adsabs/SciX_UAT_keywords huggingface dataset:
Effects of Thermal Emission on the Transmission Spectra of Hot Jupiters

The atmosphere on the dayside of a highly irradiated close-in gas giant (also known as a hot Jupiter) absorbs a significant part of the incident stellar radiation, which again gets re-emitted in the infrared wavelengths both from the day and the night sides of the planet. The re-emitted thermal radiation from the nightside facing the observers during the transit event of such a planet contributes to the transmitted stellar radiation. We demonstrate that the transit spectra at the infrared region get altered significantly when such re-emitted thermal radiation of the planet is included. We assess the effects of the thermal emission of the hot Jupiters on the transit spectra by simulating observational spectroscopic data with corresponding errors from the different channels of the upcoming James Webb Space Telescope. We find that the effect is statistically significant with respect to the noise levels of those simulated data. Hence, we convey the important message that the planetary thermal re-emission must be taken into consideration in the retrieval models of transit spectra for hot Jupiters for a more accurate interpretation of the observed transit spectra.

Keywords: radiative transfer; exoplanet atmospheres; transmission spectroscopy; atmospheric effects
The Kelvin-Helmholtz Instability at the Boundary of Relativistic Magnetized Jets

We study the linear stability of a planar interface separating two fluids in relative motion, focusing on conditions appropriate for the boundaries of relativistic jets. The jet is magnetically dominated, whereas the ambient wind is gas-pressure-dominated. We derive the most general form of the dispersion relation and provide an analytical approximation of its solution for an ambient sound speed much smaller than the jet Alfvén speed v A, as appropriate for realistic systems. The stability properties are chiefly determined by the angle ψ between the wavevector and the jet magnetic field. For ψ = π/2, magnetic tension plays no role, and our solution resembles the one of a gas-pressure-dominated jet. Here, only sub-Alfvénic jets are unstable ( $0\lt {M}_{e}\equiv (v/{v}_{{\rm{A}}})\cos \theta \lt 1$ , where v is the shear velocity and θ the angle between the velocity and the wavevector). For ψ = 0, the free energy in the velocity shear needs to overcome the magnetic tension, and only super-Alfvénic jets are unstable ( $1\lt {M}_{e}\lt \sqrt{{(1+{{\rm{\Gamma }}}_{w}^{2})/[1+({v}_{{\rm{A}}}/c)}^{2}{{\rm{\Gamma }}}_{w}^{2}]}$ , with Γ w the wind adiabatic index). Our results have important implications for the propagation and emission of relativistic magnetized jets.

Keywords: plasma astrophysics; plasma jets; high energy astrophysics; relativistic jets; magnetohydrodynamics; relativistic fluid dynamics
Extended X-Ray Emission Associated with the Radio Lobes and the Environments of 60 Radio Galaxies

This paper studied the faint, diffuse extended X-ray emission associated with the radio lobes and the hot gas in the intracluster medium (ICM) environment for a sample of radio galaxies. We used shallow (∼10 ks) archival Chandra observations for 60 radio galaxies (7 FR I and 53 FR II) with 0.0222 ≤ z ≤ 1.785 selected from the 298 extragalactic radio sources identified in the 3CR catalog. We used Bayesian statistics to look for any asymmetry in the extended X-ray emission between regions that contain the radio lobes and regions that contain the hot gas in the ICM. In the Chandra broad band (0.5-7.0 keV), which has the highest detected X-ray flux and the highest signal-to-noise ratio, we found that the nonthermal X-ray emission from the radio lobes dominates the thermal X-ray emission from the environment for ∼77% of the sources in our sample. We also found that the relative amount of on-jet axis nonthermal emission from the radio lobes tends to increase with redshift compared to the off-jet axis thermal emission from the environment. This suggests that the dominant X-ray mechanism for the nonthermal X-ray emission in the radio lobes is due to the inverse Compton upscattering of cosmic microwave background (CMB) seed photons by relativistic electrons in the radio lobes, a process for which the observed flux is roughly redshift independent due to the increasing CMB energy density with increasing redshift.

Keywords: radio galaxies; x-ray quasars; fanaroff-riley radio galaxies; radio active galactic nuclei; x-ray active galactic nuclei; radio source catalogs; radio jets; radio lobes; active galaxies; active galactic nuclei; radio hot spots; radio cores
The Time Delay Distribution and Formation Metallicity of LIGO-Virgos Binary Black Holes

We derive the first constraints on the time delay distribution of binary black hole (BBH) mergers using the LIGO-Virgo Gravitational-Wave Transient Catalog. Assuming that the progenitor formation rate follows the star formation rate (SFR), the data favor that 43100 of mergers have delay times <4.5 Gyr (90 credibility). Adopting a model for the metallicity evolution, we derive joint constraints for the metallicity-dependence of the BBH formation efficiency and the distribution of time delays between formation and merger. Short time delays are favored regardless of the assumed metallicity dependence, although the preference for short delays weakens as we consider stricter low-metallicity thresholds for BBH formation. For a p() 1 time delay distribution and a progenitor formation rate that follows the SFR without metallicity dependence, we find that min < 2.2 Gyr, whereas considering only the low-metallicity Z < 0.3 Z SFR, min < 3.0 Gyr (90 credibility). Alternatively, if we assume long time delays, the progenitor formation rate must peak at higher redshifts than the SFR. For example, for a p() 1 time delay distribution with min 4 Gyr, the inferred progenitor rate peaks at z > 3.9 (90 credibility). Finally, we explore whether the inferred formation rate and time delay distribution vary with BBH mass.

Keywords: gravitational waves; gravitational wave astronomy; astrophysical black holes; stellar mass black holes; cosmological evolution; bayesian statistics
Multi-gigayear White Dwarf Cooling Delays from Clustering-enhanced Gravitational Sedimentation

Cooling white dwarfs (WDs) can yield accurate ages when theoretical cooling models fully account for the physics of the dense plasma of WD interiors. We use MESA to investigate cooling models for a set of massive and ultramassive WDs (0.9-1.3 ${M}_{\odot }$ ) for which previous models have failed to match kinematic age indicators based on Gaia DR2. We find that the WDs in this population can be explained as C/O cores experiencing unexpectedly rapid 22Ne sedimentation in the strongly liquid interior just prior to crystallization. We propose that this rapid sedimentation is due to the formation of solid clusters of 22Ne in the liquid C/O background plasma. We show that these heavier solid clusters sink faster than individual 22Ne ions and enhance the sedimentation heating rate enough to dramatically slow WD cooling. MESA models including our prescription for cluster formation and sedimentation experience cooling delays of ≈4 Gyr on the WD Q branch, alleviating tension between cooling ages and kinematic ages. This same model then predicts cooling delays coinciding with crystallization of 6 Gyr or more in lower-mass WDs (0.6-0.8 ${M}_{\odot }$ ). Such delays are compatible with, and perhaps required by, observations of WD populations in the local 100 pc WD sample and the open cluster NGC 6791. These results motivate new investigations of the physics of strongly coupled C/O/Ne plasma mixtures in the strongly liquid state near crystallization and tests through comparisons with observed WD cooling.

Keywords: white dwarf stars; stellar diffusion; cosmochronology
A Comprehensive Perturbative Formalism for Phase Mixing in Perturbed Disks. I. Phase Spirals in an Infinite, Isothermal Slab

Galactic disks are highly responsive systems that often undergo external perturbations and subsequent collisionless equilibration, predominantly via phase mixing. We use linear perturbation theory to study the response of infinite isothermal slab analogs of disks to perturbations with diverse spatiotemporal characteristics. Without self-gravity of the response, the dominant Fourier modes that get excited in a disk are the bending and breathing modes, which, due to vertical phase mixing, trigger local phase-space spirals that are one- and two-armed, respectively. We demonstrate how the lateral streaming motion of slab stars causes phase spirals to damp out over time. The ratio of the perturbation timescale (τ P) to the local, vertical oscillation time (τ z ) ultimately decides which of the two modes is excited. Faster, more impulsive (τ P < τ z ) and slower, more adiabatic (τ P > τ z ) perturbations excite stronger breathing and bending modes, respectively, although the response to very slow perturbations is exponentially suppressed. For encounters with satellite galaxies, this translates to more distant and more perpendicular encounters triggering stronger bending modes. We compute the direct response of the Milky Way disk to several of its satellite galaxies and find that recent encounters with all of them excite bending modes in the solar neighborhood. The encounter with Sagittarius triggers a response that is at least 1-2 orders of magnitude larger than that due to any other satellite, including the Large Magellanic Cloud. We briefly discuss how ignoring the presence of a dark matter halo and the self-gravity of the response might impact our conclusions.

Keywords: disk galaxies; milky way disk; milky way dynamics; perturbation methods; galaxy dynamics; gravitational interaction; galaxy encounters; galaxy stellar disks
Closing the Gap between Observed Low-mass Galaxy H I Kinematics and Cold Dark Matter Predictions

Testing the standard cosmological model (ΛCDM) at small scales is challenging. Galaxies that inhabit low-mass dark matter halos provide an ideal test bed for dark matter models by linking observational properties of galaxies at small scales (low mass, low velocity) to low-mass dark matter halos. However, the observed kinematics of these galaxies do not align with the kinematics of the dark matter halos predicted to host them, obscuring our understanding of the low-mass end of the galaxy–halo connection. We use deep H I observations of low-mass galaxies at high spectral resolution in combination with cosmological simulations of dwarf galaxies to better understand the connection between dwarf galaxy kinematics and low-mass halos. Specifically, we use H I line widths to directly compare to the maximum velocities in a dark matter halo and find that each deeper measurement approaches the expected one-to-one relationship between the observed kinematics and the predicted kinematics in ΛCDM. We also measure baryonic masses and place these on the baryonic Tully–Fisher relation (BTFR). Again, our deepest measurements approach the theoretical predictions for the low-mass end of this relation, a significant improvement on similar measurements based on line widths measured at 50% and 20% of the peak. Our data also hint at the rollover in the BTFR predicted by hydrodynamical simulations of ΛCDM for low-mass galaxies.

Keywords: dwarf galaxies; galaxy kinematics; galaxy structure; galaxy evolution; dark matter; circumgalactic medium
Rapid Formation of Gas-giant Planets via Collisional Coagulation from Dust Grains to Planetary Cores. II. Dependence on Pebble Bulk Density and Disk Temperature

Thanks to "dust-to-planet" simulations (DTPSs), which treat the collisional evolution directly from dust to giant-planet cores in a protoplanetary disk, we showed that giant-planet cores are formed in ≲10 au in several 105 yr, because porous pebbles grow into planetesimals via collisions prior to drift in 10 au. However, such porous pebbles are unlikely to reproduce the polarized millimeter wavelength light observed from protoplanetary disks. We thus investigate gas-giant core formation with nonporous pebbles via DTPSs. Even nonporous bodies can grow into planetesimals and massive cores that are possible to be gas giants are also formed in several 105 yr. The rapid core formation is mainly via the accretion of planetesimals produced by collisional coagulation of pebbles drifting from the outer disk. The formation mechanism is similar to the case with porous pebbles, while core formation occurs in a wider region (5-10 au) than that with porous pebbles. Although pebble growth and core formation depend on the disk temperature, core formation is likely to occur with disk temperatures in typical optical thick disks around protostars.

Keywords: planet formation; protoplanetary disks
An Interferometric View of H-MM1. I. Direct Observation of NH3 Depletion

Spectral lines of ammonia, NH3, are useful probes of the physical conditions in dense molecular cloud cores. In addition to advantages in spectroscopy, ammonia has also been suggested to be resistant to freezing onto grain surfaces, which should make it a superior tool for studying the interior parts of cold, dense cores. Here we present high-resolution NH3 observations with the Very Large Array and Green Bank Telescope toward a prestellar core. These observations show an outer region with a fractional NH3 abundance of X(NH3) = (1.975 ± 0.005) × 10-8 (±10% systematic), but it also reveals that, after all, the X(NH3) starts to decrease above a H2 column density of ≈2.6 × 1022 cm-2. We derive a density model for the core and find that the break point in the fractional abundance occurs at the density n(H2) ~ 2 × 105 cm-3, and beyond this point the fractional abundance decreases with increasing density, following the power law n -1.1. This power-law behavior is well reproduced by chemical models where adsorption onto grains dominates the removal of ammonia and related species from the gas at high densities. We suggest that the break-point density changes from core to core depending on the temperature and the grain properties, but that the depletion power law is anyway likely to be close to n -1 owing to the dominance of accretion in the central parts of starless cores.

Keywords: star formation; interstellar medium; molecular clouds; interstellar molecules; astrochemistry; dense interstellar clouds; interferometry
First Detection of the Powerful Gamma-Ray Burst GRB 221009A by the THEMIS ESA and SST Particle Detectors on 2022 October 9

We present the first results study of the effects of the powerful gamma-ray burst GRB 221009A that occurred on 2022 October 9, and was serendipitously recorded by electron and proton detectors on board the four spacecraft of the NASA THEMIS mission. Long-duration gamma-ray bursts (GRBs) are powerful cosmic explosions, signaling the death of massive stars, and, among them, GRB 221009A is so far the brightest burst ever observed due to its enormous energy (E γ iso ≈ 1055 erg) and proximity (the redshift is z ≈ 0.1505). The THEMIS mission launched in 2008 was designed to study the plasma processes in the Earth's magnetosphere and the solar wind. The particle flux measurements from the two inner magnetosphere THEMIS probes, THA and THE, and two outer probes (renamed ARTEMIS after 2010), THB and THC, orbiting the Moon captured the dynamics of GRB 221009A with a high time resolution of 4 (up to 8) measurements per second. This allowed us to resolve the fine structure of the GRB and determine the temporal scales of the two main bursts' spiky structure, complementing the results from gamma-ray space telescopes and detectors.

Keywords: gamma-ray bursts
Detection of 7Be II in the Classical Nova V5669 Sgr (Nova Sagittarii 2015 No.3)

We report the new detection of 7Be II in the ultraviolet spectra of V5669 Sgr during its early decline phase (+24 and +28 d). We identified three blueshifted absorption systems in our spectra. The first two, referred to as low- and high-velocity components, were noticeably identified among H I Balmer, Na I D, and Fe II whose lower energies of transients are low (<4 eV). The third absorption component was identified among N II, He I, and C II lines whose lower energy levels are relatively high (9-21 eV). The absorption lines of 7Be II at 3130.583 Å and 3132.228 Å were identified as the first and second components in our observations. No evidence suggested the existence of Li I at 6708 Å in any velocity components. The estimated number density ratio of lithium relative to hydrogen, which was finally produced by this object using the equivalent widths of 7Be and Ca II K, $N{(}^{7}\mathrm{Li})/N{\left({\rm{H}}\right)}_{\mathrm{final}}$, is 4.0 ± 0.7 × 10-6. This value is an order of magnitude lower than the average observed values for classical novae wherein 7Be has been detected, and is comparable to the most optimistic value of theoretical predictions.

Keywords: classical novae; nuclear abundances; cataclysmic variable stars; galaxy chemical evolution; spectroscopy; high resolution spectroscopy
Effects of Impact and Target Parameters on the Results of a Kinetic Impactor: Predictions for the Double Asteroid Redirection Test (DART) Mission

The Double Asteroid Redirection Test (DART) spacecraft will impact into the asteroid Dimorphos on 2022 September 26 as a test of the kinetic impactor technique for planetary defense. The efficiency of the deflection following a kinetic impactor can be represented using the momentum enhancement factor, β, which is dependent on factors such as impact geometry and the specific target material properties. Currently, very little is known about Dimorphos and its material properties, which introduces uncertainty in the results of the deflection efficiency observables, including crater formation, ejecta distribution, and β. The DART Impact Modeling Working Group (IWG) is responsible for using impact simulations to better understand the results of the DART impact. Pre-impact simulation studies also provide considerable insight into how different properties and impact scenarios affect momentum enhancement following a kinetic impact. This insight provides a basis for predicting the effects of the DART impact and the first understanding of how to interpret results following the encounter. Following the DART impact, the knowledge gained from these studies will inform the initial simulations that will recreate the impact conditions, including providing estimates for potential material properties of Dimorphos and β resulting from DART's impact. This paper summarizes, at a high level, what has been learned from the IWG simulations and experiments in preparation for the DART impact. While unknown, estimates for reasonable potential material properties of Dimorphos provide predictions for β of 1-5, depending on end-member cases in the strength regime.

Keywords: impact phenomena; asteroids; planetary science
First Experimental Confirmation of the CH3O + H2CO → CH3OH + HCO Reaction: Expanding the CH3OH Formation Mechanism in Interstellar Ices

The successive addition of H atoms to CO in the solid phase has been hitherto regarded as the primary route to form methanol in dark molecular clouds. However, recent Monte Carlo simulations of interstellar ices alternatively suggested the radical-molecule H-atom abstraction reaction CH3O + H2CO → CH3OH + HCO, in addition to CH3O + H → CH3OH, as a very promising and possibly dominating (70%-90%) final step to form CH3OH in those environments. Here, we compare the contributions of these two steps leading to methanol by experimentally investigating hydrogenation reactions on H2CO and D2CO ices, which ensures comparable starting points between the two scenarios. The experiments are performed under ultrahigh vacuum conditions and astronomically relevant temperatures, with H:H2CO (or D2CO) flux ratios of 10:1 and 30:1. The radical-molecule route in the partially deuterated scenario, CHD2O + D2CO → CHD2OD + DCO, is significantly hampered by the isotope effect in the D-abstraction process, and can thus be used as an artifice to probe the efficiency of this step. We observe a significantly smaller yield of D2CO + H products in comparison to H2CO + H, implying that the CH3O-induced abstraction route must play an important role in the formation of methanol in interstellar ices. Reflection-absorption infrared spectroscopy and temperature-programmed desorption-quadrupole mass spectrometry analyses are used to quantify the species in the ice. Both analytical techniques indicate constant contributions of ~80% for the abstraction route in the 10-16 K interval, which agrees well with the Monte Carlo calculations. Additional H2CO + D experiments confirm these conclusions.

Keywords: astrochemistry; laboratory astrophysics; dark interstellar clouds
TESS Hunt for Young and Maturing Exoplanets (THYME). V. A Sub-Neptune Transiting a Young Star in a Newly Discovered 250 Myr Association

The detection and characterization of young planetary systems offer a direct path to study the processes that shape planet evolution. We report on the discovery of a sub-Neptune-sized planet orbiting the young star HD 110082 (TOI-1098). Transit events we initially detected during TESS Cycle 1 are validated with time-series photometry from Spitzer. High-contrast imaging and high-resolution, optical spectra are also obtained to characterize the stellar host and confirm the planetary nature of the transits. The host star is a late-F dwarf (M⋆ = 1.2M⊙) with a low-mass, M dwarf binary companion (M⋆ = 0.26M⊙) separated by nearly one arcminute (∼6200 au). Based on its rapid rotation and Lithium absorption, HD 110082 is young, but is not a member of any known group of young stars (despite proximity to the Octans association). To measure the age of the system, we search for coeval, phase-space neighbors and compile a sample of candidate siblings to compare with the empirical sequences of young clusters and to apply quantitative age-dating techniques. In doing so, we find that HD 110082 resides in a new young stellar association we designate MELANGE-1, with an age of ${250}_{-70}^{+50}$ Myr. Jointly modeling the TESS and Spitzer light curves, we measure a planetary orbital period of 10.1827 days and radius of Rp = 3.2 ± 0.1R⊕. HD 110082 b's radius falls in the largest 12% of field-age systems with similar host-star mass and orbital period. This finding supports previous studies indicating that young planets have larger radii than their field-age counterparts.

Keywords: exoplanet astronomy; exoplanets; mini neptunes; stellar astronomy; wide binary stars; moving clusters; stellar ages; transits
A Small-scale Structure Model of a Jet Based on Observations of Microvariability

We developed a multiregion radiation model for the evolution of flux and spectral index with time. In this model, each perturbation component in the jet produces an independent flare. The model can be used to study the decomposition of microvariability, the structural scale of the perturbed components, and the physical parameters of the acceleration processes. Based on the shock acceleration model for a relativistic jet, the influence of the acceleration parameters on multiband flare parameters is calculated. We present the results of multiband optical microvariability of the blazar BL Lacertae observed during 89 nights in the period from 2009 to 2021, and use them as a sample for model fitting. The results show that both the amplitude and duration of flares decomposed from the microvariability light curves conform to a log-normal distribution. The time delays between the optical bands follow a normal distribution and amount to several minutes, which corroborate with both predictions from the theoretical model and the calculation of the discrete correlation function. Using the spectral index evolution and the simultaneous fitting of the multiband variability curves, we obtain the acceleration and radiation parameters to constrain and distinguish the origins of different flares. Based on the flare decomposition, we can effectively reproduce the time-domain evolution trends of the optical variations and energy spectrum, and explain the various redder-when-brighter and bluer-when-brighter behaviors.

Keywords: blazars; bl lacertae objects; jets