Sazuna/UAT_keywords huggingface dataset:
Strong Calcium Emission Indicates that the Ultraviolet-flashing SN Ia 2019yvq Was the Result of a Sub-Chandrasekar-mass Double-detonation Explosion. We present nebular spectra of the Type Ia supernova (SN Ia) SN 2019yvq, which had a bright flash of blue and ultraviolet light after exploding, followed by a rise similar to other SNe Ia. Although SN 2019yvq displayed several other rare characteristics, such as persistent high ejecta velocity near peak brightness, it was not especially peculiar, and if the early "excess" emission were not observed, it would likely be included in cosmological samples. The excess flux can be explained by several different physical models linked to the details of the progenitor system and explosion mechanism. Each has unique predictions for the optically thin emission at late times. In our nebular spectra, we detect strong [Ca II] λλ7291, 7324 and Ca near-IR triplet emission, consistent with a double-detonation explosion. We do not detect H, He, or [O I] emission, predictions for some single-degenerate progenitor systems and violent white dwarf mergers. The amount of swept-up H or He is &lt;2.8 × 10-4 and 2.4 × 10-4 M⊙, respectively. Aside from strong Ca emission, the SN 2019yvq nebular spectrum is similar to those of typical SNe Ia with the same light-curve shape. Comparing to double-detonation models, we find that the Ca emission is consistent with a model with a total progenitor mass of 1.15 M⊙. However, we note that a lower progenitor mass better explains the early light-curve and peak luminosity. The unique properties of SN 2019yvq suggest that thick He-shell double detonations only account for ${1.1}_{-1.1}^{+2.1} \% $ of the total "normal" SN Ia rate. The SN 2019yvq is one of the best examples yet that multiple progenitor channels appear necessary to reproduce the full diversity of "normal" SNe Ia.

Keywords: Observational astronomy, White dwarf stars, Type Ia supernovae, Supernovae
New Limits on Axionic Dark Matter from the Magnetar PSR J1745-2900. Axions are a promising dark matter candidate that were motivated to solve the strong charge-parity problem and that may also address the cosmological matter-antimatter asymmetry. Axion-photon conversion is possible in the presence of the strong magnetic fields, and the photon so produced will have energy equal to the axion mass. Here we report new limits on axionic dark matter obtained from radio spectra of the Galactic Center magnetar PSR J1745-2900. The magnetar has a magnetic field of 1.6 × 1014 G that interacts with a dark matter density 2 × 105 to 2 × 109 times greater than the local dark matter encountered by terrestrial haloscopes, depending on the Galactic dark matter profile. No significant spectral features are detected across 62% of the axion mass range 4.1-165.6 μeV (1-40 GHz). The interpretation of flux limits into limits on the two-photon coupling strength gaγγ depends on the magnetospheric conversion model and on the dark matter density at the Galactic Center. For a standard dark matter profile, we exclude axion models with gaγγ &gt; 6-34 ×10-12 GeV-1 with 95% confidence over the mass ranges 4.2-8.4, 8.9-10.0, 12.3-16.4, 18.6-26.9, 33.0-62.1, 70.1-74.3, 78.1-80.7, 105.5-109.6, 111.6-115.2, 126.0-159.3, and 162.5-165.6 μeV. For the maximal dark matter cusp allowed by stellar orbits near Sgr A*, these limits reduce to gaγγ &gt; 6-34 × 10-14 GeV-1, which exclude some theoretical models for masses &gt;33 μeV. Limits may be improved by modeling stimulated axion conversion, by ray-tracing conversion pathways in the magnetar magnetosphere, and by obtaining deeper broad-band observations of the magnetar.

Keywords: Neutron stars, Navarro-Frenk-White profile, Partial eclipses, Magnetars, Dark matter, Particle physics
Chromospheric Resonances above Sunspots and Potential Seismological Applications. Oscillations in sunspot umbrae exhibit remarkable differences between the photosphere and chromosphere. We evaluate two competing scenarios proposed for explaining those observations: a chromospheric resonant cavity and waves traveling from the photosphere to upper atmospheric layers. We have employed numerical simulations to analyze the oscillations in both models. They have been compared with observations in the low (Na I D2) and high (He I 10830 Å) chromosphere. The nodes of the resonant cavity can be detected as phase jumps or power dips, although the identification of the latter is not sufficient to claim the existence of resonances. In contrast, phase differences between velocity and temperature fluctuations reveal standing waves and unequivocally prove the presence of an acoustic resonator above umbrae. Our findings offer a new seismic method to probe active region chromospheres through the detection of resonant nodes.

Keywords: Observational astronomy, Solar atmosphere, Sunspots, Computational methods, Solar oscillations, Solar chromosphere
Giant Metrewave Radio Telescope Detections of Two High-opacity HI 21 cm Absorbers at z ≈ 1.2. We report the discovery of two remarkable high-opacity HI 21 cm absorbers against low-luminosity active galactic nuclei (AGNs), at z = 1.2166 toward J0229+0044 and at z = 1.1630 toward J0229+0053. The absorbers were detected in an unbiased Giant Metrewave Radio Telescope survey for HI 21 cm absorption against radio sources in the DEEP2 survey fields, covering z ≈ 0.73-1.53, and including sources without known redshifts. The velocity-integrated HI 21 cm optical depths are (74.2 ± 7.8) km s-1 (J0229+0044) and (78.41 ± 0.81) km s-1 (J0229+0053), higher than that of any known redshifted HI 21 cm absorber at z &gt; 0.12, and implying high HI column densities, &gt;1022 cm-2. The emission redshift of J0229+0044 is consistent with the HI 21 cm absorption redshift, while the strength and velocity spread of the absorption against J0229+0053 suggest that it too arises from gas in the AGN environment: both absorbers are thus likely to be "associated" systems. The two AGNs have low rest-frame 1.4 GHz radio and 1215 Å ultraviolet luminosities (≲1026.1 W Hz-1 and ≲1021.7 W Hz-1, respectively), both significantly lower than the typical luminosities of AGNs against which HI 21 cm searches have hitherto been carried out at z ≳ 1. The paucity of HI 21 cm absorbers at z ≳ 1 may be due to a luminosity bias in high-z AGN samples that have been searched for HI 21 cm absorption, where the high AGN ultraviolet luminosity affects physical conditions in its environment, ionizing the neutral hydrogen.

Keywords: Radio spectroscopy, Active galactic nuclei, Neutral hydrogen clouds
Carbon Isotope Ratios in Planetary Nebulae: The Unexpected Enhancement of <SUP>13</SUP>C. The 12C/13C ratio has been measured toward a sample of planetary nebulae (PNe) using millimeter observations of CO, HCN, HNC, CN, and other species, conducted with the 12 m antenna and the Submillimeter Telescope of the Arizona Radio Observatory. The observed nebulae spanned the entire lifetime of PNe, from ∼900 to 12,000 yr, and include well-known objects such as NGC 7293 (Helix), NGC 6720 (Ring), and NGC 2440, as well as relatively unexplored nebulae (M3-28, M2-48, and M3-55). In most cases, multiple molecules and transitions were used in the ratio determination, resulting in the most accurate values available to date, with 10%-40% uncertainties. The ratios found were unexpectedly low, lying in the range 12C/13C ∼1.0 ± 0.7-13.2 ± 4.9, with an average value of 3.7—drastically less than found in the envelopes of C-rich AGB stars, and, in some cases, lower than the minimum value achieved in equilibrium CNO burning. Such low values are expected for the two O-rich nebulae studied (M2-9 and M2-48), because of insufficient third dredge-up events. However, most of the PNe observed were clearly carbon-rich, as deduced from the large number of C-bearing molecules present in them. Because nucleosynthesis ceases in the PN stage, both the C/O and the 12C/13C ratios must reflect abundances at the end of the AGB. These consistently low 12C/13C ratios, combined with the bipolar/multipolar morphologies of all planetary nebulae observed, suggest an explosive process involving proton-capture occurred at the AGB-PN transition.

Keywords: Interstellar molecules, Molecular spectroscopy, Isotope shifts, Planetary nebulae, Stellar nucleosynthesis, Radio astronomy
Cross Helicity of the 2018 November Magnetic Cloud Observed by the Parker Solar Probe. Magnetic clouds are large-scale transient structures in the solar wind with low plasma-β, low-amplitude magnetic field fluctuations, and twisted field lines with both ends often connected to the Sun. Their inertial-range turbulent properties have not been examined in detail. In this Letter, we analyze the normalized cross helicity, σc, and residual energy, σr, of plasma fluctuations in the 2018 November magnetic cloud observed at 0.25 au by the Parker Solar Probe. A low value of $| {\sigma }_{c}| $ was present in the cloud core, indicating that wave power parallel and antiparallel to the mean field was approximately balanced, while the cloud's outer layers displayed larger amplitude Alfvénic fluctuations with high $| {\sigma }_{c}| $ values and σr ∼ 0. These properties are discussed in terms of the cloud's solar connectivity and local interaction with the solar wind. We suggest that low $| {\sigma }_{c}| $ is likely a common feature of magnetic clouds given their typically closed field structure. Antisunward fluctuations propagating immediately upstream of the cloud had strongly negative σr values.

Keywords: Interplanetary turbulence, Solar wind, Interplanetary magnetic fields, Solar coronal mass ejections
A Statistical Standard Siren Measurement of the Hubble Constant from the LIGO/Virgo Gravitational Wave Compact Object Merger GW190814 and Dark Energy Survey Galaxies. We present a measurement of the Hubble constant H0 using the gravitational wave (GW) event GW190814, which resulted from the coalescence of a 23 M⊙ black hole with a 2.6 M⊙ compact object, as a standard siren. No compelling electromagnetic counterpart has been identified for this event; thus our analysis accounts for thousands of potential host galaxies within a statistical framework. The redshift information is obtained from the photometric redshift (photo-z) catalog from the Dark Energy Survey. The luminosity distance is provided by the LIGO/Virgo gravitational wave sky map. Since this GW event has the second-smallest localization volume after GW170817, GW190814 is likely to provide the best constraint on cosmology from a single standard siren without identifying an electromagnetic counterpart. Our analysis uses photo-z probability distribution functions and corrects for photo-z biases. We also reanalyze the binary black hole GW170814 within this updated framework. We explore how our findings impact the H0 constraints from GW170817, the only GW merger associated with a unique host galaxy. From a combination of GW190814, GW170814, and GW170817, our analysis yields ${H}_{0}={72.0}_{-8.2}^{+12}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ (68% highest-density interval, HDI) for a prior in H0 uniform between $[20\mathrm{and}140]\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ . The addition of GW190814 and GW170814 to GW170817 improves the 68% HDI from GW170817 alone by ∼18%, showing how well-localized mergers without counterparts can provide a significant contribution to standard siren measurements, provided that a complete galaxy catalog is available at the location of the event.

Keywords: Cosmology, Cosmological parameters, Surveys, Hubble constant, Gravitational wave astronomy, Gravitational waves, Redshift surveys
Dragon's Lair: On the Large-scale Environment of BL Lac Objects. The most elusive and extreme subclass of active galactic nuclei (AGNs), known as BL Lac objects, shows features that can only be explained as the result of relativistic effects occurring in jets pointing at a small angle with respect to the line of sight. A longstanding issue is the identification of the BL Lac parent population with jets oriented at larger angles. According to the "unification scenario" of AGNs, radio galaxies with low luminosity and an edge-darkened radio morphology are the most promising candidate parent population of BL Lacs. Here we compare the large-scale environment, an orientation-independent property, of well-defined samples of BL Lacs with samples of radio galaxies all lying in the local universe. Our study reveals that BL Lacs and radio galaxies live in significantly different environments, challenging predictions of the unification scenario. We propose a solution to this problem proving that large-scale environments of BL Lacs are statistically consistent with those of compact radio sources, known as FR 0s, and share similar properties. This implies that highly relativistic jets are ubiquitous and are the natural outcome of the accretion of gas into the deep gravitational potential well produced by supermassive black holes.

Keywords: Galaxy clusters, BL Lacertae objects, Active galaxies, Relativistic jets, Astrostatistics, Radio galaxies
Magnetically Driven Baryon Winds from Binary Neutron Star Merger Remnants and the Blue Kilonova of 2017 August. The observation of a radioactively powered kilonova associated with the first binary neutron star (BNS) merger detected in gravitational waves proved that these events are ideal sites for the production of heavy r-process elements. However, the physical origin of the ejected material responsible for the early ("blue") and late ("red") components of this kilonova is still debated. Here, we investigate the possibility that the early/blue kilonova originated from the magnetically driven baryon wind launched after merger by the metastable neutron star remnant. Exploiting a magnetized BNS merger simulation with over 250 ms of post-merger evolution, we can follow for the first time the full mass-ejection process up to its final decline. We find that the baryon wind carries ≃0.010-0.028 M⊙ of unbound material, proving that the high mass estimated for the blue kilonova can be achieved. We also find expansion velocities of up to ∼0.2c, consistent with the lower end of the observational estimates, and we discuss possible effects neglected here that could further increase the final ejecta velocity. Overall, our results show that the magnetically driven baryon wind represents a viable channel to explain the blue kilonova.

Keywords: Neutron stars, Gamma-ray bursts, Compact binary stars, Gravitational wave sources, Magnetohydrodynamical simulations
Electron Heating in Perpendicular Low-beta Shocks. Collisionless shocks heat electrons in the solar wind, interstellar blast waves, and hot gas permeating galaxy clusters. How much shock heating goes to electrons instead of ions, and what plasma physics controls electron heating? We simulate 2D perpendicular shocks with a fully kinetic particle-in-cell code. For magnetosonic Mach number ${{ \mathcal M }}_{\mathrm{ms}}\sim 1\mbox{--}10$ and plasma beta ${\beta }_{{\rm{p}}}\lesssim 4$ , the post-shock electron/ion temperature ratio ${T}_{{\rm{e}}}/{T}_{{\rm{i}}}$ decreases from 1 to 0.1 with increasing ${{ \mathcal M }}_{\mathrm{ms}}$ . In a representative ${{ \mathcal M }}_{\mathrm{ms}}=3.1$ , ${\beta }_{{\rm{p}}}=0.25$ shock, electrons heat above adiabatic compression in two steps: ion-scale ${E}_{\parallel }={\boldsymbol{E}}\cdot \hat{{\boldsymbol{b}}}$ accelerates electrons into streams along ${\boldsymbol{B}}$ , which then relax via two-stream-like instability. The ${\boldsymbol{B}}$ -parallel heating is mostly induced by waves; ${\boldsymbol{B}}$ -perpendicular heating is mostly adiabatic compression by quasi-static fields.

Keywords: Shocks, Planetary bow shocks, Space plasmas, Plasma astrophysics
A Year-long Superoutburst from an Ultracompact White Dwarf Binary Reveals the Importance of Donor Star Irradiation. SDSS J080710+485259 is the longest-period outbursting ultracompact white dwarf binary. Its first-ever detected superoutburst started in 2018 November and lasted for a year, the longest detected so far for any short orbital period accreting white dwarf. Here we show the superoutburst duration of SDSS J080710+485259 exceeds the ∼2 month viscous time of its accretion disk by a factor of about 5. Consequently it follows that neither the empirical relation nor the theoretical relation between the orbital period and the superoutburst duration for AM CVn systems. Six months after the end of the superoutburst the binary remained 0.4 mag brighter than its quiescent level before the superoutburst. We detect a variable X-ray behavior during the post-outburst cooling phase, demonstrating changes in the mass accretion rate. We discuss how irradiation of the donor star, a scenario poorly explored so far and that ultimately can have important consequences for AM CVns as gravitational-wave sources, might explain the unusual observed features of the superoutburst.

Keywords: White dwarf stars, AM Canum Venaticorum stars, Compact binary stars, Interacting binary stars, Dwarf novae, Gravitational wave sources, Hydrogen deficient stars, Transient detection, Stellar accretion, Stellar accretion disks, Cataclysmic variable stars, Common envelope binary stars
The Influence of Stellar Phosphorus on Our Understanding of Exoplanets and Astrobiology. When searching for exoplanets and ultimately considering their habitability, it is necessary to consider the planet's composition, geophysical processes, and geochemical cycles in order to constrain the bioessential elements available to life. Determining the elemental ratios for exoplanetary ecosystems is not yet possible, but we generally assume that planets have compositions similar to those of their host stars. Therefore, using the Hypatia Catalog of high-resolution stellar abundances for nearby stars, we compare the C, N, Si, and P abundance ratios of main-sequence stars with those in average marine plankton, Earth's crust, as well as bulk silicate Earth and Mars. We find that, in general, plankton, Earth, and Mars are N-poor and P-rich compared with nearby stars. However, the dearth of P abundance data, which exists for only ∼1% of all stars and 1% of exoplanet hosts, makes it difficult to deduce clear trends in the stellar data, let alone the role of P in the evolution of an exoplanet. Our Sun has relatively high P and Earth biology requires a small, but finite, amount of P. On rocky planets that form around host stars with substantially less P, the strong partitioning of P into the core could rule out the potential for surface P and, consequently, for life on that planet's surface. Therefore, we urge the stellar abundance community to make P observations a priority in future studies and telescope designs.

Keywords: Exoplanet structure, Stellar abundances, Interdisciplinary astronomy, Astrobiology
The Persistence of Pancakes and the Revival of Self-gravity in Tidal Disruption Events. The destruction of a star by the tides of a supermassive black hole (SMBH) powers a bright accretion flare, and the theoretical modeling of such tidal disruption events (TDEs) can provide a direct means of inferring SMBH properties from observations. Previously it has been shown that TDEs with β = rt/rp = 1, where rt is the tidal disruption radius and rp is the pericenter distance of the star, form an in-plane caustic, or "pancake," where the tidally disrupted debris is compressed into a one-dimensional line within the orbital plane of the star. Here we show that this result applies generally to all TDEs for which the star is fully disrupted, i.e., that satisfy β ≳ 1. We show that the location of this caustic is always outside of the tidal disruption radius of the star and the compression of the gas near the caustic is at most mildly supersonic, which results in an adiabatic increase in the gas density above the tidal density of the black hole. As such, this in-plane pancake revitalizes the influence of self-gravity even for large β, in agreement with recent simulations. This finding suggests that for all TDEs in which the star is fully disrupted, self-gravity is revived post-pericenter, keeps the stream of debris narrowly confined in its transverse directions, and renders the debris prone to gravitational instability.

Keywords: Black hole physics, Tidal disruption, Analytical mathematics, Active galactic nuclei, Astrophysical fluid dynamics
Cosmic Amorphous Dust Model as the Origin of Anomalous Microwave Emission. We have shown that the thermal emission of the amorphous dust composed of amorphous silicate dust (a-Si) and amorphous carbon dust (a-C) provides an excellent fit both to the observed intensity and the polarization spectra of molecular clouds. The anomalous microwave emission (AME) originates from the resonance transition of the two-level systems attributed to the a-C with an almost spherical shape. On the other hand, the observed polarized emission in submillimeter wave bands is coming from a-Si. By taking into account a-C, the model prediction of the polarization fraction of the AME is reduced dramatically. Our model prediction of the 3σ lower limits of the polarization fraction of the Perseus and W 43 molecular clouds at 17 GHz are 8.129 × 10-5 and 8.012 × 10-6, respectively. The temperature dependence of the heat capacity of a-C shows the peculiar behavior compared with that of a-Si. So far, the properties of a-C are unique to interstellar dust grains. Therefore, we coin our dust model as the cosmic amorphous dust model.

Keywords: Interstellar dust, Cosmic microwave background radiation, Molecular clouds, Radio continuum emission
Mass Ratios of Merging Double Neutron Stars as Implied by the Milky Way Population. Of the seven known double neutron stars (DNSs) with precisely measure masses in the Milky Way that will merge within a Hubble time, all but one has a mass ratio, q, close to unity. Recently, precise measurements of three post-Keplerian parameters in the DNS J1913+1102 constrain this system to have a significantly non-unity mass ratio of 0.78 ± 0.03. One may be tempted to conclude that approximately one out of seven (14%) DNS mergers detected by gravitational-wave observatories will have mass ratios significantly different from unity. However J1913+1102 has a relatively long lifetime (pulsar characteristic age plus the system's merger time due to gravitational-wave radiation) of ≈3 Gyr. We show that when system lifetimes and observational biases are taken into account, the population of Galactic DNSs implies that ≃98% of all merging DNSs will have q &gt; 0.9. We then apply two separate fitting formulas informed by 3D hydrodynamic simulations of DNS mergers to our results on Galactic DNS masses, finding that either ≃0.004 ${M}_{\odot }$ or ≃0.009 ${M}_{\odot }$ of material will be ejected at merger, depending on which formula is used. These ejecta masses have implications for both the peak bolometric luminosities of electromagnetic counterparts (which we find to be ∼1041 erg s-1) as well as the r-process enrichment of the Milky Way.

Keywords: Neutron stars, Binary pulsars, Gravitational wave sources, Compact objects