adsabs/SciX_UAT_keywords huggingface dataset:
Milky Way Satellites Shining Bright in Gravitational Waves

The population of Milky Way satellite galaxies is of great interest for cosmology, fundamental physics, and astrophysics. They represent the faint end of the galaxy luminosity function, are the most dark-matter-dominated objects in the local universe, and contain the oldest and most metal-poor stellar populations. Recent surveys have revealed around 60 satellites, but this could represent less than half of the total. Characterization of these systems remains a challenge due to their low luminosity. We consider the gravitational-wave observatory LISA as a potential tool for studying these satellites through observations of their short-period double white dwarf populations. LISA will observe the entire sky without selection effects due to dust extinction, complementing optical surveys, and could potentially discover massive satellites hidden behind the disk of the Galaxy.

Keywords: gravitational wave astronomy; white dwarf stars; magellanic clouds; dwarf galaxies
A Catalog of Early-type Hα Emission-line Stars and 62 Newly Confirmed Herbig Ae/Be Stars from LAMOST Data Release 7

We derive a catalog of early-type emission-line stars including 30,023 spectra of 25,867 stars from LAMOST Data Release 7, in which 4189 have Simbad records. The spectra are classified into three morphological types (10 subtypes) based on Hα emission-line profiles. Some spectra contaminated by nebula emission lines such as from H II regions are flagged in the catalog. We also provide a specific catalog of 20 stars with stellar winds or accretion flows by calculating the terminal and peak velocities based on P-Cygni or inverse P-Cygni profiles. More important, with two color-color diagrams, (H-Ks, J-H) and (Ks-W1, H-Ks), of a collection of known Herbig Ae/Be stars (HAeBes) and classical Ae/Be stars (CAeBes), we propose an updated criterion to separate HAeBes from CAeBes. By the criterion, we select 118 HAeBe candidates and 2636 CAeBe candidates from the sample. We confirm 71 of the 118 HAeBes based on the data from LAMOST (optical spectra) and WISE (photometry and images), 62 of which are newly identified. The 71 identified HAeBes are compiled into a specific catalog, and their SEDs and MIR images are also presented. The distances of 76% confirmed HAeBes are further than 1 kpc, which enlarges the number of known HAeBes in further distance. Most of the 71 HAeBes are located in the Galactic disk while 6 of them have ∣Z gal∣ > 400 pc. Four HAeBes show the forbidden emission lines of [Fe II] and [O I], in which J051425.20+411310.7 is a newly discovered B[e]. In addition, four HAeBes having Spitzer IRS spectra all show PAH features.

Keywords: ae stars; pre-main sequence; be stars; herbig ae/be stars
Kinetic Simulation of Nonrelativistic Perpendicular Shocks of Young Supernova Remnants. IV. Electron Heating

High-Mach-number collisionless shocks are found in planetary systems and supernova remnants (SNRs). Electrons are heated at these shocks to temperatures well above the Rankine-Hugoniot prediction. However, the processes responsible for causing the electron heating are still not well understood. We use a set of large-scale particle-in-cell simulations of nonrelativistic shocks in the high-Mach-number regime to clarify the electron heating processes. The physical behavior of these shocks is defined by ion reflection at the shock ramp. Further interactions between the reflected ions and the upstream plasma excites electrostatic Buneman and two-stream ion-ion Weibel instabilities. Electrons are heated via shock surfing acceleration, the shock potential, magnetic reconnection, stochastic Fermi scattering, and shock compression. The main contributor is the shock potential. The magnetic field lines become tangled due to the Weibel instability, which allows for parallel electron heating by the shock potential. The constrained model of electron heating predicts an ion-to-electron temperature ratio within observed values at SNR shocks and in Saturn's bow shock.

Keywords: shocks; plasma astrophysics; supernova remnants; interstellar medium
Investigating the Drivers of Electron Temperature Variations in H II Regions with Keck-KCWI and VLT-MUSE

H II region electron temperatures are a critical ingredient in metallicity determinations, and recent observations have revealed systematic variations in the temperatures measured using different ions. We present electron temperatures (T e ) measured using the optical auroral lines ([N II]λ5756, [O II]λ λ7320, 7330, [S II]λ λ4069, 4076, [O III]λ4363, and [S III]λ6312) for a sample of H II regions in seven nearby galaxies. We use observations from the Physics at High Angular resolution in Nearby Galaxies survey (PHANGS) obtained with integral field spectrographs on Keck (Keck Cosmic Web Imager) and the Very Large Telescope (Multi-Unit Spectroscopic Explorer). We compare the different T e measurements with H II region and ISM environmental properties such as electron density, ionization parameter, molecular gas velocity dispersion, and stellar association/cluster mass and age obtained from PHANGS. We find that the temperatures from [O II] and [S II] are likely overestimated due to the presence of electron density inhomogeneities in H II regions. We measure high [O III] temperatures in a subset of regions with high molecular gas velocity dispersion and low ionization parameter, which may be explained by the presence of low-velocity shocks. In agreement with previous studies, the T e–T e between [N II] and [S III] temperatures have the lowest observed scatter and follow predictions from photoionization modeling, which suggests that these tracers reflect H II region temperatures across the various ionization zones better than [O II], [S II], and [O III].

Keywords: interstellar medium; h ii regions; spiral galaxies
Origin of the Weak Plasma Emission Line Detected by Voyager 1 in the Interstellar Medium: Evidence for Suprathermal Electrons

Recently, a very weak, nearly continuous plasma wave emission line has been discovered in the nearby interstellar medium at the electron plasma frequency. The new observations were made by the plasma wave instrument on the Voyager 1 spacecraft, which crossed into the interstellar medium in 2012 August. Several questions remained unanswered after the initial discovery. Why was the emission line not observed until several years after Voyager 1 entered the interstellar medium, what is the wavelength of the plasma oscillations responsible for the emission line, and what is the origin of the oscillations? Here, we provide answers to these questions. On the most important question, namely the origin of the oscillations, the evidence strongly suggest that the emission is driven by suprathermal electrons that excite plasma oscillations comparable to the quasi-thermal noise (QTN) that is commonly observed by space plasma wave instruments with long, thin electric dipole antennas. These results imply the existence of a relatively dense population of suprathermal electrons that could contribute significantly to the overall pressure in the interstellar medium. Although the similarities to the previous QTN observations are impressive, there is no certainty that the emissions are driven by thermal excitation, and other sources should be explored, such as the possibility that they are driven by pressure fluctuations associated with the short-wavelength cascade of interstellar turbulence.

Keywords: interstellar plasma
Atmospheric Monitoring and Precise Spectroscopy of the HR 8799 Planets with SCExAO/CHARIS

The atmospheres of gas giant planets are thought to be inhomogeneous due to weather and patchy clouds. We present two full nights of coronagraphic observations of the HR 8799 planets using the CHARIS integral field spectrograph behind the SCExAO adaptive optics system on the Subaru Telescope to search for spectrophomometric variability. We did not detect significant variability signals, but placed the lowest variability upper limits for HR 8799c and d. Based on injection-recovery tests, we expected to have a 50% chance to detect signals down to 10% H-band photometric variability for HR 8799c and down to 30% H-band variability for HR 8799d. We also investigated spectral variability and expected a 50% chance to recover 20% variability in the H/K flux ratio for HR 8799c. We combined all the data from the two nights to obtain some of the most precise spectra obtained for HR 8799c, d, and e. Using a grid of cloudy radiative-convective-thermochemical equilibrium models, we found all three planets prefer supersolar metallicity with effective temperatures of ~1100 K. However, our high signal-to-noise spectra show that HR 8799d has a distinct spectrum from HR 8799c, possibly preferring more vertically extended and uniform clouds and indicating that the planets are not identical. * Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Keywords: exoplanet atmospheres; exoplanet atmospheric variability; spectrophotometry
Abell 746: A Highly Disturbed Cluster Undergoing Multiple Mergers

We present deep XMM-Newton, Karl G. Jansky Very Large Array, and upgraded Giant Metrewave Radio Telescope observations of Abell 746, a cluster that hosts a plethora of diffuse emission sources that provide evidence for the acceleration of relativistic particles. Our new XMM-Newton images reveal a complex morphology of the thermal gas with several substructures. We observe an asymmetric temperature distribution across the cluster: the southern regions exhibit higher temperatures, reaching ∼9 keV, while the northern regions have lower temperatures (≤4 keV), likely due to a complex merger. We find evidence of three surface brightness edges and one candidate edge, of which three are merger-driven shock fronts. Combining our new data with published LOw-Frequency ARray observations has unveiled the nature of diffuse sources in this system. The bright NW relic shows thin filaments and a high degree of polarization with aligned magnetic field vectors. We detect a density jump, aligned with the fainter relic to the north. To the south, we detect high-temperature regions, consistent with the shock-heated regions and a density jump coincident with the northern tip of the southern radio structure. Its integrated spectrum shows a high-frequency steepening. Lastly, we find that the cluster hosts large-scale radio halo emission. A comparison of the thermal and nonthermal emission reveals an anticorrelation between the bright radio and X-ray features at the center. Our findings suggest that Abell 746 is a complex system that involves multiple mergers.

Keywords: galaxy clusters; radio continuum emission; intracluster medium; large-scale structure of the universe
Mars Climate Sounder Observations of Gravity-wave Activity throughout Mars's Lower Atmosphere

Gravity waves are one way Mars's lower atmospheric weather can affect the circulation and even composition of Mars's middle and upper atmosphere. A recent study showed how on-planet observations near the center of the 15 μm CO2 band by the A3 channel (635-665 cm-1) of the Mars Climate Sounder on board the Mars Reconnaissance Orbiter could sense horizontally short, vertically broad gravity waves at ≈25 km above the surface by looking at small-scale radiance variability in temperature-sensitive channels. This approach is extended here to two additional channels closer to the wings of the 15 μm CO2 band, A1 (595-615 cm-1) and A2 (615-645 cm-1), to sense gravity waves throughout the lower atmosphere. Using information from all three channels demonstrates that gravity-wave activity in Mars's lowermost atmosphere is dominated by orographic sources, particularly over the extremely rough terrain of Valles Marineris. Much of this orographic population is either trapped or filtered in the lowest two scale heights, such that variations in filtering and nonorographic sources shape the gravity-wave population observed at 25 km above the surface. During global dust storms, however, gravity-wave activity in the first scale height decreases by approximately a factor of 2, yet trapping/filtering of what activity remains in the tropics substantially weakens. Exceptionally high radiance variability at night in the tropics during the less dusty part of the year is the result of observing mesospheric clouds rather than gravity waves.

Keywords: mars; planetary atmospheres; atmospheric variability
Screening Effects on Electron Capture Rates and Type Ia Supernova Nucleosynthesis

Type Ia supernovae (SNe Ia) are believed to be a thermonuclear explosion of a white dwarf, but the mass of their progenitors is still an open problem. In near-Chandrasekhar-mass (near-MCh) models of SNe Ia, the central density reaches ≳109 g cm-3. The electron chemical potential becomes higher than the Q-values of electron capture (EC) transitions between fp-shell nuclei, so a portion of the available electrons is captured by iron group elements and thus neutron-rich isotopes are formed. Since EC reaction rates are sensitive to the density, the degree of neutronization is a key to distinguish near- and sub-MCh models. In order to compare observations and theoretical models, an accurate treatment of EC reactions is necessary. In previous theoretical works, however, effects of electron screening on ECs are ignored. Screening lowers EC rates and thus leads to a higher electron fraction. We implement electron screening on ECs to calculate explosive SN Ia nucleosynthesis in a near-MCh single degenerate model. It is found that some of neutron-rich nuclear abundances, namely, those of 46,48Ca, 50Ti, 54Cr, 58Fe, 64Ni, and 67,70Zn, decrease when screening effects on ECs are considered. Of these, 50Ti, 54Cr, and 58Fe are particularly interesting because a significant portion of the solar abundance of these nuclei is presumed to originate from SNe Ia. We conclude that implementing the screening effect on ECs in modern SN Ia models is desirable to precisely calculate abundances of neutron-rich nuclides.

Keywords: explosive nucleosynthesis; type ia supernovae
A Dragon Out of Breath? Monitoring High-velocity Outflows from the High-mass Gamma-Ray Binary LS 2883/PSR B1259-63 During the 2017-2021 Binary Cycle

Observations of the high-mass gamma-ray binary LS 2883/PSR B1259-63 with the Chandra X-ray Observatory during the 2011-2014 and 2014-2017 binary cycles have shown X-ray-emitting clumps, presumably ejected from the binary during periastron passages. These clumps traveled at projected velocities of ~0.1c and have shown evidence of being accelerated. The clumps also evolved in shape, size, and flux. We monitored this binary with Chandra during the 2017-2021 binary cycle to search for additional X-ray-emitting ejections. While we find evidence of extended emission in two of the six observations, it is unlike the clumps observed in the previous three binary cycles. More specifically, the extended emission is not well localized, and no bright clump is observed moving away from the binary. It is still unclear what caused the lack of X-ray-emitting clump in this orbital cycle, but it may be due to changes in the decretion disk of the Be star.

Keywords: high mass x-ray binary stars; radio pulsars; neutron stars; be stars
The Statistical Relationship between White-light Emission and Photospheric Magnetic Field Changes in Flares

Continuum emission, also called white-light emission (WLE), and permanent changes of the magnetic field (ΔBLOS) are often observed during solar flares. However, their relation and precise mechanisms are still unknown. We study statistically the relationship between ΔBLOS and WLE during 75 solar flares of different strengths and locations on the solar disk. We analyze SDO/HMI data and determine for each pixel in each flare if it exhibited WLE and/or ΔBLOS. We then investigate the occurrence, strength, and spatial size of the WLE, its dependence on flare energy, and its correlation to the occurrence of ΔBLOS. We detected WLE in 44/75 flares and ΔBLOS in 59/75 flares. We find that WLE and ΔBLOS are related, and their locations often overlap between 0% and 60%. Not all locations coincide, thus potentially indicating differences in their origin. We find that the WL area is related to the flare class by a power law, and extend the findings of previous studies, that the WLE is related to the flare class by a power law, to also be valid for C-class flares. To compare unresolved (Sun-as-a-star) WL measurements with our data, we derive a method to calculate temperatures and areas of such data under the blackbody assumption. The calculated unresolved WLE areas improve, but still differ to the resolved flaring area by about a factor of 5-10 (previously 10-20), which could be explained by various physical or instrumental causes. This method could also be applied to stellar flares to determine their temperatures and areas independently.

Keywords: solar flares; solar magnetic fields; solar photosphere; solar white-light flares
Excitation Properties of Photopigments and Their Possible Dependence on the Host Star

Photosynthesis is a plausible pathway for the sustenance of a substantial biosphere on an exoplanet. In fact, it is also anticipated to create distinctive biosignatures detectable by next-generation telescopes. In this work, we explore the excitation features of photopigments that harvest electromagnetic radiation by constructing a simple quantum-mechanical model. Our analysis suggests that the primary Earth-based photopigments for photosynthesis may not function efficiently at wavelengths >1.1 μm. In the context of (hypothetical) extrasolar photopigments, we calculate the potential number of conjugated π-electrons (N⋆) in the relevant molecules, which can participate in the absorption of photons. By hypothesizing that the absorption maxima of photopigments are close to the peak spectral photon flux of the host star, we utilize the model to estimate N⋆. As per our formalism, N⋆ is modulated by the stellar temperature, and is conceivably higher (lower) for planets orbiting stars cooler (hotter) than the Sun; exoplanets around late-type M-dwarfs might require an N⋆ twice that of the Earth. We conclude the analysis with a brief exposition of how our model could be empirically tested by future observations.

Keywords: astrobiology; biosignatures; low mass stars; stellar types
Using JWST Transits and Occultations to Determine ∼1% Stellar Radii and Temperatures of Low-mass Stars

Using JWST observations of a primary transit and two secondary eclipses for GJ 1214b, we determine an eccentricity that is more precise than a decade of HARPS data, which enables us to measure the stellar density to 2.62%. Coupled with a prior on the stellar mass from a dynamically calibrated K S–M * relation, we determine R * to 1.13%—3 times more precise than any other published analysis of this system. Then, using the bolometric flux from a spectral energy distribution model, we determine T eff to 1.39%—40% more precise than systematic floors from spectroscopy. Within the global model, these also improve the planetary radius and insolation. This is a proof of concept for a new method to determine accurate R * and T eff to a precision currently achieved for only a small number of low-mass stars. By applying our method to all high signal-to-noise ratio planetary transits and occultations, we can expand the sample of precisely measured stars without assuming tidal circularization and calibrate new relations to improve our understanding of all low-mass stars.

Keywords: super earths; low mass stars; exoplanet astronomy; eclipses; occultation
Curvature of the Spectral Energy Distribution, Compton Dominance, and Synchrotron Peak Frequency in Jetted Active Galactic Nuclei

We collect a large sample with a reliable redshift detected by the Fermi satellite after 10 yr of data (4FGL-DR2), including blazars, gamma-ray narrow-line Seyfert 1 galaxies (γNLS1s), and radio galaxies. The spectral energy distributions of these Fermi sources are fitted by using a second-degree polynomial, and some important parameters including spectral curvature, synchrotron peak frequency, and peak luminosity are obtained. Based on those parameters, we discuss the Fermi blazar sequence and the particle acceleration mechanism. Our main results are as follows: (i) By studying the relationship between the synchrotron peak frequency and the synchrotron peak frequency luminosity, jet kinetic power, and gamma-ray luminosity for jetted active galactic nuclei (AGNs), we find an "L" shape in the Fermi blazar sequence. (ii) There is a significant anticorrelation between the Compton dominance, the black hole spin, and the synchrotron peak frequency for jetted AGNs, respectively. These results support that the γNLS1s and radio galaxies belong to the Fermi blazar sequence. (iii) On the basis of previous work, statistical or stochastic acceleration mechanisms can be used to explain the relationship between the synchrotron peak frequency and synchrotron curvature. For different subclasses, the correlation slopes are different, which implies that the Fermi sources of different subclasses have different acceleration mechanisms. (iv) Flat-spectrum radio quasars and γNLS1s have a higher median spin of a black hole than BL Lac objects and radio galaxies.

Keywords: blazars; radio loud quasars; bl lacertae objects; seyfert galaxies; active galactic nuclei; gamma-rays
The JCMT BISTRO Survey: A Spiral Magnetic Field in a Hub-filament Structure, Monoceros R2

We present and analyze observations of polarized dust emission at 850 μm toward the central 1 × 1 pc hub-filament structure of Monoceros R2 (Mon R2). The data are obtained with SCUBA-2/POL-2 on the James Clerk Maxwell Telescope (JCMT) as part of the B-fields in Star-forming Region Observations survey. The orientations of the magnetic field follow the spiral structure of Mon R2, which are well described by an axisymmetric magnetic field model. We estimate the turbulent component of the magnetic field using the angle difference between our observations and the best-fit model of the underlying large-scale mean magnetic field. This estimate is used to calculate the magnetic field strength using the Davis-Chandrasekhar-Fermi method, for which we also obtain the distribution of volume density and velocity dispersion using a column density map derived from Herschel data and the C18O (J = 3 - 2) data taken with HARP on the JCMT, respectively. We make maps of magnetic field strengths and mass-to-flux ratios, finding that magnetic field strengths vary from 0.02 to 3.64 mG with a mean value of 1.0 ± 0.06 mG, and the mean critical mass-to-flux ratio is 0.47 ± 0.02. Additionally, the mean Alfvén Mach number is 0.35 ± 0.01. This suggests that, in Mon R2, the magnetic fields provide resistance against large-scale gravitational collapse, and the magnetic pressure exceeds the turbulent pressure. We also investigate the properties of each filament in Mon R2. Most of the filaments are aligned along the magnetic field direction and are magnetically subcritical.

Keywords: star formation; magnetic fields; polarimetry; molecular clouds; submillimeter astronomy