Sazuna/UAT_keywords huggingface dataset:
The Star Formation History of a Post-starburst Galaxy Determined from Its Cluster Population. The recent star formation histories (SFHs) of post-starburst galaxies have been determined almost exclusively from detailed modeling of their composite starlight. This has provided important but limited information on the number, strength, and duration of bursts of star formation. In this work, we present a direct and independent measure of the recent SFH of the post-starburst galaxy S12 (plate-mjd-fiber for SDSS 623-52051-207; designated EAS12 in Smercina et al.) from its star cluster population. We detect clusters from high-resolution, UBR optical images taken with the Hubble Space Telescope and compare their luminosities and colors with stellar population models to estimate the ages and masses of the clusters. No clusters younger than ~70 Myr are found, indicating star formation shut off at this time. Clusters formed ~120 Myr ago reach masses up to a ~few × 107 M⊙, several times higher than similar-age counterparts formed in actively merging galaxies like the Antennae and NGC 3256. We develop a new calibration based on known properties for eight nearby galaxies to estimate the star formation rate (SFR) of a galaxy from the mass of the most massive cluster, Mmax. The cluster population indicates that S12 experienced an extremely intense but short-lived burst ~120 Myr ago, with an estimated peak of ${500}_{-250}^{+500}\,{M}_{\odot }\,{{\rm{yr}}}^{-1}$ and duration of 50 ± 25 Myr, one of the highest SFRs estimated for any galaxy in the modern universe. The cluster population also allows us to fill in more of the backstory of S12. Prior to the recent, intense burst, S12 was forming stars at a moderate rate of ~3-5 M⊙ yr-1, typical of spiral galaxies, but the system experienced an earlier burst at some point, approximately 1-3 Gyr ago. While fairly uncertain, we estimate that the SFR during this earlier burst was ~20-30 M⊙ yr-1, similar to the current SFR in the Antennae and NGC 3256.

Keywords: Galaxy formation
Laboratory Observation of C and O Emission Lines of the White Dwarf H1504+65-like Atmosphere Model. White dwarfs play important roles in stellar evolution and help us gauge the age of our galaxy. The white dwarf H1504+65, the hottest known post-asymptotic giant branch star, is peculiar due to its C- and O-rich but He- and H- deficient atmosphere whose composition cannot be well predicted by current stellar evolution models. The analysis of the elemental abundance and the benchmark of stellar atmospheric models depends heavily on spectral data under cosmic conditions, which are currently extremely scarce. We created a well-defined, uniform, relatively large-scale ~millimeter plasma sample in the laboratory with a temperature and a C/O ratio similar to those of H1504+65's atmosphere. The emission spectra with high precision in the range of 10-80 nm were obtained and identified according to databases such as NIST and Kelly. A detailed comparison between our emission lines and the Chandra-observed white dwarf H1504+65 atmosphere's absorption lines was performed. The stongly isolated O VI lines in the range of 10-13 nm are observed in both cases. We observed a wealth of O V lines in the range of 13-14 nm that cannot be well identified or predicted by models due to the weak flux and also probably due to the blending effect of Fe group elements in the Chandra spectrum. Long-wavelength lines ranging from 14 to 80 nm, which are not observed in the Chandra spectrum because of the high interstellar neutral hydrogen column density, show abundant O IV-V, C IV lines, and strong O VI lines. Moreover, the intensities of the lines at 62.973 and 17.216 nm are analyzed to characterize the plasma temperature.

Keywords: White dwarf stars, DQ stars
ASASSN-15hy: An Underluminous, Red 03fg-like Type Ia Supernova. We present photometric and spectroscopic observations of the 03fg-like Type Ia supernova (SN Ia) ASASSN-15hy from the ultraviolet (UV) to the near-infrared (NIR). ASASSN-15hy shares many of the hallmark characteristics of 03fg-like SNe Ia, previously referred to as "super-Chandrasekhar" SNe Ia. It is bright in the UV and NIR, lacks a clear i-band secondary maximum, shows a strong and persistent C II feature, and has a low Si II λ6355 velocity. However, some of its properties are also extreme among the subgroup. ASASSN-15hy is underluminous (MB,peak = $-{19.14}_{-0.16}^{+0.11}$ mag), red ( ${(B-V)}_{B\max }={0.18}_{-0.03}^{+0.01}$ mag), yet slowly declining (∆m15(B) = 0.72 ± 0.04 mag). It has the most delayed onset of the i-band maximum of any 03fg-like SN. ASASSN-15hy lacks the prominent H-band break emission feature that is typically present during the first month past maximum in normal SNe Ia. Such events may be a potential problem for high-redshift SN Ia cosmology. ASASSN-15hy may be explained in the context of an explosion of a degenerate core inside a nondegenerate envelope. The explosion impacting the nondegenerate envelope with a large mass provides additional luminosity and low ejecta velocities. An initial deflagration burning phase is critical in reproducing the low 56Ni mass and luminosity, while the large core mass is essential in providing the large diffusion timescales required to produce the broad light curves. The model consists of a rapidly rotating 1.47 M☉ degenerate core and a 0.8 M☉ nondegenerate envelope. This "deflagration core-degenerate" scenario may result from the merger between a white dwarf and the degenerate core of an asymptotic giant branch star.

Keywords: White dwarf stars, Type Ia supernovae, Supernovae
Weather on Other Worlds. VI. Optical Spectrophotometry of Luhman 16B Reveals Large-amplitude Variations in the Alkali Lines. Using a novel wide-slit, multiobject approach with the GMOS spectrograph on the 8 m Gemini South telescope, we have obtained precise time-series spectrophotometry of the binary brown dwarf Luhman 16 at optical wavelengths over two full nights. The B component of this binary system is known to be variable in the red optical and near-infrared with a period of 5 hr and an amplitude of 5%-20%. Our observations probe its spectrally resolved variability in the 6000-10000 Å range. At wavelengths affected by the extremely strong, broadened spectral lines of the neutral alkali metals (the potassium doublet centered near 7682 Å and the sodium doublet at 5893 Å), we see photometric variations that differ strikingly from those of the 8000-10000 Å "red continuum" that dominates our detected flux. On UT 2014 February 24, these variations are anticorrelated with the red continuum, while on February 25 they have a large relative phase shift. The extent to which the wavelength-dependent photometric behavior diverges from that of the red continuum appears to correlate with the strength of the alkali absorption. We consider but ultimately reject models in which our observations are explained by lightning or auroral activity. A more likely cause is cloud-correlated, altitude-dependent variations in the gas-phase abundances of sodium and potassium, which are in chemical equilibrium with their chlorides in brown dwarf atmospheres. Clouds could influence these chemical equilibria by changing the atmospheric temperature profile and/or through cloud particles acting as chemical catalysts.

Keywords: Brown dwarfs, Atmospheric clouds, Time series analysis, Exoplanet atmospheric variability, Variable stars, Spectrophotometry
Survival Times of Supramassive Neutron Stars Resulting from Binary Neutron Star Mergers. A binary neutron star (BNS) merger can lead to various outcomes, from indefinitely stable neutron stars, through supramassive neutron stars (SMNSs) or hypermassive neutron stars supported only temporarily against gravity, to black holes formed promptly after the merger. Up-to-date constraints on the BNS total mass and the neutron star equation of state suggest that a long-lived SMNS may form in ~0.45-0.9 of BNS mergers. A maximally rotating SMNS needs to lose ~(3-6) × 1052 erg of its rotational energy before it collapses, on a fraction of the spin-down timescale. An SMNS formation imprints on the electromagnetic counterparts to the BNS merger. However, a comparison with observations reveals tensions. First, the distribution of collapse times is too wide and that of released energies too narrow (and the energy itself too large) to explain the observed distributions of internal X-ray plateaus, invoked as evidence for SMNS-powered energy injection. Second, the immense energy injection into the blast wave should lead to extremely bright radio transients, which previous studies found to be inconsistent with deep radio observations of short gamma-ray bursts (GRBs). Furthermore, we show that upcoming all-sky radio surveys will constrain the extracted energy distribution, independently of a GRB jet formation. Our results can be self-consistently understood, provided that most BNS merger remnants collapse shortly after formation (even if their masses are low enough to allow for SMNS formation). This naturally occurs if the remnant retains half or less of its initial energy by the time it enters solid-body rotation.

Keywords: Neutron stars, Gamma-ray bursts, Gravitational waves
The Final Fates of Close Hot Subdwarf-White Dwarf Binaries: Mergers Involving He/C/O White Dwarfs and the Formation of Unusual Giant Stars with C/O-Dominated Envelopes. Recently, a class of Roche-lobe-filling binary systems consisting of hot subdwarf stars and white dwarfs (WDs) with sub-hour periods has been discovered. At present, the hot subdwarf is in a shell He-burning phase and is transferring some of its remaining thin H envelope to its WD companion. As the evolution of the hot subdwarf continues, it is expected to detach, leaving behind a low-mass C/O-core WD secondary with a thick He layer. Then, on a timescale of ~10 Myr, gravitational wave radiation will again bring the systems into contact. If the mass transfer is unstable and results in a merger and a catastrophic thermonuclear explosion is not triggered, it creates a remnant with a C/O-dominated envelope, but one still rich enough in He to support an R Corona Borealis-like shell-burning phase. We present evolutionary calculations of this phase and discuss its potential impact on the cooling of the remnant WD.

Keywords: R Coronae Borealis variable stars, White dwarf stars, Subdwarf stars, Stellar mergers
A New "Non-energetic" Route to Complex Organic Molecules in Astrophysical Environments: The C + H<SUB>2</SUB>O → H<SUB>2</SUB>CO Solid-state Reaction. The solid-state reaction C + H2O → H2CO was studied experimentally following the co-deposition of C atoms and H2O molecules at low temperatures. In spite of the reaction barrier and absence of energetic triggering, the reaction proceeds fast on the experimental timescale pointing to its quantum tunneling mechanism. This route to formaldehyde shows a new "non-energetic" pathway to complex organic and prebiotic molecules in astrophysical environments. Energetic processing by UV irradiation of the ice produced by co-deposition of C and H2O reactants leads mainly to the destruction of H2CO and the formation of CO2, challenging the role of energetic processing in the synthesis of complex organic molecules under astrophysically relevant conditions.

Keywords: Surface processes, Astrochemistry
A Detailed View of the Broad-line Region in NGC 3783 from Velocity-resolved Reverberation Mapping. We have modeled the full velocity-resolved reverberation response of the Hβ and He II optical broad emission lines in NGC 3783 to constrain the geometry and kinematics of the low-ionization and high-ionization broad-line region (BLR). The geometry is found to be a thick disk that is nearly face-on, inclined at ~18° to our line of sight, and exhibiting clear ionization stratification, with an extended Hβ-emitting region ( ${r}_{\mathrm{median}}={10.07}_{-1.12}^{+1.10}$ lt-day) and a more compact and centrally located He II-emitting region ( ${r}_{\mathrm{median}}={1.33}_{-0.42}^{=+0.34}$ lt-day). In the Hβ-emitting region, the kinematics are dominated by near-circular Keplerian orbits, but with ~40% of the orbits inflowing. The more compact He II-emitting region, on the other hand, appears to be dominated by outflowing orbits. The black hole mass is constrained to be MBH = ${2.82}_{-0.63}^{+1.55}\times {10}^{7}$ M⊙, which is consistent with the simple reverberation constraint on the mass based on a mean time delay, line width, and scale factor of ⟨f⟩ = 4.82. The difference in kinematics between the Hβ- and He II-emitting regions of the BLR is intriguing given the recent history of large changes in the ionizing luminosity of NGC 3783 and evidence for possible changes in the BLR structure as a result.

Keywords: Supermassive black holes, Reverberation mapping, Seyfert galaxies
Collision between Radiative and Adiabatic Supersonic Flows. The self-similar dynamics of the collision between radiative and adiabatic supersonic planar flows are performed assuming homogeneous radiation cooling. New self-similar solutions relevant to both astrophysical objects and laboratory experiments are derived. Numerical simulations investigate the formation of the radiative cooling shock in the interstellar medium and laboratory Xenon plasma to demonstrate the self-similarity of the interaction in the special case of balanced ram pressure. When the radiation cooling is inhomogeneous, the flow can become thermally unstable and deviate from the self-similar solution.

Keywords: Shocks, Laboratory astrophysics, Cooling flows
Evolution of a Mode of Oscillation within Turbulent Accretion Disks. We investigate the effects of subsonic turbulence on a normal mode of oscillation (a possible origin of the high-frequency quasi-periodic oscillations (HFQPOs) within some black hole accretion disks). We consider perturbations of a time-dependent background (steady-state disk plus turbulence), obtaining an oscillator equation with stochastic damping, (mildly) nonlinear restoring, and stochastic driving forces. The (long-term) mean values of our turbulent functions vanish. In particular, turbulence does not damp the oscillation modes, so "turbulent viscosity" is not operative. However, the frequency components of the turbulent driving force near that of the mode can produce significant changes in the amplitude of the mode. Even with an additional (phenomenological constant) source of damping, this leads to an eventual "blowout" (onset of effects of nonlinearity) if the turbulence is sufficiently strong or the damping constant is sufficiently small. The infrequent large increases in the energy of the mode could be related to the observed low duty cycles of the HFQPOs. The width of the peak in the power spectral density (PSD) is proportional to the amount of nonlinearity. A comparison with observed continuum PSDs indicates the conditions required for the visibility of the mode.

Keywords: Accretion, Quasinormal modes, Astrophysical black holes
Simulating Observations of Ices in Protoplanetary Disks. Ices are an important constituent of protoplanetary disks. New observational facilities, notably the James Webb Space Telescope (JWST), will greatly enhance our view of disk ices by measuring their infrared spectral features. We present a suite of models to complement these upcoming observations. Our models use a kinetics-based gas-grain chemical evolution code to simulate the distribution of ices in a disk, followed by a radiative transfer code using a subset of key ice species to simulate the observations. We present models reflecting both molecular inheritance and chemical reset initial conditions. We find that near-to-mid-IR absorption features of H2O, CO2, and CH3OH are readily observable in disk-integrated spectra of highly inclined disks while CO, NH3, and CH4 ice do not show prominent features. CH3OH ice has low abundance and is not observable in the reset model, making this species an excellent diagnostic of initial chemical conditions. CO2 ice features exhibit the greatest change over disk lifetime, decreasing and increasing for the inheritance and reset models, respectively. Spatially resolved spectra of edge-on disks, possible with JWST's integral field unit observing modes, are ideal for constraining the vertical distribution of ices and may be able to isolate features from ices closer to the midplane (e.g., CO) given sufficient sensitivity. Spatially resolved spectra of face-on disks can trace scattered-light features from H2O, CO2, and CH3OH, plus CO and CH4 from the outermost regions. We additionally simulate far-IR H2O ice emission features and find they are strongest for disks viewed face-on.

Keywords: Protoplanetary disks, Astrochemistry
Forward Modeling of Solar Coronal Magnetic-field Measurements Based on a Magnetic-field-induced Transition in Fe X. It was recently proposed that the intensity ratios of several extreme ultraviolet spectral lines from Fe X ions can be used to measure the solar coronal magnetic field based on magnetic-field-induced transition (MIT) theory. To verify the suitability of this method, we performed forward modeling with a three-dimensional radiation magnetohydrodynamic model of a solar active region. Intensities of several spectral lines from Fe X were synthesized from the model. Based on MIT theory, the intensity ratios of the MIT line Fe X 257 Å to several other Fe X lines were used to derive magnetic-field strengths, which were then compared with the field strengths in the model. We also developed a new method to simultaneously estimate the coronal density and temperature from the Fe X 174/175 and 184/345 Å line ratios. Using these estimates, we demonstrated that the MIT technique can provide reasonably accurate measurements of the coronal magnetic field in both on-disk and off-limb solar observations. Our investigation suggests that a spectrometer that can simultaneously observe the Fe X 174, 175, 184, 257, and 345 Å lines and allow an accurate radiometric calibration for these lines is highly desired to achieve reliable measurements of the coronal magnetic field. We have also evaluated the impact of the uncertainty in the Fe x 3p4 3d 4D5/2 and 4D7/2 energy difference on the magnetic-field measurements.

Keywords: Solar corona, Magnetohydrodynamics, Solar magnetic fields
Multi-Wavelength Study of 4C+28.07. 4C+28.07 is a γ-ray flat-spectrum-radio-quasar-type source. It is often monitored at different frequencies, though long-term multi-wavelength data of this source have not been modeled in detail before. We have analyzed ~12 yr (2008 August-2020 May) of Fermi-LAT data with a binning of 10 day timescale and observed three distinctive flaring states. Each flaring state consists of different phases of activity, namely, pre-flare, flare, and post-flare regions. γ-ray spectral analysis of these different activity phases has been performed and the best-fit model for its spectra is found to be a log-parabola model. We have also studied the correlation of simultaneous γ-ray light curves with the optical &amp; radio counterparts in these flaring states and report the DCF with 95&amp;percnt; significance level. A large time delay is found between radio and gamma-ray data for two flares, indicating two zones of emission. We have fitted the multi-wavelength data with a two-zone leptonic model. In our two-zone leptonic model the maximum required power in the jet is 9.64 × 1046 erg s-1, which is lower than its Eddington luminosity 2.29 × 1047 erg s-1.

Keywords: Active galaxies, Gamma-rays
The JCMT Transient Survey: Four-year Summary of Monitoring the Submillimeter Variability of Protostars. We present the four-year survey results of monthly submillimeter monitoring of eight nearby (&lt;500 pc) star-forming regions by the JCMT Transient Survey. We apply the Lomb-Scargle Periodogram technique to search for and characterize variability on 295 submillimeter peaks brighter than 0.14 Jy beam-1, including 22 disk sources (Class II), 83 protostars (Class 0/I), and 190 starless sources. We uncover 18 secular variables, all of them protostars. No single-epoch burst or drop events and no inherently stochastic sources are observed. We classify the secular variables by their timescales into three groups: Periodic, Curved, and Linear. For the Curved and Periodic cases, the detectable fractional amplitude, with respect to mean peak brightness, is ~4% for sources brighter than ~0.5 Jy beam-1. Limiting our sample to only these bright sources, the observed variable fraction is 37% (16 out of 43). Considering source evolution, we find a similar fraction of bright variables for both Class 0 and Class I. Using an empirically motivated conversion from submillimeter variability to variation in mass accretion rate, six sources (7% of our full sample) are predicted to have years-long accretion events during which the excess mass accreted reaches more than 40% above the total quiescently accreted mass: two previously known eruptive Class I sources, V1647 Ori and EC 53 (V371 Ser), and four Class 0 sources, HOPS 356, HOPS 373, HOPS 383, and West 40. Considering the full protostellar ensemble, the importance of episodic accretion on few years timescale is negligible-only a few percent of the assembled mass. However, given that this accretion is dominated by events on the order of the observing time window, it remains uncertain as to whether the importance of episodic events will continue to rise with decades-long monitoring.

Keywords: FU Orionis stars, Protostars, Young stellar objects, Pre-main sequence stars, Star formation, Variable stars, Submillimeter astronomy
Multi-wavelength Observations of AT2019wey: a New Candidate Black Hole Low-mass X-ray Binary. AT2019wey (SRGA J043520.9+552226, SRGE J043523.3+552234) is a transient first reported by the ATLAS optical survey in 2019 December. It rose to prominence upon detection, three months later, by the Spektrum-Roentgen-Gamma (SRG) mission in its first all-sky survey. X-ray observations reported in Yao et al. suggest that AT2019wey is a Galactic low-mass X-ray binary (LMXB) with a black hole (BH) or neutron star (NS) accretor. Here we present ultraviolet, optical, near-infrared, and radio observations of this object. We show that the companion is a short-period (P ≲ 16 hr) low-mass (&lt;1 M⊙) star. We consider AT2019wey to be a candidate BH system since its locations on the Lradio-LX and Lopt-LX diagrams are closer to BH binaries than NS binaries. We demonstrate that from 2020 June to August, despite the more than 10 times brightening at radio and X-ray wavelengths, the optical luminosity of AT2019wey only increased by 1.3-1.4 times. We interpret the UV/optical emission before the brightening as thermal emission from a truncated disk in a hot accretion flow and the UV/optical emission after the brightening as reprocessing of the X-ray emission in the outer accretion disk. AT2019wey demonstrates that combining current wide-field optical surveys and SRG provides a way to discover the emerging population of short-period BH LMXB systems with faint X-ray outbursts.

Keywords: Low-mass x-ray binary stars, Accretion, Sky surveys, Astrophysical black holes