Sazuna/UAT_keywords huggingface dataset:
Eight Millisecond Pulsars Discovered in the Arecibo PALFA Survey. We report on eight millisecond pulsars (MSPs) in binary systems discovered with the Arecibo L-Band Feed Array (PALFA) pulsar survey. Phase-coherent timing solutions derived from 2.5-5 yr of observations carried out at the Arecibo and Jodrell Bank observatories are provided. PSR J1921+1929 is a 2.65 ms pulsar in a 39.6 day orbit for which we detect γ-ray pulsations in archival Fermi data. PSR J1928+1245 is a very low-mass-function system with an orbital period of 3.3 hr that belongs to the non-eclipsing black widow population. We also present PSR J1932+1756, the longest-orbital-period (41.5 days) intermediate-mass binary pulsar known to date. In light of the numerous discoveries of binary MSPs over the past years, we characterize the Galactic distribution of known MSP binaries in terms of binary class. Our results support and strengthen previous claims that the scatter in the Galactic scale height distribution correlates inversely with the binary mass function. We provide evidence of observational biases against detecting the most recycled pulsars near the Galactic plane, which overestimates the scale height of lighter systems. A possible bimodality in the mass function of MSPs with massive white dwarfs is also reported.

Keywords: Neutron stars, Pulsar timing method, Millisecond pulsars, Galactic radio sources, Surveys, Pulsars, Radio astronomy, Binary pulsars, Radio pulsars
The Formation and Decay of Sunspot Penumbrae in Active Region NOAA 12673. To better understand the formation and decay of sunspot penumbrae, we studied the evolution of sunspots in three regions of the active region NOAA 12673 in detail. The evolution of sunspots in the three regions was involved in the interaction of two magnetic field systems: the preexisting magnetic field system and the later-emerging magnetic field system. Through analyzing the photospheric magnetic field properties, it is found that the formation of the penumbra originated from newly emerging magnetic bipoles that were trapped in the photosphere. The change in magnetic field in a penumbra from horizontal to vertical can cause the disappearance of the penumbra. A transformation of the magnetic field between the umbra and the penumbra is found, and the outward moat flow around the sunspot gradually decreased and vanished during decay of the sunspot. In addition, we found that the mean longitudinal magnetic strength in the penumbra decreased and the mean transverse magnetic strength in the penumbra increased with the increasing penumbral area during the formation of sunspots. However, during the decay of sunspots, the mean longitudinal magnetic strength in the penumbra increased, and the mean transverse magnetic strength in the penumbra decreased with decreasing penumbral area. Comparatively, the dependence of the area and the mean transverse/longitudinal magnetic field strength in the umbra is not remarkable. These results reveal that the formation and decay process of umbra are different from penumbra.

Keywords: Solar magnetic fields, Sunspots, Solar photosphere, Penumbra
Reverberation Measurements of the Inner Radii of the Dust Tori in Quasars. We present the results of a dust-reverberation survey of quasars at redshifts z &lt; 0.6. We found a delayed response of the K-band flux variation after the optical flux variation in 25 out of 31 targets, and obtained the lag time between them for 22 targets. Combined with the results for nearby Seyfert galaxies, we provide the largest homogeneous collection of K-band dust-reverberation data for 36 type 1 active galactic nuclei (AGNs). This doubles the sample and includes the most distant AGN and the largest lag so far measured. We estimated the optical luminosity of the AGN component of each target using three different methods: spectral decomposition, the flux-variation-gradient method, and image decomposition. We found a strong correlation between the reverberation radius for the innermost dust torus and the optical luminosity over a range of approximately four orders of magnitude in luminosity, as is already known for Seyfert galaxies. We estimated the luminosity distances of the AGNs based on their dust-reverberation lags, and found that the data in the redshift-distance diagram are consistent with the current standard estimates of the cosmological parameters. We also present the radius-luminosity relations for isotropic luminosity indicators such as the hard X-ray (14-195 keV), [O IV] 25.89 μm, and mid-infrared (12 μm) continuum luminosities, which are applicable to obscured AGNs.

Keywords: Dust continuum emission, Active galactic nuclei, Cosmological parameters, Quasars
The Ubiquitous Imprint of Radiative Acceleration in the Mean Absorption Spectrum of Quasar Outflows. Observational evidence revealing the main mechanisms that accelerate quasar outflows has proven difficult to obtain due to the complexity of the absorption features that this gas produces in the spectra of the emission sources. We build 36 composite outflow spectra, covering a large range of outflow and quasar parameters, by stacking broad (&gt; 450 {km} {{{s}}}-1) absorption line systems in the spectra of SDSS-III/BOSS DR12 quasars. The two lines of the atomic doublet of C IV, with a separation of ≈497 km s-1, as well as those of other species, appear well resolved in most of our composites. This agrees with broad outflow troughs consisting of the superposition of narrow absorbers. We also report on the ubiquitous detection of the radiative-acceleration signature known as line-locking in all our composite outflow spectra, including one spectrum that was strictly built from broad absorption line (BAL) systems. This is the first line-locking detection in BAL composite spectra. Line-locking is driven by the C IV atomic doublet and is visible on the blue side of most strong absorption transitions. Similar effects from the doublets of O VI, Si IV, or N V, however, seem to not be present. Our results confirm that radiation pressure is a prevalent mechanism for accelerating outflows in quasars.

Keywords: AGN host galaxies, Galaxy formation, Quasar absorption line spectroscopy, Broad-absorption line quasar, Interstellar scattering
ZTF Early Observations of Type Ia Supernovae. I. Properties of the 2018 Sample. Early-time observations of Type Ia supernovae (SNe Ia) are essential to constrain the properties of their progenitors. In this paper, we present high-quality light curves of 127 SNe Ia discovered by the Zwicky Transient Facility (ZTF) in 2018. We describe our method to perform forced point-spread function photometry, which can be applied to other types of extragalactic transients. With a planned cadence of six observations per night (three g + three r), all of the 127 SNe Ia are detected in both g and r bands more than 10 days (in the rest frame) prior to the epoch of g-band maximum light. The redshifts of these objects range from z = 0.0181 to 0.165; the median redshift is 0.074. Among the 127 SNe, 50 are detected at least 14 days prior to maximum light (in the rest frame), with a subset of nine objects being detected more than 17 days before g-band peak. This is the largest sample of young SNe Ia collected to date; it can be used to study the shape and color evolution of the rising light curves in unprecedented detail. We discuss six peculiar events in this sample: one 02cx-like event ZTF18abclfee (SN 2018crl), one Ia-CSM SN ZTF18aaykjei (SN 2018cxk), and four objects with possible super-Chandrasekhar mass progenitors: ZTF18abhpgje (SN 2018eul), ZTF18abdpvnd (SN 2018dvf), ZTF18aawpcel (SN 2018cir), and ZTF18abddmrf (SN 2018dsx).

Keywords: Sky surveys, Surveys, Type Ia supernovae, Photometry, Supernovae, Catalogs
Tracing Kinematic and Chemical Properties of Sagittarius Stream by K-Giants, M-Giants, and BHB stars. We characterize the kinematic and chemical properties of ∼3000 Sagittarius (Sgr) stream stars, including K-giants, M-giants, and blue horizontal branch stars (BHBs), selected from SEGUE-2, Large Sky Area Multi-Object Fibre Spectroscopic Telescope, and Sloan Digital Sky Survey separately in Integrals-of-Motion space. The orbit of the Sgr stream is quite clear from the velocity vector in the X-Z plane. Stars traced by K-giants and M-giants show that the apogalacticon of the trailing steam is ∼100 kpc. The metallicity distributions of Sgr K-giants, M-giants, and BHBs indicate that the M-giants are on average the most metal-rich population, followed by K-giants and BHBs. All of the K-giants, M-giants, and BHBs indicate that the trailing arm is on average more metal-rich than the leading arm, and the K-giants show that the Sgr debris is the most metal-poor part. The α-abundance of Sgr stars exhibits a similar trend with the Galactic halo stars at lower metallicity ([Fe/H] &lt;∼ -1.0 dex), and then evolve down to lower [α/Fe] than disk stars at higher metallicity, which is close to the evolution pattern of the α-element of Milky Way dwarf galaxies. We find that V  Y  and metallicity of K-giants have gradients along the direction of the line of sight from the Galactic center in the X-Z plane, and the K-giants show that V  Y  increases with metallicity at [Fe/H] &gt;∼ -1.5 dex. After dividing the Sgr stream into bright and faint streams according to their locations in equatorial coordinates, the K-giants and BHBs show that the bright and faint streams present different V  Y  and metallicities, the bright stream is on average higher in V  Y  and metallicity than the faint stream.

Keywords: Galaxy formation, Galaxy dynamics, Galaxy stellar halos, Galaxy kinematics, Galaxy evolution
Measuring the Star Formation Rate with Gravitational Waves from Binary Black Holes. A measurement of the history of cosmic star formation is central to understanding the origin and evolution of galaxies. The measurement is extremely challenging using electromagnetic radiation: significant modeling is required to convert luminosity to mass, and to properly account for dust attenuation, for example. Here we show how detections of gravitational waves from inspiraling binary black holes made by proposed third-generation detectors can be used to measure the star formation rate (SFR) of massive stars with high precision up to redshifts of ∼10. Depending on the time-delay model, the predicted detection rates ranges from ∼2310 to ∼56,740 per month with the current measurement of local merger rate density. With 30,000 detections, parameters describing the volumetric SFR can be constrained at the few percent level, and the volumetric merger rate can be directly measured to 3% at z ∼ 2. Given a parameterized SFR, the characteristic delay time between binary formation and merger can be measured to ∼60%.

Keywords: Gravitational wave detectors, Stellar mass black holes, Gravitational wave sources, Gravitational wave astronomy, Star formation, Gravitational waves, Metallicity, Astrophysical black holes
Secondary Infall in the Seyfert’s Sextet: A Plausible Way Out of the Short Crossing Time Paradox. We used integral field spectroscopy from CALIFA DR3 and multiwavelength publicly available data to investigate the star formation histories of galaxies in the Seyfert’s Sextet (SS; HCG 79). The galaxies H79a, H79b, H79c, and H79f have low star formation rates despite showing strong signs of interaction. By exploring their individual specific star formation histories, we identified three earlier episodes of strong star formation common to these four galaxies. We use the last two episodes as markers of the epochs when the galaxies were crossing. We suggest that after the first turnaround, initially gas-rich galaxies crossed for the first time, consuming most of their gas. Hence, after the second turnaround most mergers from second crossings would be mixed or dry. The exception would be gas-rich galaxies intruding for the first time. Therefore, we suggest that SS galaxies have survived one crossing during a Hubble time. Strong Balmer absorption lines and the presence of counter-rotating disks provide independent bounds to the second and first crossing, respectively. This scenario provides a plausible way out of the short crossing time paradox.

Keywords: Hickson compact group, Disk galaxies, Galaxy collisions, Galaxy dynamics, Stellar evolutionary models, E+A galaxies, Galactic and extragalactic astronomy, Star formation, Galaxy mergers, Galaxy groups, Galaxies, Stellar evolution
EDGE: The Origin of Scatter in Ultra-faint Dwarf Stellar Masses and Surface Brightnesses. We demonstrate how the least luminous galaxies in the universe, ultra-faint dwarf galaxies, are sensitive to their dynamical mass at the time of cosmic reionization. We select a low-mass (∼ 1.5× {10}9 {M}⊙ ) dark matter halo from a cosmological volume, and perform zoom hydrodynamical simulations with multiple alternative histories using “genetically modified” initial conditions. Earlier-forming ultra-faints have higher stellar mass today, due to a longer period of star formation before their quenching by reionization. Our histories all converge to the same final dynamical mass, demonstrating the existence of extended scatter (≥1 dex) in stellar masses at fixed halo mass due to the diversity of possible histories. One of our variants builds less than 2% of its final dynamical mass before reionization, rapidly quenching in situ star formation. The bulk of its final stellar mass is later grown by dry mergers, depositing stars in the galaxy’s outskirts and hence expanding its effective radius. This mechanism constitutes a new formation scenario for highly diffuse ({r}1/2∼ 820 {pc}, ∼ 32 {{{mag}}{{arcsec}}}-2), metal-poor (≤ft[{Fe}/{{H}}\right]=-2.9), ultra-faint ({{ \mathcal M }}V=-5.7) dwarf galaxies within the reach of next-generation low surface brightness surveys.

Keywords: Hydrodynamical simulations, Galaxy formation, Dwarf galaxies, Galaxy evolution, Dark matter, Low surface brightness galaxies
Discovery of a Photoionized Bipolar Outflow toward the Massive Protostar G45.47+0.05. Massive protostars generate strong radiation feedback, which may help set the mass that they achieve by the end of the accretion process. Studying such feedback is therefore crucial for understanding the formation of massive stars. We report the discovery of a photoionized bipolar outflow toward the massive protostar G45.47+0.05 using high-resolution observations at 1.3 mm with the Atacama Large Millimeter/Submillimeter Array (ALMA) and at 7 mm with the Karl G. Jansky Very Large Array (VLA). By modeling the free-free continuum, the ionized outflow is found to be a photoevaporation flow with an electron temperature of 10,000 K and an electron number density of ∼1.5 × 107 cm-3 at the center, launched from a disk of radius of 110 au. H30α hydrogen recombination line emission shows strong maser amplification, with G45 being one of very few sources to show such millimeter recombination line masers. The mass of the driving source is estimated to be 30-50 M ⊙ based on the derived ionizing photon rate, or 30-40 M ⊙ based on the H30α kinematics. The kinematics of the photoevaporated material is dominated by rotation close to the disk plane, while accelerated to outflowing motion above the disk plane. The mass loss rate of the photoevaporation outflow is estimated to be ∼(2-3.5) × 10-5 M ⊙ yr-1. We also found hints of a possible jet embedded inside the wide-angle ionized outflow with nonthermal emissions. The possible coexistence of a jet and a massive photoevaporation outflow suggests that, in spite of the strong photoionization feedback, accretion is still ongoing.

Keywords: Stellar jets, H II regions, Interstellar medium, Protostars, Star counts
An Ongoing Mid-infrared Outburst in the White Dwarf 0145+234: Catching in Action the Tidal Disruption of an Exoasteroid?. We report the detection of a large-amplitude MIR outburst in the white dwarf (WD) 0145+234 in the NEOWISE Survey data. The source had a stable MIR flux before 2018, and was brightened by about 1.0 magnitude in the W1 and W2 bands within half a year and has been continuously brightening since then. No significant variations are found in the optical photometry data during the same period. This suggests that this MIR outburst is caused by recent replenishing or redistribution of dust, rather than intrinsic variations of the WD. Spectral energy distribution modeling of 0145+234 suggests that there was already a dust disk around the WD in the quiescent state, and both of the temperature and surface area of the disk evolved rapidly since the outburst. The dust temperature was ≃1770 K in the initial rising phase, close to the sublimation temperature of silicate grains, and gradually cooled down to around 1150 K, while the surface area increased by a factor of about six during the same period. The inferred closest distance of dust to the WD is within the tidal disruption radius of a gravitationally bounded asteroid. We estimated the dust mass to be between 3 × 1015 and 3 × 1017 ρ/(1 g cm-3) kg for silicate grains of a power-law size distribution with a high cutoff size from 0.1 to 1000 μm. We interpret this as a possible tidal breakup of an exoasteroid by the WD. Further follow-up observations of this rare event may provide insights on the origin of dust disk and metal pollution in some WDs.

Keywords: Infrared excess, White dwarf stars, Circumstellar dust, Variable radiation sources
Phase-space Correlation in Stellar Streams of the Milky Way Halo: The Clash of Kshir and GD-1. We report the discovery of a 70^\circ long stellar stream in the Milky Way halo, which criss-crosses the well known “GD-1” stream. We show that this new stellar structure (“Kshir”) and GD-1 lie at similar distance, and are remarkably correlated in kinematics. We propose several explanations for the nature of this new structure and its possible association with GD-1. However, a scenario in which these two streams were accreted onto the Milky Way within the same dark matter sub-halo seems to provide a natural explanation for their phase-space entanglement, and other complexities of this coupled system. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientique of France, and the University of Hawaii.

Keywords: Globular star clusters, Milky Way stellar halo, Dark matter, Stellar kinematics
Discovery of a New Stellar Subpopulation Residing in the (Inner) Stellar Halo of the Milky Way. We report the discovery of a unique collection of metal-poor giant stars that exhibit anomalously high levels of 28Si, clearly above typical Galactic levels. Our sample spans a narrow range of metallicities, peaking at -1.07 ± 0.06, and exhibits abundance ratios of [Si, Al/Fe] that are as extreme as those observed in Galactic globular clusters (GCs), and Mg is slightly less overabundant. In almost all the sources we used, the elemental abundances were redetermined from high-resolution spectra, which were reanalyzed assuming LTE. Thus, we compiled the main element families, namely, the light elements (C, N), α-elements (O, Mg, Si), iron-peak element (Fe), s-process elements (Ce, Nd), and the light odd-Z element (Al). We also provide dynamical evidence that most of these stars lie on tight (inner) halo-like and retrograde orbits passing through the bulge. Such kinds of objects have been found in present-day halo GCs, providing the clearest chemical signature of past accretion events in the (inner) stellar halo of the galaxy, possibly formed as the result of dissolved halo GCs. Their chemical composition is, in general, similar to that of typical GC populations, although several differences exist.

Keywords: High resolution spectroscopy, Silicon stars, Stellar kinematics, Stellar abundances, Stellar dynamics, Galaxy stellar halos, Chemically peculiar stars
Evidence of a Substellar Companion to AB Dor C. Studies of fundamental parameters of very low-mass objects are indispensable to provide tests of stellar evolution models that are used to derive theoretical masses of brown dwarfs and planets. However, only objects with dynamically determined masses and precise photometry can effectively evaluate the predictions of stellar models. AB Dor C (0.090 M ☉) has become a prime benchmark for calibration of theoretical evolutionary models of low-mass young stars. One of the ambiguities remaining in AB Dor C is the possible binary nature of this star. We observed AB Dor C with the VLTI/AMBER instrument in low-resolution mode at the J, H, and K bands. The interferometric observables at the K band are compatible with a binary brown dwarf system with tentative components AB Dor Ca/Cb with a K-band flux ratio of 5% ± 1% and a separation of 38 ± 1 mas. This implies theoretical masses of 0.072 ± 0.013 M ☉ and 0.013 ± 0.001 M ☉ for each component, near the hydrogen-burning limit for AB Dor Ca, and near the deuterium-burning limit, straddling the boundary between brown dwarfs and giant planets, for AB Dor Cb. The possible binarity of AB Dor C alleviates the disagreement between observed magnitudes and theoretical mass-luminosity relationships.

Keywords: Brown dwarfs, Binary stars, Exoplanets, Stellar evolutionary models, Stellar evolution, Infrared astronomy, Young stellar objects, Pre-main sequence stars, Low mass stars, Interferometric binary stars, Stellar evolutionary tracks, Interferometry
Rovibrational Spectral Analysis of CO<SUB>3</SUB> and C<SUB>2</SUB>O<SUB>3</SUB>: Potential Sources for O<SUB>2</SUB> Observed in Comet 67P/Churyumov-Gerasimenko. The recent ROSETTA mission to comet 67P/Churyumov-Gerasimenko detected surprisingly high levels of molecular oxygen (O2; hypervolatile species) in the coma. Current models predict that considerable levels of other hypervolatiles (such as molecular nitrogen, N2, methane, CH4, and Argon) should be found at similar levels, whereas they are more depleted. One explanation explored here is that larger (less volatile) parent molecules may have been formed during radiolysis of cometary ices and, upon sublimation, are subsequently broken down within the coma into smaller, more volatile fragments. In support of this hypothesis, this work employs reliable quantum chemical techniques to provide the spectral data necessary for the detection of two candidate precursor “parent” molecules, cyclic carbon trioxide (c-CO3), and cyclic dicarbon trioxide (c-C2O3). Benchmark computations performed for gas-phase CO2 give vibrational frequencies to within 1.5 cm-1 or better for the three fundamentals. Both c-CO3 and c-C2O3 have strong infrared features in the 4.5-5.5 μm (1800-2200 cm-1) range and other notable infrared features closer to 1100 cm-1 (9.10 μm). These molecules are both rotationally active, unlike CO2, and are therefore potentially observable and present new targets for radio telescope observations. Due to the stronger dipole moment, c-CO3 should be more easily detectable than the nearly non-polar c-C2O3. These data may help observations of these molecules and can provide insights as to how radiation-driven derivatization of CO/CO2 precursors could contribute to the generation of higher-mass parent species that subsequently degrade to produce more volatile species, such as O2, observed in cometary comae.

Keywords: Comets, Molecular spectroscopy, Astrochemistry