adsabs/SciX_UAT_keywords huggingface dataset:
Physical Properties of the Star-forming Regions in the Interacting Galaxies NGC 3395/NGC 3396

We report long-slit spectroscopy of the early major merger galaxies NGC 3395/NGC 3396. The spectra are consistent with those for star-forming galaxies, but there is some indication of LINER-like active galactic nucleus activity in the center of NGC 3396. The total star formation rate in the regions observed is 2.83 M ⊙ yr-1, consistent with estimates for the entire galaxies. The highest abundances are in the centers of the galaxies, with the abundances decreasing with distance. There is a correlation between high abundance and high ionization parameter, both of which can be attributed to the presence of massive stars. Modeling with SB 99 indicates the star-forming regions are younger than 10 Myr. There are 1000-2000 WNL stars in the system, along with several thousand O stars, consistent with the ages of the star-forming regions. The highest electron densities are found in young regions with high star formation rates. The electron temperatures are higher than results for non-interacting galaxies, which is probably due to shock waves produced by the galaxy-galaxy interaction, the outflow of gas from massive stars, and/or collisions between gas clouds in the galaxies. There is star formation in the bridge of material between the galaxies. These regions are among the youngest in the system and have low abundances, suggesting the gas was pulled from the outer parts of the galaxies. X-ray point sources, probably high-mass X-ray binaries, are associated with several star-forming regions.

Keywords: interacting galaxies
Chandra Observations of High-energy X-Ray Sources Discovered by INTEGRAL

The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) satellite has detected in excess of 1000 sources in the ∼20-100 keV band during its surveys of the sky over the past 17 years. We obtained 5 ks observations of 15 unclassified INTEGRAL Gamma-Ray (IGR) sources with the Chandra X-ray Observatory in order to localize them, to identify optical/IR counterparts, to measure their soft X-ray spectra, and to classify them. For 10 of the IGR sources, we detect Chandra sources that are likely (or in some cases certain) to be the counterparts. IGR J18007-4146 and IGR J15038-6021 both have Gaia parallax distances, placing them at ${2.5}_{-0.4}^{+0.5}$ and ${1.1}_{-0.4}^{+1.5}$ kpc, respectively. We tentatively classify both of them as intermediate polar-type cataclysmic variables. Also, IGR J17508-3219 is likely to be a Galactic source, but it is unclear if it is a Dwarf Nova or another type of transient. For IGR J17118-3155, we provide a Chandra localization, but it is unclear if the source is Galactic or extragalactic. Based on either near-IR/IR colors or the presence of extended near-IR emission, we classify four sources as active galactic nuclei (AGNs; IGR J16181-5407, IGR J16246-4556, IGR J17096-2527, and IGR J19294+1327), and IGR J20310+3835 and IGR J15541-5613 are AGN candidates. In addition, we identified an AGN in the INTEGRAL error circle of IGR J16120-3543 that is a possible counterpart.

Keywords: x-ray sources; cataclysmic variable stars; high mass x-ray binary stars; active galactic nuclei; galaxy stellar content
The Similar Seven: A Set of Very Alike Exoplanets to Test Correlations between System Parameters and Atmospheric Properties

Studies of exoplanetary atmospheres have found no definite correlations between observed high-altitude aerosols and other system parameters. This could be, in part, because of the lack of homogeneous exoplanet samples for which specific parameters can be isolated and inspected. Here, we present a set of seven exoplanets with very similar system parameters. We analyze existing photometric time series, Gaia parallax, and high-resolution spectroscopic data to produce a new set of homogeneous stellar, planetary, and orbital parameters for these systems. With this, we confirm that most measured parameters for all systems are very similar, except for the host stars' metallicities and possibly high-energy irradiation levels, which require UV and X-ray observations to constrain. From the sample, WASP-6b, WASP-96b, and WASP-110b have observed transmission spectra that we use to estimate their aerosol coverage levels using the Na I doublet 5892.9 Å. We find a tentative correlation between the metallicity of the host stars and the planetary aerosol levels. The trend we find with stellar metallicity can be tested by observing transmission spectra of the remaining planets in the sample. Based on our prediction, WASP-25b and WASP-55b should have higher levels of aerosols than WASP-124b and HATS-29b. Finally, we highlight how targeted surveys of alike planets similar to the ones presented here might prove key for identifying driving factors for atmospheric properties of exoplanets in the future and could be used as a sample selection criterion for future observations with, e.g., JWST, ARIEL, and the next generation of ground-based telescopes.

Keywords: atmospheric clouds; exoplanet atmospheres; exoplanet atmospheric composition; ephemerides
Gaia May Detect Hundreds of Well-characterized Stellar Black Holes

Detection of black holes (BHs) with detached luminous companions (LCs) can be instrumental in connecting the BH properties with their progenitors since the latter can be inferred from the observable properties of the LC. Past studies showed the promise of Gaia astrometry in detecting BH-LC binaries. We build on these studies by (1) initializing the zero-age binary properties based on realistic, metallicity-dependent star formation history in the Milky Way (MW); (2) evolving these binaries to current epoch to generate realistic MW populations of BH-LC binaries; (3) distributing these binaries in the MW, preserving the complex age-metallicity-Galactic position correlations; (4) accounting for extinction and reddening using three-dimensional dust maps; and (5) examining the extended Gaia mission's ability to resolve BH-LC binaries. We restrict ourselves to detached BH-LC binaries with orbital period P orb ≤ 10 yr such that Gaia can observe at least one full orbit. We find that (1) the extended Gaia mission can astrometrically resolve ~30-300 detached BH-LC binaries depending on our assumptions of supernova physics and astrometric detection threshold; (2) Gaia's astrometry alone can indicate BH candidates for ~10-100 BH-LC binaries by constraining the dark primary mass ≥3 M ⊙; and (3) distributions of observables, including orbital periods, eccentricities, and component masses, are sensitive to the adopted binary evolution model and hence can directly inform binary evolution models. Finally, we comment on the potential to further characterize these BH binaries through radial velocity measurements and observation of X-ray counterparts.

Keywords: astrometric binary stars; astrophysical black holes; stellar populations; astrometry; detached binary stars; compact binary stars; stellar evolution; x-ray binary stars; x-ray sources
New Solar Flare Calcium Abundances with No Surprises: Results from the Solar Maximum Mission Bent Crystal Spectrometer

The calcium abundance in flare plasmas is estimated using X-ray spectra from the Solar Maximum Mission Bent Crystal Spectrometer (BCS) during the decays of 194 flares (Geostationary Operational Environmental Satellite, GOES, classifications from B6.4 to X13) occurring between 1980 and 1989. Previous work by Sylwester et al. found that the abundance varied from flare to flare. That analysis is improved on here using updated instrument parameters and by including all calcium lines viewed by the BCS instead of only the resonance line, so greatly enhancing the photon count statistics. The abundance variations are confirmed with the average abundance, A(Ca) (expressed logarithmically with A(H) = 12), equal to 6.77 ± 0.20 for 194 flares (141 of which are new in this study). This range corresponds to factors of between 1.7 and 7.2 larger than the photospheric abundance, and so our results are in line with a "first ionization potential" (FIP) effect whereby low-FIP elements like Ca (FIP = 6.11 eV) have enhanced coronal abundances. The Ca flare abundance is uncorrelated with solar activity indices, but weak correlations are suggested with GOES flare class and duration (larger A(Ca) for smaller and shorter flares). The ponderomotive force theory of Laming explaining the FIP effect gives a range of parameters within which our estimates of A(Ca) agree with the theory. However, this then gives rise to disagreements with previous estimates of the flare silicon and sulfur abundances, although those of argon and iron are in good agreement. Small adjustments of the theory may thus be necessary.

Keywords: solar x-ray flares; solar x-ray emission
The GALAH Survey: No Chemical Evidence of an Extragalactic Origin for the Nyx Stream

The results from the ESA Gaia astrometric mission and deep photometric surveys have revolutionized our knowledge of the Milky Way. There are many ongoing efforts to search these data for stellar substructure to find evidence of individual accretion events that built up the Milky Way and its halo. One of these newly identified features, called Nyx, was announced as an accreted stellar stream traveling in the plane of the disk. Using a combination of elemental abundances and stellar parameters from the GALAH and Apache Point Observatory Galactic Evolution Experiment (APOGEE) surveys, we find that the abundances of the highest likelihood Nyx members are entirely consistent with membership of the thick disk, and inconsistent with a dwarf galaxy origin. We conclude that the postulated Nyx stream is most probably a high-velocity component of the Milky Way's thick disk. With the growing availability of large data sets including kinematics, stellar parameters, and detailed abundances, the probability of detecting chance associations increases, and hence new searches for substructure require confirmation across as many data dimensions as possible.

Keywords: milky way disk; milky way dynamics; galactic abundances; stellar abundances; stellar streams; galaxy structure
Black Hole Leftovers: The Remnant Population from Binary Black Hole Mergers

The inspiral and merger of two black holes produces a remnant black hole with mass and spin determined by the properties of its parent black holes. Using the inferred population properties of component black holes from the first two and a half observing runs of Advanced LIGO and Virgo, we calculate the population properties of the leftover remnant black holes. By integrating their rate of formation over the age of the universe, we estimate the number density of remnant black holes today. Using simple prescriptions for the cosmic star formation rate and black hole inspiral delay times, we determine the number density of this leftover black hole population to be ${660}_{-240}^{+440}\,{\mathrm{Mpc}}^{-3}$ , corresponding to ∼60,000 black hole remnants per Milky Way-equivalent galaxy. The mass spectrum of these remnants starts at ∼10 M⊙ and can be approximated by a decreasing exponential with characteristic length ∼15 M⊙, the final spin distribution is sharply peaked at χf ∼ 0.7, and the kick velocities range from tens to thousands of kilometers per second. These kick velocities suggest that globular clusters and nuclear star clusters may retain up to ${3}_{-2}^{+3} \%$ and ${46}_{-15}^{+17} \%$ of their remnant black holes, respectively, while young star clusters would only retain a few tenths of a percent. The estimates in this work assume that none of the remnants participate in subsequent hierarchical mergers. If hierarchical mergers occur, the overall number density would drop accordingly and the remnant mass distribution shape would evolve over time. This population of leftover black holes is an inescapable result from gravitational-wave observations of binary black hole mergers.

Keywords: black holes; gravitational waves
Multiwavelength Analysis and the Difference in the Behavior of the Spectral Features during the 2010 and 2014 Flaring Periods of the Blazar 3C 454.3

Over the years, the flat-spectrum radio quasar 3C 454.3 has presented phases of very high activity (flares) in which the different wave bands increase their flux dramatically. In this work, we perform multiwavelength analysis from radio to gamma-rays and study the Mg II λ2798 emission line and the UV Fe II band from 2008 to 2018. We found that an increase in the 43 GHz flux density of the quasi-stationary component C coincides with the estimated time at which a superluminal blob ejected from the radio core (which caused the brightest flare of 2010) collides with the quasi-stationary component (at a projected distance of ∼4.6 pc from the radio core). The different behavior of the spectral index in the first (5000 < JD - 2,450,000 < 5600) and second (6600 < JD - 2,450,000 < 7900) flaring periods suggests changes in the physical conditions. The complex nature of the second period can be a result of a superposition of multiple events at different locations. The Mg II line has an anticorrelation with the UV continuum while Fe II correlates positively, except at the time of the brightest flare of 2010, when both have a strong response at high continuum luminosities. Our results suggest that the dominant gamma-ray emission mechanism for the first flaring period is external Compton. For the second flaring period the region emitting seed photons is co-spatial with that emitting gamma-rays. However, a study of the spectral energy distribution using a multizone jet emission model is required to confirm the nature of each significant flare during the second period.

Keywords: active galaxies; galaxy jets; gamma-rays; emission line galaxies; quasars; active galactic nuclei
The Radio Structure of the γ-Ray Narrow-line Seyfert 1 Galaxy SDSS J211852.96-073227.5

The γ-ray narrow-line Seyfert 1 (NLS1) galaxies can be considered to be the third class of γ-ray active galactic nuclei possessing relativistic jets. In this paper, we present multi-band high-resolution Very Long Baseline Array (VLBA) images of the γ-ray NLS1, SDSS J211852.96-073227.5 (J2118-0732, z = 0.26). We find a core-jet radio morphology and significant flux density variations in the radio core. The high brightness temperature estimated from VLBA images and core variability demonstrate that it exhibits substantial relativistic beaming effects. By considering radio emission in several bands, we find that the source has an inverted spectrum above 1 GHz but a steep spectrum at low frequencies ranging from 74 MHz-1 GHz; these may arise from the present activity and the old diffuse/extended emission, respectively. The core-jet morphology, significant flux density variations, and beaming effect make J2118-0732 resemble a blazar. Considering the low mass of its central black hole and the ongoing merger environment, J2118-0732 may represent a low-mass, low-power counterpart of blazars, and may finally evolve into a blazar.

Keywords: radio jets; active galactic nuclei; seyfert galaxies; radio cores
Merger of a Neutron Star with a Black Hole: One-family versus Two-families Scenario

A kilonova (KN) signal is generally expected after a black hole-neutron star merger. The strength of the signal is related to the equation of state of neutron star matter, and it increases with the stiffness of the latter. The recent results obtained by NICER from the analyses of PSR J0740+6620 suggest a rather stiff equation of state, and the expected KN signal is therefore strong, at least if the mass of the black hole does not exceed ~10 M ⊙, the adimensional spin parameter is not too small, and the orbit is prograde. We compare the predictions obtained by considering equations of state of neutron star matter satisfying the most recent observations and assuming that only one family of compact stars exists with the results predicted in the two-families scenario. In the latter a soft hadronic equation of state produces very compact stellar objects, while a rather stiff quark matter equation of state produces massive strange quark stars, satisfying NICER results. The expected KN signal in the two-families scenario is very weak: in particular, the hadronic star-black hole merger produces a much weaker signal than in the one-family scenario because the hadronic equation of state is very soft. Moreover, according to the only existing simulation, the strange quark star-black hole merger does not produce a KN signal because the amount of mass ejected is negligible. These predictions will be easily tested with the new generation of detectors if black holes with an adimensional spin parameter χ BH ≳ 0.2 or a mass M BH ≲ 4 M ⊙ can be present in the merger.

Keywords: neutron stars; compact objects; stellar mergers; nuclear physics; black holes; stellar mass black holes
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 (<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: protostars; young stellar objects; pre-main sequence stars; fu orionis stars; submillimeter astronomy; star formation; variable stars
Large-scale Dynamics of Winds Originating from Black Hole Accretion Flows. II. Magnetohydrodynamics

The great difference in dynamical range between small-scale accretion disk simulations and large-scale or cosmological simulations creates difficulties in tracking the disk wind kinematics. In the first paper of this series, we studied the dynamics of hydrodynamic winds from the outer edge of the accretion disk toward galactic scales. In this paper, we further incorporate magnetic fields by employing a one-dimensional magnetohydrodynamic model, with fiducial boundary conditions set for hot accretion flows. The wind solution is achieved through requiring gas to pass smoothly through the slow, Alfvén, and fast magnetosonic points. Beyond the fast magnetosonic point, physical quantities are found to show power-law dependences with cylindrical radius R, I.e., $\rho \propto {R}^{-2},{V}_{{\rm{p}}}\propto \mathrm{const}.,{V}_{\phi }\propto {R}^{-1},{B}_{\phi }\propto {R}^{-1},$ and $\beta \propto {\rho }^{\gamma -1}$ . The magnetization of wind is dominant in determining the wind properties. The wind is accelerated to greater terminal velocities with stronger magnetizations. The fiducial parameters result in a terminal velocity of about 0.016c. The dependence of the wind physical quantities on temperature, field line angular velocity, and adiabatic index is also discussed.

Keywords: black holes; high energy astrophysics; astrophysical black holes; supermassive black holes; active galactic nuclei; magnetohydrodynamics; astrophysical fluid dynamics
A Broadband Digital Spectrometer for the Deep Space Network

The Deep Space Network (DSN) enables NASA to communicate with its spacecraft in deep space. By virtue of its large antennas, the DSN can also be used as a powerful instrument for radio astronomy. Specifically, the Deep Space Station (DSS)-43, the 70 m antenna at the Canberra Deep Space Communications Complex (CDSCC), has a K-band radio astronomy system covering a 10 GHz bandwidth at 17-27 GHz. This spectral range covers a number of atomic and molecular lines, produced in a rich variety of interstellar gas conditions. Lines include hydrogen radio recombination lines (RRLs), cyclopropenylidene (C3H2), water masers (H2O), and ammonia (NH3). A new high-resolution spectrometer was deployed at CDSCC in 2019 November and connected to the K-band down converter. The spectrometer has a total bandwidth of 16 GHz. Such a large total bandwidth enables, for example, the simultaneous observations of a large number of RRLs, which can be combined together to significantly improve the sensitivity of these observations. The system has two firmware modes: (1) a 65k-pt fast Fourier transform to provide 32,768 spectral channels at 30.5 kHz and (2) a 16k-pt polyphase filter bank to provide 8192 spectral channels with a 122 kHz resolution. The observation process is designed to maximize autonomy, from the principle investigator&'s inputs to the output data in FITS file format. We present preliminary mapping observations of hydrogen RRLs in Orion KL mapping taken using the new spectrometer.

Keywords: spectrometers; astronomical instrumentation
Observational Constraints on Direct Electron Heating in the Hot Accretion Flows in Sgr A* and M87*

An important parameter in the theory of hot accretion flows around black holes is δ, which describes the fraction of "viscously" dissipated energy in the accretion flow that goes directly into heating electrons. For a given mass accretion rate, the radiative efficiency of a hot accretion flow is determined by δ. Unfortunately, the value of δ is hard to determine from first principles. The recent Event Horizon Telescope Collaboration (EHTC) results on M87* and Sgr A* provide us with a different way of constraining δ. By combining the mass accretion rates in M87* and Sgr A* estimated by the EHTC with the measured bolometric luminosities of the two sources, we derive good constraints on the radiative efficiencies of the respective accretion flows. In parallel, we use a theoretical model of hot magnetically arrested disks (MADs) to calculate the expected radiative efficiency as a function of δ (and accretion rate). By comparing the EHTC-derived radiative efficiencies with the theoretical results from MAD models, we find that Sgr A* requires δ ≳ 0.3. A similar comparison in the case of M87* gives inconclusive results as there is still a large uncertainty in the accretion rate in this source.

Keywords: accretion; low-luminosity active galactic nuclei; supermassive black holes; galactic center