Sazuna/UAT_keywords huggingface dataset:
Toward Assembling a Comprehensive Database of Substellar Accretion Rates. The relationship between mass and mass accretion rate in young objects is a powerful tool for interrogating formation and evolution. We analyze a comprehensive database of published accretion diagnostics for ~400 objects (0.005-2 M⊙), including 64 brown dwarfs. To eliminate systematics between studies as the source of the four orders of magnitude of observed scatter, we uniformly re-estimate masses and accretion rates from direct observables (e.g., spectral types, line luminosities). In particular, we adopt a single grid of evolutionary models to estimate masses, a single family of scaling relations to estimate accretion luminosity, and update line luminosities using Gaia DR2 distances. We find that this unification produces minimal effects on the observed relation, suggesting systematic and methodological variation is not responsible for the scatter. This paves the way for investigation of physical sources of scatter, including: age variation, intrinsic variability, formation mechanism, and accretion paradigm.

Keywords: Accretion, Brown dwarfs, Pre-main sequence stars, Low mass stars, Stellar accretion, Stellar accretion disks
Detection and Removal of Periodic Noise in Kepler/K2 Photometry with Principal Component Analysis. We present a novel method for detrending systematic noise from time series data using Principal Component Analysis (PCA) in Fast Fourier Transforms. This method is demonstrated on time series data obtained from the inaugural campaign of the Kepler K2 mission, as well as three objects of interest from Campaign 4. Unlike previous detrending techniques that utilize PCA, this method performs the detrending in Fourier space rather than temporal space. The advantage of performing the analysis in frequency space is that the technique is sensitive purely to the periodicity of the unwanted signal and not to its morphological characteristics. This method could improve measurements of low signal-to-noise photometric features by reducing systematics. We also discuss challenges and limitations associated with this technique.

Keywords: Principal component analysis
Testing the Speed of Light Variation with Strong Gravitational Lensing of SNe 1a. The constancy of the speed of light c is the foundation of most physical theories and is found to be indeed constant from local measurements. Whether or not the same is true at cosmological timescale has been of interest for some time. The measurement of time delay difference in the peaking of the luminosity between two gravitationally lensed images of a type 1a-supernova has recently been proposed to determine if c was different from its current value at the time the images were produced by a lensing galaxy. Since the geometrical time delay and the Shapiro time delay both scale as G/c3 we show that this method of constraining c is valid only when the potential variation of the gravitational constant G is ignored: c variation is imperceptible when G ~ c3.

Keywords: Cosmology, Cosmological models, Dirac cosmology
Stars on the Verge: Investigating Semiregular Light Variations and Changing Multiperiods of the Luminous Red Supergiant μ Cephei from over 175 yr of Photometry. μ Cephei is a 4th mag semi-regular variable M2Ia star. It is among the largest, most luminous red supergiants in our galactic neighborhood and a probable SN-II core-collapse progenitor. Analyses of ~175 yr of photometry were conducted. The observations are mostly from the AAVSO database. Period analyses were conducted using the Period Analysis Software (Peranso-3) package. The CLEANest and Wavelet (WWZ) programs were utilized. Two dominant "periods" were found: P = 870 ± 50 days (~2.39 yr) and a long period of ~5300 ± 155 days (~14.5 yr). The long period was prominent during the first ~90 yr but weakened and was followed by multiple transitory periods ranging from ~3000 to 4600 days. μ Cephei has interesting features including multiple periods, period-splitting, period-merging and period-decays.

Keywords: Red supergiant stars, Stellar pulsations
WISEA J052305.94-015356.1: A New EsdT Candidate. I present WISEA J052305.94-015356.1 as a new candidate extremely metal-poor T subdwarf (esdT), based on its distinctive infrared colors and high proper motion (~500 mas yr-1). Spectroscopic follow-up is now needed to confirm it is a member of this newly discovered class of substellar objects.

Keywords: Brown dwarfs, T subdwarfs
The 1991 24 hr Ultraviolet Monitoring of 21 Com with IUE. The comparison of 10 far ultraviolet spectra of 21 Com taken over continuous 24 hr (half of the recently determined rotational period) reveals large variations shortwards of 1700 Å. In contrast, the flux variations at wavelengths larger then 2200 Å are of smaller amplitudes. The large FUV variability is probably caused by changes in the continuous opacity driven by modest horizontal gradients of the abundances of chemical elements over the surface of 21 Com.

Keywords: Chemically peculiar stars
Vortex Solution in Elliptic Coordinates. Vortices (flows with closed elliptic streamlines) are exact nonlinear solutions to the compressible Euler equation. In this contribution, we use differential geometry to derive the transformations between Cartesian and elliptic coordinates, and show that in elliptic coordinates a constant vorticity flow reduces to $\dot{\mu }=0$ and $\dot{\nu }=\mathrm{const}$ along the streamline μ0 that matches the vortex eccentricity.

Keywords: Planet formation
Solar Cycle 25 is Currently Very Similar to Solar Cycle 24. Solar Cycle 25 started in 2019 December. Different predictions for its amplitude have been published so far without general consensus. We compared the evolution of Solar Cycle 25, using the first available values of the smoothed sunspot number, with past solar cycles. Our analysis shows that Solar Cycle 25 is very similar to Solar Cycles 24 and 7. Therefore, the maximum amplitude for this Solar Cycle 25 could be small-moderate.

Keywords: Solar activity, Solar cycle, Sunspot number
Multiwavelength Properties of the Newly Discovered Dwarf Nova ASASSN-21kt. We report on archival XMM-Newton and post-outburst Swift observations of the newly discovered dwarf nova ASASSN-21kt. Its pre-outburst X-ray emission is consistent with that of a collisionally ionized, thermal plasma with ${kT}={8.1}_{-2.5}^{+10.2}$ keV and LX 0.2-12 keV = 7 × 1032 erg s-1, with no clear modulation. Multiple optical outbursts revealed by Gaia and time evolution of the last one followed by the All-Sky Automated Survey for Supernovae, and X-ray properties presented here support the dwarf nova classification of ASASSN-21kt.

Keywords: Cataclysmic variable stars, Dwarf novae
Light-curve Test of GRB 090717 as a Gravitationally Lensed Echo. Light curve comparison is a simple but statistically powerful test for the presence of gravitational lensing in gamma-ray bursts (GRBs). Since gravitational lensing does not change relative timing internal to images, all source images created by gravitational lensing should show the same light curve to within a scale factor in amplitude. Applied to the recent claim that the two pulses in GRB 090717 are lensed images of the same pulse, it was found that the light curves for these pulses actually differ at about the 5.0σ confidence level (99.999956%) in a χ2 comparison test. Under the given assumptions, GRB 090717 therefore does not present a compelling example of gravitational lensing.

Keywords: Chi-squared statistic, Gamma-ray astronomy, Gamma-ray bursts, Gravitational lensing
Understanding Gamma-Ray Burst Jet Structures from Afterglow Light Curves. Gamma-ray bursts, associated with the collapse of massive stars or the collisions of compact objects, are the most luminous events in our universe. However, there is still much to learn about the nature of the relativistic jets launched from the central engines of these objects. We examine how jet structure-that is, the energy and velocity distribution as a function of angle-affects observed GRB afterglow light curves. Using the package afterglowpy, we compute light curves arising from an array of possible jet structures, and present the suite of models that can fit the coincident electromagnetic observations of GW190814 (which is likely due to a background AGN). Our work emphasizes not only the need for broadband spectral and timing data to distinguish among jet structure models, but also the necessity for high resolution radio follow-up to help resolve background sources that may mimic a GRB afterglow.

Keywords: Gamma-ray bursts
HaloSat Observation of the Virgo Intracluster Medium. Contained within a galaxy cluster, the Intracluster Medium is comprised of hot, X-ray emitting material between member galaxies. The nearest (~16.1 Mpc) large galaxy cluster is Virgo. Virgo covers an approximately 12° diameter field, making it challenging to observe in its entirety. The HaloSat satellite utilized a 7° radius field of view to obtain the first full cluster observations since 1994. We then fit the cluster spectra with a plasma emission model of fixed metallicity. Our best fit temperature is kT = 1.39 ± 0.11 keV. We report a cluster luminosity of 5.8 ± 0.7 × 1043 erg s-1 and an emission measure of 5.8 ± 0.6 × 1066 cm-3.

Keywords: Galaxy clusters, X-ray astronomy, Virgo Cluster, X-ray sources, Intracluster medium
An Evocative Image of the Moon from Lick Observatory. The provenance of a singular picture of the nearside of the Moon made at Lick Observatory is discussed.

Keywords: The Moon, Astrophotography
An Assessment of the LEISA Spectrometer for Extragalactic Background Light Measurements. The extragalactic background light (EBL) is the summed emission from sources beyond the Milky Way. An accurate measurement of the EBL can be used as a benchmark to search for any diffuse components in excess of the integrated light from galaxies. We have studied archival data from the Linear Etalon Imaging Spectral Array (LEISA) aboard the New Horizons spacecraft to assess its capability to measure the near-IR EBL at wavelengths between 1.2 and 2.5 μm. We estimate LEISAs sensitivity to diffuse brightness to be ~105 nW m-2 sr-1 in 1.5 s exposures, which precludes the possibility of reaching EBL signals at the level of 10 nW m-2 sr-1.

Keywords: Diffuse radiation, Space vehicle instruments
Orbital Periods and Waveforms of Dwarf Novae Observed by Kepler. Kepler high cadence data are used to measure the orbital periods and to determine the orbital waveforms of five dwarf novae. A significant improvement of the period of V1504 Cyg is achieved, while for the other systems periods are derived which are compatible with previous determinations. The orbital waveforms of the short period systems V1504 Cyg, V344 Lyr and V516 Lyr are very nearly sinusoidal, while the longer period dwarf nova V447 Lyr appears almost to be a twin of U Gem. The unusual system KIC 9202990 exhibits distinct variations of its waveform as a function of brightness during its outburst cycle.

Keywords: Close binary stars, Dwarf novae, Cataclysmic variable stars, Variable stars
Seeing-sorted Visible Multi-Object Spectrograph U-band Imaging of the GOODS-south Field. We present the optimal resolution and optimal depth U-filter mosaics using the seeing-sorted method of Ashcraft et al. on deep, ground-based U-bandimaging of the Great Observatories Origins Deep Survey South field as part of the near-UV imaging program UVCANDELS. We use the U-bandimages obtained with the VIsible Multi-Object Spectrograph on the European Southern Observatory Very Large Telescope by Nonino et al. Our best resolution mosaic includes images with a seeing full-width half maximum (FWHM) ≤ 0"8, and encompasses 50% of the data. Our best depth mosaic includes images with FWHM ≤ 1"5, corresponding to 100% of the data. Prior to being combined, the source fluxes in each individual background-subtracted image are corrected to match a 3D-HST photometric catalog of the same field to correct variations in the U-band zero-points. These mosaics provide deep U-banddata complementary to the UVCANDELS HST WFC3 F275W and ACS F435W images. We assess the depth of both U-bandmosaics. * Based on data acquired using the Very Large Telescope (VLT) of the European Southern Observatory (ESO).

Keywords: Ultraviolet astronomy, Astronomical seeing, Astronomy data analysis
X-Ray Luminosity of Decades-old Supernovae. The transition from supernovae (SNe) to supernova remnants (SNRs) remains poorly understood, given the age gap between well-studied examples of the two. In order to bridge this gap, we analyzed archival Chandra data for some of the oldest supernovae detected in X-rays, in order to extend their light curves out to late times. We fitted the spectra with thermal models. All the SNe with multiple X-ray data points were found to have similar X-ray luminosity, which was decreasing with time. The X-ray luminosity will likely continue to decrease while the SNe are evolving in a wind medium, but is anticipated to increase in the Sedov phase when the SNe are interacting with a constant density interstellar medium, bringing it in line with observed SNRs

Keywords: Type II supernovae, Light curves, Supernova remnants, X-ray sources, Supernovae
Forecasting Solar Cycle 25 with a Principled Bayesian Two-stage Statistical Model. We update the Bayesian analysis of sunspot numbers (SSNs) developed by Yu et al. prior to the peak of Solar Cycle 24 to account for the recalibration of the SSN index. We show that the model yields an accurate hindcast of Cycle 24 with the revised SSN, and use the data acquired since then to predict the strength and peak of Cycle 25. We predict the behavior of Cycle 25 to be moderate to weak, with a peak SSN of 120±27 to occur c. 2025 July (±7 months).

Keywords: Solar cycle, Hierarchical models, Sunspot number
Evidence for a Transient Emission Feature at 1524 Å in the Far Ultraviolet Spectrum of 21 Com. Evidence is presented for the presence of a transient emission feature at 1524 Å in the far ultraviolet spectrum of 21 Com recorded by the International Ultraviolet Explorer during the 1979 event. This event is characterized by he sudden appearance of broad and intense absorption features shortwards of 1720 Å. The emission feature at 1524 Å is tentatively identified as a Si I line also present in the FUV spectra of quiescent dMe dwarfs. During the event, the flux level in the continuum adjacent to this line is about 1.6 times higher than in the mean spectrum outside event.

Keywords: Ap stars, Chemically peculiar stars
Belatedly Habitable Planets. Stars do not remain static, so their habitable zones evolve in time. Over a star's evolution, its habitable zone encompasses new planets, and it remains uncertain whether these planets can become habitable. We refer to this often overlooked class of planets as lying in the belatedly habitable zone, and stress that many planets found in the habitable zones of other stars will belong to this class. Future studies should take belated habitability into account and not implicitly assume that these planets are habitable.

Keywords: Exoplanets, Exoplanet astronomy, Exoplanet evolution, Astrobiology, Habitable zone, Habitable planets
H-α Variability of V1298 Tau c. The 23 Myr system V1298 Tau hosts four transiting planets and is a valuable laboratory for exploring the early stages of planet evolution soon after formation of the star. We observe the innermost planet, V1298 Tau c, during transit using LBT PEPSI to obtain high spectral resolution characterization of escaping material near the H-α line. We find no strong evidence for atmospheric material escaping at the orbital velocity of the planet. Instead, we find a deep stellar feature that is variable on the few percent level, similar to a previous observation of the planet and can be explained by stellar activity. We attempted to monitor the broadband optical transit with LBT MODS but do not achieve the precision needed to characterize the atmosphere or improve the ephemeris.

Keywords: Exoplanet astronomy, Exoplanet atmospheres, Stellar activity
Discovery of a Low-mass Comoving System Using NOIRLab Source Catalog DR2. We present the discovery of a low-mass comoving system found by means of the NOIRLab Source Catalog DR2. The system consists of the high proper-motion star LEHPM 5005 and an ultracool companion 2MASS J22410186-4500298 with an estimated spectral type of L2. The primary (LEHPM 5005) is likely a mid-M dwarf but over-luminous for its color, indicating a possible close equal mass binary. According to the Gaia EDR3 parallax of the primary, the system is located at a distance of 58 ± 2 pc. We calculated an angular separation of 7"2 between both components, resulting in a projected physical separation of 418 au.

Keywords: Binary stars, Low mass stars
The Altered State of η Carinae: HST's Photometric Record 1998-2021. Hubble Space Telescope photometry of η Carinae spans 23 yr, including five spectroscopic events. The rapid brightening rate decreased after 2010, and the spectroscopic events in 2014 and 2020 had light curves different from their predecessors. Together with other indicators, these developments probably foretell the conclusion of η Car's change of state. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. Support for this work was provided by NASA through grant number GO-16176 from the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555.

Keywords: Massive stars, Emission line stars, Stellar winds
A Near-infrared Search for Molecular Gas in the Fermi Bubbles. We present Gemini/NIFS near-IR integral field spectroscopy of the fields-of-view around two AGNs behind the Fermi Bubbles (PDS 456 and 1H1613-097 ) to search for molecular gas in the Milky Way's nuclear wind. These two AGN sightlines were selected by the presence of high-velocity neutral and ionized gas seen in UV absorption. We do not detect any extended emission from the H2 rovibrational S(0) and S(1) lines at 2.224 and 2.122 μm in either direction. For the H2 1-0 S(1) line, the 3σ surface brightness limits derived from spectra extracted across the full 3″ × 3″ NIFS field-of-view are 2.4 × 10-17 erg cm-2 s-1 Å-1 arcsec-2 for PDS 456 and 4.9 × 10-18 erg cm-2 s-1 Å-1 arcsec-2 for 1H1613-097. Given these non-detections, we conclude that CO emission studies and H2 UV absorption studies are more promising approaches for characterizing molecular gas in the Fermi Bubbles.

Keywords: Interstellar molecules, Galactic winds, Galactic center, Molecular spectroscopy, Interstellar emissions, Interstellar medium, Milky Way Galaxy
Probabilistic Modeling of Asteroid Diameters from Gaia DR2 Errors. The Gaia Data Release 2 provides precise astrometry for nearly 1.5 billion sources across the entire sky, including several thousand asteroids. In this work, we provide evidence that reasonably large asteroids (diameter &gt;20 km) have high correlations with Gaia relative flux uncertainties and systematic R.A. errors. We further capture these correlations using a logistic Bayesian additive regression tree model. We compile a small list of probable large asteroids that can be targeted for direct diameter measurements and shape reconstruction.

Keywords: Astrostatistics techniques, Solar system, Asteroids
Full-sky unWISE Coadds at Seven Years' Depth. unWISE is a wide-ranging data analysis effort aimed at repurposing the combined Wide-field Infrared Survey Explorer (WISE) plus NEOWISE imaging archive for Galactic and extragalactic astrophysics. We present updated static sky maps incorporating seven years of W1 (3.4 μm) and W2 (4.6 μm) single-exposure images, uniformly coadding nearly a quarter petabyte of input pixel data. These new unWISE atlases now constitute the deepest ever full-sky maps at wavelengths of 3-5 μm, and will be used to select millions of Dark Energy Spectroscopic Instrument quasar and luminous red galaxy targets.

Keywords: Sky surveys, Surveys, Astronomy data analysis, Infrared astronomy, Astronomy data reduction
Brown Dwarfs are Violet: A New Calculation of Human-eye Colors of Main-sequence Stars and Substellar Objects. There has always been interest in the perceived colors of stars. They were key to the development of the Hertzsprung-Russell diagram, and they are also used widely in educational and public-outreach imagery. Thus, it is useful to develop tools to compute these colors from spectral energy distributions. This paper presents a collection of objective (CIE coordinate) and subjective (RGB triple) colors for main-sequence stars and brown dwarfs, as well as links to related codes and tables. Using the proposed conversion from CIE to RGB colors, O and B stars are bluer than equivalent blackbodies because of Paschen continuum absorption, and M dwarfs tend to be less red and more beige. Although brown dwarfs over a wide range of effective temperatures (400-2000 K) emit most of their flux in the infrared, their visible spectra are dominated by short wavelengths. Thus, they may appear violet to human eyes.

Keywords: Brown dwarfs, Late-type stars, Stellar colors, Spectroscopy, Stellar atmospheres
Jupiter as a Rotating Bipolytrope. Polytropes have long been used to model a wide variety of astrophysical objects. A bipolytrope (composite polytrope) may be used for bodies with a distinct core-envelope structure. In this short paper, I demonstrate that a rotating bipolytrope is a reasonable approximation for Jovian interior. Similar models may be used to probe rotating exoplanets to gain an intuitive understanding of their internal structure.

Keywords: Computational methods, Planetary interior, Jupiter
The Mean Overabundance of Manganese over the Surface of 21 Com from its Midultraviolet Spectra Recorded by IUE. The coaddition of 21 mid ultraviolet spectra of 21 Com taken over the International Ultraviolet Explorer (IUE) mission reveals three strong lines of Mn II at 2576.10, 2593.72 and 2605.68 Å. The synthesis of these lines consistently yields a sizable overabundance of manganese about 10 times the solar manganese abundance. Inspection of the 10 individual spectra taken over the 24 hr monitoring of 21 Com with IUE on 1991 April 17 does not reveal convincing variations of these lines between rotational phases 0.18 and 0.65 of the 2 days period.

Keywords: Chemically peculiar stars, Chemical abundances
Spitzer Infrared Observations of the Galactic Classical Nova V2615 Ophiuchus. Classical novae contribute to the cycle of chemical enrichment of the interstellar medium through through explosive nucleosynthesis and the violent ejection of material dredged from the white dwarf progenitor and mixed with the accreted surface layers. Analysis of archival NASA Spitzer spectroscopic observations of V2615 Ophiuchus shows that [O IV] 25.89 μm is a strong coolant and that no evidence for deceleration of the ejecta was present ~1000 days after outburst, based on observed Spitzer InfraRed Spectrograph emission line average FWHM velocities of ≃600 km s-1.

Keywords: Spectroscopy, Classical novae
Roaming the Relativistic Realm: Short-term Dynamical Evolution of Atira 2021 PH<SUB>27</SUB>. General relativity effects coupled with those derived from the von Zeipel-Lidov-Kozai mechanism may play a significant role on the evolution of members of the Atira dynamical class, particularly in the case of those with the shortest sidereal orbital periods. Here, we provide a preliminary assessment of the short-term orbital evolution of 2021 PH27, a recently discovered Atira that has the shortest period among known asteroids. Our calculations, based on a publicly available orbit determination and including post-Newtonian terms in the numerical integrations, show that 2021 PH27 is a robust member of the Atira class and it may indeed be used to explore the combined effects of general relativity and the von Zeipel-Lidov-Kozai mechanism once its orbit determination is sufficiently improved.

Keywords: Solar system, Asteroids