Sazuna/UAT_keywords huggingface dataset:
Revealing the CO X-factor in Dark Molecular Gas through Sensitive ALMA Absorption Observations. Carbon-bearing molecules, particularly CO, have been widely used as tracers of molecular gas in the interstellar medium (ISM). In this work, we aim to study the properties of molecules in diffuse, cold environments, where CO tends to be underabundant and/or subthermally excited. We performed one of the most sensitive (down to ${\tau }_{\mathrm{rms}}^{\mathrm{CO}}\sim 0.002$ and ${\tau }_{\mathrm{rms}}^{{\mathrm{HCO}}^{+}}\sim 0.0008$ ) submillimeter molecular absorption line observations toward 13 continuum sources with the ALMA. CO absorption was detected in diffuse ISM down to ${A}_{{\rm{V}}}\lt 0.32\,\mathrm{mag}$ and HCO+ was detected down to ${A}_{{\rm{V}}}\lt 0.2\,\mathrm{mag}$ , where atomic gas and dark molecular gas start to dominate. Multiple transitions measured in absorption toward 3C454.3 allow for a direct determination of excitation temperatures Tex of 4.1 and 2.7 K, for CO and for HCO+, respectively, which are close to the cosmic microwave background and explain their being undercounted in emission surveys. A stronger linear correlation was found between ${N}_{{\mathrm{HCO}}^{+}}$ and ${N}_{{{\rm{H}}}_{2}}$ (Pearson correlation coefficient P ∼ 0.93) than that of NCO and ${N}_{{{\rm{H}}}_{2}}$ (P ∼ 0.33), suggesting HCO+ is a better tracer of H2 than CO in diffuse gas. The derived CO-to-H2 conversion factor (the CO X-factor) of (14 ± 3) × 1020 cm-2 (K $\mathrm{km}\,{{\rm{s}}}^{-1}$ )-1 is approximately six times larger than the average value found in the Milky Way.

Keywords: Interstellar molecules, Interstellar absorption, Interstellar medium
GeV-TeV Counterparts of SS 433/W50 from Fermi-LAT and HAWC Observations. The extended jets of the microquasar SS 433 have been observed in optical, radio, X-ray, and recently very-high-energy γ-rays by High Altitude Water Cerenkov (HAWC). The detection of HAWC γ-rays with energies as great as 25 TeV motivates searches for high-energy γ-ray counterparts in the Fermi-Large Area Telescope (LAT) data in the 100 MeV-300 GeV band. In this paper, we report on the first joint analysis of Fermi-LAT and HAWC observations to study the spectrum and location of γ-ray emission from SS 433. Our analysis finds common emission sites of GeV-to-TeV γ-rays inside the eastern and western lobes of SS 433. The total flux above 1 GeV is $\sim 1\times {10}^{-10}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}$ in both lobes. The γ-ray spectrum in the eastern lobe is consistent with inverse Compton emission by an electron population that is accelerated by jets. To explain both the GeV and TeV flux, the electrons need to have a soft intrinsic energy spectrum, or undergo a quick cooling process due to synchrotron radiation in a magnetized environment.

Keywords: Gamma-ray sources, Stellar jets, High mass x-ray binary stars
The Most Rapidly Declining Type I Supernova 2019bkc/ATLAS19dqr. We report observations of the hydrogen-deficient supernova (SN) 2019bkc/ATLAS19dqr. With B- and r-band decline between peak and 10 days post peak of ${\rm{\Delta }}{m}_{10}(B)=5.24\pm 0.07$ mag and ${\rm{\Delta }}{m}_{10}(r)=3.85\pm 0.10$ mag, respectively, SN 2019bkc is the most rapidly declining SN I discovered so far. While its closest matches are the rapidly declining SN 2005ek and SN 2010X, the light curves and spectra of SN 2019bkc show some unprecedented characteristics. SN 2019bkc appears "hostless," with no identifiable host galaxy near its location, although it may be associated with the galaxy cluster MKW1 at z = 0.02. We evaluate a number of existing models of fast-evolving SNe, and we find that none of them can satisfactorily explain all aspects of SN 2019bkc observations.

Keywords: Supernovae
Direct Measurement of the [C I] Luminosity to Molecular Gas Mass Conversion Factor in High-redshift Star-forming Galaxies. The amount of cold, molecular gas in high-redshift galaxies is typically inferred from proxies of molecular hydrogen (H2), such as carbon monoxide (CO) or neutral atomic carbon ([C I]) and molecular gas mass conversion factors. The use of these proxies, however, relies on modeling and observations that have not been directly measured outside the local universe. Here, we use recent samples of high-redshift gamma-ray burst (GRB) and quasar molecular gas absorbers to determine this conversion factor ${\alpha }_{[{\rm{C}}{\rm{I}}]}={M}_{\mathrm{mol}}/{L}_{[{\rm{C}}\,{\rm{I}}](1-0)}^{{\prime} }$ from the column density of H2, which gives us the mass per unit column, and the [C I](J = 1) column density, which provides the luminosity per unit column. This technique allows us to make direct measurements of the relative abundances in high-redshift absorption-selected galaxies. Our sample spans redshifts of z = 1.9-3.4 and covers two orders of magnitude in gas-phase metallicity. We find that the [C I]-to-Mmol conversion factor is metallicity dependent, with α[C I] scaling linearly with the metallicity: $\mathrm{log}{\alpha }_{[{\rm{C}}{\rm{I}}]}=-1.13\times \mathrm{log}(Z/{Z}_{\odot })+1.33$ , with a scatter of σ α[CI] = 0.2 dex. Using a sample of emission-selected galaxies at z ∼ 0-5, with both [C I] and CO line detections, we apply the α[C I] conversion to derive independent estimates of the molecular gas mass and the CO-to-Mmol, αCO, conversion factor. We find a remarkable agreement between the molecular gas masses inferred from the absorption-derived α[C I] compared to typical αCO-based estimates, which we confirm here to be metallicity-dependent as well, with an inferred slope that is consistent with αCI and previous estimates from the literature. These results thus support the use of the absorption-derived α[C I] conversion factor for emission-selected star-forming galaxies and demonstrate that both methods probe the same universal properties of molecular gas in the local and high-redshift universe.

Keywords: Interstellar molecules, Gamma-ray bursts, Quasar absorption line spectroscopy, Interstellar abundances, Interstellar absorption, Star formation, Interstellar medium, High-redshift galaxies, Galaxies
Ring Morphology with Dust Coagulation in Protoplanetary Disks. Tidal interactions between the embedded planets and their surrounding protoplanetary disks are often postulated to produce the observed complex dust substructures, including rings, gaps, and asymmetries. In this Letter, we explore the consequences of dust coagulation on the dust dynamics and ring morphology. Coagulation of dust grains leads to dust size growth that, under typical disk conditions, produces faster radial drifts, potentially threatening the dust ring formation. Utilizing 2D hydrodynamical simulations of protoplanetary disks that include a full treatment of dust coagulation, we find that if the planet does not open a gap quickly enough, the formation of an inner ring is impeded due to dust coagulation and subsequent radial drift. Furthermore, we find that a "buildup" of submillimeter-sized grains often appears in the dust emission at the outer edge of the dust disk.

Keywords: Accretion, Gas-to-dust ratio, Astrophysical dust processes, Dust continuum emission, Protoplanetary disks, Submillimeter astronomy, Circumstellar dust
Detection of a Water Tracer in Interstellar Comet 2I/Borisov. We present high spectral resolution optical spectra obtained with the ARCES instrument at Apache Point Observatory showing detection of the [O I] 6300 Å line in interstellar comet 2I/Borisov. We employ the observed flux in this line to derive an H2O production rate of (6.3 ± 1.5) × 1026 mol s-1. Comparing to previously reported observations of CN, this implies a CN/H2O ratio of ∼0.3%-0.6%. The lower end of this range is consistent with the average value in comets, while the upper end is higher than the average value for solar system comets, but still within the range of observed values. C2/H2O is depleted, with a value likely less than 0.1%. The dust-to-gas ratio is consistent with the normal value for solar system comets. Using a simple sublimation model we estimate an H2O active area of 1.7 km2, which for current estimates for the size of Borisov suggests active fractions between 1% and 150%, consistent with values measured in solar system comets. More detailed characterization of 2I/Borisov, including compositional information and properties of the nucleus, is needed to fully interpret the observed H2O production rate.

Keywords: Comets, Planet formation, Astrochemistry
First Detection of the [O I] 63 μm Emission from a Redshift 6 Dusty Galaxy. We report a ground-based detection of the [O I] 63 μm line in a z = 6.027 gravitationally lensed dusty star-forming galaxy (DSFG) G09.83808 using the Atacama Pathfinder EXperiment SEPIA 660 receiver, the first unambiguous detection of the [O I]63 line beyond redshift 3, and the first obtained from the ground. The [O I]63 line is robustly detected at 22 ± 5 Jy km s-1, corresponding to an intrinsic (de-lensed) luminosity of (5.4 ± 1.3) × 109 L☉. With the [O I]63/[C II] luminosity ratio of 4, the [O I]63 line is the main coolant of the neutral gas in this galaxy, in agreement with model predictions. The high [O I]63 luminosity compensates for the pronounced [C II] deficit ([C II]/FIR ≃ 4 × 10-4). Using photon-dominated region models, we derive a source-averaged gas density n = 104.0 cm-3, and FUV field strength G = 104 G0, comparable to the z = 2-4 DSFG population. If G09.83808 represents a typical high-redshift DSFG, the [O I]63 line from z = 6 non-lensed DSFGs should be routinely detectable in the Atacama Large Millimeter/submillimeter Array Band 9 observations with ∼15 minutes on-source, opening a new window to study the properties of the earliest DSFGs.

Keywords: Submillimeter astronomy, Ultraluminous infrared galaxies, High-redshift galaxies
Deep Hubble Space Telescope Imaging on the Extended Lyα Emission of a QSO at z = 2.19 with a Damped Lyman Alpha System as a Natural Coronagraph. Recent observations suggest that proximate damped Lyα (PDLA) systems can be used to study the host galaxies of quasi-stellar objects (QSOs), because the PDLAs can block the bright point-spread function from central QSOs. Using six orbits of narrowband imaging with Hubble Space Telescope (HST)/WFC3, we present the first high-resolution narrowband image of the Lyα emission in the PDLA trough of the QSO SDSS J115432.67-021537.9. We detect one major component and one minor component in the narrowband imaging. Combining the ${HST}$ /WFC3 imaging with deep Magellan/MagE spectra, we measure that the Lyα flux ${F}_{\mathrm{Ly}\alpha }$ = $1.56\pm 0.10\,\times {10}^{-16}\,\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}$ , which is among the luminous (≈2.7 ${\text{}}{L}_{\mathrm{Ly}\alpha }^{\star }$ ) Lyα emitters at $z=$ 2.19. The $\mathrm{Ly}\alpha $ -based star formation rate is ∼7 ${M}_{\odot }\,{\mathrm{yr}}^{-1}$ . These observational results favor that the star formation from the host galaxy could be the main mechanism powering the Lyα emission. This new method sheds light on the study of the kinematic structure and the spatial distribution of the extended Lyα emitting regions around the QSO host.

Keywords: Quasar absorption line spectroscopy, Quasars
The Extreme CNO-enhanced Composition of the Primitive Iron-poor Dwarf Star J0815+4729. We present an analysis of high-resolution Keck/HIRES spectroscopic observations of J0815+4729, an extremely carbon-enhanced, iron-poor dwarf star. These high-quality data allow us to derive a metallicity of [Fe/H] = -5.49 ± 0.14 from the three strongest Fe I lines and to measure a high [Ca/Fe] = 0.75 ± 0.14. The large carbon abundance of A(C) = 7.43 ± 0.17 (or [C/Fe] ∼ 4.49 ± 0.11) places this star in the upper boundary of the low-carbon band in the A(C)-[Fe/H] diagram, suggesting no contamination from a binary AGB companion. We detect the oxygen triplet at 777 nm for the first time in an ultra-metal-poor star, indicating a large oxygen-to-iron abundance ratio of [O/Fe] = 4.03 ± 0.12 (A(O) = 7.23 ± 0.14), significantly higher than the previously most metal-poor dwarf J2209-0028 with an oxygen triplet detection with [O/Fe] ∼ 2.2 dex at [Fe/H] ∼ -3.9. Nitrogen is also dramatically enhanced with (A(N) = 6.75 ± 0.08) and an abundance ratio [N/Fe] ∼ 4.41 ± 0.08. We also detect Ca, Na, and Mg, while providing upper limits for eight other elements. The abundance pattern of J0815+4729 resembles that of HE 1327-2326, indicating that both are second-generation stars contaminated by a ∼21-27 M☉ single, zero-metallicity, low-energy supernova with very little mixing and substantial fallback. The absence of lithium implies an upper limit abundance A(Li) &lt; 1.3 dex, about 0.7 dex below the detected Li abundance in J0023+0307, which has a similar metallicity, exacerbating the cosmological lithium problem.

Keywords: Early universe, Explosive nucleosynthesis, Population III stars, Core-collapse supernovae, Stellar abundances, Chemical abundances, Halo stars, Overabundances, Big Bang nucleosynthesis
Dependence of Ion Temperatures on Alpha-Proton Differential Flow Vector and Heating Mechanisms in the Solar Wind. According to Wind observations between 2004 June and 2019 May, this Letter investigates the proton and alpha particle temperatures in the space of (θd, Vd/VA) for the first time, where θd and Vd are the radial angle and magnitude of alpha-proton differential flow vector ${{\boldsymbol{V}}}_{d}$ , respectively, VA is the local Alfvén speed. Results show that the temperatures significantly depend on θd as well as Vd/VA. In case of low proton parallel beta (βp∥ &lt; 1), it is found that the proton perpendicular temperature is clearly enhanced when θd is small (≲45°) and Vd/VA ≳ 0.5. On the contrary, the perpendicular temperature of alpha particles is considerably enhanced when θd is large (≳90°) or Vd/VA is sufficiently small. The maximum of proton parallel temperature takes place at θd ∼ 90° accompanied by higher βp∥ and by larger turbulence amplitude of magnetic fluctuations in inertial range. This study should present strong evidence for cyclotron resonance heating of protons and alpha particles in the solar wind. Other mechanisms including Landau resonance and stochastic heating are also proposed, which tend to have different (θd, Vd/VA) spaces than cyclotron resonance heating.

Keywords: Space plasmas, Plasma physics, Interplanetary turbulence, Solar wind, Solar coronal heating, Alfven waves
Constraints on Aquatic Photosynthesis for Terrestrial Planets around Other Stars. Aquatic photosynthesis plays a major role in carbon fixation and O2 production on Earth. In this Letter, we analyze the prospects for oxygenic photosynthesis in aquatic environments on modern Earth-analogs around F-, G-, K-, and M-type stars. Our analysis takes into account the spectral type of the host star, attenuation of light by aquatic organisms, and rates of respiration and photosynthesis. We study the compensation depth ( ${{ \mathcal Z }}_{\mathrm{CO}}$ ) and the critical depth ( ${{ \mathcal Z }}_{\mathrm{CR}}$ ), defined respectively as the locations where the net growth rates and vertically integrated net growth rates of photoautotrophs become zero. Our analysis suggests that ${{ \mathcal Z }}_{\mathrm{CO}}$ declines by more than an order of magnitude as one moves from the habitable zones around Sun-like stars to late-type M-dwarfs, but ${{ \mathcal Z }}_{\mathrm{CR}}$ decreases by only a modest amount (∼40%). For M-dwarf exoplanets, we propose that the photosynthetic red edge may constitute a more robust biosignature of aquatic photosynthesis compared to atmospheric O2.

Keywords: Extrasolar rocky planets, Exoplanet surface composition, Astrobiology, Exoplanet surface characteristics, Biosignatures, Habitable planets
Plasma-beta Modulated Characteristics of Magnetohydrodynamic Waves around the Heliospheric Current Sheet. The magnetohydrodynamics (MHD) wave modes in the heliospheric current sheet (HCS) and the associated heliospheric plasma sheet (HPS) have not been comprehensively investigated in the literature. Based on a frequency-related identification approach, the properties of MHD waves are investigated during 154 HCS crossings observed by the Wind spacecraft from 1995 to 2013. Statistically, the incidence of MHD waves around HCS/HPS is found to be modulated by the plasma β within the HPS: (1) β &gt; 5, both Alfvén and slow waves obviously decay within the HPS, with the occurrence rate (OR) decreasing from 60% and 20% in the upstream/downstream to 41% and 14% in the HPS vicinity, respectively; (2) 1 &lt; β ≤ 5, the OR of Alfvén waves (AWs) remains nearly stable. However, more slow waves are generated after the HCS crossing, with OR increasing from 13% in the upstream/downstream to 22%; (3) β ≤ 1, the OR of Alfvén and slow waves remains at ∼58% and 20% during the entire crossing, in spite of some irregular fluctuations. The results for the HCS without a clear HPS are similar to the situations of a low β HPS. The parametric decay instability of AWs is proposed as being responsible for the more slow waves generated in the moderate β HPS, and some indirect observational clues are also given.

Keywords: Magnetohydrodynamics, Solar wind, Interplanetary magnetic fields, Alfven waves, Interplanetary physics
Unveiling the Temporal Properties of MAXI J1820+070 through AstroSat Observations. We present here the results of the first broadband simultaneous spectral and temporal studies of the newly detected black hole binary MAXI J1820+070 as seen by Soft X-ray Telescope and Large Area X-ray Proportional Counter (LAXPC) on board AstroSat. The observed combined spectra in the energy range 0.7-80 keV were well modeled using disk blackbody emission, thermal Comptonization, and a reflection component. The spectral analysis revealed that the source was in its hard spectral state (Γ = 1.61) with a cool disk (kTin = 0.22 keV). We report the energy dependent time-lag and root mean squared (rms) variability at different frequencies in the energy range 3-80 keV using LAXPC data. We also modeled the flux variability using a single-zone stochastic propagation model to quantify the observed energy dependence of time lag and fractional rms variability, and then compared the results with that of Cygnus X-1. Additionally, we confirm the detection of a quasi-periodic oscillation with the centroid frequency at 47.7 mHz.

Keywords: X-ray astronomy, Black hole physics, Black holes, Stellar mass black holes, Low-mass x-ray binary stars, X-ray transient sources, Stellar accretion, Stellar accretion disks
Coronal Properties of Black Hole X-Ray Binaries in the Hard State as Seen by NuSTAR and Swift. In this work we measure two important phenomenological parameters of corona (and hot accretion flow) in black hole X-ray binaries: the photon index Γ and the electron temperature ${{kT}}_{{\rm{e}}}$ . Thanks to the capability of the Nuclear Spectroscopic Telescope Array in hard X-rays, we measure these two parameters over six orders of magnitude in the 0.1-100 keV X-ray luminosity ${L}_{{\rm{X}}}$ , from ∼5 × 1038 $\mathrm{erg}\,{{\rm{s}}}^{-1}$ down to as low as ∼5 × 1032 $\mathrm{erg}\,{{\rm{s}}}^{-1}$ . We confirm the existence of a "V"-shaped correlation between Γ and ${L}_{{\rm{X}}}$ . Surprisingly, we observe a "Λ"-shaped correlation between ${{kT}}_{{\rm{e}}}$ and ${L}_{{\rm{X}}}$ . The "cooler when brighter" branch in the high-luminosity regime ( ${L}_{{\rm{X}}}$ ≳ 3 × 1036 $\mathrm{erg}\,{{\rm{s}}}^{-1}$ ) agrees with previous results and can be understood under the existing model of Compton scattering in the corona. On the other hand, the apparent "cooler when fainter" (positive ${{kT}}_{{\rm{e}}}$ - ${L}_{{\rm{X}}}$ correlation) branch in the low-luminosity regime ( ${L}_{{\rm{X}}}$ ≲ 3 × 1036 $\mathrm{erg}\,{{\rm{s}}}^{-1}$ ) is unexpected, thus it puts a new challenge to existing models of hot accretion flow/corona.

Keywords: Accretion, Black hole physics, X-ray binary stars, Black holes, High energy astrophysics, Compact binary stars, Compact objects
Magnetic Field Dependence of Bipolar Magnetic Region Tilts on the Sun: Indication of Tilt Quenching. The tilt of the bipolar magnetic region (BMR) is crucial in the Babcock-Leighton process for the generation of the poloidal magnetic field in the Sun. Based on the thin flux-tube model of the BMR formation, the tilt is believed to be caused by the Coriolis force acting on the rising flux tube of the strong toroidal magnetic field from the base of the convection zone. We analyze the magnetic field dependence of BMR tilts using the magnetograms of the Michelson Doppler Imager (1996-2011) and Helioseismic and Magnetic Imager (2010-2018). We observe that the distribution of the maximum magnetic field (Bmax) of BMRs is bimodal. Its first peak at the low field corresponds to BMRs that do not have sunspots as counterparts in the white-light images, whereas the second peak corresponds to sunspots as recorded in both type of images. We find that the slope of Joy's law (γ0) initially increases slowly with the increase of Bmax. However, when Bmax ≳ 2 kG, γ0 decreases. Scatter of the BMR tilt around Joy's law systematically decreases with the increase of Bmax. The decrease of observed γ0 with Bmax provides a hint to a nonlinear tilt quenching in the Babcock-Leighton process. We finally discuss how our results may be used to make a connection with the thin flux-tube model.

Keywords: Solar cycle, Solar active region magnetic fields, Bipolar sunspot groups, Solar physics, Solar active regions, Solar activity
On the Habitable Lifetime of Terrestrial Worlds with High Radionuclide Abundances. The presence of a liquid solvent is widely regarded as an essential prerequisite for habitability. We investigate the conditions under which worlds outside the habitable zones of stars are capable of supporting liquid solvents on their surface over geologically significant timescales via combined radiogenic and primordial heat. Our analysis suggests that super-Earths with radionuclide abundances that are ≳103 times higher than Earth can host long-lived water oceans. In contrast, the requirements for long-lived ethane oceans, which have been explored in the context of alternative biochemistries, are less restrictive: relative radionuclide abundances of ≳102 could be sufficient. We find that this class of worlds might be detectable (10σ detection over ∼10 day integration time at 12.8 μm) in principle by the James Webb Space Telescope at distances of ∼10 pc if their ages are ≲1 Gyr.

Keywords: Extrasolar rocky planets, Planetary theory, Exoplanet surface composition, Exoplanet evolution, Free floating planets, Astrobiology, Planetary interior, Habitable planets
The Eroding Disk of AU Mic. We report Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph imaging of AU Mic's debris disk from 2017 and archival data. Outward motion of the features in the southeast arm continues. At least three features have reached or exceeded projected escape velocity in the past decade, yielding a combined feature mass-loss rate of ∼1.2 × 10-7 MEarth yr-1, or ∼1.2 × 10-13 M⊙ yr-1, ∼10% of AU Mic's stellar wind mass-loss rate, and similar to the ratio of coronal mass ejection mass loss to the stellar wind mass-loss rate. We confirm the 2018 finding of feature height changes for one feature (B/SE4), but the HST data are too sparse to compare (yet) with the stellar activity cycle. Detection of what appears to be a chain of features in a second system suggests that the disk of AU Mic is not unique, although a larger sample of disks is required to quantify how common the phenomenon is.

Keywords: M dwarf stars, Debris disks, Stellar activity