Bursts Using the IceCube Neutrino Observatory

Gamma-ray bursts (GRBs) are considered as promising sources of ultra-high-energy cosmic rays (UHECRs) due to their large power output. Observing a neutrino flux from GRBs would offer evidence that GRBs are hadronic accelerators of UHECRs. Previous IceCube analyses, which primarily focused on neutrinos arriving in temporal coincidence with the prompt gamma-rays, found no significant neutrino excess. The four analyses presented in this paper extend the region of interest to 14 days before and after the prompt phase, including generic extended time windows and targeted precursor searches. GRBs were selected between 2011 May and 2018 October to align with the data set of candidate muon-neutrino events observed by IceCube. No evidence of correlation between neutrino events and GRBs was found in these analyses. Limits are set to constrain the contribution of the cosmic GRB population to the diffuse astrophysical neutrino flux observed by IceCube. Prompt neutrino emission from GRBs is limited to ≲1% of the observed diffuse neutrino flux, and emission on timescales up to 104 s is constrained to 24% of the total diffuse flux.

Keywords: neutrino astronomy; gamma-ray bursts
Binarity as the Origin of Long Secondary Periods in Red Giant Stars

Long secondary periods (LSPs), observed in a third of pulsating red giant stars, are the only unexplained type of large-amplitude stellar variability known at this time. Here we show that this phenomenon is a manifestation of a substellar or stellar companion orbiting the red giant star. Our investigation is based on a sample of about 16,000 well-defined LSP variables detected in the long-term OGLE photometric database of the Milky Way and Magellanic Clouds, combined with the mid-infrared data extracted from the NEOWISE-R archive. From this collection, we selected about 700 objects with stable, large-amplitude, well-sampled infrared light curves and found that about half of them exhibit secondary eclipses, thus presenting an important piece of evidence that the physical mechanism responsible for LSPs is binarity. Namely, the LSP light changes are due to the presence of a dusty cloud orbiting the red giant together with the companion and obscuring the star once per orbit. The secondary eclipses, visible only in the infrared wavelength, occur when the cloud is hidden behind the giant. In this scenario, the low-mass companion is a former planet that has accreted a significant amount of mass from the envelope of its host star and grown into a brown dwarf.

Keywords: asymptotic giant branch stars; long period variable stars; close binary stars; circumstellar dust; brown dwarfs
KMT-2017-BLG-2820 and the Nature of the Free-floating Planet Population

We report a new free-floating planet (FFP) candidate, KMT-2017-BLG-2820, with Einstein radius θE ≃ 6 μas, lens-source relative proper motion μrel ≃ 8 mas yr-1, and Einstein timescale tE = 6.5 hr. It is the third FFP candidate found in an ongoing study of giant-source finite-source point-lens (FSPL) events in the KMTNet database and the sixth FSPL FFP candidate overall. We find no significant evidence for a host. Based on their timescale distributions and detection rates, we argue that five of these six FSPL FFP candidates are drawn from the same population as the six point-source point-lens (PSPL) FFP candidates found by Mróz et al. in the OGLE-IV database. The θE distribution of the FSPL FFPs implies that they are either sub-Jovian planets in the bulge or super-Earths in the disk. However, the apparent "Einstein desert" (10 ≲ θE/μas ≲ 30) would argue for the latter. Whether each of the 12 (six FSPL and six PSPL) FFP candidates is truly an FFP or simply a very wide-separation planet can be determined at first adaptive optics (AO) light on 30 m telescopes, and earlier for some. If the latter, a second epoch of AO observations could measure the projected planet-host separation with a precision of ${ \mathcal O }(10\,\mathrm{au})$ . At the present time, the balance of evidence favors the unbound-planet hypothesis.

Keywords: gravitational microlensing
Solar-Stellar Connection: X-Ray Flares to Energetic (E > 10 MeV) Particle Events

Energetic particle environments are an important factor for the viability of life on exoplanets surrounding flare stars. In the heliosphere, large gradual solar energetic (E > 10 MeV) particle (SEP) events are produced by shocks from fast coronal mass ejections (CMEs). Extensive observations of solar X-ray flares, CMEs, and SEP events can provide guidance for flare star models of stellar energetic particle (StEP) events, for which stellar flares, but only rarely the associated CMEs, are observed. Comparing an extensive list of peak fluxes, timescales, and peak temperatures of 585 ≥ M3.0 solar X-ray flares with the occurrence of associated SEP events of peak flux Ip > 1.4 proton flux units, enhanced with proxy decametric-hectometric type II radio bursts, we determine guidelines for StEP event outcomes, given only stellar X-ray flare inputs. Longer timescales and lower peak temperatures of X-ray flares with a given peak X-ray flux Fp are more favorable for occurrence of associated SEP/StEP events, which, however, are only a minority of all solar flare outcomes. Most solar flares do not result in SEP events, invalidating scaling laws between stellar flares, CMEs, and StEP events. We discuss recent observations and models of the flare-CME relationship and suggest that StEP intensities Ip may often be overestimated.

Keywords: exoplanets; astrobiology; solar flares; stellar flares; solar energetic particles; stellar coronal mass ejections; solar coronal mass ejection shocks
Reionization in the Light of Dark Stars

We investigate the effect of dark stars (DSs) on the reionization history of the universe, and the interplay between them and feedback due to Lyman-Werner (LW) radiation in reducing the cosmic microwave background (CMB) optical depth to a value within the τ = 0.054 ± 0.007 range measured by Planck. We use a semianalytic approach to evaluate reionization histories and CMB optical depths, which includes Population II stars in atomic cooling halos and Population III stars in minihalos with LW feedback, preceded by a DS phase. We show that while LW feedback by itself can reduce the integrated optical depth to the last scattering surface to ~0.05 only if the Population III star formation efficiency is less than ~0.2%, the inclusion of a population of DSs can naturally lead to the measured CMB optical depth for much larger Population III star formation efficiencies ≳1%.

Keywords: population iii stars; reionization
Bimodal Behavior and Convergence Requirement in Macroscopic Properties of the Multiphase Interstellar Medium Formed by Atomic Converging Flows

We systematically perform hydrodynamics simulations of 20 $\mathrm{km}\,{{\rm{s}}}^{-1}$ converging flows of the warm neutral medium (WNM) to calculate the formation of the cold neutral medium (CNM), focusing especially on the mean properties of the multiphase interstellar medium (ISM), such as the mean density on a 10 pc scale. Our results show that convergence in those mean properties requires a 0.02 pc spatial resolution that resolves the cooling length of the thermally unstable neutral medium (UNM) to follow the dynamical condensation from the WNM to the CNM. We also find that two distinct postshock states appear in the mean properties depending on the amplitude of the upstream WNM density fluctuation ${\rm{\Delta }}{\rho }_{0}$ ( $=\,\sqrt{\langle \delta {\rho }_{0}^{2}\rangle }{/\rho }_{0}$ ). When ${\rm{\Delta }}{\rho }_{0}\gt 10 \% $ , the interaction between shocks and density inhomogeneity leads to a strong driving of the postshock turbulence of >3 km s-1, which dominates the energy budget in the shock-compressed layer. The turbulence prevents dynamical condensation by cooling, and the CNM mass fraction remains at ∼45%. In contrast, when ${\rm{\Delta }}{\rho }_{0}\leqslant 10 \% $ , the CNM formation proceeds efficiently, resulting in the CNM mass fraction of ∼70%. The velocity dispersion is limited to the thermal-instability-mediated level of ∼2-3 km s-1, and the layer is supported by both turbulent and thermal energy equally. We also propose an effective equation of state that models the multiphase ISM formed by the WNM converging flow as a one-phase ISM in the form of P ∝ ργeff, where γeff varies from 0.9 (for a large pre-shock Δρ0) to 0.7 (for a small pre-shock Δρ0).

Keywords: interstellar medium; warm neutral medium; cold neutral medium; interstellar dynamics
SN 2016dsg: A Thermonuclear Explosion Involving a Thick Helium Shell

A thermonuclear explosion triggered by a He-shell detonation on a carbon-oxygen white-dwarf core has been predicted to have strong UV line blanketing at early times due to the iron-group elements produced during He-shell burning. We present the photometric and spectroscopic observations of SN 2016dsg, a subluminous peculiar Type I supernova consistent with a thermonuclear explosion involving a thick He shell. With a redshift of 0.04, the i-band peak absolute magnitude is derived to be around -17.5. The object is located far away from its host, an early-type galaxy, suggesting it originated from an old stellar population. The spectra collected after the peak are unusually red, show strong UV line blanketing and weak O I λ7773 absorption lines, and do not evolve significantly over 30 days. An absorption line around 9700-10500 Å is detected in the near-infrared spectrum and is likely from the unburnt He in the ejecta. The spectroscopic evolution is consistent with the thermonuclear explosion models for a sub-Chandrasekhar-mass white dwarf with a thick He shell, while the photometric evolution is not well described by existing models.

Keywords: supernovae; type ia supernovae
Formation and Characteristics of Filament Threads in Double-dipped Magnetic Flux Tubes

As one of the main formation mechanisms of solar filament formation, the chromospheric evaporation-coronal condensation model has been confirmed by numerical simulations to explain the formation of filament threads very well in flux tubes with single dips. However, coronal magnetic extrapolations indicated that some magnetic field lines might possess more than one dip. It is expected that the formation process would be significantly different in this case compared to a single-dipped magnetic flux tube. In this paper, based on the evaporation-condensation model, we study filament thread formation in double-dipped magnetic flux tubes by numerical simulations. We find that only with particular combinations of magnetic configuration and heating, e.g., concentrated localized heating and a long magnetic flux tube with deep dips, can two threads form and persist in a double-dipped magnetic flux tube. Comparing our parametric survey with observations, we conclude that such magnetically connected threads due to multiple dips are more likely to exist in quiescent filaments than in active-region filaments. Moreover, we find that these threads are usually shorter than independently trapped threads, which might be one of the reasons why quiescent filaments have short threads. These characteristics of magnetically connected threads could also explain barbs and vertical threads in quiescent filaments.

Keywords: hydrodynamical simulations; solar corona; solar filaments
Spatial Intermittency of Particle Distribution in Relativistic Plasma Turbulence

Relativistic magnetically dominated turbulence is an efficient engine for particle acceleration in a collisionless plasma. Ultrarelativistic particles accelerated by interactions with turbulent fluctuations form nonthermal power-law distribution functions in the momentum (or energy) space, f(γ)d γ ∝ γ -α d γ, where γ is the Lorenz factor. We argue that in addition to exhibiting non-Gaussian distributions over energies, particles energized by relativistic turbulence also become highly intermittent in space. Based on particle-in-cell numerical simulations and phenomenological modeling, we propose that the bulk plasma density has lognormal statistics, while the density of the accelerated particles, n, has a power-law distribution function, $P(n){dn}\,\propto \,{n}^{-\beta }{dn}$ . We argue that the scaling exponents are related as β ≈ α + 1, which is broadly consistent with numerical simulations. Non-space-filling, intermittent distributions of plasma density and energy fluctuations may have implications for plasma heating and for radiation produced by relativistic turbulence.

Keywords: plasma physics; plasma astrophysics; relativistic fluid dynamics