Sazuna/UAT_keywords huggingface dataset:
Evidence of Accretion Burst: The Viscously Heated Inner Disk of the Embedded Protostar IRAS 16316-1540. Outbursts of young stellar objects occur when the mass accretion rate suddenly increases. However, such outbursts are difficult to detect for deeply embedded protostars due to their thick envelope and the rarity of outbursts. The near-IR spectroscopy is a useful tool to identify ongoing outburst candidates by the characteristic absorption features that indicate a disk origin. However, without high-resolution spectroscopy, the spectra of outburst candidates can be confused with the late-type stars since they have similar spectral features. For the protostar IRAS 16316-1540, the near-IR spectrum has line equivalent widths that are consistent with M-dwarf photospheres. However, our high-resolution IGRINS spectra reveal that the absorption lines have boxy and/or double-peaked profiles, as expected from a disk and not the star. The continuum emission source is likely the hot, optically thick disk, heated by viscous accretion. The projected disk rotation velocity of 41 ± 5 km s-1 corresponds to ~0.1 au. Based on the result, we suggest IRAS 16316-1540 as an ongoing outburst candidate. Viscous heating of disks is usually interpreted as evidence for ongoing bursts, which may be more common than previously estimated from low-resolution near-IR spectra.

Keywords: High resolution spectroscopy, Protostars, Young stellar objects, Protoplanetary disks
Effect of Dust Size on the Near-infrared Spectra (1.0-5.0 μm) of Brown Dwarf Atmospheres. In this study, we demonstrate the dependence of atmospheric dust size on the near-infrared spectra of ten L dwarfs, and constrain the sizes of dust grains in each L dwarf atmosphere. In previous studies, by comparing observed and modeled spectra, it was suggested that the deviations of their spectral shapes from theoretical prediction are general characteristics. Here, we focus on the dust size in brown dwarf atmospheres to understand the observed spectra. We confirm that changing the dust size changes the temperature-pressure structure of the atmosphere, with the shape of the spectrum changing accordingly. At the wavelength at which dust is the main absorber of radiation (the dust-dominated regime), a large dust opacity combined with a medium grain size, e.g., 0.1 μm, results in a low photospheric temperature, and thus a small flux. Conversely, for the wavelength at which gas absorption is dominant (the gas-dominated regime), a large dust opacity modifies the temperature-pressure structure, resulting in a high photospheric temperature, which corresponds to large flux emissions. Taking into account the size effect, we compare the model spectral fluxes in the wavelength range 1-5 μm with the observational ones to constrain the main dust size in the atmosphere of each of the ten L dwarfs observed with AKARI and SpeX or CGS4. Ultimately, we reveal that the observed data are reproduced with higher fidelity by models based on a medium dust size of 0.1-3.0 μm for six of these L dwarfs; therefore, we suggest that such atmospheric dust sizes apply to the majority of L dwarfs.

Keywords: Brown dwarfs, Molecular spectroscopy, L dwarfs, Spectroscopy, Stellar photospheres, Stellar atmospheres, Near infrared astronomy
On the Use of Field RR Lyrae As Galactic Probes: IV. New Insights Into and Around the Oosterhoff Dichotomy. We discuss the largest and most homogeneous spectroscopic data set of field RR Lyrae variables (RRLs) available to date. We estimated abundances using both high-resolution and low-resolution (∆S method) spectra for fundamental (RRab) and first overtone (RRc) RRLs. The iron abundances for 7941 RRLs were supplemented with similar estimates that are available in the literature, ending up with 9015 RRLs (6150 RRab, 2865 RRc). The metallicity distribution shows a mean value of ⟨[Fe/H]⟩ = -1.51 ± 0.01, and σ(standard deviation) = 0.41 dex with a long metal-poor tail approaching [Fe/H] ≃ - 3 and a sharp metal-rich tail approaching solar iron abundance. The RRab variables are more metal-rich (⟨[Fe/H]⟩ab = -1.48 ± 0.01, σ = 0.41 dex) than RRc variables (⟨[Fe/H]⟩c = -1.58 ± 0.01, σ = 0.40 dex). The relative fraction of RRab variables in the Bailey diagram (visual amplitude versus period) located along the short-period (more metal-rich) and the long-period (more metal-poor) sequences are 80% and 20%, while RRc variables display an opposite trend, namely 30% and 70%, respectively. We found that the pulsation period of both RRab and RRc variables steadily decreases when moving from the metal-poor to the metal-rich regime. The visual amplitude shows the same trend, but RRc amplitudes are almost two times more sensitive than RRab amplitudes to metallicity. We also investigated the dependence of the population ratio (Nc/Ntot) of field RRLs on the metallicity and we found that the distribution is more complex than in globular clusters. The population ratio steadily increases from ~0.25 to ~0.36 in the metal-poor regime, it decreases from ~0.36 to ~0.18 for -1.8 ≤ [Fe/H] ≤ -0.9 and it increases to a value of ~0.3 approaching solar iron abundance. * Based on observations obtained with the du Pont telescope at Las Campanas Observatory, operated by Carnegie Institution for Science. Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. Based partly on data obtained with the STELLA robotic telescopes in Tenerife, an AIP facility jointly operated by AIP and IAC. Some of the observations reported in this paper were obtained with the Southern African Large Telescope (SALT). Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere.

Keywords: RR Lyrae variable stars, Milky Way stellar halo, Spectroscopy
Energetic Electron Observations by Parker Solar Probe/IS⊙IS during the First Widespread SEP Event of Solar Cycle 25 on 2020 November 29. At the end of 2020 November, two coronal mass ejections (CMEs) erupted from the Sun and propagated through the interplanetary medium in the direction of Parker Solar Probe while the spacecraft was located at ~0.81 au. The passage of these interplanetary CMEs (ICMEs) starting on November 29 (DOY 334) produced the largest enhancement of energetic ions and electrons observed by the Integrated Science Investigation of the Sun (IS⊙IS) energetic particle instrument suite on board Parker Solar Probe during the mission's first eight orbits. This was also the first spatially widespread solar energetic particle event observed in solar cycle 25. We investigate several key characteristics of the energetic electron event including the time profile and anisotropy distribution of near-relativistic electrons as measured by IS⊙IS's low-energy Energetic Particle Instrument (EPI-Lo) and compare these observations with contextual data from the Parker Solar Probe Fields Experiment magnetometer. These are the first electron anisotropy measurements from IS⊙IS/EPI-Lo, demonstrating that the instrument can successfully produce these measurements. We find that the electron count rate peaks at the time of the shock driven by the faster of the two ICMEs, implying that the shock parameters of this ICME are conducive to the acceleration of electrons. Additionally, the angular distribution of the electrons during the passage of the magnetic clouds associated with the ICMEs shows significant anisotropy, with electrons moving primarily parallel and antiparallel to the local magnetic field as well as bidirectionally, providing an indication of the ICME's magnetic topology and connectivity to the Sun or magnetic structures in the inner heliosphere.

Keywords: Interplanetary shocks, Solar flares, Solar energetic particles, Solar coronal mass ejection shocks, Solar activity, Solar particle emission
The Evolution of the Lyman-alpha Luminosity Function during Reionization. The time frame in which hydrogen reionization occurred is highly uncertain, but can be constrained by observations of Lyman-alpha (Lyα) emission from distant sources. Neutral hydrogen in the intergalactic medium (IGM) attenuates Lyα photons emitted by galaxies. As reionization progressed the IGM opacity decreased, increasing Lyα visibility. The galaxy Lyα luminosity function (LF) is thus a useful tool to constrain the timeline of reionization. In this work, we model the Lyα LF as a function of redshift, z = 5-10, and average IGM neutral hydrogen fraction, ${\overline{x}}_{{\rm\small{H\unicode{x0026A}}}}$ . We combine the Lyα luminosity probability distribution obtained from inhomogeneous reionization simulations with a model for the UV LF to model the Lyα LF. As the neutral fraction increases, the average number density of Lyα emitting galaxies decreases, and are less luminous, though for ${\overline{x}}_{{\rm\small{H\unicode{x0026A}}}}\lesssim 0.4$ there is only a small decrease in the Lyα LF. We use our model to infer the IGM neutral fraction at z = 6.6, 7.0, and 7.3 from observed Lyα LFs. We conclude that there is a significant increase in the neutral fraction with increasing redshift: ${\overline{x}}_{{\rm\small{H\unicode{x0026A}}}}(z=6.6)={0.08}_{-0.05}^{+0.08},{\overline{x}}_{{\rm\small{H\unicode{x0026A}}}}(z=7.0)=0.28\pm 0.05$ and ${\overline{x}}_{{\rm\small{H\unicode{x0026A}}}}(z=7.3)={0.83}_{-0.07}^{+0.06}$ . We predict trends in the Lyα luminosity density and Schechter parameters as a function of redshift and the neutral fraction. We find that the Lyα luminosity density decreases as the universe becomes more neutral. Furthermore, as the neutral fraction increases, the faint-end slope of the Lyα LF steepens, and the characteristic Lyα luminosity shifts to lower values; hence, we conclude that the evolving shape of the Lyα LF-not just its integral-is an important tool to study reionization.

Keywords: Luminosity function, Early universe, Galaxy evolution, Intergalactic medium, Lyman-alpha galaxies, Reionization, Lyman-break galaxies
Evidence for Cold Plasma in Planetary Nebulae From Radio Observations With the LOw Frequency ARray (LOFAR). We present observations of planetary nebulae with the LOw Frequency ARray (LOFAR) between 120 and 168 MHz. The images show thermal free-free emission from the nebular shells. We have determined the electron temperatures for spatially resolved, optically thick nebulae. These temperatures are 20%-60% lower than those estimated from collisionally excited optical emission lines. This strongly supports the existence of a cold plasma component, which co-exists with hot plasma in planetary nebulae. This cold plasma does not contribute to the collisionally excited lines, but does contribute to recombination lines and radio flux. Neither of the plasma components are spatially resolved in our images, although we infer that the cold plasma extends to the outer radii of planetary nebulae. However, more cold plasma appears to exist at smaller radii. The presence of cold plasma should be taken into account in modeling of radio emission of planetary nebulae. Modelling of radio emission usually uses electron temperatures calculated from collisionally excited optical and/or infrared lines. This may lead to an underestimate of the ionized mass and an overestimate of the extinction correction from planetary nebulae when derived from the radio flux alone. The correction improves the consistency of extinction derived from the radio fluxes when compared to estimates from the Balmer decrement flux ratios.

Keywords: Radio continuum emission, Planetary nebulae, Post-asymptotic giant branch stars, Interstellar dust extinction
A Spatially Resolved Survey of Distant Quasar Host Galaxies. I. Dynamics of Galactic Outflows. We present observations of ionized gas outflows in 11 z = 1.39-2.59 radio-loud quasar host galaxies. Data were taken with the integral field spectrograph OSIRIS and the adaptive optics system at the W.M. Keck Observatory targeting nebular emission lines (Hβ, [O III], Hα, [N II], and [S II]) redshifted into the near-infrared (1-2.4 μm). Outflows with velocities of 500-1700 km s-1 are detected in 10 systems on scales ranging from &lt;1 kpc to 10 kpc with outflow rates from 8-2400 M⊙ yr-1 . For five sources, the outflow momentum rates are 4-80 times LAGN/c, consistent with outflows being driven by an energy-conserving shock. The five other outflows are either driven by radiation pressure or an isothermal shock. The outflows are the dominant source of gas depletion, and we find no evidence for star formation along the outflow paths. For eight objects, the outflow paths are consistent with the orientation of the jets. Yet, given the calculated pressures, we find no evidence of the jets currently doing work on these galactic-scale ionized outflows. We find that galactic-scale feedback occurs well before galaxies establish a substantial fraction of their stellar mass, as expected from local scaling relationships.

Keywords: AGN host galaxies, Supermassive black holes, Quasars, Emission line galaxies, Radio loud quasars, Galaxy evolution
ALMA CO Observations of the Mixed-morphology Supernova Remnant W49B: Efficient Production of Recombining Plasma and Hadronic Gamma Rays via Shock-Cloud Interactions. We carried out new CO(J = 2-1) observations toward the mixed-morphology supernova remnant (SNR) W49B with the Atacama Large Millimeter/submillimeter Array. We found that CO clouds at ~10 km s-1 show a good spatial correspondence to the synchrotron radio continuum as well as to an X-ray deformed shell. The bulk mass of molecular clouds accounts for the western part of the shell, not the eastern shell, where near-infrared H2 emission is detected. The molecular clouds at ~10 km s-1 show higher kinetic temperatures of ~20-60 K, suggesting that modest shock heating occurred. The expanding motion of the clouds with ΔV ~ 6 km s-1 was formed by strong winds from the progenitor system. We argue that the barrel-like structure of Fe-rich ejecta was possibly formed not only by an asymmetric explosion, but also by interactions with dense molecular clouds. We also found a negative correlation between the CO intensity and the electron temperature of recombining plasma, implying that the origin of the high-temperature recombining plasma in W49B can be understood to be the thermal conduction model. The total energy of accelerated cosmic-ray protons Wp is estimated to be ~2 × 1049 erg by adopting an averaged gas density of ~650 ± 200 cm-3. The SNR age-Wp diagram indicates that W49B shows one of the highest in situ values of Wp among gamma-ray-bright SNRs.

Keywords: Gamma-ray sources, Supernova remnants, Cosmic ray sources, X-ray sources, Interstellar medium
Long Term Evolution of Surface Features on the Red Supergiant AZ Cyg. We present H-band interferometric observations of the red supergiant (RSG) AZ Cyg that were made with the Michigan Infra-Red Combiner (MIRC) at the six-telescope Center for High Angular Resolution Astronomy (CHARA) Array. The observations span 5 yr (2011-2016), which offers insight into the short and long-term evolution of surface features on RSGs. Using a spectrum of AZ Cyg obtained with SpeX on the NASA InfraRed Telescope Facility (IRTF) and synthetic spectra calculated from spherical MARCS, spherical PHOENIX, and SAtlas model atmospheres, we derive Teff is between 3972 K and 4000 K and $\mathrm{log}\,g$ between -0.50 and 0.00, depending on the stellar model used. Using fits to the squared visibility and GAIA parallaxes, we measure its average radius $R={911}_{-50}^{+57}\,{R}_{\odot }$ . Reconstructions of the stellar surface using our model-independent imaging codes SQUEEZE and OITOOLS.jl show a complex surface with small bright features that appear to vary on a timescale of less than one year and larger features that persist for more than one year. The 1D power spectra of these images suggest a characteristic size of 0.52-0.69 R⋆ for the larger, long lived features. This is close to the values of 0.51-0.53 R⋆ that are derived from 3D RHD models of stellar surfaces. We conclude that interferometric imaging of this star is in line with predictions of 3D RHD models but that short-term imaging is needed to more stringently test predictions of convection in RSGs.

Keywords: Optical interferometry, Stellar properties, Red supergiant stars, Evolved stars, Stellar surfaces
Solar Cycle Evolution of Filaments over a Century: Investigations with the Meudon and McIntosh Hand-drawn Archives. Hand-drawn synoptic maps from the Meudon Observatory (1919 onwards) and the McIntosh archive (1967 onwards) are two important sources of long-term, manually recorded filament observations. In this study, we calibrate the Meudon maps and subsequently identify filaments through an automated method. We extract physical parameters from this filament database and perform a comparative study of their long-term evolution focusing on the cotemporal period of the McIntosh and Meudon observations. The spatiotemporal evolution of filaments manifests in the form of a filament butterfly diagram, further indicating that they are intimately related to the large-scale solar cycle. Physical descriptors such as the number and length of filaments, which are tracers of the solar surface magnetic field, have cycles which are phase locked with the ~11 yr sunspot cycle. The tilt-angle distribution of filaments-both near to or distant from active region locations-indicates that their origin is due to either large-scale surface magnetic field or inter-active-region field evolution. This study paves the way for constructing a composite series of hand-drawn filament data with minimal gaps stretching over the time span of solar filament observations up to a century. On the one hand, this would serve as a useful constraint for models of magnetic field emergence and evolution on the Sun's surface over multiple solar cycles, and on the other hand, this filament database may be used to guide the reconstruction of filament/prominence associated eruptive events before the space age.

Keywords: Solar cycle, Solar activity, Solar filaments
Multidimensional Parameter Study of Double Detonation Type Ia Supernovae Originating from Thin Helium Shell White Dwarfs. Despite the importance of Type Ia supernovae (SNe Ia) throughout astronomy, the precise progenitor systems and explosion mechanisms that drive SNe Ia are still unknown. An explosion scenario that has gained traction recently is double detonation, in which an accreted shell of He detonates and triggers a secondary detonation in the underlying white dwarf. Our research presents a number of high-resolution, multidimensional, full-star simulations of thin-He-shell, sub-Chandrasekhar-mass white dwarf progenitors that undergo a double detonation. This suite of thin-shell progenitors incorporates He shells that are thinner than those in previous multidimensional studies. We confirm the viability of the double detonation across a range of He-shell parameter space, as well as present bulk yields and ejecta profiles for each progenitor. The yields obtained are generally consistent with previous works and indicate the likelihood of producing observables that resemble SNe Ia. The dimensionality of our simulations allow us to examine features of the double detonation more closely, including the details of the off-center secondary ignition and asymmetric ejecta. We find considerable differences in the high-velocity extent of postdetonation products across different lines of sight. The data from this work will be used to generate predicted observables and may further support the viability of the double detonation scenario as an SN Ia channel, as well as show how the properties of the progenitor or viewing angle may influence trends in observable characteristics.

Keywords: Explosive nucleosynthesis, White dwarf stars, Type Ia supernovae, Supernova dynamics
Radio Observations of an Ordinary Outflow from the Tidal Disruption Event AT2019dsg. We present detailed radio observations of the tidal disruption event (TDE) AT2019dsg, obtained with the Karl G. Jansky Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA), and spanning 55-560 days post disruption. We find that the peak brightness of the radio emission increases until ~200 days and subsequently begins to decrease steadily. Using a standard equipartition analysis, including the effects of synchrotron cooling as determined by the joint VLA-ALMA spectral energy distributions, we find that the outflow powering the radio emission is in roughly free expansion with a velocity of ≈0.07 c, while its kinetic energy increases by a factor of about 5 from 55 to 200 days and plateaus at ≈4.4 × 1048 erg thereafter. The ambient density traced by the outflow declines as radius ≈R-1.7 on a scale of ≈(1-4) × 1016 cm (≈6300-25,000 Rs), followed by a steeper decline to ≈7 × 1016 cm (≈44,000 Rs). Allowing for a collimated geometry, we find that to reach even mildly relativistic velocities (Γ = 2) the outflow requires an opening angle of θj ≈ 2°, which is narrow even by the standards of gamma-ray burst jets; a truly relativistic outflow requires an unphysically narrow jet. The outflow velocity and kinetic energy in AT2019dsg are typical of previous non-relativistic TDEs, and comparable to those from type Ib/c supernovae, raising doubts about the claimed association with a high-energy neutrino event.

Keywords: Black hole physics, Tidal disruption, Radio astronomy, Astrophysical black holes
Prospects of Gravitational Wave Detections from Common Envelope Evolution with LISA. Understanding common envelope (CE) evolution is an outstanding problem in binary evolution. Although the CE phase is not driven by gravitational wave (GW) emission, the inspiraling binary emits GWs that passively trace CE dynamics. Detecting this GW signal would provide direct insight into gas-driven physics. Even a non-detection might offer invaluable constraints. We investigate the prospects of detection of a Galactic CE by LISA. While the dynamical phase of the CE is likely sufficiently loud for detection, it is short and thus rare. We focus instead on the self-regulated phase that proceeds on a thermal timescale. Based on population-synthesis calculations and the (unknown) signal duration in the LISA band, we expect ~0.1-100 sources in the Galaxy during the mission duration. We map the GW observable parameter space of frequency fGW and its derivative ${\dot{f}}_{\mathrm{GW}}$ , remaining agnostic on the specifics of the inspiral and find that signals with signal-to-noise ratios &gt; 10 are possible if the CE stalls at separations such that fGW ≳ 2 × 10-3 Hz. We investigate the possibility of misidentifying the signal with other known sources. If the second derivative ${\ddot{f}}_{\mathrm{GW}}$ can also be measured, the signal can be distinguished from other sources using a GW braking index. Alternatively, coupling LISA with electromagnetic observations of peculiar red giant stars and/or infrared and optical transients, might allow for the disentangling of a Galactic CE from other Galactic and extragalactic GW sources.

Keywords: Binary stars, Interacting binary stars, Gravitational wave astronomy, Common envelope evolution, Common envelope binary stars