adsabs/SciX_UAT_keywords huggingface dataset:
The Chemodynamics of the Stellar Populations in M31 from APOGEE Integrated-light Spectroscopy

We present an analysis of nearly 1000 near-infrared, integrated-light spectra from APOGEE in the inner ~7 kpc of M31. We utilize full-spectrum fitting with A-LIST simple stellar population spectral templates that represent a population of stars with the same age, [M/H], and [α/M]. With this, we determine the mean kinematics, metallicities, α abundances, and ages of the stellar populations of M31's bar, bulge, and inner disk (~4-7 kpc). We find a nonaxisymmetric velocity field in M31 resulting from the presence of a bar. The bulge of M31 is less metal-rich (mean [M/H] = $-{0.149}_{-0.081}^{+0.067}$ dex) than the disk, features minima in metallicity on either side of the bar ([M/H] ~ -0.2), and is enhanced in α abundance (mean [α/M] = ${0.281}_{-0.038}^{+0.035}$ ). The disk of M31 within ~7 kpc is enhanced in both metallicity ([M/H] = $-{0.023}_{-0.052}^{+0.050}$ ) and α abundance ([α/M] = ${0.274}_{-0.025}^{+0.020}$ ). Both of these structural components are uniformly old at ≃12 Gyr. We find the mean metallicity increases with distance from the center of M31, with the steepest gradient along the disk major axis (0.043 ± 0.021 dex kpc-1). This gradient is the result of changing light contributions from the bulge and disk. The chemodynamics of stellar populations encodes information about a galaxy's chemical enrichment, star formation history, and merger history, allowing us to discuss new constraints on M31's formation. Our results provide a stepping stone between our understanding of the Milky Way and other external galaxies.

Keywords: andromeda galaxy; galaxy abundances; galaxy ages; galaxy bars; galaxy bulges; galaxy disks; galaxy dynamics; galaxy kinematics; galaxy rotation curves; galaxy spectroscopy; galaxy structure
Investigating the IBEX Ribbon Structure a Solar Cycle Apart

A "Ribbon" of enhanced energetic neutral atom (ENA) emissions was discovered by the Interstellar Boundary Explorer in 2009, redefining our understanding of the heliosphere boundaries and the physical processes occurring at the interstellar interface. The Ribbon signal is intertwined with that of a globally distributed flux (GDF) that spans the entire sky. To a certain extent, Ribbon separation methods enabled examining its evolution independent of the underlying GDF. Observations over a full solar cycle revealed the Ribbon's evolving nature, with intensity variations closely tracking those of the solar wind (SW) structure after a few years delay, accounting for the SW-ENA recycling process. In this work, we examine the Ribbon structure, namely its ENA fluxes, angular extent, width, and circularity properties for two years, 2009 and 2019, representative of the declining phases of two adjacent solar cycles. We find that, (i) the Ribbon ENA fluxes have recovered in the nose direction and south of it down to ~25° (for energies below 1.7 keV) and not at mid and high ecliptic latitudes; (ii) the Ribbon width exhibits significant variability as a function of azimuthal angle; (iii) circularity analysis suggests that the 2019 Ribbon exhibits a statistically consistent radius with that in 2009. The Ribbon's partial recovery is aligned with the consensus of a heliosphere with its closest point being southward of the nose region. The large variability of the Ribbon width as a function of azimuth in 2019 compared to 2009 is likely indicative of small-scale processes within the Ribbon.

Keywords: heliosphere; solar wind; pickup ions; heliosheath; interstellar magnetic fields; solar cycle
GRB 200716C: Evidence for a Short Burst Being Lensed

A tiny fraction of observed gamma-ray bursts (GRBs) may be lensed. The time delays induced by the gravitational lensing are milliseconds to seconds if the point lenses are intermediate-mass black holes. The prompt emission of the lensed GRBs, in principle, should have repeated pulses with identical light curves and spectra but different fluxes and slightly offset positions. In this work, we search for such candidates within the GRBs detected by Fermi/GBM, Swift/Burst Alert Telescope, and HXMT/HE and report the identification of an attractive event GRB 200716C that consists of two pulses. Both the autocorrelation analysis and the Bayesian inference of the prompt emission light curve are in favor of the gravitational-lensing scenario. Moreover, the spectral properties of the two pulses are rather similar and follow the so-called Amati relation of short GRBs rather than long-duration bursts. The measured flux ratios between the two pulses are nearly constant in all channels, as expected from gravitational lensing. We therefore suggest that the long-duration burst GRB 200716C was a short event being lensed. The redshifted mass of the lens was estimated to be ${4.25}_{-1.36}^{+2.46}\times {10}^{5}\,{M}_{\odot }$ (90% credibility). If correct, this could point toward the existence of an intermediate-mass black hole along the line of sight of GRB 200716C.

Keywords: gamma-ray bursts; gravitational lensing
High-resolution UV/Optical/IR Imaging of Jupiter in 2016-2019

Imaging observations of Jupiter with high spatial resolution were acquired beginning in 2016, with a cadence of 53 days to coincide with atmospheric observations of the Juno spacecraft during each perijove pass. The Wide Field Camera 3 (WFC3) aboard the Hubble Space Telescope (HST) collected Jupiter images from 236 to 925 nm in 14 filters. The Near-Infrared Imager (NIRI) at Gemini North imaged Jovian thermal emission using a lucky-imaging approach (co-adding the sharpest frames taken from a sequence of short exposures), using the M' filter at 4.7 μm. We discuss the data acquisition and processing and an archive collection that contains the processed WFC3 and NIRI data (doi:10.17909/T94T1H). Zonal winds remain steady over time at most latitudes, but significant evolution of the wind profile near 24°N in 2016 and near 15°S in 2017 was linked with convective superstorm eruptions. Persistent mesoscale waves were seen throughout the 2016-2019 period. We link groups of lightning flashes observed by the Juno team with water clouds in a large convective plume near 15°S and in cyclones near 35°N-55°N. Thermal infrared maps at the 10.8 micron wavelength obtained at the Very Large Telescope show consistent high brightness temperature anomalies, despite a diversity of aerosol properties seen in the HST data. Both WFC3 and NIRI imaging reveal depleted aerosols consistent with downwelling around the periphery of the 15°S storm, which was also observed by the Atacama Large Millimeter/submillimeter Array. NIRI imaging of the Great Red Spot shows that locally reduced cloud opacity is responsible for dark features within the vortex. The HST data maps multiple concentric polar hoods of high-latitude hazes.

Keywords: jupiter; planetary atmospheres; time series analysis; direct imaging; seasonal phenomena; astrophysical fluid dynamics; hubble space telescope; ground-based astronomy; atmospheric variability; earth's clouds
Consistent Dynamical and Stellar Masses with Potential Light IMF in Massive Quiescent Galaxies at 3 < z < 4 Using Velocity Dispersions Measurements with MOSFIRE

We present the velocity dispersion measurements of four massive ∼1011M⊙ quiescent galaxies at 3.2 < z < 3.7 based on deep H and K-band spectra using the Keck/MOSFIRE near-infrared spectrograph. We find high velocity dispersions of order σe ∼250 km s-1 based on strong Balmer absorption lines, and we combine these with size measurements based on HST/WFC3 F160W imaging to infer dynamical masses. The velocity dispersions are broadly consistent with the high stellar masses and small sizes. Together with evidence for quiescent stellar populations, the spectra confirm the existence of a population of massive galaxies that formed rapidly and quenched in the early universe z > 4. Investigating the evolution at constant velocity dispersion between z ∼3.5 and z ∼2, we find a large increase in effective radius 0.35 ± 0.12 dex and in dynamical-to-stellar mass ratio $\langle \mathrm{log}({M}_{\mathrm{dyn}}/M* )\rangle $ of 0.33 ± 0.08 dex, with low expected contribution from dark matter. The dynamical masses for our z ∼3.5 sample are consistent with the stellar masses for a Chabrier initial mass function (IMF), with the ratio $\langle \mathrm{log}({M}_{\mathrm{dyn}}/{M}_{\mathrm{Ch}}^{* })\rangle =-0.13\pm 0.10$ dex suggesting an IMF lighter than Salpeter may be common for massive quiescent galaxies at z > 3. This is surprising in light of the Salpeter or heavier IMFs found for high velocity dispersion galaxies at z ∼2 and cores of present-day ellipticals, which these galaxies are thought to evolve into. Future imaging and spectroscopic observations with resolved kinematics using the upcoming James Webb Space Telescope could rule out potential systematics from rotation and confirm these results.

Keywords: galaxy evolution; galaxy kinematics; high-redshift galaxies
High-resolution Optical Spectroscopic Observations of Comet 21P/Giacobini-Zinner in Its 2018 Apparition

Comet 21P/Giacobini-Zinner is a peculiar comet from the viewpoints of the chemical and physical properties of its dust grains. We conduct optical high-resolution spectroscopic observations of the comet. The intensity ratios of forbidden oxygen lines (at 557.7, 630.0, and 636.4 nm) and ortho-to-para abundance ratios (OPRs) of water cations (H2O+) and amidogen radicals (NH2) are obtained while only the upper limit for 14N/15N in the amidogen radical is restricted. The OPRs of H2O+ and NH2 are similar to those of other comets, although the real meaning of these OPRs is still debated. Based on the observation of the forbidden emission lines of oxygen atoms, it can be concluded that the comet is depleted in CO2. In consideration with the depletion in other highly volatile species found in the near-infrared region and the presence of complex organics in comet 21P/Giacobini-Zinner, this comet might form in a warmer region in the solar nebula compared with other comets.

Keywords: comets; short period comets; spectroscopy; comet volatiles
Light Curve and Period Change Analysis of KIC3347485

High precision photometry with the space-based Kepler telescope offers an opportunity to analyze the physical processes occurring in stars in detail. In this study, we examined the light curve of the Kepler binary system KIC 3347485, which is a semi-detached binary system. We calculated minima and maxima times of four years of Kepler observation of this system using our newly developed Python code. We did period change analysis (O - C) of this system, and we discuss the existence of a possible third or even fourth component.

Keywords: variable star period change; eclipsing binary stars; stellar photometry; stellar evolution
Searching for Nuclear Obscuration in the Infrared Spectra of Nearby FR I Radio Galaxies

How do active galactic nuclei with low optical luminosities produce powerful radio emission? Recent studies of active galactic nuclei with moderate radio and low optical luminosities (Fanaroff & Riley class I, FR I) searching for broad nuclear emission lines in polarized light, as predicted by some active galactic nucleus unification models, have found heterogeneous results. These models typically consist of a central engine surrounded by a torus of discrete dusty clouds. These clouds would absorb and scatter optical emission, blocking broad nuclear emission lines, and reradiate in mid-infrared. Some scattered broad-line emission may be observable, depending on geometry, which would be polarized. We present a wide-band infrared spectroscopic analysis of 10 nearby FR I radio galaxies to determine whether there is significant emission from a dusty obscuring structure. We used Markov Chain Monte Carlo algorithms to decompose Spitzer/IRS spectra of our sample. We constrained the wide-band behavior of our models with photometry from the Two Micron All Sky Survey, Spitzer/IRAC, Spitzer/MIPS, and Herschel/SPIRE. We find that one galaxy is best fit by a clumpy torus and three others show some thermal mid-infrared component. This suggests that in those three there is likely some obscuring dust structure that is inconsistent with our torus models and there must be some source of photons heating the dust. We conclude that 40% of our FR I radio galaxies show evidence of obscuring dusty material, possibly some other form of hidden broad-line nucleus, but only 10% favor the clumpy torus model specifically.

Keywords: spectroscopy; low-luminosity active galactic nuclei; infrared astronomy; markov chain monte carlo
Local Star-forming Galaxies Build Up Central Mass Concentration Most Actively near M ∗ = 1010 M ⊙

To understand in what mass regime star-forming galaxies (SFGs) build up central mass concentration most actively, we present a study on the luminosity-weighted stellar age radial gradient (∇age) distribution of ~3600 low-redshift SFGs using the MaNGA Pipe3D data available in Data Release 17 from the Sloan Digital Sky Survey. The mean age gradient is negative, with ∇age = -0.14 log Gyr/R e, consistent with the inside-out disk formation scenario. Specifically, SFGs with positive ∇age consist of ~28% at log (M */M ⊙) < 9.5, while this fraction rises up to its peak (~40%) near log (M */M ⊙) = 10 and then decreases to ~15% at log (M */M ⊙) = 11. At fixed M *, SFGs with positive ∇age typically have more compact sizes and more centrally concentrated star formation than their counterparts, indicative of recent central mass buildup events. These results suggest that the buildup of central stellar mass concentration in local SFGs is mostly active near M * = 1010 M ⊙. Our findings provide new insights into the origin of morphological differences between low-mass and high-mass SFGs.

Keywords: galaxy evolution
Alpha Element Populations Among Local Halo Stars

Previous studies have shown that the halo of the Milky Way galaxy is made up of two distinct stellar populations, one from dissipative collapse and the other accreted. Elemental abundances with small relative uncertainties along with kinematics are determined for 20 local halo stars in the metallicity range -2.2 ≤ [Fe/H] ≤-1.2. Stars with metallicities [Fe/H] > -1.75 show clear separation into high-α and low-α groups. New results extend the work of Nissen & Schuster to the elements Co and K and to lower metallicities. The five program stars with [Fe/H] < -1.75 appear to follow the low-α sequence and may be distinguishable by lower [Ba/Fe] abundances. The results for potassium help to clarify its behavior for -2.2 ≤ [Fe/H] ≤ -1.2 with [K/Fe] ~ 0.25 and approximately constant with [Fe/H]. Evidence is discussed regarding the cause of the low [α/Fe] abundances, i.e., whether a lower star-formation rate resulted in slower chemical evolution or if the initial mass function was deficient in high-mass stars. The low-α stars show larger dispersions in U and W velocities, as expected for an accreted population, but unlike Nissen & Schuster we find that the high-α and low-α stars do not have significantly different net orbital rotation (V).

Keywords: stellar abundances; population ii stars; milky way stellar halo
The Search for Thermonuclear Transients from the Tidal Disruption of a White Dwarf by an Intermediate-mass Black Hole

The close encounter of a white dwarf (WD) with a black hole (BH) could result in the tidal disruption of the WD. During this encounter, the WD can undergo a thermonuclear explosion due to its tidal compression, resulting in an optical transient similar to a Type Ia supernova, hereafter a Ia-TDE. Nevertheless, this will only be physically observable if the BH is ≲105 M ⊙. Finding a Ia-TDE would therefore imply the discovery of an intermediate-mass BH (IMBH) ≲105 M ⊙. Here, we search the entire Zwicky Transient Facility alert stream for these elusive Ia-TDEs. We restrict our search to nuclear transients in dwarf galaxies, the likely sites for IMBHs, and find a total of six possible nuclear Ia-TDE candidates. We find SN 2020lrt to be the most likely Ia-TDE candidate, thanks to its strong resemblance to light-curve and spectroscopic models of Ia-TDEs. We measure the stellar masses of the dwarf galaxies hosting these transients to be ≲109 M ⊙; if confirmed to harbor BHs, these would prove the existence of IMBHs in some of the lowest-mass galaxies known. Additionally, we searched for off-nuclear Ia-TDEs, but were unable to find more robust candidates in the outskirts of galaxies than in their nuclei. This supports the hypothesis that the nuclear Ia-TDE candidates are WDs tidally compressed by IMBHs in the cores of galaxies, as opposed to a class of transient that can occur anywhere in a galaxy. We have laid the groundwork to systematically search for Ia-TDE candidates in existing and future time-domain surveys. The rapid characterization of their nature will result in not only the confirmation of a Ia-TDE, but also the unambiguous discovery of bona fide IMBHs.

Keywords: black hole physics; supernovae; white dwarf stars; surveys
Cycle-StarNet: Bridging the Gap between Theory and Data by Leveraging Large Data Sets

Advancements in stellar spectroscopy data acquisition have made it necessary to accomplish similar improvements in efficient data analysis techniques. Current automated methods for analyzing spectra are either (a) data driven, which requires prior knowledge of stellar parameters and elemental abundances, or (b) based on theoretical synthetic models that are susceptible to the gap between theory and practice. In this study, we present a hybrid generative domain-adaptation method that turns simulated stellar spectra into realistic spectra by applying unsupervised learning to large spectroscopic surveys. We apply our technique to the APOGEE H-band spectra at R = 22,500 and the Kurucz synthetic models. As a proof of concept, two case studies are presented. The first is the calibration of synthetic data to become consistent with observations. To accomplish this, synthetic models are morphed into spectra that resemble observations, thereby reducing the gap between theory and observations. Fitting the observed spectra shows an improved average ${\chi }_{R}^{2}$ reduced from 1.97 to 1.22, along with a mean residual reduced from 0.16 to -0.01 in normalized flux. The second case study is the identification of the elemental source of missing spectral lines in the synthetic modeling. A mock data set is used to show that absorption lines can be recovered when they are absent in one of the domains. This method can be applied to other fields that use large data sets and are currently limited by modeling accuracy. The code used in this study is made publicly available on GitHub (https://github.com/teaghan/Cycle_SN).

Keywords: computational methods; neural networks; spectroscopy; spectral line identification
The Impact of Metallicity on the Evolution of the Rotation and Magnetic Activity of Sun-like Stars

The rotation rates and magnetic activity of Sun-like and low-mass (≲1.4M⊙) main-sequence stars are known to decline with time, and there now exist several models for the evolution of rotation and activity. However, the role that chemical composition plays during stellar spin-down has not yet been explored. In this work, we use a structural evolution code to compute the rotational evolution of stars with three different masses (0.7, 1.0, and 1.3 M⊙) and six different metallicities, ranging from [Fe/H] = -1.0 to [Fe/H] = +0.5. We also implement three different wind-braking formulations from the literature (two modern and one classical) and compare their predictions for rotational evolution. The effect that metallicity has on stellar structural properties, and in particular the convective turnover timescale, leads the two modern wind-braking formulations to predict a strong dependence of the torque on metallicity. Consequently, they predict that metal-rich stars spin down more effectively at late ages (≳1 Gyr) than metal-poor stars, and the effect is large enough to be detectable with current observing facilities. For example, the formulations predict that a Sun-like (solar-mass and solar-aged) star with [Fe/H] = -0.3 will have a rotation period of less than 20 days. Even though old, metal-poor stars are predicted to rotate more rapidly at a given age, they have larger Rossby numbers and are thus expected to have lower magnetic activity levels. Finally, the different wind-braking formulations predict quantitative differences in the metallicity dependence of stellar rotation, which may be used to test them.

Keywords: stellar rotation; metallicity; stellar evolution; stellar activity
Cosmic Reionization on Computers: Baryonic Effects on Halo Concentrations during the Epoch of Reionization

Baryons both increase halo concentration through adiabatic contraction and expel mass through feedback processes. However, it is not well understood how the radiation fields prevalent during the epoch of reionization affect the evolution of concentration in dark matter halos. We investigate how baryonic physics during the epoch of reionization modify the structure of dark matter halos in the Cosmic Reionization On Computers (CROC) simulations. We use two different measures of halo concentration to quantify the effects. We compare concentrations of halos matched between full-physics simulations and dark-matter-only simulations with identical initial conditions between 5 ≤ z ≤ 9. Baryons in full-physics simulations do pull matter toward the center, increasing the maximum circular velocity compared to dark-matter-only simulations. However, their overall effects are much less than if all the baryons were simply centrally concentrated indicating that heating processes efficiently counteract cooling effects. Finally, we show that the baryonic effects on halo concentrations at z ≈ 5 are relatively insensitive to environmental variations of reionization history. These results are pertinent to models of galaxy-halo connection during the epoch of reionization.

Keywords: reionization; galaxy formation
Interpretation of the Observed Neutrino Emission from Three Tidal Disruption Events

Three Tidal Disruption Event candidates (AT2019dsg, AT2019fdr, and AT2019aalc) have been associated with high-energy astrophysical neutrinos in multimessenger follow-ups. In all cases, the neutrino observation occurred ${ \mathcal O }(100)$ days after the maximum of the optical-ultraviolet (OUV) luminosity. We discuss unified fully time-dependent interpretations of the neutrino signals where the neutrino delays are not a statistical effect, but rather the consequence of a physical scale of the post-disruption system. Noting that X-ray flares and infrared (IR) dust echoes have been observed in all cases, we consider three models in which quasi-isotropic neutrino emission is due to the interactions of accelerated protons of moderate, medium, and ultra-high energies with X-rays, OUV, and IR photons, respectively. We find that the neutrino time delays can be well described in the X-ray model assuming magnetic confinement of protons in a calorimetric approach if the unobscured X-ray luminosity is roughly constant over time, and in the IR model, where the delay is directly correlated with the time evolution of the echo luminosity (for which a model is developed here). The OUV model exhibits the highest neutrino production efficiency. In all three models, the highest neutrino fluence is predicted for AT2019aalc, due to its high estimated supermassive black hole mass and low redshift. All models result in diffuse neutrino fluxes that are consistent with observations.

Keywords: neutrino astronomy; tidal disruption