adsabs/SciX_UAT_keywords huggingface dataset:
Cluster Difference Imaging Photometric Survey. II. TOI 837: A Young Validated Planet in IC 2602

We report the discovery of TOI 837b and its validation as a transiting planet. We characterize the system using data from the NASA Transiting Exoplanet Survey Satellite mission, the ESA Gaia mission, ground-based photometry from El Sauce and ASTEP400, and spectroscopy from CHIRON, FEROS, and Veloce. We find that TOI 837 is a T = 9.9 mag G0/F9 dwarf in the southern open cluster IC 2602. The star and planet are therefore ${35}_{-5}^{+11}$ million years old. Combining the transit photometry with a prior on the stellar parameters derived from the cluster color-magnitude diagram, we find that the planet has an orbital period of $8.3\,\mathrm{days}$ and is slightly smaller than Jupiter ( ${R}_{{\rm{p}}}={0.77}_{-0.07}^{+0.09}\,{R}_{\mathrm{Jup}}$ ). From radial velocity monitoring, we limit ${M}_{{\rm{p}}}\sin i$ to less than 1.20 MJup (3σ). The transits either graze or nearly graze the stellar limb. Grazing transits are a cause for concern, as they are often indicative of astrophysical false-positive scenarios. Our follow-up data show that such scenarios are unlikely. Our combined multicolor photometry, high-resolution imaging, and radial velocities rule out hierarchical eclipsing binary scenarios. Background eclipsing binary scenarios, though limited by speckle imaging, remain a 0.2% possibility. TOI 837b is therefore a validated adolescent exoplanet. The planetary nature of the system can be confirmed or refuted through observations of the stellar obliquity and the planetary mass. Such observations may also improve our understanding of how the physical and orbital properties of exoplanets change in time.

Keywords: exoplanets; transits; exoplanet evolution; stellar ages; young star clusters
Limits on Leptonic TeV Emission from the Cygnus Cocoon with Swift-XRT

γ-ray observations of the Cygnus Cocoon, an extended source surrounding the Cygnus X star-forming region, suggest the presence of a cosmic-ray accelerator reaching energies up to a few PeV. The very-high-energy (VHE; 0.1-100 TeV) γ-ray emission may be explained by the interaction of cosmic-ray hadrons with matter inside the Cocoon, but an origin of inverse Compton radiation by relativistic electrons cannot be ruled out. Inverse Compton γ-rays at VHE are accompanied by synchrotron radiation peaked in X-rays. Hence, X-ray observations may probe the electron population and magnetic field of the source. We observed 11 fields in or near the Cygnus Cocoon with the Neil Gehrels Swift Observatory's X-Ray Telescope (Swift-XRT) totaling 110 ks. We fit the fields to a Galactic and extragalactic background model and performed a log-likelihood ratio test for an additional diffuse component. We found no significant additional emission and established upper limits in each field. By assuming that the X-ray intensity traces the TeV intensity and follows a ${dN}/{dE}\propto {E}^{-2.5}$ spectrum, we obtained a 90% upper limit of F X < 8.7 × 10-11 erg cm-2 s-1 or <5.2 × 10-11 erg cm-2 s-1 on the X-ray flux of the entire Cygnus Cocoon between 2 and 10 keV depending on the choice of hydrogen column density model for the absorption. The obtained upper limits suggest that no more than one-quarter of the γ-ray flux at 1 TeV is produced by inverse Compton scattering, when assuming an equipartition magnetic field of ~20 μG.

Keywords: gamma-ray sources; x-ray sources
The Anatomy of an Unusual Edge-on Protoplanetary Disk. II. Gas Temperature and a Warm Outer Region

We present high-resolution 12CO and 13CO 2-1 ALMA observations, as well as optical and near-infrared spectroscopy, of the highly inclined protoplanetary disk around SSTC2D J163131.2-242627. The spectral type we derive for the source is consistent with a 1.2 M⊙ star inferred from the ALMA observations. Despite its massive circumstellar disk, we find little to no evidence for ongoing accretion on the star. The CO maps reveal a disk that is unusually compact along the vertical direction, consistent with its appearance in scattered light images. The gas disk extends about twice as far away as both the submillimeter continuum and the optical scattered light. CO is detected from two surface layers separated by a midplane region in which CO emission is suppressed, as expected from freeze-out in the cold midplane. We apply a modified version of the tomographically reconstructed distribution method presented by Dutrey et al. to derive the temperature structure of the disk. We find a temperature in the CO-emitting layers and the midplane of ∼33 K and ∼20 K at R < 200 au, respectively. Outside of R > 200 au, the disk's midplane temperature increases to ∼30 K, with a nearly vertically isothermal profile. The transition in CO temperature coincides with a dramatic reduction in the submicron and submillimeter emission from the disk. We interpret this as interstellar UV radiation providing an additional source of heating to the outer part of the disk.

Keywords: protoplanetary disks; t tauri stars; circumstellar gas
MAGICal GRB 190114C: Implications of Cutoff in the Spectrum at sub-GeV Energies

GRB 190114C is an unusual gamma-ray burst (GRB) due to its detection at sub-TeV energies by MAGIC, seen at redshift z = 0.42. This burst is one of the brightest GRB detected by Fermi. A joint GBM-LAT analysis of the prompt emission reveals the presence of sub-GeV spectral cutoff when the LAT low-energy event (LLE) data is also examined. A similar high-energy cutoff was likewise reported in GRB 160509A and GRB 100724B earlier, as well as a handful of other sources. The cutoff can be explained by the intrinsic opacity due to pair production within the emitting region. GRB 190114C shows a transition from nonthermal to a quasi-thermal-like spectrum and a radiation component that can be attributed to afterglow. Based on spectral analysis, we constrain the site of the prompt emission and Lorentz factor. Knowing that sub-TeV photons are detected in MAGIC, we perceive that the observed spectrum is indeed an overlap from two emission sites, where the emission observed in Fermi is more consistent with prompt emission produced via photospheric dissipation along with a concurrent component from the external shock.

Keywords: gamma-ray bursts; high energy astrophysics; transient sources; jets
The Warm Gas in the MW: A Kinematical Model

We develop a kinematical model for the Milky Way Si IV-bearing gas to determine its density distribution and kinematics. This model is constrained by a column density line-shape sample extracted from the Hubble Space Telescope/Cosmic Origins Spectrograph archival data, which contains 186 active galactic nucleus sight lines. We find that the Si IV ion density distribution is dominated by an extended disk along the z-direction (above or below the midplane), I.e., $n{(z)={n}_{0}\exp (-(z/{z}_{0})}^{0.82})$ , where z0 is the scale height of ${6.3}_{-1.5}^{+1.6}$ kpc (northern hemisphere) and ${3.6}_{-0.9}^{+1.0}$ kpc (southern hemisphere). The density distribution of the disk in the radial direction shows a sharp edge at 15-20 kpc given by, $n{({r}_{\mathrm{XY}})={n}_{0}\exp (-({r}_{\mathrm{XY}}/{r}_{0})}^{3.36})$ , where r0 ≈ 12.5 ± 0.6 kpc. The difference of density distributions over rXY and z directions indicates that the warm gas traced by Si IV is mainly associated with disk processes (e.g., feedback or cycling gas) rather than accretion. We estimate the mass of the warm gas (within 50 kpc) is $\mathrm{log}(M(50\mathrm{kpc})/{M}_{\odot })\approx 8.1$ (assuming Z ≈ 0.5 Z⊙), and a 3σ upper limit of $\mathrm{log}(M(250\mathrm{kpc})/{M}_{\odot })\approx 9.1$ (excluding the Magellanic system). Kinematically, the warm gas disk is nearly co-rotating with the stellar disk at ${V}_{\mathrm{rot}}=215\pm 3\,\mathrm{km}\,{{\rm{s}}}^{-1}$ , which lags the midplane rotation by about $8\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{kpc}}^{-1}$ (within 5 kpc). Meanwhile, we note that the warm gas in the northern hemisphere has significant accretion with Vacc of 69 ± 7 $\mathrm{km}\,{{\rm{s}}}^{-1}$ at 10 kpc (an accretion rate of $-{0.60}_{-0.13}^{+0.11}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$), while in the southern hemisphere, there is no measurable accretion, with an upper limit of 0.4 M⊙ yr-1.

Keywords: circumgalactic medium; milky way galaxy fountains; quasar absorption line spectroscopy; interstellar absorption
Evolution of Retrograde Orbiters in an Active Galactic Nucleus Disk

Active galactic nucleus (AGN) disks have been proposed as promising locations for the mergers of stellar-mass black hole binaries (BBHs). Much recent work has been done on this merger channel, but the majority focuses on stellar-mass black holes (BHs) orbiting in the prograde direction. Little work has been done to examine the impact of retrograde orbiters (ROs) on the formation and mergers of BBHs in AGN disks. Quantifying the retrograde contribution is important, as roughly half of all orbiters should initially be on retrograde orbits when the disk forms. We perform an analytic calculation of the evolution of ROs in an AGN disk. Because this evolution could cause the orbits of ROs to cross those of prograde BBHs, we derive the collision rate between a given RO and a given BBH orbiting in the prograde direction. In the examples given here, ROs in the inner region of the disk experience a rapid decrease in the semimajor axis of their orbits while also becoming highly eccentric in less than a million years. This rapid orbital evolution could lead to extreme mass ratio inspirals detectable by the Laser Interferometer Space Antenna. The collision rates of our example ROs with prograde BBHs in the migration trap depend strongly on the volume of the inner radiation-pressure-dominated region, which depends on the mass of the supermassive black hole (SMBH). Rates are lowest for larger-mass SMBHs, which dominate the AGN merger channel, suggesting that merger rates for this channel may not be significantly altered by ROs.

Keywords: ligo; active galactic nuclei; black hole physics; stellar dynamics; stellar mass black holes; supermassive black holes; gravitational waves
The Pulsating Helium-atmosphere White Dwarfs. I. New DBVs from the Sloan Digital Sky Survey

We present a dedicated search for new pulsating helium-atmosphere (DBV) white dwarfs from the Sloan Digital Sky Survey using the McDonald 2.1 m Otto Struve Telescope. In total we observed 55 DB and DBA white dwarfs with spectroscopic temperatures between 19,000 and 35,000 K. We find 19 new DBVs and place upper limits on variability for the remaining 36 objects. In combination with previously known DBVs, we use these objects to provide an update to the empirical extent of the DB instability strip. With our sample of new DBVs, the red edge is better constrained, as we nearly double the number of DBVs known between 20,000 and 24,000 K. We do not find any new DBVs hotter than PG 0112+104, the current hottest DBV is at T eff ≈ 31,000 K, but do find pulsations in four DBVs with temperatures between 27,000 and 30,000 K, improving empirical constraints on the poorly defined blue edge. We investigate the ensemble pulsation properties of all currently known DBVs, finding that the weighted mean period and total pulsation power exhibit trends with effective temperature that are qualitatively similar to the pulsating hydrogen-atmosphere white dwarfs.

Keywords: white dwarf stars; db stars; stellar oscillations; asteroseismology; time series analysis
TOI 564 b and TOI 905 b: Grazing and Fully Transiting Hot Jupiters Discovered by TESS

We report the discovery and confirmation of two new hot Jupiters discovered by the Transiting Exoplanet Survey Satellite (TESS): TOI 564 b and TOI 905 b. The transits of these two planets were initially observed by TESS with orbital periods of 1.651 and 3.739 days, respectively. We conducted follow-up observations of each system from the ground, including photometry in multiple filters, speckle interferometry, and radial velocity measurements. For TOI 564 b, our global fitting revealed a classical hot Jupiter with a mass of ${1.463}_{-0.096}^{+0.10}$ MJ and a radius of ${1.02}_{-0.29}^{+0.71}$ RJ. Also a classical hot Jupiter, TOI 905 b has a mass of ${0.667}_{-0.041}^{+0.042}$ MJ and radius of ${1.171}_{-0.051}^{+0.053}$ RJ. Both planets orbit Sun-like, moderately bright, mid-G dwarf stars with V ∼ 11. While TOI 905 b fully transits its star, we found that TOI 564 b has a very high transit impact parameter of ${0.994}_{-0.049}^{+0.083}$ , making it one of only ∼20 known systems to exhibit a grazing transit and one of the brightest host stars among them. Therefore, TOI 564 b is one of the most attractive systems to search for additional nontransiting, smaller planets by exploiting the sensitivity of grazing transits to small changes in inclination and transit duration over a timescale of several years.

Keywords: exoplanet astronomy; exoplanet detection methods; radial velocity; transit photometry; extrasolar gaseous giant planets; hot jupiters
Chromium Nucleosynthesis and Silicon-Carbon Shell Mergers in Massive Stars

We analyze the production of the element Cr in galactic chemical evolution (GCE) models using the NuGrid nucleosynthesis yields set. We show that the unusually large [Cr/Fe] abundance at [Fe/H] ≈ 0 reported by previous studies using those yields and predicted by our Milky Way model originates from the merging of convective Si-burning and C-burning shells in a 20 M⊙ model at metallicity Z = 0.01, about an hour before the star explodes. This merger mixes the incomplete burning material in the Si shell, including 51V and 52Cr, out to the edge of the carbon/oxygen (CO) core. The adopted supernova model ejects the outer 2 M⊙ of the CO core, which includes a significant fraction of the Cr-rich material. When including this 20 M⊙ model at Z = 0.01 in the yields interpolation scheme of our GCE model for stars between 15 and 25 M⊙, we overestimate [Cr/Fe] by an order of magnitude at [Fe/H] ≈ 0 relative to observations in the Galactic disk. This raises a number of questions regarding the occurrence of Si-C shell mergers in nature, the accuracy of different simulation approaches, and the impact of such mergers on the presupernova structure and explosion dynamics. According to the conditions in this 1D stellar model, the substantial penetration of C-shell material into the Si shell could launch a convective-reactive global oscillation if a merger does take place. In any case, GCE provides stringent constraints on the outcome of this stellar evolution phase.

Keywords: galaxy chemical evolution; chemical enrichment; stellar abundances; massive stars; chemical abundances; stellar nucleosynthesis; galaxy abundances; stellar evolutionary models
Gravitational Wave Backgrounds from Coalescing Black Hole Binaries at Cosmic Dawn: An Upper Bound

The successive discoveries of binary merger events by Advanced LIGO-Virgo have been revealing the statistical properties of binary black hole (BBH) populations. A stochastic gravitational wave background (GWB) is a useful tool to probe the cosmological evolution of those compact mergers. In this paper, we study the upper bound on a GWB produced by BBH mergers, whose stellar progenitors dominate the reionization process at the cosmic dawn. Since early reionization by those progenitors yields a high optical depth of the universe inconsistent with the Planck measurements, the cumulative mass density is limited to ρ⋆ ≲ 107 M⊙ Mpc-3. Even with this upper bound, the amplitude of a GWB owing to the high-z BBH mergers is expected to be as high as ${{\rm{\Omega }}}_{\mathrm{gw}}\simeq {1.48}_{-1.27}^{+1.80}\times {10}^{-9}$ at f ≃ 25 Hz, while their merger rate at the present day is consistent or lower than the observed GW event rate. This level of GWB is detectable at the design sensitivity of Advanced LIGO-Virgo and would indicate a major contribution of the high-z BBH population to the local GW events. The spectral index is expected to be substantially flatter than the canonical value of ≃2/3 generically produced by lower-redshift and less-massive BBHs. Moreover, if their mass function is more top heavy than in the local universe, the GWB spectrum is even more skewed toward lower frequencies, which would allow us to extract information on the mass function of merging BBHs at high redshifts.

Keywords: gravitational wave astronomy
Stabilizing Effect of Magnetic Helicity on Magnetic Cavities in the Intergalactic Medium

We investigate the effect of magnetic helicity on the stability of buoyant magnetic cavities as found in the intergalactic medium. In these cavities we insert helical magnetic fields and test whether or not helicity can increase their stability to shredding through the Kelvin-Helmholtz instability and, with that, their lifetime. This is compared to the case of an external vertical magnetic field that is known to reduce the growth rate of the Kelvin-Helmholtz instability. By comparing a low-helicity configuration with a high-helicity one with the same magnetic energy, we find that an internal helical magnetic field stabilizes the cavity. This effect increases as we increase the helicity content. Stabilizing the cavity with an external magnetic field requires instead a significantly stronger field at higher magnetic energy. We conclude that the presence of helical magnetic fields is a viable mechanism to explain the stability of intergalactic cavities on timescales longer than 100 Myr.

Keywords: warm-hot intergalactic medium; magnetic fields
Constraining Free–Free Emission and Photoevaporative Mass-loss Rates for Known Proplyds and New VLA–identified Candidate Proplyds in NGC 1977

We present NSF's Karl G. Jansky Very Large Array observations covering the NGC 1977 region at 3.0, 6.4, and 15.0 GHz. We search for compact radio sources and detect continuum emission from 34 NGC 1977 cluster members and 37 background objects. Of the 34 radio-detected cluster members, 3 are associated with known proplyds in NGC 1977, 22 are associated with additional young stellar objects in NGC 1977, and 9 are newly identified cluster members. We examine the radio spectral energy distributions, circular polarization, and variability of the detected NGC 1977 sources and identify 10 new candidate proplyds whose radio fluxes are dominated by optically thin free–free emission. We use measurements of free–free emission to calculate the mass-loss rates of known proplyds and new candidate proplyds in NGC 1977, and find values ∼10‑9 to 10‑8 M ⊙ yr‑1, which are lower than the mass-loss rates measured toward proplyds in the Orion Nebula Cluster but consistent with the mass-loss rates predicted by external photoevaporation models for spatially extended disks that are irradiated by the typical external ultraviolet (UV) fields encountered in NGC 1977. Finally, we show that photoevaporative disk winds in NGC 1977 may be illuminated by internal or external sources of ionization, depending on their positions within the cluster. This study provides new constraints on disk properties in a clustered star-forming region with a weaker UV environment than the Orion Nebula Cluster but a stronger UV environment than low-mass star-forming regions like Taurus. Such intermediate UV environments represent the typical conditions of Galactic star and planet formation.

Keywords: protoplanetary disks; proplyds; young star clusters; photoionization; planet formation; radio sources; radio interferometry
Zodiacal Exoplanets in Time (ZEIT). XIV. He I Transit Spectroscopy of the 650 Myr Hyades Planet K2-136c

We report the non-detection of excess absorption in the 1083.2 nm line of neutral triplet helium during a transit of K2-136c, a 2.9R⊕ planet on a 17.3 days orbit around a K-type dwarf in the 650 Myr old Hyades cluster. We limit the equivalent width of any transit-associated absorption in the He I line to <25 mÅ at 99% confidence.

Keywords: exoplanet astronomy; exoplanet atmospheres; young star clusters
Which Molecular Cloud Structures Are Bound?

We analyze surveys of molecular cloud structures defined by tracers ranging from CO J = 1 → 0 through 13CO J = 1 → 0 to dust emission together with NH3 data. The mean value of the virial parameter and the fraction of mass in bound structures depends on the method used to identify structures. Generally, the virial parameter decreases and the fraction of mass in bound structures increases with the effective density of the tracer, the surface density and mass of the structures, and the distance from the center of a galaxy. For the most complete surveys of structures in the Galaxy defined by CO J = 1 → 0, the fraction of mass that is in bound structures is 0.19. For catalogs of other galaxies based on CO J = 2 → 1, the fraction is 0.35. These results offer substantial alleviation of the fundamental problem of slow star formation. If only clouds found to be bound are counted and they are assumed to collapse in a freefall time at their mean cloud density, the sum over all clouds in a complete survey of the Galaxy yields a predicted star formation rate of 46 M⊙ yr-1, a factor of 6.5 less than if all clouds are bound.

Keywords: molecular clouds
Formation of the First Two Black Hole-Neutron Star Mergers (GW200115 and GW200105) from Isolated Binary Evolution

In this work we study the formation of the first two black hole-neutron star (BHNS) mergers detected in gravitational waves (GW200115 and GW200105) from massive stars in wide isolated binary systems-the isolated binary evolution channel. We use 560 BHNS binary population synthesis model realizations and show that the system properties (chirp mass, component masses, and mass ratios) of both GW200115 and GW200105 match predictions from the isolated binary evolution channel. We also show that most model realizations can account for the local BHNS merger rate densities inferred by LIGO-Virgo. However, to simultaneously also match the inferred local merger rate densities for BHBH and NSNS systems we find we need models with moderate kick velocities (σ ≲ 102 km s-1) or high common-envelope efficiencies (αCE ≳ 2) within our model explorations. We conclude that the first two observed BHNS mergers can be explained from the isolated binary evolution channel for reasonable model realizations.

Keywords: astrophysical black holes; neutron stars; gravitational waves; stellar evolution; compact binary stars
Diverse Properties of Molecular Gas in the Host Galaxies of Fast Radio Bursts

We report the properties of molecular gas in a sample of six host galaxies of fast radio bursts (FRBs) obtained from CO observations with the Atacama Large Millimeter/submillimeter Array (FRBs 20180924B, 20190102C, and 20190711A), the results of one nondetection in a dwarf galaxy (FRB 20121102A), and two events detected in M81 (FRB 20200120E) and the Milky Way (FRB 20200428A). The CO observations resulted in the detection of CO(3-2) emission in the FRB 20180924B host and nondetections of CO(3-2) and CO(2-1) emission in the hosts of FRB 20190102C and FRB 20190711A, respectively. The derived molecular gas mass and 3σ upper limit is (2.4 ± 0.2) × 109 M ⊙, <3.8 × 108 M ⊙, and <6.7 × 109 M ⊙ for the hosts of FRB 20180924B, FRB 20190102C, and FRB 20190711A, respectively. We found diversity in molecular gas properties (gas mass, gas depletion time, and gas fraction to stellar mass) in the sample. Compared to other star-forming galaxies, the FRB 20180924B host is gas-rich (the larger molecular gas fraction), and the hosts of FRB 20190102C and FRB 20200120E are gas-poor with a shorter depletion time for their stellar mass and star formation rate. Our findings suggest that FRBs arise from multiple progenitors or single progenitors that can exist in a wide range of galaxy environments. Statistical analysis shows a significant difference in the distribution of molecular gas fraction between the FRB hosts and local star-forming galaxies. However, the difference is not substantial when an outlier, the FRB 20200120E host, is excluded, and analysis with a larger sample is needed.

Keywords: radio transient sources; extragalactic radio sources; radio bursts; galaxies; co line emission; molecular gas; interstellar medium; star formation; radio astronomy; radio interferometry; observational astronomy