adsabs/SciX_UAT_keywords huggingface dataset:
Outlier Detection in the DESI Bright Galaxy Survey

We present an unsupervised search for outliers in the Bright Galaxy Survey (BGS) data set from the DESI Early Data Release. This analysis utilizes an autoencoder to compress galaxy spectra into a compact, redshift-invariant latent space, and a normalizing flow to identify low-probability objects. The most prominent outliers show distinctive spectral features, such as irregular or double-peaked emission lines or originate from galaxy mergers, blended sources, and rare quasar types, including one previously unknown broad absorption line system. A significant portion of the BGS outliers are stars spectroscopically misclassified as galaxies. By building our own star model trained on spectra from the DESI Milky Way Survey, we have determined that the misclassification likely stems from the principle component analysis of stars in the DESI pipeline. To aid follow-up studies, we make the full probability catalog of all BGS objects and our pretrained models publicly available.

Keywords: galaxy spectroscopy; outlier detection
Latent Stochastic Differential Equations for Modeling Quasar Variability and Inferring Black Hole Properties

Quasars are bright and unobscured active galactic nuclei (AGN) thought to be powered by the accretion of matter around supermassive black holes at the centers of galaxies. The temporal variability of a quasar's brightness contains valuable information about its physical properties. The UV/optical variability is thought to be a stochastic process, often represented as a damped random walk described by a stochastic differential equation (SDE). Upcoming wide-field telescopes such as the Rubin Observatory Legacy Survey of Space and Time (LSST) are expected to observe tens of millions of AGN in multiple filters over a ten year period, so there is a need for efficient and automated modeling techniques that can handle the large volume of data. Latent SDEs are machine learning models well suited for modeling quasar variability, as they can explicitly capture the underlying stochastic dynamics. In this work, we adapt latent SDEs to jointly reconstruct multivariate quasar light curves and infer their physical properties such as the black hole mass, inclination angle, and temperature slope. Our model is trained on realistic simulations of LSST ten year quasar light curves, and we demonstrate its ability to reconstruct quasar light curves even in the presence of long seasonal gaps and irregular sampling across different bands, outperforming a multioutput Gaussian process regression baseline. Our method has the potential to provide a deeper understanding of the physical properties of quasars and is applicable to a wide range of other multivariate time series with missing data and irregular sampling.

Keywords: quasars; active galactic nuclei; neural networks; time series analysis; irregular cadence
Astrometric Accelerations as Dynamical Beacons: A Giant Planet Imaged inside the Debris Disk of the Young Star AF Lep

We present the direct-imaging discovery of a giant planet orbiting the young star AF Lep, a 1.2 M ⊙ member of the 24 ± 3 Myr β Pic moving group. AF Lep was observed as part of our ongoing high-contrast imaging program targeting stars with astrometric accelerations between Hipparcos and Gaia that indicate the presence of substellar companions. Keck/NIRC2 observations in $L^{\prime} $ with the vector vortex coronagraph reveal a point source, AF Lep b, at ≈340 mas, which exhibits orbital motion at the 6σ level over the course of 13 months. A joint orbit fit yields precise constraints on the planet's dynamical mass of ${3.2}_{-0.6}^{+0.7}$ M Jup, semimajor axis of ${8.4}_{-1.3}^{+1.1}$ au, and eccentricity of ${0.24}_{-0.15}^{+0.27}$ . AF Lep hosts a debris disk located at ~50 au, but it is unlikely to be sculpted by AF Lep b, implying there may be additional planets in the system at wider separations. The stellar inclination (i * = ${54}_{-9}^{{+11}^\circ} $ ) and orbital inclination (i o = ${50}_{-12}^{{+9}^\circ} $ ) are in good agreement, which is consistent with the system having spin-orbit alignment. AF Lep b is the lowest-mass imaged planet with a dynamical mass measurement and highlights the promise of using astrometric accelerations as a tool to find and characterize long-period planets.

Keywords: extrasolar gaseous giant planets; astrometric exoplanet detection; direct imaging; orbit determination; debris disks
Unified Picture of the Local Interstellar Magnetic Field from Voyager and IBEX

Prior to the Voyagers' heliopause crossings, models and the community expected the magnetic field to show major rotations across the boundary. Surprisingly, the field showed no significant change in direction from the heliospheric Parker Spiral at either Voyager location. Meanwhile, a major result from the IBEX mission is the derived magnitude and direction of the interstellar field far from the Sun (~1000 au) beyond the influence of the heliosphere. Using a self-consistent model fit to IBEX ribbon data, Zirnstein et al. reported that this "pristine" local interstellar magnetic field has a magnitude of 0.293 nT and direction of 227° in ecliptic longitude and 34.°6 in ecliptic latitude. These values differ by 27% (51%) and 44° (12°) from what Voyager 1 (2) currently observes (as of ~2022.75). While differences are to be expected as the field undrapes away from the heliosphere, the global structure of the draping across hundreds of astronimcal units has not been reconciled. This leads to several questions: How are these distinct sets of observations reconcilable? What is the interstellar magnetic field's large-scale structure? How far out would a future mission need to go to sample the unperturbed field? Here, we show that if realistic errors are included for the difficult-to-calibrate radial field component, the measured transverse field is consistent with that predicted by IBEX, allowing us to answer these questions through a unified picture of the behavior of the local interstellar magnetic field from its draping around the heliopause to its unfolding into the pristine interstellar medium.

Keywords: interplanetary magnetic fields; heliosphere; heliopause; heliosheath; interstellar plasma; plasma astrophysics; space plasmas; interstellar medium; astrosphere interstellar medium interactions
A Catalog of Galactic Multiple Systems with a Red Supergiant and a B Star

Binary systems composed of a red supergiant and a B star are useful probes of stellar evolution. We have searched the literature to create a catalog of 108 Galactic systems of such type, which is presented here.

Keywords: binary stars; catalogs; early-type stars; late-type stars; late-type supergiant stars; red supergiant stars; b stars
Radar Observations of the Arid Meteor Shower Outburst from Comet 15P/Finlay

We report on observations of the anticipated, first time occurrence, Arid meteor shower produced by comet 15P/Finlay. This comet, which has not been noteworthy for over a century, produced two major outbursts of activity during perihelion passage between 2014 December and 2015 January. Various authors predicted that Earth would cross the resulting ejecta on 2021 October 6-7 UT with a radiant in the constellation Ara, optimally placed to be observed from the Southern Hemisphere. We observed two outbursts using the Southern Argentina Agile Meteor Radar-Orbital System: one on 2021 September 29 and a second more dominant peak on 2021 October 7, centered around α = 260.°34, δ = -57.°63 and α = 255.°01, δ = -48.°47, respectively. The 6.5 mag limit flux and zenithal hourly rates were 0.073 meteors km-2 hr-1 and 491 hr-1, respectively. The time of occurrence of the two detected peaks are in good agreement with predictions of this shower reported by several authors, confirming the validity of the models used for the predictions.

Keywords: meteor showers; meteors; radar observations
Tracking the Rapid Opening and Closing of Polar Coronal Holes through IBEX ENA Observations

Fast solar wind (SW) flows outward from polar coronal holes (PCHs). The latitudinal extent of the fast SW varies during different phases of the solar cycle. The fast SW in the inner heliosheath produces a flatter proton spectrum than the slow SW that can be observed through energetic neutral atoms (ENAs) by the Interstellar Boundary Explorer (IBEX). In this study, we investigate the evolution of PCHs as reflected in the high-time resolution ENA flux measurements from IBEX-Hi, where the PCHs are identified by ENA spectral indices <1.8. The ENA spectral index over the poles shows a periodic evolution over the solar cycle 24. The surface area with flatter ENA spectra (<1.8) around the ecliptic south pole increases slightly from 2009-2011 and then decreased gradually from 2012-2014. The PCH completely disappears in 2016 and then starts to appear again starting in 2017, gradually growing until 2019. This evolution shows a clear correlation with the change in the PCH area observed at the Sun once the delay in the ENA observation time is included. In addition, the higher-cadence ENA data at the highest latitudes show a rapid evolution of the ENA spectrum near the south pole in 2014 and 2017. The rapid evolution in 2014 is related to a rapid closing of PCHs in 2012 and that in 2017 is related to a rapid opening of PCHs in late 2014. These results also agree qualitatively with the evolution of the ENA spectral index from simulations using a simple time-dependent heliospheric flow model.

Keywords: solar wind; solar coronal holes; pickup ions; heliosphere; heliosheath; charge exchange ionization; termination shock; spectral index
Variability in Protoplanetary Nebulae. X. Multiyear Periods as an Indicator of Potential Binaries

New observations are presented of four evolved objects that display long, multiyear variations in their light curves. These are interpreted as good evidence of their binary nature, with the modulation caused by the barycenter motion of the evolved star resulting in a periodic obscuration by a circumbinary disk. Although protoplanetary nebulae (PPNe) commonly possess bipolar nebulae, which are thought to be shaped by a binary companion, there are very few PPNe in which a binary companion has been found. Three of the objects in this study appear to be PPNe, IRAS 07253-2001, 08005-2356, and 17542-0603, with long periods of 5.2, 6.9, and 8.2 yr, respectively. The binary nature of IRAS 08005-2356 has recently been confirmed by a radial velocity study. Two samples, one of PPNe and the other of post-AGB star candidates, are investigated for further evidence on how common is a long-period light-curve variation. Both samples suggest such light-curve variations are not common. The fourth object, IRAS 20056+1834 (QY Sge), is an obscured RV Tau variable of the RVb subclass, with a long period of 3.9 yr and pulsation periods of 102.9 and 51.5 days. The period of this object is seen to vary by 2%. Evidence is presented for a recent mass ejection in IRAS 17542-0603.

Keywords: post-asymptotic giant branch stars; evolved stars; binary stars; long period variable stars; rv tauri variable stars; protoplanetary nebulae
A Binary Comb Model for Periodic Fast Radio Bursts

We show that the periodic FRB 180916.J0158+65 can be interpreted by invoking an interacting neutron star binary system with an orbital period of ∼16 days. The FRBs are produced by a highly magnetized pulsar, whose magnetic field is "combed" by the strong wind from a companion star, either a massive star or a millisecond pulsar. The FRB pulsar wind retains a clear funnel in the companion's wind that is otherwise opaque to induced Compton or Raman scatterings for repeating FRB emission. The 4 day active window corresponds to the time when the funnel points toward Earth. The interaction also perturbs the magnetosphere of the FRB pulsar and may trigger emission of FRBs. We derive the physical constraints on the comb and the FRB pulsar from the observations and estimate the event rate of FRBs. In this scenario, a lower limit on the period of observable FRBs is predicted. We speculate that both the intrinsic factors (strong magnetic field and young age) and the extrinsic factor (interaction) may be needed to generate FRBs in neutron star binary systems.

Keywords: radio transient sources; binary pulsars; neutron stars; magnetars; non-thermal radiation sources; relativistic mechanics; magnetic fields; periodic orbit
VLA and NOEMA Views of Bok Globule CB 17: The Starless Nature of a Proposed First Hydrostatic Core Candidate

We use 3 mm continuum NOrthern Extended Millimeter Array and NH3 Very Large Array observations toward the First Hydrostatic Core (FHSC) candidate CB 17 MMS in order to reveal the dust structure and gas properties to 600–1100 au scales and to constrain its evolutionary stage. We do not detect any compact source at the previously identified 1.3 mm point source, despite expecting a minimum signal-to-noise ratio of 9. The gas traced by NH3 exhibits subsonic motions, with an average temperature of 10.4 K. A fit of the radial column density profile derived from the ammonia emission finds a flat inner region of radius ∼1800 au and a central density of ∼6 × 105 cm‑3. Virial and density structure analysis reveals the core is marginally bound (α vir = 0.73). The region is entirely consistent with that of a young starless core, hence ruling out CB 17 MMS as an FHSC candidate. Additionally, the core exhibits a velocity gradient aligned with the major axis, showing an arc-like structure in the position–velocity diagram and an off-center region with high velocity dispersion, caused by two distinct velocity peaks. These features could be due to interactions with the nearby outflow, which appears to deflect due to the dense gas near the NH3 column density peak. We investigate the specific angular momentum profile of the starless core, finding that it aligns closely with previous studies of similar radial profiles in Class 0 sources. This similarity to more evolved objects suggests that motions at 1000 au scales are determined by large-scale dense cloud motions, and may be preserved throughout the early stages of star formation.

Keywords: star formation; protostars; bok globules; interferometry; interstellar medium
Phase-curve Pollution of Exoplanet Transmission Spectra

The occurrence of a planet transiting in front of its host star offers the opportunity to observe the planet's atmosphere filtering starlight. The fraction of occulted stellar flux is roughly proportional to the optically thick area of the planet, the extent of which depends on the opacity of the planet's gaseous envelope at the observed wavelengths. Chemical species, haze, and clouds are now routinely detected in exoplanet atmospheres through rather small features in transmission spectra, i.e., collections of planet-to-star area ratios across multiple spectral bins and/or photometric bands. Technological advances have led to a shrinking of the error bars down to a few tens of parts per million (ppm) per spectral point for the brightest targets. The upcoming James Webb Space Telescope (JWST) is anticipated to deliver transmission spectra with precision down to 10 ppm. The increasing precision of measurements requires a reassessment of the approximations hitherto adopted in astrophysical models, including transit light-curve models. Recently, it has been shown that neglecting the planet's thermal emission can introduce significant biases in the transit depth measured with the JWST/Mid-InfraRed Instrument, integrated between 5 and 12 μm. In this paper, we take a step forward by analyzing the effects of the approximation on transmission spectra over the 0.6-12 μm wavelength range covered by various JWST instruments. We present open-source software to predict the spectral bias, showing that, if not corrected, it may affect the inferred molecular abundances and thermal structure of some exoplanet atmospheres.

Keywords: exoplanet atmospheres; transmission spectroscopy; exoplanet systems; exoplanets; infrared observatories
Where to Find Overmassive Brown Dwarfs: New Benchmark Systems for Binary Evolution

Under the right conditions, brown dwarfs that gain enough mass late in their lives to cross the hydrogen-burning limit will not turn into low-mass stars, but rather remain essentially brown dwarf-like. While these objects, called either beige dwarfs or overmassive brown dwarfs, may exist in principle, it remains unclear exactly how they would form astrophysically. We show that accretion from AGB winds, aided by the wind Roche lobe overflow mechanism, is likely to produce a substantial population of observable overmassive brown dwarfs, though other mechanisms are still plausible. Specifically, we predict that Sun-like stars born with a massive brown dwarf companion on an orbit with a semimajor axis of order 10 au will likely produce overmassive brown dwarfs, which may be found today as companions to the donor star's remnant white dwarf. The identification and characterization of such an object would produce unique constraints on binary evolution, because there is a solid upper limit on the brown dwarf's initial mass.

Keywords: brown dwarfs; stellar evolutionary types; stellar evolution; binary stars; asymptotic giant branch stars; white dwarf stars; low mass stars
Spectral Line Depth Variability in Radial Velocity Spectra

Stellar active regions, including spots and faculae, can create radial velocity (RV) signals that interfere with the detection and mass measurements of low-mass exoplanets. In doing so, these active regions affect each spectral line differently, but the origin of these differences is not fully understood. Here we explore how spectral line variability correlated with S-index (Ca H and K emission) is related to the atomic properties of each spectral line. Next, we develop a simple analytic stellar atmosphere model that can account for the largest sources of line variability with S-index. Then, we apply this model to HARPS spectra of α Cen B to explain Fe I line depth changes in terms of a disk-averaged temperature difference between active and quiet regions on the visible hemisphere of the star. This work helps establish a physical basis for understanding how stellar activity manifests differently in each spectral line and may help future work mitigating the impact of stellar activity on exoplanet RV surveys.

Keywords: radial velocity; stellar faculae; exoplanet detection methods; stellar activity
Regularized Maximum Likelihood Image Synthesis and Validation for ALMA Continuum Observations of Protoplanetary Disks

Regularized Maximum Likelihood (RML) techniques are a class of image synthesis methods that achieve better angular resolution and image fidelity than traditional methods like CLEAN for sub-mm interferometric observations. To identify best practices for RML imaging, we used the GPU-accelerated open source Python package MPoL, a machine learning-based RML approach, to explore the influence of common RML regularizers (maximum entropy, sparsity, total variation, and total squared variation) on images reconstructed from real and synthetic Atacama Large millimeter/submillimeter Array (ALMA) continuum observations of protoplanetary disks. We tested two different cross-validation (CV) procedures to characterize their performance and determine optimal prior strengths, and found that CV over a coarse grid of regularization strengths easily identifies a range of models with comparably strong predictive power. To evaluate the performance of RML techniques against a ground truth image, we used MPoL on a synthetic protoplanetary disk data set and found that RML methods successfully resolve structures at fine spatial scales present in the original simulation. We used ALMA DSHARP observations of the protoplanetary disk around HD 143006 to compare the performance of MPoL and CLEAN, finding that RML imaging improved the spatial resolution of the image by up to a factor of 3 without sacrificing sensitivity. We provide general recommendations for building an RML workflow for image synthesis of ALMA protoplanetary disk observations, including effective use of CV. Using these techniques to improve the imaging resolution of protoplanetary disk observations will enable new science, including the detection of protoplanets embedded in disks.

Keywords: protoplanetary disks; submillimeter astronomy; radio interferometry; deconvolution; open source software
White Dwarf Photospheric Abundances in Cataclysmic Variables. I. SS Aurigae and TU Mensae

Chemical abundance studies of cataclysmic variables have revealed high nitrogen to carbon ratios in a number of cataclysmic variable white dwarfs (based on ultraviolet emission and absorption lines), as well as possible carbon deficiency in many secondaries (based on the absence of infrared CO absorption lines). These indicate that the accreted material on the white dwarf surface and the donor itself might be contaminated with CNO processed material. To further understand the origin of this abundance anomaly, there is a need for further chemical abundance study. In the present work, we carry out a far-ultraviolet spectral analysis of the extreme SU UMa dwarf nova TU Men and the U Gem dwarf nova SS Aur using archival spectra. We derive the mass and temperature of the WD using the recently available DR2 Gaia parallaxes. The analysis of HST STIS spectra yields a WD mass ${M}_{\mathrm{wd}}={0.77}_{-0.13}^{+0.16}{M}_{\odot }$ with a temperature of 27,750 ± 1000 K for TU Men and a WD mass Mwd ∼ 0.80 ± 0.15 M⊙ with a temperature of ∼30,000 ± 1000 K for SS Aur. However, the analysis of a FUSE spectrum for SS Aur gives a higher temperature of ∼33,375 ± 1875 K, yielding a higher WD mass of ∼1 ± 0.25 M⊙, which could be due to the effect of a second hot emitting component present in the short wavelengths of FUSE. Most importantly, based on the white dwarf far-ultraviolet absorption lines, we find that both systems have subsolar carbon and silicon abundances. For TU Men, we also find suprasolar nitrogen abundance, evidence of CNO processing. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of University for Research in Astronomy, Inc. under NASA contract NAS 5-26555.

Keywords: white dwarf stars; cataclysmic variable stars; dwarf novae; su ursae majoris stars; u geminorum stars
The unpopular Package: A Data-driven Approach to Detrending TESS Full-frame Image Light Curves

The majority of observed pixels on the Transiting Exoplanet Survey Satellite (TESS) are delivered in the form of full-frame images (FFIs). However, the FFIs contain systematic effects such as pointing jitter and scattered light from the Earth and Moon that must be removed (i.e., "detrended") before downstream analysis. We present unpopular, an open-source Python package to obtain detrended TESS FFI light curves optimized for variable sources. The unpopular package implements a variant of the causal pixel model to remove systematics and allows for simultaneous fitting with a polynomial component to capture nontransit astrophysical variations, such as supernova signals or stellar variability, that tend to be removed in techniques optimized for exoplanet detection. We validate our method by detrending different sources (e.g., supernovae, tidal disruption events (TDEs), exoplanet-hosting stars, fast-rotating stars) and comparing our light curves to those obtained by other pipelines when appropriate. Our supernova and TDE light curves are visually similar to those obtained by others using the ISIS image subtraction package, indicating that unpopular can be used to extract multisector light curves by preserving astrophysical signals on timescales of a TESS sector (~27 days). We note that our method contains tuning parameters that are currently set heuristically, and that the optimal set of tuning parameters will likely depend on the particular signal the user is interested in obtaining. The unpopular source code and tutorials are freely available online.

Keywords: astronomy data analysis; linear regression; light curves; time domain astronomy; time series analysis; transient sources; variable stars; exoplanet astronomy; transit photometry