Sazuna/UAT_keywords huggingface dataset:
Constrained Reference Star Differential Imaging: Enabling High-fidelity Imagery of Highly Structured Circumstellar Disks. High-contrast imaging presents us with the opportunity to study circumstellar disks and the planets still embedded within them, providing key insights into the formation and evolution of planetary systems. However, the postprocessing techniques that are often needed to suppress stellar halo light typically result in significant and variable loss of circumstellar light, even when using relatively conservative approaches like reference star differential imaging (RDI). We introduce "constrained reference star differential imaging" (constrained RDI), a new class of RDI point-spread-function (PSF) subtraction techniques for systems with circumstellar disks. Constrained RDI utilizes either high-resolution polarized-intensity (PI) images or disk models to severely limit or even eliminate the signal loss due to oversubtraction that is common to RDI. We demonstrate the ability of constrained RDI utilizing polarimetric data to yield an oversubtraction-free detection of the AB Aurigae protoplanetary disk in total intensity. PI-constrained RDI allows us to decisively recover the spectral signature of the confirmed, recently discovered protoplanet, AB Aurigae b. We further demonstrate that constrained RDI can be a powerful analysis tool for soon-to-be-acquired James Webb Space Telescope coronagraphic imaging of disks. In both cases, constrained RDI provides analysis-ready products that enable more detailed studies of disks and more robust verification of embedded exoplanets. * Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Keywords: Polarimetry, Coronagraphic imaging, Direct imaging, Protoplanetary disks, Circumstellar disks, Exoplanet detection methods, Debris disks
Limits on Hierarchical Black Hole Mergers from the Most Negative χ <SUB>eff</SUB> Systems. It has been proposed that some black holes (BHs) in binary black hole (BBH) systems are born from "hierarchical mergers" (HMs), i.e., earlier mergers of smaller BHs. These HM products have spin magnitudes χ ~ 0.7, and, if they are dynamically assembled into BBH systems, their spin orientations will sometimes be antialigned with the binary orbital angular momentum. In fact, as Baibhav et al. showed, ~16% of BBH systems that include HM products will have an effective inspiral spin parameter, χ eff &lt; -0.3. Nevertheless, the LIGO-Virgo-KAGRA (LVK) gravitational-wave (GW) detectors have yet to observe a BBH system with χ eff ≲ -0.2, leading to upper limits on the fraction of HM products in the population. We fit the astrophysical mass and spin distribution of BBH systems and measure the fraction of BBH systems with χ eff &lt; -0.3, which implies an upper limit on the HM fraction. We find that fewer than 26% of systems in the underlying BBH population include HM products (90% credibility). Even among BBH systems with primary masses m 1 = 60 M ⊙, the HM fraction is less than 69%, which may constrain the location of the pair-instability mass gap. With 300 GW events (to be expected in the LVK's next observing run), if we fail to observe a BBH with χ eff &lt; -0.3, we can conclude that the HM fraction is smaller than ${2.5}_{-2.2}^{+9.1} \% $ .

Keywords: Massive stars, Stellar dynamics, Gravitational wave sources, Astrostatistics, Gravitational wave astronomy, Gravitational waves, Astrophysical black holes
Solar Chromospheric Network as a Source for Solar Wind Switchbacks. Recent studies suggest that the magnetic switchbacks (SBs) detected by the Parker Solar Probe carry information on the scales of solar supergranulation (large scale) and granulation (medium scale). We test this claim using high-resolution Hα images obtained with the visible spectropolarimeters of the Goode Solar Telescope in Big Bear Solar Observatory. As possible solar sources, we count all the spicule-like features standing along the chromospheric networks near the coronal hole boundary visible in the Hα blue-wing but absent in the red-wing images and measure the geometric parameters of dense sections of individual flux tubes. Intervals between adjacent spicules located along the chromospheric networks are found in the range of 0.4-1.5 Mm (0.°03-0.°12) tending to be smaller than the medium scale of SBs. Interdistances between all pairs of the flux tubes are also counted and they appear in a single peak distribution around 0.7 Mm (0.°06) unlike the waiting-time distribution of SBs in a scale-free single power-law form. The length-to-diameter ratio of the dense section of flux tubes is as high as 6-40, similar to the aspect ratio of SBs. The number of spicules along a network can be as high as 40-100, consistent with numerous SBs within a patch. With these numbers, it is argued that the medium scale of SBs can be understood as an equilibrium distance resulting from a random walk within each diverging magnetic field funnel connected to the chromospheric networks.

Keywords: Solar wind, Solar chromosphere, Interplanetary magnetic fields, Solar magnetic fields
A Robust Test of the Existence of Primordial Black Holes in Galactic Dark Matter Halos. If very low mass primordial black holes (PBH) within the asteroid/moon-mass range indeed reside in galactic dark matter halos, they must necessarily collide with galactic neutron stars (NSs). These collisions must, again necessarily, form light black holes (LBHs) with masses of typical NSs, M LBH ≈ 1-2 M ⊙. LBHs may be behind events already detected by ground-based gravitational-wave detectors (GW170817, GW190425, and others such as a mixed stellar black hole-NS-mass event GW191219_163120), and most recently by microlensing (OGLE-BLG-2011-0462). Although the status of these observations as containing LBHs is not confirmed, there is no question that gravitational-wave detectors and microlensing are in principle and in practice capable of detecting LBHs. We have calculated the creation rate of LBHs resulting from these light primordial black hole (PBH) collisions with NSs. On this basis, we claim that if improved gravitational-wave detectors and microlensing statistics of the LBH events would indicate that the number of LBHs is significantly lower that what follows from the calculated creation rate, then this would be an unambiguous proof that there is no significant light PBH contribution to the galactic dark matter halos. Otherwise, if observed and calculated numbers of LBHs roughly agree, then the hypothesis of primordial black hole existence gets strong observational support, and in addition their collisions with NSs may be considered a natural creation channel for the LBHs, solving the problem of their origin, as it is known that they cannot be a product of standard stellar evolution.

Keywords: Neutron stars, Dark matter, Primordial black holes, Black holes
Preferential Heating of Protons over Electrons from Coherent Structures during the First Perihelion of the Parker Solar Probe. The solar wind undergoes significant heating as it propagates away from the Sun; the exact mechanisms responsible for this heating remain unclear. Using data from the first perihelion of the Parker Solar Probe mission, we examine the properties of proton and electron heating occurring within magnetic coherent structures identified by means of the Partial Variance of Increments (PVI) method. Statistically, regions of space with strong gradients in the magnetic field, PVI ≥ 1, are associated with strongly enhanced proton but only slightly elevated electron temperatures. Our analysis indicates a heating mechanism in the nascent solar wind environment facilitated by a nonlinear turbulent cascade that preferentially heats protons over electrons.

Keywords: Interplanetary turbulence, Solar coronal heating, Solar wind, Magnetohydrodynamics
Is Thermohaline Mixing the Full Story? Evidence for Separate Mixing Events near the Red Giant Branch Bump. The abundances of mixing-sensitive elements including lithium, [C/N], and 12C/13C are known to change near the red giant branch bump. The explanation most often offered for these alterations is double diffusive thermohaline mixing in the stellar interior. In this analysis, we investigate the ability of thermohaline mixing to explain the observed timing of these chemical depletion events. Recent observational measurements of lithium and [C/N] show that the abundance of lithium decreases before the abundance of [C/N], whereas numerical simulations of the propagation of the thermohaline-mixing region computed with MESA show that the synthetic abundances drop simultaneously. We therefore conclude that thermohaline mixing alone cannot explain the distinct events of lithium depletion and [C/N] depletion, as the simultaneity predicted by simulations is not consistent with the observation of separate drops. We thus invite more sophisticated theoretical explanations for the observed temporal separation of these chemical depletion episodes as well as more extensive observational explorations across a range of masses and metallicities.

Keywords: Stellar abundances, Stellar physics, Stellar interiors, Stellar evolution
Misaligned Circumbinary Disks as Efficient Progenitors of Interstellar Asteroids. Gaseous circumbinary disks (CBDs) that are highly inclined to the binary orbit are commonly observed in nature. These disks harbor particles that can reach large mutual inclinations as a result of nodal precession once the gas disk has dissipated. With n-body simulations that include fragmentation we demonstrate that misaligned disks of particles can be efficient progenitors of interstellar asteroids (ISAs). Collisions that take place between particles with large mutual inclinations have large impact velocities, which can result in mass ejection, with a wide range of fragment sizes and ejection velocities. We explore the binary parameters for which the majority of the terrestrial planet-forming material is ejected rather than accreted into planets. The misalignment required to eject significant material decreases with binary eccentricity. If the distribution of binary eccentricity is uniform and the initial particle CBD orientation relative to the binary orbit is isotropic, about 59% of binaries are more likely to eject the majority of their CBD terrestrial planet disk mass through high-velocity body-body collisions than to retain this material and build terrestrial planets. However, binary-disk interactions during the gas disk phase with nonzero disk viscosity will reduce this fraction. The composition, small size, highly elongated shape, and tumbling motion of 'Oumuamua are consistent with ISAs generated by misaligned CBDs.

Keywords: Extrasolar rocky planets, Binary stars, Asteroids, Interstellar objects, Exoplanet formation
The Discovery of the 528.6 Hz Accreting Millisecond X-Ray Pulsar MAXI J1816-195. We present the discovery of 528.6 Hz pulsations in the new X-ray transient MAXI J1816-195. Using NICER, we observed the first recorded transient outburst from the neutron star low-mass X-ray binary MAXI J1816-195 over a period of 28 days. From a timing analysis of the 528.6 Hz pulsations, we find that the binary system is well described as a circular orbit with an orbital period of 4.8 hr and a projected semimajor axis of 0.26 lt-s for the pulsar, which constrains the mass of the donor star to 0.10-0.55 M ⊙. Additionally, we observed 15 thermonuclear X-ray bursts showing a gradual evolution in morphology over time, and a recurrence time as short as 1.4 hr. We did not detect evidence for photospheric radius expansion, placing an upper limit on the source distance of 8.6 kpc.

Keywords: Low-mass x-ray binary stars, X-ray bursts, Millisecond pulsars
Hubble Space Telescope Imaging Reveals That SN 2015bh Is Much Fainter than Its Progenitor. We present Hubble Space Telescope (HST) imaging of the site of SN 2015bh in the nearby spiral galaxy NGC 2770 taken between 2017 and 2019, nearly four years after the peak of the explosion. In 2017-2018, the transient fades steadily in optical filters before declining more slowly to F814W = -7.1 mag in 2019, ≈4 mag below the level of its eruptive luminous blue variable (LBV) progenitor observed with HST in 2008-2009. The source fades at a constant color of F555W - F814W = 0.4 mag until 2018, similar to SN 2009ip and consistent with a spectrum dominated by interaction of the ejecta with circumstellar material (CSM). A deep optical spectrum obtained in 2021 lacks signatures of ongoing interaction (L Hα  ≲ 1038 erg s-1 for broadened emission ≲2000 km s-1), but indicates the presence of a nearby H II region (≲300 pc). The color evolution of the fading source makes it unlikely that emission from a scattered-light echo or binary OB companion of the progenitor contributes significantly to the flattening of the late-time light curve. The remaining emission in 2019 may plausibly be attributed an evolved/inflated companion or an unresolved (≲3 pc), young stellar cluster. Importantly, the color evolution of SN 2015bh rules out scenarios in which the surviving progenitor is obscured by nascent dust and does not clearly indicate a transition to a hotter, optically faint state. The simplest explanation is that the massive progenitor did not survive. SN 2015bh likely represents a remarkable example of the terminal explosion of a massive star preceded by decades of end-stage eruptive variability.

Keywords: Evolved stars, Massive stars, Luminous blue variable stars, Stellar mass loss, Supernovae
Magnetar Engines in Fast Blue Optical Transients and Their Connections with SLSNe, SNe Ic-BL, and lGRBs. We fit the multiband lightcurves of 40 fast blue optical transients (FBOTs) with the magnetar engine model. The mass of the FBOT ejecta, the initial spin period, and the polar magnetic field of the FBOT magnetars are respectively constrained to ${M}_{\mathrm{ej}}={0.11}_{-0.09}^{+0.22}\,{M}_{\odot }$ , ${P}_{{\rm{i}}}={9.1}_{-4.4}^{+9.3}\,\mathrm{ms}$ , and ${B}_{{\rm{p}}}={11}_{-7}^{+18}\times {10}^{14}\,{\rm{G}}$ . The wide distribution of the value of B p spreads the parameter ranges of the magnetars from superluminous supernovae (SLSNe) to broad-line Type Ic supernovae (SNe Ic-BL; some are observed to be associated with long-duration gamma-ray bursts), which are also suggested to be driven by magnetars. Combining FBOTs with the other transients, we find a strong universal anticorrelation of ${P}_{{\rm{i}}}\propto {M}_{\mathrm{ej}}^{-0.41}$ , indicating they could share a common origin. To be specific, it is suspected that all of these transients originate from the collapse of extremely stripped stars in close binary systems, but with different progenitor masses. As a result, FBOTs distinguish themselves by their small ejecta masses with an upper limit of ~1 M ⊙, which leads to an observational separation in the rise time of the lightcurves of ~10 days. In addition, FBOTs together with SLSNe can be separated from SNe Ic-BL by an empirical line in the M peak-t rise plane corresponding to an energy requirement of the mass of 56Ni of ~0.3M ej, where M peak is the peak absolute magnitude of the transients and t rise is the rise time.

Keywords: Magnetars, Light curves, Supernovae
The Planetary Nebula in the 500 Myr Old Open Cluster M37. We report confirmation of a large, evolved, bipolar planetary nebula and its blue, white dwarf central star as a member of the ~500 Myr old Galactic open star cluster M37 (NGC 2099). This is only the third known example of a planetary nebula in a Galactic open cluster and was found via our ongoing program of identifying and studying planetary nebulae-open cluster associations. High confidence in the association comes from the consistent radial velocities and proper motions for the confirmed central star and cluster stars from Gaia, reddening agreement, and location of the planetary nebula well within the tidal cluster boundary. Interestingly, all three Galactic examples have bipolar morphology and likely Type-I chemistry, both characteristics of higher mass progenitors. In this case the progenitor star mass is in the midrange of ~2.8 M ☉. It provides a valuable, additional point on the key stellar initial-to-final mass relation independent of cluster white dwarf estimates and also falls in a gap in the poorly sampled mass region. This planetary nebula also appears to have the largest kinematical age ever determined and implies increased visibility lifetimes when they are located in clusters.

Keywords: Open star clusters, Planetary nebulae
Discovery of γ-Ray Pulsations from PSR J1835-3259B in the Globular Cluster NGC 6652. Motivated by the recent discovery of the pulsar J1835-3259B with a spin period 1.83 ms in the globular cluster (GC) NGC 6652, we analyze the γ-ray data obtained with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope (Fermi) for the GC and detect the pulsations of this millisecond pulsar (MSP) at a 5.4σ confidence level (the weighted H-test value is ~41). From timing analysis of the data, a pulse profile that is similar to the radio one is established. We thus consider that we have detected the γ-ray emission of the MSP, and discuss the implications. Based on the results of our analysis and different studies of the sources in the GC, the observed γ-ray emission from the GC could mainly arise from this MSP, like the previous two cases in the GCs NGC 6624 and NGC 6626. Assuming this is the case, the pulsar, at the GC's distance of 9.46 kpc and having a spin-down luminosity of ≤4.3 × 1035 erg s-1, would have a γ-ray luminosity of ≃(5.04 ± 0.44) × 1034 erg s-1 and a γ-ray efficiency of ≳0.12.

Keywords: Globular star clusters, Gamma-rays, Pulsars
A New Cold Stream near the Southern Galactic Pole. We report the discovery of a cold stream near the southern Galactic pole (dubbed as SGP-S) detected in Gaia Early Data Release 3. The stream is at a heliocentric distance of ~9.5 kpc and spans nearly 58° by 0.°6 on sky. The color-magnitude diagram of SGP-S indicates an old and metal-poor (age ~12 Gyr, [M/H] ~ -2.0 dex) stellar population. The stream's surface brightness reaches an exceedingly low level of Σ G  ≃ 36.2 mag arcsec-2. Neither extant globular clusters nor other known streams are associated with SGP-S.

Keywords: Globular star clusters, Tidal tails, Milky Way stellar halo, Milky Way Galaxy
The Ratio of Perpendicular and Parallel Diffusion Coefficients of Low-energy Particles in Turbulent Space Plasmas. Recently an improved nonlinear theory for the transport of energetic particles across a mean magnetic field has been developed. The latter theory is called the field line-particle decorrelation theory and is the first analytical theory that agrees with test-particle simulations without the need of a correction parameter, nor does the theory contain any other free parameter. In the current paper we derive analytical forms for the ratio of perpendicular and parallel spatial diffusion coefficients κ ⊥/κ ∥ of low-energy particles. In the considered limit the latter ratio is constant meaning that it does not depend on particle energy or rigidity. It is shown that the ratio always has the form ${\kappa }_{\perp }/{\kappa }_{\parallel }={a}^{2}\delta {B}_{x}^{2}/{B}_{0}^{2}$ if a two-dimensional turbulence model is employed. Furthermore, the parameter a 2 depends only on the shape of the turbulence spectrum but not on the magnetic fields. The obtained results can be important for a variety of applications such as studies of solar modulation and diffusive shock acceleration.

Keywords: Interplanetary turbulence, Cosmic rays
Transit Light Curves for Exomoons: Analytical Formalism. The photometric transit method has been the most effective method to detect and characterize exoplanets as several ground based as well as space based survey missions have discovered thousands of exoplanets using this method. With the advent of the upcoming next generation large telescopes, the detection of exomoons in a few of these exoplanetary systems is very plausible. In this paper, we present a comprehensive analytical formalism in order to model the transit light curves for such moon-hosting exoplanets. In order to achieve analytical formalism, we have considered circular orbit of the exomoon around the host planet, which is indeed the case for tidally locked moons. The formalism uses the radius and orbital properties of both the host planet and its moon as model parameters. The coalignment or noncoalignment of the orbits of the planet and the moon are parameterized using two angular parameters and thus can be used to model all the possible orbital alignments for a star-planet-moon system. This formalism also provides unique and direct solutions to every possible star-planet-moon three circular body alignment. Using the formula derived, a few representative light curves are also presented.

Keywords: Transit photometry, Natural satellites (Extrasolar), Exoplanets
Broadband X-Ray Spectroscopy and Estimation of Spin of the Galactic Black Hole Candidate GRS 1758-258. We present the results of a broadband (0.5-78 keV) X-ray spectral study of the persistent Galactic black hole X-ray binary GRS 1758-258 observed simultaneously by Swift and NuSTAR. Fitting with an absorbed power-law model revealed a broad Fe line and reflection hump in the spectrum. We used different flavors of the relativistic reflection model for the spectral analysis. All models indicate the spin of the black hole in GRS 1758-258 is &gt;0.92. The source was in the low hard state during the observation, with the hot electron temperature of the corona estimated to be kT  e  ~ 140 keV. The black hole is found to be accreting at ~1.5% of the Eddington limit during the observation, assuming the black hole mass of 10 M ⊙ and distance of 8 kpc.

Keywords: Accretion, Black hole physics, High energy astrophysics, Low-mass x-ray binary stars, Astrophysical black holes
The Impact of Inelastic Collisions with Hydrogen on NLTE Copper Abundances in Metal-poor Stars. We investigate the non-local thermodynamic equilibrium (non-LTE, hereafter NLTE) analysis for Cu I lines with the updated model atom that includes quantum-mechanical rate coefficients of Cu + H and Cu+ + H- inelastic collisions from the recent study of Belyaev et al. The influence of these data on NLTE abundance determinations has been performed for six metal-poor stars in a metallicity range of -2.59 dex ≤ [Fe/H] ≤ -0.95 dex. For Cu I lines, the application of accurate atomic data leads to a decrease in the departure from LTE and lower copper abundances compared to that obtained with Drawin's theoretical approximation. To verify our adopted copper atomic model, we also derived the LTE copper abundances of Cu II lines for the sample stars. A consistent copper abundance from the Cu I (NLTE) and Cu II (LTE) lines has been obtained, which indicates the reliability of our copper atomic model. It is noted that the [Cu/Fe] ratios increase with increasing metallicity when ~-2.0 dex &lt; [Fe/H] &lt; ~-1.0 dex, favoring a secondary (metallicity-dependent) copper production.

Keywords: Stellar abundances, Stellar physics, Milky Way evolution
Extremely Low-mass White Dwarf Stars Observed in Gaia DR2 and LAMOST DR8. We present the first results from our ongoing project to study extremely low-mass (ELM) white dwarfs (WDs) (M ≤ 0.3M ⊙) with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectra. Based on the LAMOST DR8 spectral database, we analyzed 136 ELM WD candidates selected from Gaia DR2 data and 12 known objects previously identified by the ELM Survey. The atmospheric parameters and radial velocities of these stars were obtained by fitting the LAMOST low-resolution spectra. After comparing the atmospheric parameters of the 12 known objects from this work to the results reported by the ELM Survey, we demonstrated the potential of LAMOST spectra in probing into the nature of ELM WDs. Based on the atmospheric parameters and Gaia EDR3 data, we identified 21 new high-probability ELM WDs with masses M ≤ 0.3M ⊙ and parallax estimates that agree to within a factor of 3. Two of them, J0338+4134 and J1129+4715, show significant radial velocity variability and are very likely to be binary systems containing at least one ELM WD.

Keywords: White dwarf stars, Compact objects