adsabs/SciX_UAT_keywords huggingface dataset:
Characterization of HD 206893 B from Near- to Thermal-infrared

HD 206893 B is a brown-dwarf companion orbiting inside the debris disk of its host star. We detect the brown dwarf in the Ms band using the Keck/NIRC2 instrument and vortex coronagraph. We measure its magnitude to be ${Ms}={12.97}_{-0.11}^{0.10}$ . It is at an angular separation of 0"22 ± 0"03, and a position angle of 39.6° ± 5.4° east of north. Using this Ms-band measurement and the system age, we use three evolutionary models to estimate the mass to be 12-78 MJup. We analyze the atmospheric properties from 1-5 μm using a grid of simulated atmospheric models. We find that a sedimentation flux fsed value ~0.2 provides the best fit to the data, suggesting high vertically extended clouds. This may be indicative of high-altitude grains or a circumplanetary disk. Our model radii and luminosities for the companion find the best fits are ages of <100 Myr and masses <20 MJup, consistent with our mass estimate from the evolutionary models using the Ms-band data alone. We detect orbital motion of the brown dwarf around the host star in comparison to the discovery image and derive orbital parameters. Finally we analyze how the companion brown dwarf interacts with the debris disk by estimating the location of the chaotic zone around the brown dwarf using values derived from this study's estimated mass and orbital constraints. We find that the collisions within the debris belt are likely driven by secular perturbations from the brown dwarf, rather than self-stirring.

Keywords: brown dwarfs; debris disks; direct imaging; coronagraphic imaging; astrometry; exoplanet atmospheres
HST Survey of the Orion Nebula Cluster in ACS/Visible and WFC3/IR Bands. IV. A Bayesian Multiwavelength Study of Stellar Parameters in the Orion Nebula Cluster

We have performed a comprehensive study of the Orion Nebula Cluster (ONC) combining the photometric data obtained by the two Hubble Space Telescope Treasury programs that targeted this region. To consistently analyze the rich data set obtained in a wide variety of filters, we adopted a Bayesian approach to fit the spectral energy distribution of the sources, deriving mass, age, extinction, distance, and accretion for each source in the region. The three-dimensional study of mass distribution for bona fide cluster members shows that mass segregation in the ONC extends to subsolar masses, while the age distribution strongly supports the idea that star formation in the ONC is best described by a major episode of star formation that happened ∼1 Myr ago. For masses ≳0.1 M ⊙, our derived empirical initial mass function (IMF) is in good agreement with a Chabrier system IMF. Both the accretion luminosity (L acc) and mass accretion rates ( ${\dot{M}}_{\mathrm{acc}}$ ) are best described by broken power-law relations. This suggests that for the majority of young circumstellar disks in this cluster the excess emission may be dominated by X-ray-driven photoevaporation by the central star rather than external photoevaporation. If this is the case, the slopes of the power-law relations may be largely determined by the initial conditions set at the onset of the star formation process, which may be quite similar between regions that eventually form clusters of different sizes.

Keywords: star forming regions; star formation; low mass stars; brown dwarfs; bayesian statistics; markov chain monte carlo
Four (Super)luminous Supernovae from the First Months of the ZTF Survey

We present photometry and spectroscopy of four hydrogen-poor luminous supernovae discovered during the 2-month long science commissioning and early operations of the Zwicky Transient Facility (ZTF) survey. Three of these objects, SN 2018bym (ZTF18aapgrxo), SN 2018avk (ZTF18aaisyyp), and SN 2018bgv (ZTF18aavrmcg), resemble typical SLSN-I spectroscopically, while SN 2018don (ZTF18aajqcue) may be an object similar to SN 2007bi experiencing considerable host galaxy reddening, or an intrinsically long-lived, luminous, and red SN Ic. We analyze the light curves, spectra, and host galaxy properties of these four objects and put them in context of the population of SLSN-I. SN 2018bgv stands out as the fastest-rising SLSN-I observed to date, with a rest-frame g-band rise time of just 10 days from explosion to peak—if it is powered by magnetar spin-down, the implied ejecta mass is only ≃1 M⊙. SN 2018don also displays unusual properties—in addition to its red colors and comparatively massive host galaxy, the light curve undergoes some of the strongest light-curve undulations postpeak seen in an SLSN-I, which we speculate may be due to interaction with circumstellar material. We discuss the promises and challenges of finding SLSNe in large-scale surveys like ZTF given the observed diversity in the population.

Keywords: supernovae; surveys; stellar mass loss; magnetars
The Number of Possible CETIs within Our Galaxy and the Communication Probability among These CETIs

As the only known intelligent civilization, human beings are always curious about the existence of other communicating extraterrestrial intelligent civilizations (CETIs). Based on the latest astrophysical information, we carry out Monte Carlo simulations to estimate the number of possible CETIs within our Galaxy and the communication probability among them. Two poorly known parameters have a great impact on the results. One is the probability of life appearing on terrestrial planets and eventually evolving into a CETI (f c ), and the other determines at what stage of their host star's evolution CETIs would be born (F). In order to ensure the completeness of the simulation, we consider a variety of combinations of f c and F. Our results indicate that for optimistic situations (e.g., F = 25% and f c = 0.1%), there could be ${\mathrm{42,777}}_{-369}^{+267}$ CETIs and they need to survive for ${3}_{-2}^{+17}$ yr ( ${2000}_{-1400}^{+2000}$ yr) to achieve one-way communication (two-way communication). In this case, human beings need to survive ${0.3}_{-0.298}^{+0.6}$ Myr to receive one alien signal. For pessimistic situations (e.g., F = 75% and f c = 0.001%), only ${111}_{-17}^{+28}$ CETIs could be born and they need to survive for ${0.8}_{-0.796}^{+1.2}$ Myr ( ${0.9}_{-0.88}^{+4.1}$ Myr) to achieve one-way communication (two-way communication). In this case, human beings need to survive ${50}_{-49.6}^{+250}$ Myr to receive one signal from other CETIs. Our results may quantitatively explain why we have not detected any alien signals so far. The uncertainty of the results has been discussed in detail and would be alleviated with the further improvement of our astronomical observation ability in the future.

Keywords: astrobiology
EXOPLINES: Molecular Absorption Cross-section Database for Brown Dwarf and Giant Exoplanet Atmospheres

Stellar, substellar, and planetary atmosphere models are all highly sensitive to the input opacities. Generational differences between various state-of-the-art stellar/planetary models arise primarily because of incomplete and outdated atomic/molecular line lists. Here we present a database of precomputed absorption cross sections for all isotopologues of key atmospheric molecules relevant to late-type stellar, brown dwarf, and planetary atmospheres: MgH, AlH, CaH, TiH, CrH, FeH, SiO, TiO, VO, and H2O. The pressure and temperature ranges of the computed opacities are 10-6-3000 bar and 75-4000 K, and their spectral ranges are 0.25-330 μm for many cases where possible. For cases with no pressure-broadening data, we use collision theory to bridge the gap. We also probe the effect of absorption cross sections calculated from different line lists in the context of ultrahot Jupiter and M-dwarf atmospheres. Using 1D self-consistent radiative-convective thermochemical equilibrium models, we report significant variations in the theoretical spectra and thermal profiles of substellar atmospheres. With a 2000 K representative ultrahot Jupiter, we report variations of up to 320 and 80 ppm in transmission and thermal emission spectra, respectively. For a 3000 K M-dwarf, we find differences of up to 125% in the spectra. We find that the most significant differences arise as a result of the choice of TiO line lists, primarily below 1 μm. In summary, (1) we present a database of precomputed molecular absorption cross sections, and (2) we quantify biases that arise when characterizing substellar/exoplanet atmospheres as a result of differences in the line lists, therefore highlighting the importance of correct and complete opacities for eventual applications to high-precision spectroscopy and photometry.

Keywords: brown dwarfs; exoplanet atmospheres; exoplanet atmospheric composition; stellar atmospheric opacity; hot jupiters; spectral line lists
TESS Delivers Five New Hot Giant Planets Orbiting Bright Stars from the Full-frame Images

We present the discovery and characterization of five hot and warm Jupiters—TOI-628 b (TIC 281408474; HD 288842), TOI-640 b (TIC 147977348), TOI-1333 b (TIC 395171208, BD+47 3521A), TOI-1478 b (TIC 409794137), and TOI-1601 b (TIC 139375960)—based on data from NASA's Transiting Exoplanet Survey Satellite (TESS). The five planets were identified from the full-frame images and were confirmed through a series of photometric and spectroscopic follow-up observations by the TESS Follow-up Observing Program Working Group. The planets are all Jovian size (RP = 1.01-1.77 RJ) and have masses that range from 0.85 to 6.33 MJ. The host stars of these systems have F and G spectral types (5595 ≤ Teff ≤ 6460 K) and are all relatively bright (9.5 < V < 10.8, 8.2 < K < 9.3), making them well suited for future detailed characterization efforts. Three of the systems in our sample (TOI-640 b, TOI-1333 b, and TOI-1601 b) orbit subgiant host stars ( $\mathrm{log}$ g < 4.1). TOI-640 b is one of only three known hot Jupiters to have a highly inflated radius (RP > 1.7 RJ, possibly a result of its host star's evolution) and resides on an orbit with a period longer than 5 days. TOI-628 b is the most massive, hot Jupiter discovered to date by TESS with a measured mass of ${6.31}_{-0.30}^{+0.28}$ MJ and a statistically significant, nonzero orbital eccentricity of e = ${0.074}_{-0.022}^{+0.021}$ . This planet would not have had enough time to circularize through tidal forces from our analysis, suggesting that it might be remnant eccentricity from its migration. The longest-period planet in this sample, TOI-1478 b (P = 10.18 days), is a warm Jupiter in a circular orbit around a near-solar analog. NASA's TESS mission is continuing to increase the sample of well-characterized hot and warm Jupiters, complementing its primary mission goals.

Keywords: exoplanet astronomy; exoplanet migration; exoplanet detection methods; exoplanets; transits; radial velocity; direct imaging
The Role of Pressure Anisotropy in Cosmic-Ray Hydrodynamics

The mean free path of cosmic rays in diffuse interstellar and intracluster gas is determined primarily by pitch angle scattering from hydromagnetic waves with wavelength of order the cosmic-ray gyroradius. In the theory of cosmic-ray self confinement, the waves are generated by instabilities driven by the cosmic rays themselves. The dominant instability is due to bulk motion, or streaming, of the cosmic rays, parallel to the background magnetic field ${\boldsymbol{B}}$ , and transfers cosmic-ray momentum and energy to the thermal gas as well as confining the cosmic rays. Classical arguments and recent numerical simulations show that self confinement due to the streaming instability breaks down unless the cosmic-ray pressure and thermal gas density gradients parallel to ${\boldsymbol{B}}$ are aligned, a condition that is unlikely to always be satisfied We investigate an alternative mechanism for cosmic-ray self confinement and heating of thermal gas based on pressure anisotropy instability. Although pressure anisotropy is demonstrably less effective than streaming instability as a self-confinement and heating mechanism on global scales, it may be important on mesoscales, particularly near sites of cosmic-ray injection.

Keywords: cosmic rays; galactic winds; interstellar medium; plasma astrophysics
Periodic Eruptive Variability of the Isolated Pre-main-sequence Star V347 Aurigae

V347 Aurigae is associated with the small dark cloud L1438 and appears to be an isolated pre-main-sequence star located at distance d ≈ 200 pc. Multi-epoch, archival photometry reveals periodic brightness variations with amplitude V ≈ 2.0 mag occurring on timescales of ∼160 days that have persisted for decades. Regular-cadence, optical imaging of the source with the Zwicky Transient Facility shows that a small reflection nebula illuminated by V347 Aur also fluctuates in brightness, at times fading completely. Multi-epoch, Keck/HIRES data suggests the presence of two distinct spectral components: a prominent emission-line-dominated spectrum with a heavily veiled continuum correlated with the bright photometric state, and an M-type absorption line spectrum associated with quiescence. All spectra exhibit strong Balmer and He I line emission, consistent with accretion, as well as high velocity emission arising from the forbidden transitions of [O I], [N II], and [S II] that are generally associated with collimated jets and disk winds. There is no evidence in existing high-dispersion spectroscopy or high-resolution imaging for binarity of V347 Aur. The repeating outburst events are possibly linked to accretion instabilities induced by an undetected companion or a structure within the circumstellar disk that periodically increases the mass accretion rate. V347 Aur is perhaps analogous to an EXor-type variable, though more regularly recurring.

Keywords: pre-main sequence stars; circumstellar disks; t tauri stars; young stellar objects; accretion; stellar accretion disks
The Dynamic Evolution of Solar Wind Streams Following Interchange Reconnection

Interchange reconnection is thought to play an important role in determining the dynamics and material composition of the slow solar wind that originates from near coronal-hole boundaries. To explore the implications of this process we simulate the dynamic evolution of a solar wind stream along a newly-opened magnetic flux tube. The initial condition is composed of a piecewise continuous dynamic equilibrium in which the regions above and below the reconnection site are extracted from steady-state solutions along open and closed field lines. The initial discontinuity at the reconnection site is highly unstable and evolves as a Riemann problem, decomposing into an outward-propagating shock and inward-propagating rarefaction that eventually develop into a classic N-wave configuration. This configuration ultimately propagates into the heliosphere as a coherent structure and the entire system eventually settles to a quasi-steady wind solution. In addition to simulating the fluid evolution we also calculate the time-dependent non-equilibrium ionization of oxygen in real time in order to construct in situ diagnostics of the conditions near the reconnection site. This idealized description of the plasma dynamics along a newly-opened magnetic field line provides a baseline for predicting and interpreting the implications of interchange reconnection for the slow solar wind. Notably, the density and velocity within the expanding N-wave are generally enhanced over the ambient wind, as is the O7+/O6+ ionization ratio, which exhibits a discontinuity across the reconnection site that is transported by the flow and arrives later than the propagating N-wave.

Keywords: solar wind; solar magnetic reconnection; solar magnetic fields; solar corona; heliosphere
Chandra X-Ray Observatory Observations of 13 Fermi LAT Sources

In the latest data release from the Fermi Gamma-ray Space Telescope (the 4th Fermi LAT 14 yr Catalog, or 4FGL), more than 50% of the Galactic sources are yet to be identified. We observed 13 unidentified Fermi LAT sources with the Chandra X-Ray Observatory to explore their nature. We report the results of the classification of X-ray sources in the fields of these γ-ray sources and discuss the implications for their nature. We use multiwavelength (MW) data for a machine-learning classification, accompanied by a more detailed spectral/variability analysis for brighter sources. Eight 4FGL sources have γ-ray pulsars within their position error ellipses. We consider three of these pulsars (PSR J1906+0722, PSR J1105-6037, and PSR J1358-6025) to be detected in X-rays, while PSR J1203-6242 shows a hint of X-ray emission. Within the positional uncertainties of three of the 4FGL sources, we detect X-ray sources that may be yet unknown pulsars, depending on the MW association. In addition to point sources, we discovered two extended sources, one of which is likely to be a bow-shock pulsar-wind nebula associated with PSR J1358-6025. Finally, we classify other X-ray sources detected in these observations and report the most interesting classifications.

Keywords: x-ray surveys; catalogs; gamma-ray sources
Time-sequence Spectroscopy of Epsilon CrA: The 518 nm Mg I Triplet Region Analyzed with Broadening Functions

High-resolution spectroscopic observations of the W UMa-type binary ɛ CrA obtained as a time-monitoring sequence on four full and four partial nights within two weeks have been used to derive orbital elements of the system and discuss the validity of the Lucy model for description of the radial-velocity data. The observations had more extensive temporal coverage and better quality than similar time-sequence observations of the contact binary AW UMa. The two binaries share several physical properties and show very similar deviations from the Lucy model: the primary component is a rapidly rotating star almost unaffected by the presence of the secondary component, while the latter is embedded in a complex gas flow and appears to have its own rotation-velocity field, in contradiction to the model. The spectroscopic mass ratio is found to be larger than the one derived from the light-curve analysis, as in many other W UMa-type binaries, but the discrepancy for ɛ CrA is relatively minor, much smaller than for AW UMa. The presence of the complex velocity flows contradicting the assumption of solid-body rotation suggests a necessity of modification to the Lucy model, possibly along the lines outlined by Stȩpień in his concept of energy transfer between the binary components.

Keywords: eclipsing binary stars; w ursae majoris variable stars; spectroscopic binary stars; close binary stars; astronomical techniques
The Proper Motion of the Central Compact Object RX J0822-4300 in the Supernova Remnant Puppis A, Revisited

We present an improved proper-motion measurement of the central compact object RX J0822-4300, located in the supernova remnant Puppis A. By employing a new data set taken in 2019 February by the High Resolution Camera on board the Chandra X-ray Observatory, we approximately double the available temporal baseline for our analysis to slightly more than 19 yr (7000 days). We correct for the astrometric inaccuracy of Chandra using calibrator stars with known optical positions that are detected in all observations. Thereby, we obtain absolute positions of RX J0822-4300 accurate to around $0\buildrel{\prime\prime}\over{.} 1$ and from these a new best estimate for its total proper motion of ${\mu }_{\mathrm{tot}}=(80.4\pm 7.7)\,\mathrm{mas}\,{\mathrm{yr}}^{-1}$. For a remnant distance of 2 kpc, this corresponds to a projected kick velocity of $(763\pm 73)\ \,\mathrm{km}\,{{\rm{s}}}^{-1}$ at a position angle of ${\phi }_{0}={(247.8\pm 4.4)}^{\circ }$. The proper-motion measurement of RX J0822-4300 is used for discussing the kinematic age of Puppis A.

Keywords: neutron stars; compact objects; x-ray point sources; proper motions; pulsars; supernova remnants; x-ray astronomy
Recurrent Neutrino Emission from Supermassive Black Hole Mergers

The recent detection of possible neutrino emission from the blazar TXS 0506+056 was the first high-energy neutrino associated with an astrophysical source, making this special type of active galaxies a promising neutrino emitter. The fact that two distinct episodes of neutrino emission were detected with a separation of around 3 yr raises the possibility that emission could be periodic. Periodic emission is expected from supermassive binary black hole systems due to jet precession close to the binary's merger. Here, we show that, if TXS 0506+056 is a binary source, then the next neutrino flare could already have occurred, possibly still hidden in IceCube's not-yet-analyzed data. We derive the binary properties that would lead to the detection of gravitational waves from this system by the Laser Interferometer Space Antenna (LISA) over the next decade. Our results for the first time quantify the timescale of these correlations for the example of TXS 0506+056, connecting the possible neutrino and gravitational-wave signatures of such sources.

Keywords: cosmological neutrinos; active galactic nuclei; high energy astrophysics; blazars; particle astrophysics; gravitational waves; supermassive black holes; astrophysical black holes
Ion-scale Current Structures in Short Large-amplitude Magnetic Structures

We investigate electric current structures in Short Large-Amplitude Magnetic Structures (SLAMS) in the terrestrial ion foreshock region observed by the Magnetospheric Multiscale mission. The structures with intense currents ( $| J| \sim 1\,\mu {\rm{A}}\,{{\rm{m}}}^{-2}$ ) have scale lengths comparable to the local ion inertial length (di). One current structure type is a current sheet due to the magnetic field rotation of the SLAMS, and a subset of these current sheets can exhibit reconnection features including the electron outflow jet and X-line-type magnetic topology. The di-scale current sheet near the edge of a SLAMS propagates much more slowly than the overall SLAMS, suggesting that it may result from compression. The current structures also exist as magnetosonic whistler waves with fci < f < flh, where fci and flh are the ion cyclotron frequency and the lower-hybrid frequency, respectively. The field rotations in the current sheets and whistler waves generate comparable $| J| $ and energy conversion rates. Electron heating is clearly observed in one whistler packet embedded in a larger-scale current sheet of the SLAMS, where the parallel electric field and the curvature drift opposite to the electric field energize electrons. The results give insight about the thin current structure generation and energy conversion at thin current structures in the shock transition region.

Keywords: shocks; solar magnetic reconnection
Star Formation in the Dwarf Seyfert Galaxy NGC 4395: Evidence for Both AGN and SN Feedback?

We present a detailed multiwavelength study of star formation in the dwarf galaxy NGC 4395, which hosts an active galactic nucleus (AGN). From our observations with the Ultra-Violet Imaging Telescope, we have compiled a catalog of 284 star-forming (SF) regions, out of which we could detect 120 SF regions in Hα observations. Across the entire galaxy, we found the extinction-corrected star formation rate (SFR) in the far ultraviolet (UV) to range from 2.0 × 10-5 M ⊙ yr-1 to 1.5 × 10-2 M ⊙ yr-1 with a median of 3.0 × 10-4 M ⊙ yr-1, and the age to lie in the range of ~1 to 98 Myr with a median of 14 Myr. In Hα we found the SFR to range from 7.2 × 10-6 M ⊙ yr-1 to 2.7 × 10-2 M ⊙ yr-1 with a median of 1.7 × 10-4 M ⊙ yr-1, and the age to lie between 3 to 6 Myr with a median of 5 Myr. The stellar ages derived from Hα show a gradual decline with galactocentric distance. We found three SF regions close to the center of NGC 4395 with high SFRs both from Hα and UV, which could be attributed to feedback effects from the AGN. We also found six other SF regions in one of the spiral arms having higher SFRs. These are very close to supernova remnants, which could have enhanced the SFR locally. We obtained a specific SFR (SFR per unit mass) for the whole galaxy of 4.64 × 10-10 yr-1.

Keywords: active galactic nuclei; seyfert galaxies; star formation; galaxy photometry; radio continuum emission