Sazuna/UAT_keywords huggingface dataset:
"Ashfall" Induced by Molecular Outflow in Protostar Evolution. Dust growth and its associated dynamics play key roles in the first phase of planet formation in young stellar objects. Observations have detected signs of dust growth in very young protoplanetary disks. Furthermore, signs of planet formation, gaps in the disk at a distance of several tens of au from the central protostar, are also reported. From a theoretical point of view, however, planet formation in the outer regions is difficult due to the rapid inward drift of dust, called the radial drift barrier. Here, on the basis of three-dimensional magnetohydrodynamical simulations of disk evolution with dust growth, we propose a mechanism called the "ashfall" phenomenon, induced by a powerful molecular outflow driven by a magnetic field that may circumvent the radial drift barrier. We find that the large dust that grows to a size of about a centimeter in the inner region of a disk is entrained by an outflow from the disk. Then, large dust decoupled from gas is ejected from the outflow due to centrifugal force, enriching the grown dust in the envelope and eventually falls onto the outer edge of the disk. The overall process is similar to the behavior of ashfall from volcanic eruptions. In the ashfall phenomenon, the Stokes number of dust increases by reaccreting to the less dense disk outer edge. This may allow the dust grains to overcome the radial drift barrier. Consequently, the ashfall phenomenon can provide a crucial assist for making the formation of the planetesimals in outer regions of the disk possible, and hence the formation of wide-orbit planets and gaps.

Keywords: Circumstellar dust, Circumstellar disks
Novel Model of an Ultra-stripped Supernova Progenitor of a Double Neutron Star. Recent discoveries of double neutron star (DNS) mergers and ultra-stripped supernovae (SNe) raise the questions of their origin and connection. We present the first 1D model of a DNS progenitor system that is calculated self-consistently until an ultra-stripped iron core collapse. We apply the MESA code starting from a post-common-envelope binary consisting of a 1.35 M⊙ NS and a 3.20 M⊙ zero-age main-sequence helium star and continue the modeling via Case BB Roche-lobe overflow until the infall velocity of the collapsing iron core exceeds 1000 km s-1. The exploding star has a total mass of ~1.90 M⊙, consisting of a ~0.29 M⊙ He-rich envelope embedding a CO core of ~1.61 M⊙ and an iron-rich core of ~1.50 M⊙. The resulting second-born NS has an estimated mass of ~1.44 M⊙, and we discuss the fate of the post-SN system, as well as the mild recycling of the first-born NS. Depending on the initial conditions, this family of systems is anticipated to reproduce the DNS mergers detected by the LIGO network.

Keywords: Neutron stars, X-ray binary stars, Interacting binary stars, Gravitational wave sources, Stellar evolution
Constraints on Weak Supernova Kicks from Observed Pulsar Velocities. Observations of binary pulsars and pulsars in globular clusters suggest that at least some pulsars must receive weak natal kicks at birth. If all pulsars received strong natal kicks above 50 km s-1, those born in globular clusters would predominantly escape, while wide binaries would be disrupted. On the other hand, observations of transverse velocities of isolated radio pulsars indicate that only 5 ± 2% have velocities below 50 km s-1. We explore this apparent tension with rapid binary population synthesis modeling. We propose a model in which supernovae with characteristically low natal kicks (e.g., electron-capture supernovae) only occur if the progenitor star has been stripped via binary interaction with a companion. We show that this model naturally reproduces the observed pulsar speed distribution and without reducing the predicted merging double neutron star yield. We estimate that the zero-age main-sequence mass range for noninteracting progenitors of electron-capture supernovae should be no wider than ≈0.2 M⊙.

Keywords: Neutron stars, Supernovae, Binary pulsars, Pulsars
Molecules and Outflows in NML Cygni: New Insights from a 1 mm Spectral Line Survey. A sensitive (1σ rms ≤ 3 mK) 1 mm spectral survey (214.5-285.5 GHz) of the oxygen-rich circumstellar envelope of the red hypergiant NML Cygni (NML Cyg) has been conducted using the Sub-millimeter Telescope (SMT) of the Arizona Radio Observatory (ARO). Over 100 spectral lines were detected, arising from 17 different molecules, including the carbon-bearing species CO, HCN, HCO+, CN, and HNC; sulfur- and silicon-containing compounds H2S, SO, SO2, SiO, and SiS; and more exotic NaCl and AlO. The 1 mm spectrum of NML Cyg closely resembles that of VY Canis Majoris (VY CMa) suggesting that the chemistries of hypergiant stars are similar. The line profiles in NML Cyg consist of multiple velocity features, particularly evident in SO2 and SO. In addition to a spherical wind at the star's systemic velocity, the spectra suggest an asymmetric, blueshifted component near VLSR = -21 ± 3 km s-1 and a collimated, redshifted component near 15 ± 3 km s-1, positioned ~34° and ~12°, respectively, from the line of sight. The red- and blueshifted flows appear to be randomly oriented, and likely trace sporadic mass loss events. Their LSR velocities align closely with those of 22 GHz water masers, suggesting an NE-SE orientation. The winds may also be associated with the asymmetric nebula in F555W HST images but extending to 5″ (~600R*). NML Cyg appears to be another example of rare, massive stars with collimated, episodic ejections, analogous to Betelgeuse and VY CMa, lending support for an important new mass loss mechanism-surface activity.

Keywords: Circumstellar envelopes, Millimeter astronomy, Molecular spectroscopy, Astrochemistry, Stellar mass loss, Stellar winds, Hypergiant stars, Stellar evolution
Aqueous Alteration on Asteroids Simplifies Soluble Organic Matter Mixtures. Biologically relevant abiotic extraterrestrial soluble organic matter (SOM) has been widely investigated to study the origin of life and the chemical evolution of protoplanetary disks. Synthesis of biologically relevant organics, in particular, seems to require aqueous environments in the early solar system. However, SOM in primitive meteorites includes numerous chemical species besides the biologically relevant ones, and the reaction mechanisms that comprehensively explain the complex nature of SOM are unknown. Besides, the initial reactants, which formed before asteroid accretion, were uncharacterized. We examined the mass distribution of SOM extracted from three distinct Tagish Lake meteorite fragments, which exhibit different degrees of aqueous alteration though they originated from a single asteroid. We report that mass distributions of SOM in the primordial fragments are well fit by the Schulz-Zimm (SZ) model for the molecular weight distribution patterns found in chain-growth polymerization experiments. Also, the distribution patterns diverge further from SZ with increasing degrees of aqueous alteration. These observations imply that the complex nature of the primordial SOM (1) was established before severe alteration on the asteroid, (2) possibly existed before parent-body accretion, and (3) later became simplified on the asteroid. Therefore, aqueous reactions on asteroids are not required conditions for cultivating complex SOM. Furthermore, we found that overall H/C ratios of SOM decrease with increasing aqueous alteration, and the estimate of H loss from the SOM is 10%-30%. Organics seem to be a significant H2 source that may have caused subsequent chemical reactions in the Tagish Lake meteorite parent body.

Keywords: Solar nebulae, Solar system formation, Carbonaceous chondrites, Protoplanetary disks
Harmonic Maser Emissions from Electrons with Loss-cone Distribution in Solar Active Regions. Electron cyclotron maser emission (ECME) is regarded as a plausible source for coherent radio radiations from solar active regions (e.g., solar radio spikes). In this Letter, we present a 2D3V fully kinetic electromagnetic particle-in-cell simulation to investigate the wave excitations and subsequent nonlinear processes induced by the energetic electrons in the loss-cone distribution. The ratio of the plasma frequency to the electron gyrofrequency ωpe/Ωce is set to 0.25, adequate for solar active region conditions. As a main result, we obtain strong emissions at the second-harmonic X mode (X2). While the fundamental X mode (X1) and the Z mode are amplified directly via the electron cyclotron maser instability, the X2 emissions can be produced by nonlinear coalescence between two Z modes and between Z and X1 modes. This represents a novel generation mechanism for the harmonic emissions in plasmas with a low value of ωpe/Ωce, which may resolve the escaping difficulty of explaining solar radio emissions with the ECME mechanism.

Keywords: Plasma astrophysics, Solar active regions, Solar radio emission, Solar corona, Solar activity
Investigating Protoplanetary Disk Cooling through Kinematics: Analytical GI Wiggle. It is likely that young protostellar disks undergo a self-gravitating phase. Such systems are characterized by the presence of a spiral pattern that can be either in a quasi-steady state or in a nonlinear unstable condition. This spiral wave affects both the gas dynamics and kinematics, resulting in deviations from the Keplerian rotation. Recently, a lot of attention has been devoted to kinematic studies of planet-forming environments, and we are now able to measure even small perturbations of velocity field (≲1% of the Keplerian speed) thanks to high spatial and spectral resolution observations of protostellar disks. In this work, we investigate the kinematic signatures of gravitational instability: we perform an analytical study of the linear response of a self-gravitating disk to a spiral-like perturbation, focusing our attention on the velocity field perturbations. We show that unstable disks have clear kinematic imprints into the gas component across the entire disk extent, due to the GI spiral wave perturbation, resulting in deviations from Keplerian rotation. The shape of these signatures depends on several parameters, but they are significantly affected by the cooling factor: by detecting these features, we can put constraints on protoplanetary disk cooling.

Keywords: Stellar accretion disks, Gravitational instability, Astrophysical fluid dynamics
Black Hole Mergers of AGN Origin in LIGO-Virgo's O1-O3a Observing Periods. The origin of the black hole mergers detected by LIGO-Virgo remains an open question. While the unusual mass and spin of a few events constrain their possible astrophysical formation mechanisms, it is difficult to classify the bulk of the observed mergers. Here we consider the distribution of masses and spins in LIGO-Virgo's first two observing catalogs. We show that, for black holes in the mass gap, our fiducial active galactic nucleus (AGN) model is preferred over a parametric mass-spin model fit to the full GWTC-2 merger sample (Bayes factor ${ \mathcal B }\gt 10$ ). This preference, nevertheless, depends on uncertain AGN model parameters. We further show that a 20% fractional contribution of the detected events of an AGN-disk origin reproduces well the observed black hole mass distribution in the pair-instability mass gap, while only marginally contributing to the lower-mass detected population. The overall AGN contribution corresponds to a black hole merger rate of about 2.5 Gpc-3 yr-1, comparable to theoretical expectations.

Keywords: Gravitational wave astronomy, Gravitational waves
Observations of Forbush Decreases of Cosmic-Ray Electrons and Positrons with the Dark Matter Particle Explorer. The Forbush decrease (FD) represents the rapid decrease of the intensities of charged particles accompanied with the coronal mass ejections or high-speed streams from coronal holes. It has been mainly explored with the ground-based neutron monitor network, which indirectly measures the integrated intensities of all species of cosmic rays by counting secondary neutrons produced from interaction between atmospheric atoms and cosmic rays. The space-based experiments can resolve the species of particles but the energy ranges are limited by the relatively small acceptances except for the most abundant particles like protons and helium. Therefore, the FD of cosmic-ray electrons and positrons have just been investigated by the PAMELA experiment in the low-energy range (&lt;5 GeV) with limited statistics. In this paper, we study the FD event that occurred in 2017 September with the electron and positron data recorded by the Dark Matter Particle Explorer. The evolution of the FDs from 2 GeV to 20 GeV with a time resolution of 6 hr are given. We observe two solar energetic particle events in the time profile of the intensity of cosmic rays, the earlier, and weaker, one has not been shown in the neutron monitor data. Furthermore, both the amplitude and recovery time of fluxes of electrons and positrons show clear energy dependence, which is important in probing the disturbances of the interplanetary environment by the coronal mass ejections.

Keywords: Forbush effect, Solar coronal mass ejections, Cosmic rays
Eridanus IV: an Ultra-faint Dwarf Galaxy Candidate Discovered in the DECam Local Volume Exploration Survey. We present the discovery of a candidate ultra-faint Milky-Way satellite, Eridanus IV (DELVE J0505-0931), detected in photometric data from the DECam Local Volume Exploration survey (DELVE). Eridanus IV is a faint (MV = - 4.7 ± 0.2), extended ( ${r}_{1/2}={75}_{-13}^{+16}\,\mathrm{pc}$ ), and elliptical (ϵ = 0.54 ± 0.1) system at a heliocentric distance of ${76.7}_{-6.1}^{+4.0}\,\mathrm{kpc}$ , with a stellar population that is well described by an old, metal-poor isochrone (age of τ ~ 13.0 Gyr and metallicity of [Fe/H] ≲ - 2.1 dex). These properties are consistent with the known population of ultra-faint Milky-Way satellite galaxies. Eridanus IV is also prominently detected using proper-motion measurements from Gaia Early Data Release 3, with a systemic proper motion of $({\mu }_{\alpha }\cos \delta ,{\mu }_{\delta })=(+0.25\pm 0.06,-0.10\pm 0.05)$ mas yr-1 measured from its horizontal branch and red-giant-branch member stars. We find that the spatial distribution of likely member stars hints at the possibility that the system is undergoing tidal disruption.

Keywords: Horizontal branch stars, Dwarf galaxies
Search for Multi-flare Neutrino Emissions in 10 yr of IceCube Data from a Catalog of Sources. A recent time-integrated analysis of a catalog of 110 candidate neutrino sources revealed a cumulative neutrino excess in the data collected by IceCube between 2008 April 6 and 2018 July 10. This excess, inconsistent with the background hypothesis in the Northern Hemisphere at the 3.3σ level, is associated with four sources: NGC 1068, TXS 0506+056, PKS 1424+240, and GB6 J1542+6129. This Letter presents two time-dependent neutrino emission searches on the same data sample and catalog: a point-source search that looks for the most significant time-dependent source of the catalog by combining space, energy, and time information of the events, and a population test based on binomial statistics that looks for a cumulative time-dependent neutrino excess from a subset of sources. Compared to previous time-dependent searches, these analyses enable a feature to possibly find multiple flares from a single direction with an unbinned maximum-likelihood method. M87 is found to be the most significant time-dependent source of this catalog at the level of 1.7σ post-trial, and TXS 0506+056 is the only source for which two flares are reconstructed. The binomial test reports a cumulative time-dependent neutrino excess in the Northern Hemisphere at the level of 3.0σ associated with four sources: M87, TXS 0506+056, GB6 J1542+6129, and NGC 1068.

Keywords: Particle astrophysics, Neutrino astronomy, High energy astrophysics
Effects of Magnetic Fields in Hot White Dwarfs. In this work, we study the effects of magnetic fields on hot white dwarfs. We model their interior as a nuclei lattice surrounded by a relativistic free Fermi gas of electrons, accounting for effects from temperature, Landau levels, and anomalous magnetic moment. We find that, at low densities (corresponding to the outer regions of star), both temperature and magnetic field effects play an important role in the calculation of microscopic thermodynamical quantities. To study macroscopic stellar structures within a general-relativistic approach, we numerically solve the coupled Einstein-Maxwell equations for fixed entropy per particle configurations and discuss how temperature affects stellar magnetic field profiles, masses, and radii.

Keywords: White dwarf stars, General relativity, Stellar magnetic fields, Degenerate matter
Gamma-Ray Burst in a Binary System. Regardless of their different types of progenitors and central engines, gamma-ray bursts (GRBs) were always assumed to be standalone systems after they formed. Little attention has been paid to the possibility that a stellar companion can still accompany a GRB itself. This paper investigates such a GRB-involved binary system and studies the effects of the stellar companion on the observed GRB emission when it is located inside the jet opening angle. Assuming a typical emission radius of ~1015 cm, we show that the blockage by a companion star with a radius of Rc ~ 67 R⊙ becomes non-negligible when it is located within a typical GRB jet opening angle (e.g., ~10°) and beyond the GRB emission site. In such a case, an on-axis observer will see a GRB with a similar temporal behavior but 25% dimmer. On the other hand, an off-axis observer outside the jet opening angle (hence missing the original GRB) can see a delayed, "reflected" GRB, which is much fainter in brightness, much wider in the temporal profile, and slightly softer in energy. Our study can naturally explain the origin of some low-luminosity GRBs. Moreover, we also point out that the companion star may be shocked if it is located inside the GRB emission site, which can give rise to an X-ray transient or a GRB followed by a delayed X-ray bump on top of X-ray afterglows.

Keywords: Gamma-ray bursts, Binary stars
Observations of Shock Propagation through Turbulent Plasma in the Solar Corona. Eruptive activity in the solar corona can often lead to the propagation of shock waves. In the radio domain the primary signature of such shocks are type II radio bursts, observed in dynamic spectra as bands of emission slowly drifting toward lower frequencies over time. These radio bursts can sometimes have an inhomogeneous and fragmented fine structure, but the cause of this fine structure is currently unclear. Here we observe a type II radio burst on 2019 March 20th using the New Extension in Nançay Upgrading LOFAR, a radio interferometer observing between 10-85 MHz. We show that the distribution of size scales of density perturbations associated with the type II fine structure follows a power law with a spectral index in the range of α = -1.7 to -2.0, which closely matches the value of -5/3 expected of fully developed turbulence. We determine this turbulence to be upstream of the shock, in background coronal plasma at a heliocentric distance of ~2 R⊙. The observed inertial size scales of the turbulent density inhomogeneities range from ~62 Mm to ~209 km. This shows that type II fine structure and fragmentation can be due to shock propagation through an inhomogeneous and turbulent coronal plasma, and we discuss the implications of this on electron acceleration in the coronal shock.

Keywords: Solar coronal mass ejection shocks, Solar physics, Solar particle emission, Solar coronal mass ejections
The Role of Dust, UV Luminosity and Large-scale Environment on the Escape of Lyα Photons: A Case Study of a Protocluster Field at z = 3.1. We present a detailed characterization of the Lyα properties for 93 Lyα emitters (LAEs) at z ~ 3.1 selected from the D1 field of the Canada-France-Hawaii Telescope Legacy Survey, including 24 members of a massive protocluster. The median-stacked Lyα image shows an extended Lyα halo (LAH) surrounding the galaxy with the exponential scale length 4.9 ± 0.7 kpc, which accounts for roughly half of the total line flux. Accounting for the LAH contribution, the total Lyα escape fraction, fesc, is 40% ± 26%. Combining the data set with existing measurements, we find a dependence of fesc on the galaxy's UV slope (β) and UV luminosity (LUV). The simultaneous use of both parameters allows prediction of fesc within 0.18 dex, a substantial improvement over 0.23 dex when only β is used. The correlation between fesc and E(B - V) suggests that Lyα photons undergo interstellar dust attenuation in a similar manner to continuum photons. Yet, Lyα transmission is typically higher than that expected for continuum photons at a similar wavelength by a factor, which depends on UV luminosity, up to 2 in the samples we studied. These results hint at complex geometries and physical conditions of the interstellar medium, which affect the Lyα transmission or production. Alternatively, the dust law may change with luminosity leading to an over- or underestimation of fesc. Finally, we report that protocluster LAEs tend to be bluer and more UV luminous than their field cousins, resulting in systematically higher fesc values. We speculate that it may be due to the widespread formation of young low-mass galaxies in dense gas-rich environments.

Keywords: Galaxy formation, High-redshift galaxies, Galaxy evolution
TESS Observations of Be Stars: General Characteristics and the Impulsive Magnetic Rotator Model. Evidence of rotational light modulation in 30%-40% of normal B stars is presented, suggesting the presence of starspots and photospheric activity. On this basis, we propose that mass loss in Be stars is a result of magnetic reconnection coupled with rapid but not necessarily near-critical rotation. The ejected matter is trapped at two diametrically opposed locations where the magnetic and geometric equators intersect. Nonradial pulsation plays no role in the mass loss and in the short-period light and line profile variations, though Be stars may pulsate as SPB or β Cep variables. The model allows many of the major characteristics of Be stars to be understood, including the frequency pattern in the periodogram, allowing the approximate rotational frequency to be identified. From a large number of Be stars observed by TESS, it is shown that the resulting equatorial rotational velocities, v, are consistent with the projected rotational velocities, $v\sin i$ . Furthermore, it is shown that Be stars are rotating in a broad range of 30%-100% of the critical rotational velocity. This agrees with several statistical $v\sin i$ analyses, which all show that Be stars are very unlikely to be rotating at near-critical velocities.

Keywords: Starspots, Emission line stars, Stellar properties, Early-type emission stars, Stellar rotation, Be stars, B(e) stars