Sazuna/UAT_keywords huggingface dataset:
The Origin of Weakened Magnetic Braking in Old Solar Analogs. The rotation rates of main-sequence stars slow over time as they gradually lose angular momentum to their magnetized stellar winds. The rate of angular momentum loss depends on the strength and morphology of the magnetic field, the mass-loss rate, and the stellar rotation period, mass, and radius. Previous observations suggested a shift in magnetic morphology between two F-type stars with similar rotation rates but very different ages (88 Leo and ρ CrB). In this Letter, we identify a comparable transition in an evolutionary sequence of solar analogs with ages between 2-7 Gyr. We present new spectropolarimetry of 18 Sco and 16 Cyg A and B from the Large Binocular Telescope, and we reanalyze previously published Zeeman Doppler images of HD 76151 and 18 Sco, providing additional constraints on the nature and timing of this transition. We combine archival X-ray observations with updated distances from Gaia to estimate mass-loss rates, and we adopt precise stellar properties from asteroseismology and other sources. We then calculate the wind braking torque for each star in the evolutionary sequence, demonstrating that the rate of angular momentum loss drops by more than an order of magnitude between the ages of HD 76151 and 18 Sco (2.6-3.7 Gyr) and continues to decrease modestly to the age of 16 Cyg A and B (7 Gyr). We suggest that this magnetic transition may represent a disruption of the global dynamo arising from weaker differential rotation, and we outline plans to probe this phenomenon in additional stars spanning a wide range of spectral types.

Keywords: Spectropolarimetry, Solar analogs, Stellar magnetic fields, Stellar winds, Stellar evolution
Multiplicity Statistics of Stars in the Sagittarius Dwarf Spheroidal Galaxy: Comparison to the Milky Way. We use time-resolved spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) to examine the distribution of radial velocity (RV) variations in 249 stars identified as members of the Sagittarius (Sgr) dwarf spheroidal (dSph) galaxy by Hayes et al. We select Milky Way (MW) stars that have stellar parameters ( $\mathrm{log}(g)\ $ , T eff, and [Fe/H] ) similar to those of the Sagittarius members by means of a k-d tree of dimension 3. We find that the shape of the distribution of RV shifts in Sgr dSph stars is similar to that measured in their MW analogs, but the total fraction of RV variable stars in the Sgr dSph is larger by a factor of ~2. After ruling out other explanations for this difference, we conclude that the fraction of close binaries in the Sgr dSph is intrinsically higher than in the MW. We discuss the implications of this result for the physical processes leading to the formation of close binaries in dwarf spheroidal and spiral galaxies.

Keywords: Spectroscopic binary stars, Sagittarius dwarf spheroidal galaxy, K giant stars
Possible Systematic Rotation in the Mature Stellar Population of a z = 9.1 Galaxy. We present new observations with the Atacama Large Millimeter/submillimeter Array for a gravitationally lensed galaxy at z = 9.1, MACS1149-JD1. [O III] 88 μm emission is detected at 10σ with a spatial resolution of ∼0.3 kpc in the source plane, enabling the most distant morphokinematic study of a galaxy. The [O III] emission is distributed smoothly without any resolved clumps and shows a clear velocity gradient with ΔV obs/2σ tot = 0.84 ± 0.23, where ΔV obs is the observed maximum velocity difference and σ tot is the velocity dispersion measured in the spatially integrated line profile, suggesting a rotating system. Assuming a geometrically thin self-gravitating rotation disk model, we obtain  Vrot/σV=0.67‑0.26+0.73 , where V rot and σ  V  are the rotation velocity and velocity dispersion, respectively, still consistent with rotation. The resulting disk mass of  0.65‑0.40+1.37×109  M ⊙ is consistent with being associated with the stellar mass identified with a 300 Myr old stellar population independently indicated by a Balmer break in the spectral energy distribution. We conclude that the most of the dynamical mass is associated with the previously identified mature stellar population that formed at z ∼ 15.

Keywords: Galaxy formation, Galaxy dynamics, High-redshift galaxies, Galaxy evolution
Sunspot Shearing and Sudden Retraction Motion Associated with the 2013 August 17 M3.3 Flare. In this Letter, we give a detailed analysis of the M3.3 class flare that occurred on 2013 August 17 (SOL2013-08-17T18:16). It presents a clear picture of mutual magnetic interaction initially from the photosphere to the corona via the abrupt rapid shearing motion of a small sunspot before the flare, and then suddenly from the corona back to the photosphere via the sudden retraction motion of the same sunspot during the flare's impulsive phase. About 10 hr before the flare, a small sunspot in the active region NOAA 11818 started to move northeast along a magnetic polarity inversion line (PIL), creating a shearing motion that changed the quasi-static state of the active region. A filament right above the PIL was activated following the movement of the sunspot and then got partially erupted. The eruption eventually led to the M3.3 flare. The sunspot was then suddenly pulled back to the opposite direction upon the flare onset. During the backward motion, the Lorentz force underwent a simultaneous impulsive change both in magnitude and direction. Its directional change is found to be conformable with the retraction motion. The observation provides direct evidence for the role of the shearing motion of the sunspot in powering and triggering the flare. It especially confirms that the abrupt motion of a sunspot during a solar flare is the result of a backreaction caused by the reconfiguration of the coronal magnetic field. *Released on May 10, 2022.

Keywords: Sunspots, Solar flares
Two Candidate KH 15D-like Systems from the Zwicky Transient Facility. KH 15D contains a circumbinary disk that is tilted relative to the orbital plane of the central binary. The precession of the disk and the orbital motion of the binary together produce rich phenomena in the photometric light curve. In this work, we present the discovery and preliminary analysis of two objects that resemble the key features of KH 15D from the Zwicky Transient Facility. These new objects, Bernhard-1 and Bernhard-2, show large-amplitude ( &gt;1.5 mag), long-duration (more than tens of days), and periodic dimming events. A one-sided screen model is developed to model the photometric behavior of these objects, the physical interpretation of which is a tilted, warped circumbinary disk occulting the inner binary. Changes in the object light curves suggest potential precession periods over timescales longer than 10 yr. Additional photometric and spectroscopic observations are encouraged to better understand the nature of these interesting systems.

Keywords: Variable stars, Circumstellar disks
An Isolated Mass-gap Black Hole or Neutron Star Detected with Astrometric Microlensing. We present the analysis of five black hole candidates identified from gravitational microlensing surveys. Hubble Space Telescope astrometric data and densely sampled light curves from ground-based microlensing surveys are fit with a single-source, single-lens microlensing model in order to measure the mass and luminosity of each lens and determine if it is a black hole. One of the five targets (OGLE-2011-BLG-0462/MOA-2011-BLG-191 or OB110462 for short) shows a significant &gt;1 mas coherent astrometric shift, little to no lens flux, and has an inferred lens mass of 1.6-4.4 M ⊙. This makes OB110462 the first definitive discovery of a compact object through astrometric microlensing and it is most likely either a neutron star or a low-mass black hole. This compact-object lens is relatively nearby (0.70-1.92 kpc) and has a slow transverse motion of &lt;30 km s-1. OB110462 shows significant tension between models well fit to photometry versus astrometry, making it currently difficult to distinguish between a neutron star and a black hole. Additional observations and modeling with more complex system geometries, such as binary sources, are needed to resolve the puzzling nature of this object. For the remaining four candidates, the lens masses are &lt;2M ⊙, and they are unlikely to be black holes; two of the four are likely white dwarfs or neutron stars. We compare the full sample of five candidates to theoretical expectations on the number of black holes in the Milky Way (~108) and find reasonable agreement given the small sample size.

Keywords: Stellar populations, Astrometry, Astrometric microlensing effect, Astrophysical black holes
The Common Envelope Origins of the Fast Jet in the Planetary Nebula M 3-38. We present the analysis of Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía (MEGARA) high-dispersion integral field spectroscopic observations of the bipolar planetary nebula (PN) M 3-38. These observations unveil the presence of a fast outflow aligned with the symmetry axis of M 3-38 that expands with a velocity of up to ±225 km s-1. The deprojected space velocity of this feature can be estimated to be ≈320 ${}_{-60}^{+130}$ km s-1, which together with its highly collimated morphology suggests that it is one of the fastest jets detected in a PN. We have also used Kepler observations of the central star of M 3-38 to unveil variability associated with a dominant period of 17.7 days. We attribute this to the presence of a low-mass star with an orbital separation of ≈0.12-0.16 au. The fast and collimated ejection and the close binary system point toward a common envelope formation scenario for M 3-38.

Keywords: Stellar jets, Planetary nebulae, Low mass stars, Stellar winds
Faint Debris Disk Peering through the Superflare Light Echo. We present the detectability of strong mid-infrared (MIR) light echoes from faint debris disks illuminated by bright superflares of M-dwarf stars. Circumstellar dust grains around an M-dwarf star are simultaneously heated by superflare radiation. One can thus expect their re-emission in the MIR wavelength regime. According to our model calculations for the Proxima Centauri system, the nearest M-dwarf star system, thermal emission echoes from an inner (r &lt; 1 au) debris disk with a total mass down to that of the solar system's zodiacal dust are expected to emerge at wavelengths longer than ~10 μm with a strength comparable to or greater than a white-light superflare. Also, observable echoes from inner- (r ≲ 0.5 au) debris disks irradiated by energetic ( ≳1033.5 erg) superflares of nearby (D &lt; 3 pc) M dwarfs are expected. Our simulation results indicate that superflare monitoring using high-speed optical instruments like OASES and its prompt follow-up using ground-based MIR instruments, such as TAO/MIMIZUKU, can detect these MIR light echoes from debris disks around solar neighborhood flare stars.

Keywords: Observational astronomy, Debris disks, Time domain astronomy, Flare stars
H I Narrow-line Self-absorptions toward the High-mass Star-forming Region G176.51+00.20. Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) 19-beam tracking observational mode, high-sensitivity and high-velocity-resolution H I spectral lines have been observed toward the high-mass star-forming region G176.51+00.20. This is a pilot study searching for H I narrow-line self-absorption (HINSA) toward high-mass star-forming regions where bipolar molecular outflows have been detected. This work is confined to the central seven beams of FAST. Two HINSA components are detected in all seven beams, which correspond to a strong CO emission region (SCER; with a velocity of ~-18 km s-1) and a weak CO emission region (WCER; with a velocity of ~-3 km s-1). The SCER detected in Beam 3 is probably more suitably classified as a WCER. In the SCER, the HINSA is probably associated with the molecular material traced by the CO. The fractional abundance of HINSA ranges from ~1.1 × 10-3 to ~2.6 × 10-2. Moreover, the abundance of HINSA in Beam 1 is lower than that in the surrounding beams (i.e., Beams 2 and 4-7). This possible ring could be caused by the ionization of H I or the relatively rapid conversion from H I to H2 in the higher-density inner region. In the WCER (including Beam 3 in the SCER), the HINSA is probably not associated with CO clouds, but with CO-dark or CO-faint gas.

Keywords: Interstellar molecules, Jets, Interstellar dynamics, Interstellar atomic gas, Interstellar abundances, Star formation
Tracing the Magnetic Field Topology of the Quiet Corona Using Propagating Disturbances. The motion of faint propagating disturbances (PDs) in the solar corona reveals an intricate structure that must be defined by the magnetic field. Applied to quiet Sun observations by the Atmospheric Imaging Assembly (AIA)/Solar Dynamics Observatory (SDO), a novel method reveals a cellular network, with cells of typical diameters 50″ in the cool 304 Å channel and 100″ in the coronal 193 Å channel. The 193 Å cells can overlie several 304 Å cells, although both channels share common source and sink regions. The sources are points, or narrow corridors, of divergence that occupy the centers of cells. They are significantly aligned with photospheric network features and enhanced magnetic elements. This shows that the bright network is important to the production of PDs and confirms that the network is host to the source footpoint of quiet coronal loops. The other footpoint, or the sinks of the PDs, form the boundaries of the coronal cells. These are not significantly aligned with the photospheric network-they are generally situated above the dark internetwork photosphere. They form compact points or corridors, often without an obvious signature in the underlying photosphere. We argue that these sink points can either be concentrations of closed field footpoints associated with minor magnetic elements in the internetwork or concentrations of an upward-aligned open field. The link between the coronal velocity and magnetic fields is strengthened by comparison with a magnetic extrapolation, which shows several general and specific similarities, thus the velocity maps offer a valuable additional constraint on models.

Keywords: Solar magnetic fields, Solar atmospheric motions, Quiet solar corona, Quiet solar chromosphere
Tidal Disruption on Stellar-mass Black Holes in Active Galactic Nuclei. Active galactic nuclei (AGNs) can funnel stars and stellar remnants from the vicinity of the galactic center into the inner plane of the AGN disk. Stars reaching this inner region can be tidally disrupted by the stellar-mass black holes in the disk. Such micro tidal disruption events (micro-TDEs) could be a useful probe of stellar interaction with the AGN disk. We find that micro-TDEs in AGNs occur at a rate of ~170 Gpc-3 yr-1. Their cleanest observational probe may be the electromagnetic detection of tidal disruption in AGNs by heavy supermassive black holes (M • ≳ 108 M ⊙) that cannot tidally disrupt solar-type stars. The reconstructed rate of such events from observations, nonetheless, appears to be much lower than our estimated micro-TDE rate. We discuss two such micro-TDE candidates observed to date (ASASSN-15lh and ZTF19aailpwl).

Keywords: Tidal disruption, Active galaxies
Radiative Magnetohydrodynamic Simulation of the Confined Eruption of a Magnetic Flux Rope: Magnetic Structure and Plasma Thermodynamics. It is widely believed that magnetic flux ropes are the key structure of solar eruptions; however, their observable counterparts are not clear yet. We study a flare associated with flux rope eruption in a comprehensive radiative magnetohydrodynamic simulation of flare-productive active regions, especially focusing on the thermodynamic properties of the plasma involved in the eruption and their relation to the magnetic flux rope. The preexisting flux rope, which carries cold and dense plasma, rises quasi-statically before the onset of eruptions. During this stage, the flux rope does not show obvious signatures in extreme ultraviolet (EUV) emission. After the flare onset, a thin "current shell" is generated around the erupting flux rope. Moreover, a current sheet is formed under the flux rope, where two groups of magnetic arcades reconnect and create a group of postflare loops. The plasma within the "current shell," current sheet, and postflare loops are heated to more than 10 MK. The postflare loops give rise to abundant soft X-ray emission. Meanwhile, a majority of the plasma hosted in the flux rope is heated to around 1 MK, and the main body of the flux rope is manifested as a bright arch in cooler EUV passbands such as the AIA 171 Å channel.

Keywords: Solar activity, Radiative magnetohydrodynamics, Solar magnetic fields, Solar extreme ultraviolet emission
Viability of Novae as Sources of Galactic Lithium. Of all the light elements, the evolution of lithium (Li) in the Milky Way is perhaps the most difficult to explain. Li is difficult to synthesize and is easily destroyed, making most stellar sites unsuitable for producing Li in sufficient quantities to account for the protosolar abundance. For decades, novae have been proposed as a potential explanation for this "Galactic Li problem," and the recent detection of 7Be in the ejecta of multiple nova eruptions has breathed new life into this theory. In this work, we assess the viability of novae as dominant producers of Li in the Milky Way. We present the most comprehensive treatment of novae in a galactic chemical evolution code to date, testing theoretically and observationally derived nova Li yields by integrating metallicity-dependent nova ejecta profiles computed using the binary population synthesis code binary_c with the galactic chemical evolution code OMEGA+. We find that our galactic chemical evolution models which use observationally derived Li yields account for the protosolar Li abundance very well, while models relying on theoretical nova yields cannot reproduce the protosolar observation. A brief exploration of physical uncertainties including single-stellar yields, the metallicity resolution of our nova treatment, common-envelope physics, and nova accretion efficiencies indicates that this result is robust to physical assumptions. Scatter within the observationally derived Li yields in novae is identified as the primary source of uncertainty, motivating further observations of 7Be in nova ejecta.

Keywords: Stellar nucleosynthesis, Galactic abundances, Nucleosynthesis, Classical novae
Searching for a Hypervelocity White Dwarf SN Ia Companion: A Proper-motion Survey of SN 1006. Type Ia supernovae (SNe Ia) are securely understood to come from the thermonuclear explosion of a white dwarf as a result of binary interaction, but the nature of that binary interaction and the secondary object is uncertain. Recently, a double white dwarf model known as the dynamically driven double-degenerate double-detonation (D6) model has become a promising explanation for these events. One realization of this scenario predicts that the companion may survive the explosion and reside within the remnant as a fast moving (V peculiar &gt; 1000 km s-1), overluminous (L &gt; 0.1 L ⊙) white dwarf. Recently, three objects that appear to have these unusual properties have been discovered in the Gaia survey. We obtained photometric observations of the SN Ia remnant SN 1006 with the Dark Energy Camera over four years to attempt to discover a similar star. We present a deep, high-precision astrometric proper-motion survey of the interior stellar population of the remnant. We rule out the existence of a high-proper-motion object consistent with our tested realization of the D6 scenario (V transverse &gt; 600 km s-1 with m  r  &lt; 21 corresponding to an intrinsic luminosity of L &gt; 0.0176 L ⊙). We conclude that such a star does not exist within the remnant or is hidden from detection by either strong localized dust or the unlikely possibility of ejection from the binary system almost parallel to the line of sight.

Keywords: White dwarf stars, Supernova remnants, Type Ia supernovae, Astrometry, Supernovae
Wide Twin Binaries are Extremely Eccentric: Evidence of Twin Binary Formation in Circumbinary Disks. The Gaia mission recently revealed an excess population of equal-mass "twin" wide binaries, with mass ratio q ≳ 0.95, extending to separations of at least 1000 au. The origin of this population is an enigma: Twin binaries are thought to form via correlated accretion in circumbinary disks, but the typical observed protostellar disks have radii of ~100 au, far smaller than the separations of the widest twins. Here, we infer the eccentricity distribution of wide twins from the distribution of their v-r angles, i.e., the angle between the components' separation and relative velocity vectors. We find that wide twins must be on extremely eccentric orbits. For the excess-twin population at 400-1000 au, we infer a near-delta-function excess of high-eccentricity systems, with eccentricity 0.95 ≲ e ≤ 1. These high eccentricities for wide twins imply pericenter distances of order 10 au and suggest that their orbits were scattered via dynamical interactions in their birth environments, consistent with a scenario in which twins are born in circumbinary disks and subsequently widened. These results further establish twin wide binaries as a distinct population and imply that wide twins can be used as a probe of the dynamical history of stellar populations.

Keywords: Wide binary stars, Binary stars, Eccentricity, Circumstellar disks
A Dynamical Model of the M101/NGC 5474 Encounter. We present the first dynamical simulation that recreates the major properties of the archetypal nearby spiral galaxy M101. Our model describes a grazing but relatively close (~14 kpc) passage of the companion galaxy NGC 5474 through M101's outer disk approximately 200 Myr ago. The passage is retrograde for both disks, yielding a relatively strong gravitational response while suppressing the formation of long tidal tails. The simulation reproduces M101's overall lopsidedness, as well as the extended NE Plume and the sharp western edge of the galaxy's disk. The post-starburst populations observed in M101's NE Plume are likely a result of star formation triggered at the point of contact where the galaxies collided. Over time, this material will mix azimuthally, leaving behind diffuse, kinematically coherent stellar streams in M101's outer disk. At late times after the encounter, the density profile of M101's disk shows a broken "upbending" profile similar to those seen in spiral galaxies in denser environments, further demonstrating the connection between interactions and long-term structural changes in galaxy disks.

Keywords: Galaxy dynamics, Galaxy interactions, Galaxy evolution
Decoding the X-Ray Flare from MAXI J0709-159 Using Optical Spectroscopy and Multiepoch Photometry. We present a follow-up study on the recent detection of two X-ray flaring events by MAXI/Gas Slit Camera observations in soft and hard X-rays from MAXI J0709-159 in the direction of HD 54786 (LY CMa), on 2022 January 25. The X-ray luminosity during the flare was around 1037 erg s-1 (MAXI), which got reduced to 1032 erg s-1 (NuSTAR) after the flare. We took low-resolution spectra of HD 54786 from the 2.01 m Himalayan Chandra Telescope and the 2.34 m Vainu Bappu Telescope (VBT) facilities in India, on 2022 February 1 and 2. In addition to Hα emission, we found emission lines of He I in the optical spectrum of this star. By comparing our spectrum of the object with those from the literature we found that He I lines show variability. Using photometric studies we estimate that the star has an effective temperature of 20,000 K. Although HD 54786 is reported as a supergiant in previous studies, our analysis favors it to be evolving off the main sequence in the color-magnitude diagram. We could not detect any infrared excess, ruling out the possibility of IR emission from a dusty circumstellar disk. Our present study suggests that HD 54786 is a Be/X-ray binary system with a compact object companion, possibly a neutron star.

Keywords: Be stars, X-ray sources, Spectroscopy, X-ray binary stars