adsabs/SciX_UAT_keywords huggingface dataset:
Dynamical He Flashes in Double White Dwarf Binaries

The detonation of an overlying helium layer on a 0.8-1.1 M ⊙ carbon-oxygen (CO) white dwarf (WD) can detonate the CO WD and create a thermonuclear supernova (SN). Many authors have recently shown that when the mass of the He layer is low (≲0.03 M ⊙), the ashes from its detonation minimally impact the spectra and light curve from the CO detonation, allowing the explosion to appear remarkably similar to Type Ia SNe. These new insights motivate our investigation of dynamical He shell burning and our search for a binary scenario that stably accumulates thermally unstable He shells in the 0.01-0.08 M ⊙ range, thick enough to detonate, but also often thin enough for minimal impact on the observables. We first show that our improved nonadiabatic evolution of convective He shell burning in this range of shell mass leads to conditions ripe for a He detonation. We also find that a stable mass transfer scenario with a high-entropy He WD donor of mass 0.15-0.25 M ⊙ yields the He shell masses needed to achieve the double detonations. This scenario also predicts that the surviving He donor leaves with a spatial velocity consistent with the unusual runaway object, D6-2. We find that hot He WD donors originate in common-envelope events when a 1.3-2.0 M ⊙ star fills its Roche lobe at the base of the red giant branch at orbital periods of 1-10 days with the CO WD.

Keywords: white dwarf stars; type ia supernovae; am canum venaticorum stars; binary stars; helium-rich stars; high-velocity stars
Lyα Radiative Transfer: Modeling Spectrum and Surface Brightness Profiles of Lyα-emitting Galaxies at Z = 3-6

We perform Lyα radiative transfer calculations to reproduce the Lyα properties of star-forming galaxies at high redshifts. We model a galaxy as a halo in which the density distributions of Lyα sources and H I plus dust medium are described with exponential functions. We also consider an outflow of the medium that represents a momentum-driven wind in a gravitational potential well. We successfully reproduce both the spectra and the surface brightness profiles of eight star-forming galaxies at z = 3-6 observed with the Multi-Unit Spectroscopic Explorer using this outflowing-halo model with Lyα scattering. The best-fit model parameters (i.e., the outflowing velocity and optical depth) for these galaxies are consistent with those in other studies. We examine the impacts of individual model parameters and input spectrum on the emerging spectrum and surface brightness profile. Further investigations of the correlations among observables (i.e., the spatial extent of Lyα halos and Lyα spectral features) and model parameters, and of spatially resolved spectra are presented as well. We demonstrate that the combination of spectrum and surface brightness profile provides strong constraints on model parameters and thus on the spatial/kinematic distributions of the medium.

Keywords: extragalactic astronomy; lyman-alpha galaxies; radiative transfer; radiative transfer simulations; high-redshift galaxies; interstellar medium; interstellar medium wind; circumgalactic medium
Inconspicuous Solar Polar Coronal X-Ray Jets as the Source of Conspicuous Hinode/EUV Imaging Spectrometer Doppler Outflows

We examine in greater detail five events previously identified as being sources of strong transient coronal outflows in a solar polar region in Hinode/Extreme Ultraviolet (EUV) Imaging Spectrometer (EIS) Doppler data. Although relatively compact or faint and inconspicuous in Hinode/X-ray Telescope (XRT) soft-X-ray (SXR) images and in Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) EUV images, we find that all of these events are consistent with being faint coronal X-ray jets. The evidence for this is that the events result from eruption of minifilaments of projected sizes spanning 5000-14,000 km and with erupting velocities spanning 19-46 km s-1, which are in the range of values observed in cases of confirmed X-ray polar coronal hole jets. In SXR images, and in some EUV images, all five events show base brightenings, and faint indications of a jet spire that (in four of five cases where determinable) moves away from the brightest base brightening; these properties are common to more obvious X-ray jets. For a comparatively low-latitude event, the minifilament erupts from near (≲few arcsec) a location of near-eruption-time opposite-polarity magnetic-flux-patch convergence, which again is consistent with many observed coronal jets. Thus, although too faint to be identified as jets a priori, otherwise all five events are identical to typical coronal jets. This suggests that jets may be more numerous than recognized in previous studies, and might contribute substantially to solar wind outflow, and to the population of magnetic switchbacks observed in Parker Solar Probe (PSP) data.

Keywords: solar filament eruptions; solar corona; solar x-ray emission; solar extreme ultraviolet emission
Nature of Compton-thick Active Galactic Nuclei in "Nonmerging" Luminous Infrared Galaxies UGC 2608 and NGC 5135 Revealed with Broadband X-Ray Spectroscopy

We have analyzed the broadband X-ray spectra of active galactic nuclei (AGNs) in two "nonmerging" luminous infrared galaxies (LIRGs), UGC 2608 and NGC 5135, utilizing the data of Nuclear Spectroscopic Telescope Array, Suzaku, XMM-Newton, and Chandra. Applying the X-ray clumpy-torus model (XCLUMPY), we find that both sources have similar spectra characterized by Compton-thick (CT) absorption ( ${N}_{{\rm{H}}}$ ∼ 5-7 × 1024 cm-2) and small torus angular width (σ < 20°). The intrinsic 2-10 keV luminosities are ${3.9}_{-1.7}^{+2.2}$ × 1043 erg s-1 (UGC 2608) and ${2.0}_{-0.9}^{+3.3}$ × 1043 erg s-1 (NGC 5135). The [O IV]-to-nuclear-12 μm luminosity ratios are larger than those of typical Seyferts, which are consistent with the torus covering factors ( ${C}_{{\rm{T}}}\,\lesssim $ 0.7) estimated from the torus angular widths and column densities by X-ray spectroscopy. The torus covering factors and Eddington ratios ( ${\lambda }_{\mathrm{Edd}}$ ∼ 0.1) follow the relation found by Ricci et al. for local AGNs, implying that their tori become geometrically thin, due to significant radiation pressure of the AGN that blows out some part of the tori. These results indicate that the CT AGNs in these "nonmerger" LIRGs are just a normal AGN population seen edge-on through a large line-of-sight column density. They are in contrast to the buried CT AGNs in late-stage mergers that have large torus covering factors even at large Eddington ratios.

Keywords: observational astronomy; infrared galaxies; black hole physics; x-ray active galactic nuclei; supermassive black holes; active galactic nuclei
A Cosmography Approach to Dark Energy Cosmologies: New Constraints Using the Hubble Diagrams of Supernovae, Quasars, and Gamma-Ray Bursts

In the context of a cosmography approach to using the data of the Hubble diagram for supernovae, quasars, and gamma-ray bursts, we study dark energy (DE) parameterizations and the concordance cold dark matter (ΛCDM) universe. Using different combinations of data samples including (i) supernovae (Pantheon), (ii) Pantheon + quasars. and (iii) Pantheon + quasars + gamma-ray bursts, and applying the minimization of χ2 function of the distance modulus of data samples in the context of the Markov Chain Monte Carlo method, we obtain constrained values of cosmographic parameters in a model-independent cosmography scenario. We then investigate our analysis, for different concordance ΛCDM cosmology, wCDM, Chevallier-Polarski-Linder, and Pade parameterizations. Comparing the numerical values of the cosmographic parameters obtained for DE scenarios with those of the model-independent method, we show that the concordance ΛCDM model has serious issues when we involve quasar and gamma-ray burst data in our analysis. While high-redshift quasars and gamma-ray bursts can falsify the concordance model, our results using a cosmography approach indicate that the other DE parameterizations are still consistent with these observations.

Keywords: cosmology; cosmological parameters; dark energy; cosmological constant
The Progenitors of Superluminous Type Ia Supernovae

Recent observations of type Ia supernovae (SNe Ia) have discovered a subclass of "super-Chandrasekhar" SNe Ia (SC SNe Ia) whose high luminosities and low ejecta velocities suggest that they originate from the explosions of white dwarfs (WDs) with masses that exceed the Chandrasekhar mass limit. Different models have been proposed to explain the progenitors of these explosions, including a "magnetized WD" model and a "WD merger" model. To test the robustness of these models, we conduct a 1D numerical parameter survey of WD explosions using these models as initial conditions. We follow the explosions using the hydrodynamics code Castro and then use the radiation transport code SuperNu to create light curves and spectra for the models. We find that while both classes of models fall within the range of SC SNe Ia observations on the light-curve width-luminosity relation, only the WD merger models reproduce the observed low ejecta velocities. The light curves of our merger models are more similar photometrically to observations than our magnetized models. Given this, we discuss possible explanations for the brightest SC SNe Ia observations that cannot be reproduced with our WD merger models. This study provides the basis for future SC SNe Ia observations and higher-dimensional numerical models.

Keywords: type ia supernovae; white dwarf stars; hydrodynamical simulations; hydrodynamics; radiative transfer simulations; astronomical simulations; supernovae
Exploring the Origin of Stars on Bound and Unbound Orbits Causing Tidal Disruption Events

Tidal disruption events (TDEs) provide a clue to the properties of a central supermassive black hole (SMBH) and an accretion disk around it, and to the stellar density and velocity distributions in the nuclear star cluster surrounding the SMBH. Deviations of TDE light curves from the standard occurring at a parabolic encounter with the SMBH depend on whether the stellar orbit is hyperbolic or eccentric and the penetration factor (β, the tidal disruption radius to the orbital pericenter ratio). We study the orbital parameters of bound and unbound stars being tidally disrupted by comparison of direct N-body simulation data with an analytical model. Starting from the classical steady-state Fokker-Planck model of Cohn & Kulsrud, we develop an analytical model of the number density distribution of those stars as a function of orbital eccentricity (e) and β. To do so, fittings of the density and velocity distribution of the nuclear star cluster and of the energy distribution of tidally disrupted stars are required and obtained from N-body data. We confirm that most of the stars causing TDEs in a spherical nuclear star cluster originate from the full loss-cone region of phase space, derive analytical boundaries in eccentricity-β space, and find them confirmed by N-body data. Since our limiting eccentricities are much smaller than critical eccentricities for full accretion or the full escape of stellar debris, we conclude that those stars are only very marginally eccentric or hyperbolic, close to parabolic.

Keywords: black hole physics; high energy astrophysics; tidal disruption; time domain astronomy; accretion; galaxy nuclei; supermassive black holes; star clusters; galaxy kinematics; intermediate-mass black holes; stellar dynamics; n-body simulations
Further Evidence for the 9 s Pulsation in LS 5039 from NuSTAR and ASCA

The present study aims to reinforce the evidence for the ~9 s pulsation in the gamma-ray binary LS 5039, derived from a Suzaku observation in 2007 and a NuSTAR observation in 2016. Through a reanalysis of the NuSTAR data incorporating the orbital Doppler correction, the 9.0538 s pulsation was confirmed successfully even in the 3-10 keV range, where it was undetectable previously. This was attained by perceiving an energy-dependent drift in the pulse phase below 10 keV and correcting the pulse timing of individual photons for that effect. Similarly, an archival 0.7-12 keV data set of LS 5039, taken with the ASCA Gas Imaging Spectrometer in 1999 October, was analyzed. The data showed possible periodicity at about 8.882 s, but again the energy-dependent phase drift was noticed below 10 keV. By correcting for this effect, and for the orbital Doppler delays in the LS 5039 system, the 2.8-12 keV periodicity became statistically significant at 8.891 ± 0.001 s. The periods measured with ASCA, Suzaku, and NuSTAR approximately follow an average period derivative of $\dot{P}\approx 3.0\times {10}^{-10}$ s s-1. These results provide further evidence for the pulsation in this object and strengthen the scenario proposed by Yoneda et al. that the compact object in LS 5039 is a strongly magnetized neutron star.

Keywords: pulsars; neutron stars; magnetars; gamma-ray sources
The PIPER Survey. I. An Initial Look at the Intergalactic Globular Cluster Population in the Perseus Cluster

We describe the goals and first results of the Program for Imaging of the PERseus cluster of galaxies (PIPER). The first phase of the program builds on imaging of fields obtained with the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS)/WFC and WFC3/UVIS cameras. Our PIPER target fields with HST include major early-type galaxies including the active central giant NGC 1275, known ultra-diffuse galaxies, and the intracluster medium. The resulting two-color photometry in F475W and F814W reaches deep enough to resolve and measure the globular cluster (GC) populations in the Perseus member galaxies. Here we present initial results for eight pairs of outer fields that confirm the presence of intergalactic GCs (IGCs) in fields as distant as 740 kpc from the Perseus center (40% of the virial radius of the cluster). Roughly 90% of these IGCs are identifiably blue (metal-poor) but there is a clear trace of a red (metal-rich) component as well, even at these very remote distances.

Keywords: globular star clusters; intracluster medium; rich galaxy clusters; perseus cluster
Effect of Multipole Moments in the Weak Field Limit of a Black Hole Plus Halo Potential

In this paper, we consider a Newtonian system whose relativistic counterpart describes a superimposed halo with a black hole. Our aim is to determine how the quadrupole and octupole moments affect the nature of the motion of a test particle, moving in the close vicinity of the black hole. The different types of trajectories for the test particle are mainly classified as bounded, collisional, and escaping, by using modern color-coded basin diagrams. Moreover, an additional analysis is carried out for distinguishing between the different types of bounded motion (regular, sticky, and chaotic). Our results strongly indicate that the multipole moments, along with the total orbital energy, highly affect the final state of the test particle, while at the same time the basin geometry of the phase space tends to be highly dominated by collision and escape orbits.

Keywords: supermassive black holes
The Nature of Low-albedo Small Bodies from 3 μm Spectroscopy: One Group that Formed within the Ammonia Snow Line and One that Formed beyond It

We present evidence, via a large survey of 191 new spectra along with previously published spectra, of a divide in the 3 μm spectral properties of the low-albedo asteroid population. One group ("sharp types," or STs, with band centers <3 μm) has a spectral shape consistent with carbonaceous chondrite meteorites, while the other group ("not sharp types," or NSTs, with bands centered >3 μm) is not represented in the meteorite literature but is as abundant as the STs among large objects. Both groups are present in most low-albedo asteroid taxonomic classes, and, except in limited cases, taxonomic classifications based on 0.5-2.5 μm data alone cannot predict whether an asteroid is an ST or NST. Statistical tests show that the STs and NSTs differ in average band depth, semimajor axis, and perihelion at confidence levels ≥98% while not showing significant differences in albedo. We also show that many NSTs have a 3 μm absorption band shape like comet 67P and likely represent an important small-body composition throughout the solar system. A simple explanation for the origin of these groups is formation on opposite sides of the ammonia snow line, with the NST group accreting H2O and NH3 and the ST group only accreting H2O, with subsequent thermal and chemical evolution resulting in the minerals seen today. Such an explanation is consistent with recent dynamical modeling of planetesimal formation and delivery and suggests that much more outer solar system material was delivered to the main asteroid belt than would be thought based on the number of D-class asteroids found today.

Keywords: spectroscopy; small solar system bodies; main belt asteroids; hilda group; asteroid surfaces
Detailed Chemical Abundances of Stars in the Outskirts of the Tucana II Ultrafaint Dwarf Galaxy

We present chemical abundances and velocities of five stars between 0.3 and 1.1 kpc from the center of the Tucana II ultrafaint dwarf galaxy (UFD) from high-resolution Magellan/MIKE spectroscopy. We find that every star is deficient in metals (-3.6 < [Fe/H] < -1.9) and in neutron-capture elements as is characteristic of UFD stars, unambiguously confirming their association with Tucana II. Other chemical abundances (e.g., C, iron peak) largely follow UFD trends and suggest that faint core-collapse supernovae (SNe) dominated the early evolution of Tucana II. We see a downturn in [α/Fe] at [Fe/H] ≈ -2.8, indicating the onset of Type Ia SN enrichment and somewhat extended chemical evolution. The most metal-rich star has strikingly low [Sc/Fe] = -1.29 ± 0.48 and [Mn/Fe] = -1.33 ± 0.33, implying significant enrichment by a sub-Chandrasekhar mass Type Ia SN. We do not detect a radial velocity gradient in Tucana II ( ${{dv}}_{\mathrm{helio}}/d{\theta }_{1}=-{2.6}_{-2.9}^{+3.0}$ km s-1 kpc-1), reflecting a lack of evidence for tidal disruption, and derive a dynamical mass of ${M}_{1/2}\,({r}_{h})={1.6}_{-0.7}^{+1.1}\times {10}^{6}$ M ⊙. We revisit formation scenarios of the extended component of Tucana II in light of its stellar chemical abundances. We find no evidence that Tucana II had abnormally energetic SNe, suggesting that if SNe drove in situ stellar halo formation, then other UFDs should show similar such features. Although not a unique explanation, the decline in [α/Fe] is consistent with an early galactic merger triggering later star formation. Future observations may disentangle such formation channels of UFD outskirts. * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: dwarf galaxies; local group; population ii stars
The Behavior of Bp He-weak Stars in the Far UV-Paper XIII: HD 161480

The analysis of four spectra of the B7 He-weak star HD 161480 recorded by the SWP camera on board the International Ultraviolet Explorer reveals instances of variations of the far ultraviolet spectral energy distribution shortwards of 1800 Å in spectra collected over 4 consecutive days with identical exposure times. The Si II doublet near 1530 Å is stronger at phase of FUV minimum. The C IV doublet at 1550 Å is absent. These variations suggest that silicon and other chemical elements are probably distributed in an inhomogeneous manner over the surface of HD 161480. The radial velocity of the Si II doublet varies over the 4 days observation, reflecting the orbital motion of this SB1 star.

Keywords: chemically peculiar stars; helium-weak stars
Double-peaked Balmer Emission Indicating Prompt Accretion Disk Formation in an X-Ray Faint Tidal Disruption Event

We present the multiwavelength analysis of the tidal disruption event (TDE) AT 2018hyz (ASASSN-18zj). From follow-up optical spectroscopy, we detect the first unambiguous case of resolved double-peaked Balmer emission in a TDE. The distinct line profile can be well-modeled by a low eccentricity (e ≈ 0.1) accretion disk extending out to ∼100 Rp and a Gaussian component originating from non-disk clouds, though a bipolar outflow origin cannot be completely ruled out. Our analysis indicates that in AT 2018hyz, disk formation took place promptly after the most-bound debris returned to pericenter, which we estimate to be roughly tens of days before the first detection. Redistribution of angular momentum and mass transport, possibly through shocks, must occur on the observed timescale of about a month to create the large Hα-emitting disk that comprises ≲5% of the initial stellar mass. With these new insights from AT 2018hyz, we infer that circularization is efficient in at least some, if not all optically bright, X-ray faint TDEs. In these efficiently circularized TDEs, the detection of double-peaked emission depends on the disk inclination angle and the relative strength of the disk contribution to the non-disk component, possibly explaining the diversity seen in the current sample.

Keywords: galaxy accretion disks; black hole physics; high energy astrophysics
Negative Lags on the Viscous Timescale in Quasar Photometry and Prospects for Detecting More with LSST

The variability of quasar light curves can be used to study the structure of quasar accretion disks. For example, continuum reverberation mapping uses delays between variability in short and long wavelength bands (short lags) to measure the radial extent and temperature profile of the disk. Recently, a potential reverse lag, where variations in shorter wavelength bands lag the longer wavelength bands at the much longer viscous timescale, was detected for Fairall 9. Inspired by this detection, we derive a timescale for these long negative lags from fluctuation propagation models and recent simulations. We use this timescale to forecast our ability to detect long lags using the Vera Rubin Legacy Survey of Space and Time (LSST). After exploring several methods, including the interpolated cross-correlation function, a Von-Neumann estimator, JAVELIN, and a maximum-likelihood Fourier method, we find that our two main methods, JAVELIN and the maximum-likelihood method, can together detect long lags of up to several hundred days in mock LSST light curves. Our methods work best on proposed LSST cadences with long season lengths, but can also work for the current baseline LSST cadence, especially if we add observations from other optical telescopes during seasonal gaps. We find that LSST has the potential to detect dozens to hundreds of additional long lags. Detecting these long lags can teach us about the vertical structure of quasar disks and how it scales with different quasar properties.

Keywords: active galactic nuclei; quasars; accretion; black holes; high energy astrophysics; reverberation mapping; disk flaring