adsabs/SciX_UAT_keywords huggingface dataset:
A Unified Spectroscopic and Photometric Model to Infer Surface Inhomogeneity: Application to Luhman 16B

Extremely large telescopes (ELTs) provide an opportunity to observe surface inhomogeneities for ultracool objects including M dwarfs, brown dwarfs (BDs), and gas giant planets via Doppler imaging and spectrophotometry techniques. These inhomogeneities can be caused by star spots, clouds, and vortices. Star spots and associated stellar flares play a significant role in habitability, either stifling life or catalyzing abiogenesis depending on the emission frequency, magnitude, and orientation. Clouds and vortices may be the source of spectral and photometric variability observed at the L/T transition of BDs and are expected in gas giant exoplanets. We develop a versatile analytical framework to model and infer surface inhomogeneities that can be applied to both spectroscopic and photometric data. This model is validated against a slew of numerical simulations. Using archival spectroscopic and photometric data, we infer starspot parameters (location, size, and contrast) and generate global surface maps for Luhman 16B (an early T dwarf and one of our solar system's nearest neighbors at a distance of ≈2 pc). We confirm previous findings that Luhman 16B's atmosphere is inhomogeneous with time-varying features. In addition, we provide tentative evidence of longer timescale atmospheric structures such as dark equatorial and bright midlatitude to polar spots. These findings are discussed in the context of atmospheric circulation and dynamics for ultracool dwarfs. Our analytical model will be valuable in assessing the feasibility of using ELTs to study surface inhomogeneities of gas giant exoplanets and other ultracool objects.

Keywords: doppler imaging; m dwarf stars; brown dwarfs; spectrophotometry; exoplanet atmospheres
Probing the Time Variation of a Fine Structure Constant Using Galaxy Clusters and the Quintessence Model

We explore a possible time variation of the fine structure constant (α ≅ e2/ℏc) using the Sunyaev-Zel'dovich effect measurements of galaxy clusters along with their X-ray observations. Specifically, the ratio of the integrated Comptonization parameter ${Y}_{\mathrm{SZ}}{D}_{A}^{2}$ and its X-ray counterpart YX is used as an observable to constrain the bounds on the variation of α. Considering the violation of the cosmic distance duality relation, this ratio depends on the fine structure constant of ~ α3. We use the quintessence model to provide the origin of α time variation. In order to give a robust test on α variation, two galaxy cluster samples, the 61 clusters provided by the Planck collaboration and the 58 clusters detected by the South Pole Telescope (SPT), are collected for analysis. Their X-ray observations are given by the XMM-Newton survey. Our results give $\zeta =-{0.203}_{-0.099}^{+0.101}$ for the Planck sample and $\zeta =-{0.043}_{-0.148}^{+0.165}$ for the SPT sample, indicating that α is constant with redshift within 3σ and 1σ for the two samples, respectively.

Keywords: quintessence; cosmological models; galaxy clusters
Librating Kozai–Lidov Cycles with a Precessing Quadrupole Potential Are Analytically Approximately Solved

The very long term evolution of the hierarchical restricted three-body problem with a slightly aligned precessing quadrupole potential is investigated analytically for librating Kozai–Lidov cycles (KLCs). Klein & Katz presented an analytic solution for the approximate dynamics on a very long timescale developed in the neighborhood of the KLCs' fixed point where the eccentricity vector is close to unity and aligned (or anti-aligned) with the quadrupole axis and for a precession rate equal to the angular frequency of the secular Kozai–Lidov equations around this fixed point. In this paper, we generalize the analytic solution to encompass a wider range of precession rates. We show that the analytic solution approximately describes the quantitative dynamics for systems with librating KLCs for a wide range of initial conditions, including values that are far from the fixed point, which is somewhat unexpected. In particular, using the analytic solution, we map the strikingly rich structures that arise for precession rates similar to the Kozai–Lidov timescale (ratio of a few).

Keywords: newtonian gravitation; keplerian orbit; eccentricity; three-body problem
Hitting a New Low: The Unique 28 hr Cessation of Accretion in the TESS Light Curve of YY Dra (DO Dra)

We present the Transiting Exoplanet Surveying Satellite light curve of the intermediate polar YY Draconis (YY Dra, also known as DO Dra). The power spectrum indicates that while there is stream-fed accretion for most of the observational period, there is a day-long, flat-bottomed low state at the beginning of 2020 during which the only periodic signal is ellipsoidal variation and there is no appreciable flickering. We interpret this low state to be a complete cessation of accretion, a phenomenon that has been observed only once before in an intermediate polar. Simultaneous ground-based observations of this faint state establish that when accretion is negligible, YY Dra fades to g = 17.37 ± 0.12, which we infer to be the magnitude of the combined photospheric contributions of the white dwarf and its red dwarf companion. Using survey photometry, we identify additional low states in 2018-2019 during which YY Dra repeatedly fades to-but never below-this threshold. This implies relatively frequent cessations in accretion. Spectroscopic observations during future episodes of negligible accretion can be used to directly measure the field strength of the white dwarf by Zeeman splitting. Separately, we search newly available catalogs of variable stars in an attempt to resolve the long-standing dispute over the proper identifier of this system.

Keywords: cataclysmic variable stars; white dwarf stars; dq herculis stars; dq stars; accretion; stellar magnetic fields
Photometric Variability of the Pre-main-sequence Stars toward the Sh 2-190 Region

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, Rc, and Ic bands covering an area of ~18'4 × 18'4 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.

Keywords: variable stars; pre-main sequence
Ultraviolet Spectroscopy and TARDIS Models of the Broad-lined Type Ic Supernova 2014ad

Few published ultraviolet (UV) spectra exist for stripped-envelope supernovae and none to date for broad-lined Type Ic supernovae (SNe Ic-bl). These objects have extremely high ejecta velocities and are the only supernova type directly linked to gamma-ray bursts (GRBs). Here we present two epochs of HST/STIS spectra of the SN Ic-bl 2014ad, the first UV spectra for this class. We supplement this with 26 new epochs of ground-based optical spectra, augmenting a rich spectral time series. The UV spectra do not show strong features and are consistent with broadened versions of other SN Ic spectra observed in the UV. We measure Fe II 5169 Å velocities and show that SN 2014ad has even higher ejecta velocities than most SNe Ic both with and without observed GRBs. We construct models of the SN 2014ad UV+optical spectra using TARDIS, a 1D Monte Carlo radiative-transfer spectral synthesis code. The models fit the data well at multiple epochs in the optical but underestimate the flux in the UV, likely due to simplifying assumptions. We find that high densities at high velocities are needed to reproduce the spectra, with ~3 M ⊙ of material at v > 22,000 km s-1, assuming spherical symmetry. Our nebular line fits suggest a steep density profile at low velocities. Together, these results imply a higher total ejecta mass than estimated from previous light-curve analysis and expected from theory. This may be reconciled by a flattening of the density profile at low velocity and extra emission near the center of the ejecta.

Keywords: supernovae; type ic supernovae
oMEGACat. I. MUSE Spectroscopy of 300,000 Stars within the Half-light Radius of ω Centauri

Omega Centauri (ω Cen) is the most massive globular cluster of the Milky Way and has been the focus of many studies that reveal the complexity of its stellar populations and kinematics. However, most previous studies have used photometric and spectroscopic data sets with limited spatial or magnitude coverage, while we aim to investigate it having full spatial coverage out to its half-light radius and stars ranging from the main sequence to the tip of the red giant branch. This is the first paper in a new survey of ω Cen that combines uniform imaging and spectroscopic data out to its half-light radius to study its stellar populations, kinematics, and formation history. In this paper, we present an unprecedented MUSE spectroscopic data set combining 87 new MUSE pointings with previous observations collected from guaranteed time observations. We extract spectra of more than 300,000 stars reaching more than 2 magnitudes below the main-sequence turnoff. We use these spectra to derive metallicity and line-of-sight velocity measurements and determine robust uncertainties on these quantities using repeat measurements. Applying quality cuts we achieve signal-to-noise ratios (S/Ns) of 16.47/73.51 and mean metallicity errors of 0.174/0.031 dex for the main-sequence stars (18 mag <mag F625W < 22 mag) and red giant branch stars (16 mag <mag F625W < 10 mag), respectively. We correct the metallicities for atomic diffusion and identify foreground stars. This massive spectroscopic data set will enable future studies that will transform our understanding of ω Cen, allowing us to investigate the stellar populations, ages, and kinematics in great detail.

Keywords: galaxy nuclei; globular star clusters; star clusters
Neutrino Production Associated with Late Bumps in Gamma-Ray Bursts and Potential Contribution to Diffuse Flux at IceCube

IceCube has detected many TeV-PeV neutrinos, but their astrophysical origins remain largely unknown. Motivated by the observed late-time X-ray/optical bumps in some gamma-ray bursts (GRBs), we examine the correlation between IceCube neutrinos and GRBs allowing delayed neutrinos ∼days after the prompt gamma-rays. Although we have not found any definitive correlation, up to ∼10% of the events observed so far at IceCube may have been neutrinos produced by the late-time GRB activities at ∼1 day. Assuming a connection between some IceCube events and the late GRB bumps, we show in a model-independent way that GRB sites capable of producing late ∼PeV neutrinos should be nonrelativistic or mildly relativistic. We estimate the diffuse neutrino flux from such sources and find that they can possibly account for a few IceCube events. Future observations of high-energy neutrinos and late-time GRB afterglows can further test the above proposed connection.

Keywords: neutrino astronomy; gamma-ray bursts; high energy astrophysics
Observation of a Magnetic Switchback in the Solar Corona

Switchbacks are sudden, large radial deflections of the solar wind magnetic field, widely revealed in interplanetary space by the Parker Solar Probe. The switchbacks' formation mechanism and sources are still unresolved, although candidate mechanisms include Alfvénic turbulence, shear-driven Kelvin-Helmholtz instabilities, interchange reconnection, and geometrical effects related to the Parker spiral. This Letter presents observations from the Metis coronagraph on board a Solar Orbiter of a single large propagating S-shaped vortex, interpreted as the first evidence of a switchback in the solar corona. It originated above an active region with the related loop system bounded by open-field regions to the east and west. Observations, modeling, and theory provide strong arguments in favor of the interchange reconnection origin of switchbacks. Metis measurements suggest that the initiation of the switchback may also be an indicator of the origin of slow solar wind.

Keywords: solar corona; solar magnetic reconnection; solar magnetic fields; magnetohydrodynamics; solar coronal waves; slow solar wind
Lowly Polarized Light from a Highly Magnetized Jet of GRB 190114C

We report multicolor optical imaging and polarimetry observations of the afterglow of the first TeV-detected gamma-ray burst (GRB), GRB 190114C, using the RINGO3 and MASTER II polarimeters. Observations begin 31 s after the onset of the GRB and continue until ∼7000 s postburst. The light curves reveal a chromatic break at ∼400-500 s, with initial temporal decay α = 1.669 ± 0.013 flattening to α ∼ 1 postbreak, which we model as a combination of reverse and forward shock components with magnetization parameter RB ∼ 70. The observed polarization degree decreases from 7.7% ± 1.1% to 2%-4% 52-109 s postburst and remains steady at this level for the subsequent ∼2000 s at a constant position angle. Broadband spectral energy distribution modeling of the afterglow confirms that GRB 190114C is highly obscured (AV,HG = 1.49 ± 0.12 mag; NH HG = (9.0 ± 0.03) × 1022 cm-2). We interpret the measured afterglow polarization as intrinsically low and dominated by dust - in contrast to the P > 10% measured previously for other GRB reverse shocks - with a small contribution from polarized prompt photons in the first minute. We test whether first- and higher-order inverse Compton scattering in a magnetized reverse shock can explain the low optical polarization and subteraelectronvolt emission but conclude that neither is explained in the reverse shock inverse Compton model. Instead, the unexpectedly low intrinsic polarization degree in GRB 190114C can be explained if large-scale jet magnetic fields are distorted on timescales prior to reverse shock emission.

Keywords: high energy astrophysics; gamma-ray bursts; magnetic fields; polarimetry; shocks; jets; photometric systems
The Spectral ANalog of Dwarfs (SAND): New Model Atmospheres with Varying Chemistry for Galactic Archaeology with Ultracool Dwarfs

The atmospheres of Ultracool Dwarfs (UCDs) are dominated by molecular chemistry, which makes their spectra and photometry particularly sensitive to elemental abundances. With lifespans in excess of the age of the universe, UCDs serve as chemical tracers in every component of the Milky Way. In this study, we present the Spectral ANalog of Dwarfs (SAND) grid of low-temperature model atmospheres that span T eff from 700 to 4000 K, $\mathrm{log}(g)$ from 4.0 to 6.0, [Fe/H] from ‑2.4 to +0.3, and a range of [α/Fe] that matches the Galactic distribution inferred from earlier spectroscopic surveys. The SAND grid primarily aims to model the spectra of brown dwarfs in the halo and thick disk of the Milky Way, and metal-poor UCDs in globular clusters.

Keywords: brown dwarfs; stellar atmospheres; galactic archaeology
Galaxy Core Formation by Supermassive Black Hole Binaries: The Importance of Realistic Initial Conditions and Galaxy Morphology

The binding energy liberated by the coalescence of supermassive black hole (SMBH) binaries during galaxy mergers is thought to be responsible for the low density cores often found in bright elliptical galaxies. We use high-resolution N-body and Monte Carlo techniques to perform single and multistage galaxy merger simulations and systematically study the dependence of the central galaxy properties on the binary mass ratio, the slope of the initial density cusps, and the number of mergers experienced. We study both the amount of depleted stellar mass (or mass deficit), Mdef, and the radial extent of the depleted region, rb. We find that rb ≃ rSOI and that Mdef varies in the range of 0.5-4M•, with rSOI the influence radius of the remnant SMBH and M• its mass. The coefficients in these relations depend weakly on the binary mass ratio and remain remarkably constant through subsequent mergers. We conclude that the core size and mass deficit do not scale linearly with the number of mergers, making it hard to infer merger histories from observations. On the other hand, we show that both Mdef and rb are sensitive to the morphology of the galaxy merger remnant, and that adopting spherical initial conditions, as done in early work, leads to misleading results. Our models reproduce the range of values for Mdef found in most observational work, but span nearly an order-of magnitude range around the true ejected stellar mass.

Keywords: galaxy formation; galaxy kinematics; galaxy dynamics; galaxy nuclei; elliptical galaxies; giant elliptical galaxies; stellar cores; galaxy evolution; supermassive black holes; gravitational waves
Evidence of Weak Circumstellar Medium Interaction in the Type II SN 2023axu

We present high-cadence photometric and spectroscopic observations of SN 2023axu, a classical Type II supernova with an absolute V-band peak magnitude of –17.2 ± 0.1 mag. SN 2023axu was discovered by the Distance Less Than 40 Mpc (DLT40) survey within 1 day of the last nondetection in the nearby galaxy NGC 2283 at 13.7 Mpc. We modeled the early light curve using a recently updated shock cooling model that includes the effects of line blanketing and found the explosion epoch to be MJD 59971.48 ± 0.03 and the probable progenitor to be a red supergiant. The shock cooling model underpredicts the overall UV data, which point to a possible interaction with circumstellar material. This interpretation is further supported by spectral behavior. We see a ledge feature around 4600 Å in the very early spectra (+1.1 and +1.5 days after the explosion), which can be a sign of circumstellar interaction. The signs of circumstellar material are further bolstered by the presence of absorption features blueward of Hα and Hβ at day >40, which is also generally attributed to circumstellar interaction. Our analysis shows the need for high-cadence early photometric and spectroscopic data to decipher the mass-loss history of the progenitor.

Keywords: core-collapse supernovae; type ii supernovae; red supergiant stars; stellar mass loss; circumstellar matter
The Ultraviolet to Mid-infrared Extinction Law of the Taurus Molecular Cloud Based on the Gaia DR3, GALEX, APASS, Pan-STARRS1, 2MASS, and WISE Surveys

Interstellar-dust extinction law is essential for interpreting observations. In this work, we investigate the ultraviolet (UV)-mid-infrared (IR) extinction law of the Taurus molecular cloud and its possible variations. We select 504,988 dwarf stars (4200 K ≤ T eff ≤ 8000 K) and 4757 giant stars (4200 K ≤ T eff ≤ 5200 K) based on the stellar parameters of Gaia DR3 as tracers. We establish the T eff-intrinsic color relations and determine the intrinsic color indices and color excesses for different types of stars. In the determination of color excess ratios (CERs), we analyze and correct the curvature of CERs and derive the UV-mid-IR CERs of 16 bands. We consider different effective wavelengths for different types of stars when converting CERs to relative extinction and obtain the extinction law with a better wavelength resolution. In addition, we analyze the possible regional variation of extinction law and derive the average extinction law of R V = 3.13 ± 0.32 for the Taurus molecular cloud. Only 0.9% of subregions have deviations >3σ, indicating limited regional variation in the extinction law. We also discuss the effect of Gaia T eff overestimation on the determination of the Taurus extinction law and find that the effect is negligible.

Keywords: interstellar dust extinction; interstellar extinction; interstellar reddening; reddening law
The Sloan Digital Sky Survey Reverberation Mapping Project: Key Results

We present the final data from the Sloan Digital Sky Survey (SDSS) Reverberation Mapping (RM) project, a precursor to the SDSS-V Black Hole Mapper RM program. This data set includes 11 yr photometric and 7 yr spectroscopic light curves for 849 broad-line quasars over a redshift range of 0.1 < z < 4.5 and a luminosity range of L bol = 1044‑47.5 erg s‑1, along with spectral and variability measurements. We report 23, 81, 125, and 110 RM lags (relative to optical continuum variability) for broad Hα, Hβ, Mg II, and C IV using the SDSS-RM sample, spanning much of the luminosity and redshift ranges of the sample. Using 30 low-redshift RM active galactic nuclei with dynamical-modeling black hole masses, we derive a new estimate of the average virial factor of $\left\langle \mathrm{log}f\right\rangle =0.62\pm 0.07$ for the line dispersion measured from the rms spectrum. The intrinsic scatter of individual virial factors is 0.31 ± 0.07 dex, indicating a factor of 2 systematic uncertainty in RM black hole masses. Our lag measurements reveal significant R–L relations for Hβ and Mg II at high redshift, consistent with the latest measurements based on heterogeneous samples. While we are unable to robustly constrain the slope of the R–L relation for C IV given the limited dynamic range in luminosity, we found substantially larger scatter in C IV lags at fixed L 1350. Using the SDSS-RM lag sample, we derive improved single-epoch (SE) mass recipes for Hβ, Mg II, and C IV, which are consistent with their respective RM masses as well as between the SE recipes from two different lines, over the luminosity range probed by our sample. The new Hβ and Mg II recipes are approximately unbiased estimators at given RM masses, but there are systematic biases in the C IV recipe. The intrinsic scatter of SE masses around RM masses is ∼0.45 dex for Hβ and Mg II, increasing to ∼0.58 dex for C IV.

Keywords: reverberation mapping; surveys; quasars