adsabs/SciX_UAT_keywords huggingface dataset:
AT2020hur: A Possible Optical Counterpart of FRB 180916B

The physical origin of fast radio bursts (FRBs) remains unclear. Finding multiwavelength counterparts of FRBs can provide a breakthrough for understanding their nature. In this work, we perform a systematic search for astronomical transients whose positions are consistent with FRBs. We find an unclassified optical transient AT2020hur (α = 01h58m00.ˢ750 ± 1″, $\delta =65^\circ {43}^{{\prime} }00\buildrel{\prime\prime}\over{.} 30\pm 1^{\prime\prime} $ ) that is spatially coincident with the repeating FRB 180916B (α = 01h58m00.ˢ7502 ± 2.3 mas, $\delta =65^\circ {43}^{{\prime} }00\buildrel{\prime\prime}\over{.} 3152\pm 2.3$ mas; Marcote et al. 2020). The chance possibility of the AT2020hur-FRB 180916B association is about 0.04%, which corresponds to a significance of 3.5σ. We develop a giant flare (GF) afterglow model to fit AT2020hur. Although the GF afterglow model can interpret the observations of AT2020hur, the derived kinetic energy of such a GF is at least three orders of magnitude larger than that of a typical GF, and a lot of fine-tuning and coincidences are required for this model. Another possible explanation is that AT2020hur might consist of two or more optical flares originating from the FRB source, e.g., fast optical bursts produced by the inverse Compton scattering of FRB emission. Besides, AT2020hur is located in one of the activity windows of FRB 180916B, which provides independent support for the association. This coincidence may be due to the optical counterparts being subject to the same periodic modulation as FRB 180916B, as implied by the prompt FRB counterparts. Future simultaneous observations of FRBs and their optical counterparts may help to reveal their physical origin.

Keywords: radio bursts; radio transient sources; magnetars
In Situ Observations of Whistler-mode Waves in Magnetic Reconnection at Mars

Whistler-mode waves are one of the most important plasma waves potentially affecting the triggering and development processes of magnetic reconnection. They are widely present in the Earth's reconnection ion diffusion region but have not yet been reported in Mars'. Based on in situ measurements from MAVEN, the Mars Atmosphere and Volatile Evolution mission, we report for the first time whistler-mode waves in the ion diffusion region at the center of the current sheet in the Martian magnetotail. Simultaneously, pancake electron distributions with high temperature anisotropy are observed. Linear instability analyses imply that these unstable electrons can trigger the observed whistler-mode waves. Such findings not only fill the gap in observations of whistler-mode waves in the magnetic reconnection at Mars but also enrich our understanding of their generation mechanism in the reconnection region at unmagnetized planets.

Keywords: space plasmas; solar magnetic reconnection
Characteristic Mass in Galaxy Quenching: Environmental versus Internal Effects

A clear transition feature of galaxy quenching is identified in the multi-parameter space of stellar mass (M*), bulge-to-total mass ratio (B/Tm), halo mass (Mh) and halo-centric distance (r/r180). For a given halo mass, the characteristic stellar mass ( ${M}_{* ,\mathrm{ch}}$ ) for the transition is about one-fifth of that of the corresponding central galaxy, and almost independent of B/Tm. Once B/Tm is fixed, the quenched fraction of galaxies with ${M}_{* }\lt {M}_{* ,\mathrm{ch}}$ increases with Mh, but decreases with M* in the inner part of halos (r/r180 < 0.5). In the outer part (r/r180 > 0.5), the trend with Mh remains but the correlation with M* is absent or becomes positive. For galaxies above ${M}_{* ,\mathrm{ch}}$ and with B/Tm fixed, the quenched fraction increases with ${M}_{* }$ , but depends only weakly on Mh in both the inner and outer regions. At fixed B/Tm and M*, the quenched fraction increases with decreasing r/r180 for galaxies with ${M}_{* }\lt {M}_{* ,\mathrm{ch}}$ , and depends only weakly on r/r180 for galaxies with ${M}_{* }\gt {M}_{* ,\mathrm{ch}}$ . Our finding provides a physically motivated way to classify galaxies in halos into two classes based on their quenching properties: an "upper class" with ${M}_{* }\gt {M}_{* ,\mathrm{ch}}$ and a "lower class" with ${M}_{* }\lt {M}_{* ,\mathrm{ch}}$ . Environmental quenching is important for "lower class" galaxies, while internal quenching plays the dominating role for the "upper class."

Keywords: galaxies; galaxy environments; galaxy evolution; galaxy dark matter halos; galaxy quenching
The Next Generation Virgo Cluster Survey (NGVS). XXVII. The Size and Structure of Globular Cluster Systems and Their Connection to Dark Matter Halos

We study the size and structure of globular cluster (GC) systems of 118 early-type galaxies from the NGVS, MATLAS, and ACSVCS surveys. Fitting Sérsic profiles, we investigate the relationship between effective radii of GC systems (R e,gc) and galaxy properties. GC systems are 2–4 times more extended than host galaxies across the entire stellar mass range of our sample (108.3 M ⊙ < M * < 1011.6 M ⊙). The relationship between R e,gc and galaxy stellar mass exhibits a characteristic "knee" at a stellar mass of M p ≃ 1010.8, similar to the galaxy R e –stellar mass relationship. We present a new characterization of the traditional blue and red GC color subpopulations, describing them with respect to host galaxy $(g^{\prime} -i^{\prime} )$ color (Δgi): GCs with similar colors to their hosts have a "red" Δgi, and those significantly bluer GCs have a "blue" Δgi. The GC populations with red Δgi, even in dwarf galaxies, are twice as extended as the stars, suggesting that formation or survival mechanisms favor the outer regions. We find a tight correlation between R e,gc and the total number of GCs, with intrinsic scatter ≲0.1 dex spanning two and three orders of magnitude in size and number, respectively. This holds for both red and blue subpopulations, albeit with different slopes. Assuming that N GC,Total correlates with M 200, we find that the red GC systems have effective radii of roughly 1%–5% R 200, while the blue GC systems in massive galaxies can have sizes as large as ∼10% R 200. Environmental dependence on R e,gc is also found, with lower-density environments exhibiting more extended GC systems at fixed mass.

Keywords: globular star clusters; early-type galaxies; dwarf galaxies; galaxy formation; virgo cluster; galaxy dark matter halos
The Value-added Catalog for LAMOST DR8 Low-resolution Spectra

We present a value-added catalog containing stellar parameters estimated from 7.10 million low-resolution spectra for 5.16 million unique stars with spectral signal-to-noise ratios (S/N) higher than 10 obtained by the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) Galactic spectroscopic surveys. The catalog presents values of stellar atmospheric parameters (effective temperature T eff, surface gravity log g, metallicity [Fe/H]/[M/H]), α-element to metal abundance ratio [α/M], carbon and nitrogen to iron abundance ratios [C/Fe] and [N/Fe], and 14 bands' absolute magnitudes deduced from LAMOST spectra using the neural network method. The spectrophotometric distances of those stars are also provided based on the distance modulus. For stars with a spectral S/N larger than 50, precisions of T eff, log g, [Fe/H], [M/H], [C/Fe], [N/Fe], and [α/M] are 85 K, 0.098 dex, 0.05 dex, 0.05 dex, 0.052 dex, 0.082 dex, and 0.027 dex, respectively. The errors of 14 band's absolute magnitudes are 0.16-0.22 mag for stars with a spectral S/N larger than 50. The spectrophotometric distance is accurate to 8.5% for stars with a spectral S/N larger than 50 and is more accurate than the geometrical distance for stars with a distance larger than 2.0 kpc. Our estimates of [Fe/H] are reliable down to [Fe/H] ~-3.5 dex, significantly better than previous results. The catalog provides 26,868 unique very metal-poor star candidates ([Fe/H] ≤-2.0). The catalog would be a valuable dataset to study the structure and evolution of the galaxy, especially the solar neighborhood and the outer disk.

Keywords: fundamental parameters of stars
Extinction at the Galactic Center Using Near- and Mid-infrared Broadband Photometry: A Twist on the Rayleigh-Jeans Color Excess Method

We present an extinction map of the inner ∼15' by 16' of the Galactic center (GC) with map pixels measuring 5″ × 5″ using integrated light color measurements in the near- and mid-infrared. We use a variant of the Rayleigh-Jeans color excess (RJCE) method first described by Majewski et al. as the basis of our work, although we have approached our problem with a Bayesian mindset and dispensed with point-source photometry in favor of surface photometry, turning the challenge of the extremely crowded field at the GC into an advantage. Our results show that extinction at the GC is not inconsistent with a single power-law coefficient, β = 2.03 ± 0.06, and compare our results with those using the red clump (RC) point-source photometry method of extinction estimation. We find that our measurement of β and its apparent lack of spatial variation are in agreement with prior studies, despite the bimodal distribution of values in our extinction map at the GC with peaks at 5 and 7.5 mag. This bimodal nature of extinction is likely due to the infrared dark clouds that obscure portions of the inner GC field. We present our extinction law and map of the GC region using the point-source catalog of infrared sources compiled by DeWitt et al. The dereddening is limited by the error in the extinction measurement (typically 0.6 mag), which is affected by the size of our map pixels and is not fine-grained enough to separate out the multiple stellar populations present toward the GC.

Keywords: galactic center; interstellar extinction; interstellar reddening; near infrared astronomy; infrared excess; infrared photometry
SOFIA Observations of 30 Doradus. II. Magnetic Fields and Large-scale Gas Kinematics

The heart of the Large Magellanic Cloud, 30 Doradus, is a complex region with a clear core-halo structure. Feedback from the stellar cluster R136 has been shown to be the main source of energy creating multiple parsec-scale expanding-shells in the outer region, and carving a nebula core in the proximity of the ionization source. We present the morphology and strength of the magnetic fields (B-fields) of 30 Doradus inferred from the far-infrared polarimetric observations by SOFIA/HAWC+ at 89, 154, and 214 μm. The B-field morphology is complex, showing bending structures around R136. In addition, we use high spectral and angular resolution [C II] observations from SOFIA/GREAT and CO(2-1) from APEX. The kinematic structure of the region correlates with the B-field morphology and shows evidence of multiple expanding-shells. Our B-field strength maps, estimated using the Davis-Chandrasekhar-Fermi method and structure-function, show variations across the cloud within a maximum of 600, 450, and 350 μG at 89, 154, and 214 μm, respectively. We estimated that the majority of the 30 Doradus clouds are subcritical and sub-Alfvénic. The probability distribution function of the gas density shows that the turbulence is mainly compressively driven, while the plasma beta parameter indicates supersonic turbulence. We show that the B-field is sufficient to hold the cloud structure integrity under feedback from R136. We suggest that supersonic compressive turbulence enables the local gravitational collapse and triggers a new generation of stars to form. The velocity gradient technique using [C II] and CO(2-1) is likely to confirm these suggestions.

Keywords: interstellar dust; interstellar dust extinction; star formation; interstellar magnetic fields; magnetic fields; interstellar dynamics; starlight polarization; large magellanic cloud
Improved Treatment of Host-galaxy Correlations in Cosmological Analyses with Type Ia Supernovae

Improving the use of Type Ia supernovae (SNe Ia) as standard candles requires a better approach to incorporate the relationship between SNe Ia and the properties of their host galaxies. Using a spectroscopically confirmed sample of ∼1600 SNe Ia, we develop the first empirical model of underlying populations for SNe Ia light-curve properties that includes their dependence on host-galaxy stellar mass; we find a significant correlation between stretch population and stellar mass (99.9% confidence) and a weaker correlation between color and stellar mass (90% confidence). These populations are important inputs to simulations that are used to model selection effects and correct distance biases within the BEAMS with Bias Correction (BBC) framework. Here we improve BBC to also account for SNe Ia-host correlations, and we validate this technique on simulated data samples. We recover the input relationship between SNe Ia luminosity and host-galaxy stellar mass (the mass step, γ) with a bias of 0.004 ±0.001 mag, which is a factor of 5 improvement over previous methods that have a γ bias of ∼0.02 ± 0.001 mag. We adapt BBC for a novel dust-based model of intrinsic brightness variations, which results in a greatly reduced mass step for data (γ = 0.017 ± 0.008) and for simulations (γ = 0.006 ± 0.007). Analyzing simulated SNe Ia, the biases on the dark energy equation of state, w, vary from Δw = 0.006(5) to 0.010(5) with our new BBC method; these biases are significantly smaller than the 0.02(5) w bias using previous BBC methods that ignore SNe Ia-host correlations.

Keywords: cosmology; astrophysical dust processes; cosmological models; cosmological parameters; origin of the universe; dark energy
Efficient Formation Pathway of Methyl Formate: The Role of OH Radicals on Ice Dust

Three structural isomers of the C2H4O2 molecule, namely, methyl formate (MF; HCOOCH3), acetic acid (CH3COOH), and glycolaldehyde (HOCH2CHO), have attracted considerable attention as targets for understanding pathways toward molecular complexity in the interstellar medium (ISM). Among these isomers, MF is decisively abundant in various astronomical objects. For various formation pathways of MF, surface reactions on cosmic dust would play an important role. However, when compared to observations, the formation of MF has been found to be relatively inefficient in laboratory experiments in which methanol (CH3OH)-dominant ices were processed by ultraviolet photons and cosmic-ray analogs. Here, we show experimental results on the effective formation of MF by the photolysis of CH3OH on water ice at 10 K. We found that the key parameter leading to the efficient formation of MF is the supply of OH radicals by the photolysis of H2O, which significantly differs from CH3OH-rich experimental conditions. Moreover, using an ultrahigh-sensitivity surface analysis method, we succeeded in constraining the decisive formation pathway of MF via the photolysis of methoxymethanol (MM; CH3OCH2OH), which would improve our current understanding of chemical evolution in the ISM.

Keywords: dense interstellar clouds; interstellar dust processes; astrochemistry
The Solar Neighborhood XLVIII: Nine Giant Planets Orbiting Nearby K Dwarfs, and the CHIRON Spectrograph's Radial Velocity Performance

We report initial results of a large radial velocity survey of K dwarfs up to a distance of 50 pc from the solar system, to look for stellar, brown dwarf, and Jovian planets using radial velocities from the CHIRON spectrograph on the CTIO/SMARTS 1.5 m telescope. We identify three new exoplanet candidates orbiting host stars in the K dwarf survey and confirm a hot Jupiter from TESS orbiting TOI 129. Our techniques are confirmed via five additional known exoplanet orbiting K dwarfs, bringing the number of orbital solutions presented here to 9, each hosting an exoplanet candidate with a minimum mass of 0.5-3.0 MJup. In addition, we provide a list of 186 nearby K dwarfs with no detected close companions that are ideal for more sensitive searches for lower-mass planets. This set of stars is used to determine CHIRON's efficiency, stability, and performance for radial velocity work. For K dwarfs with V = 7-12, we reach radial velocity precisions of 5-20 ms-1 under a wide range of observing conditions. We demonstrate the stability of CHIRON over hours, weeks, and years using radial velocity standards, and describe instrumental capabilities and operation modes available for potential users.

Keywords: astronomical techniques; extrasolar gaseous giant planets; radial velocity; solar neighborhood; surveys
Goodbye to Chi by Eye: A Bayesian Analysis of Photometric Binaries in Six Open Clusters

We present a robust methodology for identifying photometric binaries in star clusters. Using Gaia DR3, Pan-STARRS, and Two Micron All Sky Survey data, we self-consistently define the cluster parameters and binary demographics for the open clusters (OCs) NGC 2168 (M35), NGC 7789, NGC 6819, NGC 2682 (M67), NGC 188, and NGC 6791. These clusters span in age from ∼200 Myr (NGC 2168) to more than ∼8 Gyr (NGC 6791) and have all been extensively studied in the literature. We use the Bayesian Analysis of Stellar Evolution software suite to derive the age, distance, reddening, metallicity, binary fraction, and binary mass-ratio posterior distributions for each cluster. We perform a careful analysis of our completeness and also compare our results to previous spectroscopic surveys. For our sample of main-sequence stars with masses between 0.6 and 1 M ⊙, we find that these OCs have similar binary fractions that are also broadly consistent with the field multiplicity fraction. Within the clusters, the binary fraction increases dramatically toward the cluster centers, likely a result of mass segregation. Furthermore nearly all clusters show evidence of mass segregation within the single and binary populations. The OC binary fraction increases significantly with cluster age in our sample, possibly due to a combination of mass-segregation and cluster-dissolution processes. We also find a hint of an anticorrelation between binary fraction and cluster central density as well as total cluster mass, possibly due to an increasing frequency of higher-energy close stellar encounters that inhibit long-period binary survival and/or formation.

Keywords: binary stars; open star clusters; relaxation time; star formation; bayesian statistics
Blasting off with NASA's Neurodiversity Network

NASA's Neurodiversity Network (N3) is a five-year program that is funded as part of NASA's Science Activation Network. N3's main goal is to provide a pathway to NASA participation and Science, Technology, Engineering, and Mathematics (STEM) employment for neurodiverse learners, with a focus on those on the autism spectrum. Through the N3 program, we are enabling STEM education for a segment of the population that is significantly underserved through a process in which existing NASA education resources are redesigned with significant input from autistic learners and their instructors. The co-design process occurs primarily in informal environments, including high school summer programs, and camps and activity sessions for middle school students sponsored by the New York Hall of Science. N3 also offers a mentored summer internship program for at least ten neurodiverse high school students each year. Mentoring is provided by NASA Subject Matter Experts, individuals who collectively possess expertise that spans NASA's Science Mission Directorate.

Keywords: rockets; astronomy education
Local Regimes of Turbulence in 3D Magnetic Reconnection

The process of magnetic reconnection when studied in nature or when modeled in 3D simulations differs in one key way from the standard 2D paradigmatic cartoon: it is accompanied by many fluctuations in the electromagnetic fields and plasma properties. We developed a diagnostics to study the spectrum of fluctuations in the various regions around a reconnection site. We define the regions in terms of the local value of the flux function that determines the distance from the reconnection site, with positive values in the outflow and negative values in the inflow. We find that fluctuations belong to two very different regimes depending on the local plasma beta (defined as the ratio of plasma and magnetic pressures). The first regime develops in the reconnection outflows where beta is high and it is characterized by a strong link between plasma and electromagnetic fluctuations, leading to momentum and energy exchanges via anomalous viscosity and resistivity. But there is a second, low-beta regime: it develops in the inflow and in the region around the separatrix surfaces, including the reconnection electron diffusion region itself. It is remarkable that this low-beta plasma, where the magnetic pressure dominates, remains laminar even though the electromagnetic fields are turbulent.

Keywords: plasma astrophysics; plasma physics; space plasmas; interplanetary magnetic fields; geomagnetic fields; solar magnetic reconnection; solar-terrestrial interactions; interplanetary turbulence
Formation of the Transition Region for the Quiet Sun

We propose a partially ionized collisional two-fluid model of the formation of the transition region between the cool dense chromosphere and hot tenuous corona for the quiet Sun. The chromosphere is treated as an isothermal gravity-bound two-fluid stratified atmosphere without appreciable vertical flow, on average. The different scale heights of the two fluids result in vertical evolution of the ionization state, and the transition region can be defined according to the ionization fraction. The transition region starts at the altitude where the ionization fraction reaches 0.5, the demarcation between the weakly and strongly ionized gas. The upper border of the region is defined as the temperature at which the particles possess enough energy for ionization, i.e., the first ionization potential. Within the transition region is a diffusion process in which the cold chromospheric particles gain energy and ionize through random collisions with hot coronal particles diffusing upward into the corona, whereas, when colliding with cold chromospheric particles, hot coronal particles lose energy, recombine, and fall into the chromosphere. The type II spicules can be generated when and where the local heating rate is so high that the conditions for a stratified chromosphere are not satisfied; upward flow is formed, penetrating the corona where the chromospheric gas in the spicule is ionized and dispersed. The enhanced radiation via those chromospheric neutral particles cools the coronal gas, and more recombination occurs, producing enhanced downward diffusion. The model reproduces key structural features of the transition region from first principles and a minimum of arbitrary parameters.

Keywords: solar transition region; solar chromosphere; ionization