adsabs/SciX_UAT_keywords huggingface dataset:
Panspermia in a Milky Way-like Galaxy

We study the process of panspermia in Milky Way-like galaxies by modeling the probability of successful travel of organic compounds between stars harboring potentially habitable planets. To this end, we apply the modified habitability recipe of Gobat & Hong to a model galaxy from the McMaster Unbiased Galaxy Simulations suite of zoom-in cosmological simulations. We find that, unlike habitability, which only occupies a narrow dynamic range over the entire galaxy, the panspermia probability can vary by orders of magnitude between the inner (R, b &equals; 1-4 kpc) and outer disk. However, only a small fraction of star particles have very large values for the panspermia probability and, consequently, the fraction of star particles where the panspermia process is more effective than prebiotic evolution is much lower than from naïve expectations based on the ratio between the panspermia probability and natural habitability.

Keywords: exoplanet formation; astrobiology; habitable planets; milky way galaxy; interstellar dust extinction; galaxy stellar content
Estimating the Mean Free Paths of Energetic Protons Using Differential Intensity Spectra

An analytical calculation is presented to derive the mean free paths of energetic protons in large western solar energetic particle (SEP) events during the first 12 hr after the event onset utilizing the differential spectra averaged over successive time intervals of 3 hr. The model assumes diffusive transport of energetic particles in a radial magnetic flux tube and neglects solar wind convection and adiabatic cooling. The model further assumes that particles over the considered energies (>10 MeV) are injected instantaneously near the Sun. Using the model, we reproduce the differential spectra averaged over successive time intervals after event onset and derive the radial mean free paths (λmfp) for protons at the energies where the two spectra over successive time intervals intersect. We then select eight western SEP events during the past solar cycle and apply the scheme. The derived λmfp ranges from 0.016 to 0.149 au. Our method finds smaller mean free paths than the lower limit of the "Palmer consensus" (0.04 au) in approximately 35% of the cases. We also combine differential intensity spectra and fluence to estimate the number of crossings (Nc) of particles passing through 1 au at applicable energies. The average Nc, excluding a twin-CME event, is 17.7, which indicates that diffusive transport of SEPs is capable of elevating the fluence observed at 1 au by one order of magnitude compared to if particles stream through 1 au nearly scatter-free.

Keywords: solar energetic particles; interplanetary physics
A 16 au Binary in the Class 0 Protostar L1157 MMS

We present Very Large Array observations toward the Class 0 protostar L1157 MMS at 6.8 and 9 mm with a resolution of ~0.″04 (14 au). We detect two sources within L1157 MMS and interpret these sources as a binary protostar with a separation of ~16 au. The material directly surrounding the binary system within the inner 50 au radius of the system has an estimated mass of 0.11 M ☉, calculated from the observed dust emission. We interpret the observed binary system in the context of previous observations of its flattened envelope structure, low rates of envelope rotation from 5000 to 200 au scales, and an ordered, poloidal magnetic field aligned with the outflow. Thus, L1157 MMS is a prototype system for magnetically regulated collapse, and the presence of a compact binary within L1157 MMS demonstrates that multiple star formation can still occur within envelopes that likely have dynamically important magnetic fields.

Keywords: protostars; young stellar objects; radio interferometry
Stellar Masses and Star Formation Rates of Galaxies and AGNs in the eFEDS GAMA09 Field

The eFEDS is a wide ≈140 deg2 field that has extensive multiwavelength coverage. To improve the utility of the existing data, we use CIGALE to fit source Spectral Energy Distributions (SEDs) from X-rays to far-infrared (FIR) mainly to derive stellar masses (M ⋆) and star-formation rates (SFRs) for normal galaxies and X-ray Active Galactic Nuclei (AGNs). The catalog consists of 2,057,027 galaxies and 10,373 X-ray AGNs located in the ≈60 deg2 GAMA09 sub-field. Comparing our M ⋆ with other available catalogs and our SFRs with FIR-derived SFRs, we demonstrate the general reliability of our SED-fitting measurements. Our catalog is publicly available in Zenodo.

Keywords: active galactic nuclei; galaxies; sky surveys; celestial objects catalogs
Bivariate Number Distribution of Solar Soft X-Ray Flares

Conventionally, researchers investigated the number distribution of solar flares by univariate analysis using all available data. For the first time, we investigate the bivariate number distribution of peak flux (f) and duration (T) of soft X-ray flares observed by the Geostationary Operational Environmental Satellite during the past 10 years. First, the univariate number distribution of f is found to obey a power law either for each class of flares or for the B or ≥C flares in a certain range of T. But the power-law index of B-class flares is much smaller than those of other higher-class ones. For the ≥C flares, the longer the duration, the smaller the power-law index. The univariate number distribution of T deviates from the power law at shorter durations and is better fitted by a skewed Gaussian function in logarithmic coordinates for almost any given range of f, reflecting the random phenomena in solar flares. Then, based on the univariate analysis, a linear Gaussian function is proposed to describe the bivariate logarithmic number distribution of f and T, from which the local power-law index with respect to either f or T can also be analyzed. The real number distribution of B flares should be in between the observed one and the power-law distribution of stronger flares (≥C). We suggest that nanoflare activity may not be the dominant source of coronal heating.

Keywords: solar x-ray flares; solar activity; solar active regions; solar corona; solar cycle
SCUBA2 High Redshift Bright Quasar Survey: Far-infrared Properties and Weak-line Features

We present a submillimeter continuum survey ("SCUBA2 High rEdshift bRight quasaR surveY," hereafter SHERRY) of 54 high-redshift quasars at 5.6 < z < 6.9 with quasar bolometric luminosities in the range of (0.2-5) × 1014 L⊙, using the Submillimetre Common-User Bolometer Array-2 (SCUBA2) on the James Clerk Maxwell Telescope. About 30% (16/54) of the sources are detected with a typical 850 μm rms sensitivity of 1.2 mJy beam-1 (Sν,850 μm = 4-5 mJy, at >3.5σ). The new SHERRY detections indicate far-infrared (FIR) luminosities of 3.5 × 1012 to 1.4 × 1013 L⊙, implying extreme star formation rates of 90-1060 M⊙ yr-1 in the quasar host galaxies. Compared with z = 2-5 samples, the FIR-luminous quasars (LFIR > 1013 L⊙) are rarer at z ∼ 6. The optical/near-infrared spectra of these objects show that 11% (6/54) of the sources have weak Lyα emission-line features, which may relate to different subphases of the central active galactic nuclei (AGNs). Our SCUBA2 survey confirms the trend reported in the literature that quasars with submillimeter detections tend to have weaker ultraviolet (UV) emission lines compared to quasars with nondetections. The connection between weak UV quasar line emission and bright dust continuum emission powered by massive star formation may suggest an early phase of AGN-galaxy evolution, in which the broad-line region is starting to develop slowly or is shielded from the central ionization source, and has unusual properties such as weak-line features or bright FIR emission.

Keywords: observational cosmology; quasars; active galaxies; high-redshift galaxies; submillimeter astronomy
Discovery of the 5 keV Cyclotron Line Followed by Three Harmonics in Swift J1626.6-5156

We report on observations of the Be/X-ray binary system Swift J1626.6-5156 performed with the Nuclear Spectroscopic Telescope ARray (NuSTAR) during a short outburst in 2021 March, following its detection by the MAXI monitor and Spektrum-Roentgen-Gamma (SRG) observatory. Our analysis of the broadband X-ray spectrum of the source confirms the presence of two absorption-like features at energies E ~ 9 and E ~ 17 keV. These had been previously reported in the literature and interpreted as the fundamental cyclotron resonance scattering feature (CRSF) and its first harmonic (based on Rossi X-ray Timing Explorer (RXTE) data). The better sensitivity and energy resolution of NuSTAR, combined with the low-energy coverage of Neutron star Interior Composition Explorer (NICER), allowed us to detect two additional absorption-like features at E ~ 4.9 keV and E ~ 13 keV. Therefore, we conclude that, in total, four cyclotron lines are observed in the spectrum of Swift J1626.6-5156: the fundamental CRSF at E ~ 4.9 keV and three higher spaced harmonics. This discovery makes Swift J1626.6-5156 the second accreting pulsar, after 4U 0115+63, whose spectrum is characterized by more than three lines of a cyclotronic origin, and implies that the source has the weakest confirmed magnetic field among all X-ray pulsars, B ~ 4 × 1011 G. This discovery makes Swift J1626.6-5156 one of the prime targets for the upcoming X-ray polarimetry missions covering the soft X-ray band, such as Imaging X-ray Polarimetry Explorer (IXPE) and enhanced X-ray Timing and Polarimetry mission (eXTP).

Keywords: binary pulsars; neutron stars
Photometry of the 2015 Outburst of AG Pegasi

In 2015 June, the symbiotic binary star AG Pegasi underwent a period of outburst. SkyCam T, mounted onboard the 2 m Liverpool Telescope, collected over 650 unfiltered images of this event, and several thousand images from before and after. This note presents Sloan r' band light curves obtained from these images. In addition, a color-magnitude diagram (CMD) using AAVSO data is included to infer parameters of the system's white dwarf (WD). Features in the light curve allow one to classify this outburst as that of classical (or Z And) type. The CMD suggests the temperature and luminosity of the WD increase concurrently to produce the light curve maxima. Light curves either side of the event show wave-like oscillations owing to the orbital period of AG Pegasi's components, indicating quiescence.

Keywords: symbiotic binary stars; variable stars; cataclysmic variable stars; symbiotic novae
Identification and Spectroscopic Characterization of 128 New Herbig Stars

We present optical spectroscopy observations of 145 high-mass pre-main-sequence candidates from the catalog of Vioque et al. 2020 From these, we provide evidence for the Herbig nature of 128 sources. This increases the number of known objects of the class by ~50%. We determine the stellar parameters of these sources using the spectra and Gaia EDR3 data. The new sources are well distributed in mass and age, with 23 sources between 4 and 8 M ⊙ and 32 sources above 8 M ⊙. Accretion rates are inferred from Hα and Hβ luminosities for 104 of the new Herbigs. These accretion rates, combined with previous similar estimates, allow us to analyze the accretion properties of Herbig stars using the largest sample ever considered. We provide further support to the existence of a break in accretion properties at ~3-4 M ⊙, which was already reported for the previously known Herbig stars. We re-estimate the potential break in accretion properties to be at ${3.87}_{-0.96}^{+0.38}$ M ⊙. As observed for the previously known Herbig stars, the sample of new Herbig stars independently suggests intense inner-disk photoevaporation for sources with masses above ~7 M ⊙. These observations provide robust observational support to the accuracy of the Vioque et al. 2020 catalog of Herbig candidates. *Based on observations collected at the European Southern Observatory (ESO) under ESO program 0104.C-0937(A) and 0104.C-0937(B), observations made in the Observatorios de Canarias del IAC, program 103-INT13/19B, and observations collected at the Centro Astronómico Hispano-Alemán (CAHA) at Calar Alto from 2019-04-Sept to 2019-06-Sept.

Keywords: herbig ae/be stars; star formation; pre-main sequence stars; young stellar objects; massive stars; stellar accretion; hertzsprung russell diagram; emission line stars
Signatures of r-process Elements in Kilonova Spectra

Binary neutron star (NS) mergers have been expected to synthesize r-process elements and emit radioactively powered radiation, called kilonovae. Although r-process nucleosynthesis was confirmed by the observations of GW170817/AT2017gfo, no trace of individual elements has been identified except for strontium. In this paper, we perform systematic calculations of line strength for bound-bound transitions and radiative transfer simulations in NS merger ejecta toward element identification in kilonova spectra. We find that Sr II triplet lines appear in the spectrum of a lanthanide-poor model, which is consistent with the absorption feature observed in GW170817/AT2017gfo. The synthetic spectrum also shows the strong Ca II triplet lines. This is natural because Ca and Sr are coproduced in the material with relatively high electron fraction and their ions have similar atomic structures with only one s-electron in the outermost shell. The line strength, however, highly depends on the abundance distribution and temperature in the ejecta. For our lanthanide-rich model, the spectra show the features of doubly ionized heavy elements, such as Ce, Tb, and Th. Our results suggest that the line-forming region of GW170817/AT2017gfo was lanthanide-poor. We show that the Sr II and Ca II lines can be used as a probe of physical conditions in NS merger ejecta. Absence of the Ca II line features in GW170817/AT2017gfo implies that the Ca/Sr ratio is <0.002 in mass fraction, which is consistent with nucleosynthesis for electron fraction ≥0.40 and entropy per nucleon (in units of Boltzmann constant) ≥25.

Keywords: r-process; neutron stars; radiative transfer simulations; transient sources
Are NH3 and CO2 Ice Present on Miranda?

Published near-IR spectra of the four largest classical Uranian satellites display the presence of discrete deposits of CO2 ice, along with subtle absorption features around 2.2 μm. The two innermost satellites, Miranda and Ariel, also possess surfaces heavily modified by past endogenic activity. Previous observations of the smallest satellite, Miranda, have not detected the presence of CO2 ice, and a report of an absorption feature at 2.2 μm has not been confirmed. An absorption feature at 2.2 μm could result from exposed or emplaced NH3- or NH4-bearing species, which have a limited lifetime on Miranda's surface, and therefore may imply that Miranda's internal activity was relatively recent. In this work, we analyzed near-IR spectra of Miranda to determine whether CO2 ice and the 2.2 μm feature are present. We measured the band area and depth of the CO2 ice triplet (1.966, 2.012, and 2.070 μm), a weak 2.13 μm band attributed to CO2 ice mixed with H2O ice, and the 2.2 μm band. We confirmed a prior detection of a 2.2 μm band on Miranda, but we found no evidence for CO2 ice, either as discrete deposits or mixed with H2O ice. We compared a high signal-to-noise-ratio spectrum of Miranda to synthetic and laboratory spectra of various candidate compounds to shed light on what species may be responsible for the 2.2 μm band. We conclude that the 2.2 μm absorption is best matched by a combination of NH3 ice with NH3 hydrates or NH3-H2O mixtures. NH4-bearing salts like NH4Cl are also promising candidates that warrant further investigation.

Keywords: planetary surfaces; surface composition; surface ices; surface processes; uranian satellites
A Blind All-sky Search for Star Clusters in Gaia EDR3: 886 Clusters within 1.2 kpc of the Sun

Although previous searches for star clusters have been very successful, many clusters are likely still omitted, especially at high-Galactic-latitude regions. In this work, based on the astrometry of Gaia EDR3, we searched nearby (ϖ > 0.8 mas) all-sky regions, obtaining 886 star clusters, of which 270 candidates have not been cataloged before. At the same time, we have presented the physical parameters of the clusters by fitting theoretical isochrones to their optical magnitudes. More halo members and expanding structures in many star clusters were also found. Most of the new objects are young clusters that are less than 100 million years old. Our work greatly increased the sample size and physical parameters of star clusters in the solar neighborhood, in particular, 46 clusters are newly found with ∣b∣ > 20°, which represents a nearly threefold increase in the number of clusters at high-Galactic-latitude regions.

The figure sets of all clusters are also available at China-VO via https://doi.org/10.12149/101133.

Keywords: open star clusters; star clusters
KW-Sun: The Konus-Wind Solar Flare Database in Hard X-Ray and Soft Gamma-Ray Ranges

We present a database of solar flares registered by the Konus-Wind instrument during more than 27 yr of operation, from 1994 November to now (2022 June). The constantly updated database (hereafter KW-Sun) contains over 1000 events detected in the instrument's triggered mode and is accessible online at http://www.ioffe.ru/LEA/kwsun/. For each flare, the database provides time-resolved energy spectra in energy range from ~20 keV to ~15 MeV in FITS format along with count-rate light curves in three wide-energy bands, G1 (~20-80 keV), G2 (~80-300 keV), and G3 (~300-1200 keV), with high time resolution (down to 16 ms) in ASCII and IDL SAV formats. This article focuses on the instrument capabilities in the context of solar observations, the structure of the KW-Sun data, and their intended usage. The presented homogeneous data set obtained in the broad energy range with high temporal resolution during more than two full solar cycles is beneficial for both statistical and case studies as well as a source of context data for solar flare research.

Keywords: solar flare spectra; solar flares; solar electromagnetic emission; solar gamma-ray emission; solar x-ray emission; solar x-ray flares
Discovery of ATLAS17jrp as an Optical-, X-Ray-, and Infrared-bright Tidal Disruption Event in a Star-forming Galaxy

We hereby report the discovery of ATLAS17jrp as an extraordinary tidal disruption event (TDE) in the star-forming galaxy SDSS J162034.99+240726.5 in our recent sample of mid-infrared outbursts in nearby galaxies. Its optical/UV light curves rise to a peak luminosity of ~1.06 × 1044 erg s-1 in about a month and then decay as t -5/3 with a roughly constant temperature around 19,000 K, and the optical spectra show a blue continuum and very broad Balmer lines with FWHM ~ 15,000 km s-1, which gradually narrowed to 1400 km s-1 within 4 yr, all agreeing well with other optical TDEs. A delayed and rapidly rising X-ray flare with a peak luminosity of ~1.27 × 1043 erg s-1 was detected ~170 days after the optical peak. The high MIR luminosity of ATLAS17jrp (~2 × 1043 erg s-1) has revealed a distinctive dusty environment with a covering factor as high as ~0.2, which is comparable to that of a torus in active galactic nuclei but at least one order of magnitude higher than normal optical TDEs. Therefore, ATLAS17jrp turns out to be one of the rare unambiguous TDEs found in star-forming galaxies, and its high dust-covering factor implies that dust extinction could play an important role in the absence of optical TDEs in star-forming galaxies.

Keywords: accretion; galaxy nuclei
Effects of Electron Temperature Anisotropy on Proton-beam Instability in the Solar Wind

Solar wind observations often show that the drift velocity of a proton beam relative to a background proton decreases with the heliocentric distance. Proton-beam instability has been suggested to play an important role in the deceleration of the proton-beam velocity; the effects of electron temperature anisotropy on the proton-beam instability have not been examined. Based on a general kinetic dispersion relation solver for magnetized plasma (PDRK), we investigate the effects of electron temperature anisotropy on the oblique Alfvén/ion-cyclotron (A/IC) and parallel magnetosonic/whistler (M/W) instabilities driven by proton beams in the solar wind. The results show that the growth rates, real frequencies, and threshold conditions for both instabilities are sensitive to the electron temperature anisotropy Te⊥/Te∣∣ and the parallel electron beta βe∣∣. In the low-beta regime with ${\beta }_{e| | }\lt {\beta }_{e| | }^{c}\simeq 0.5$ , where ${\beta }_{e| | }^{c}$ is a critical plasma beta for which the threshold velocities of both instabilities are equal, the growth rate of the oblique A/IC instability is weakly dependent on the electron temperature anisotropy. In the high-beta regime with ${\beta }_{e| | }\gt {\beta }_{e| | }^{c}$ , the growth rate of the parallel M/W instability increases with decreasing Te⊥/Te∣∣. Moreover, the threshold velocities of both instabilities are shifted to lower values as Te⊥/Te∣∣ decreases, especially for the parallel M/W instability in the regime with βe∣∣ ≥ 1. The theoretical results for the threshold velocity together with the observed parallel electron beta and/or electron temperature anisotropy are used to explain the observed proton-beam drift velocity in the solar wind.

Keywords: solar wind; space plasmas
Collisionless Equilibria in General Relativity: Stable Configurations beyond the First Binding Energy Maximum

We numerically study the stability of collisionless equilibria in the context of general relativity. More precisely, we consider the spherically symmetric, asymptotically flat Einstein-Vlasov system in Schwarzschild and maximal areal coordinates. Our results provide strong evidence against the well-known binding energy hypothesis, which states that the first local maximum of the binding energy along a sequence of isotropic steady states signals the onset of instability. We do, however, confirm the conjecture that steady states are stable at least up to the first local maximum of the binding energy. For the first time, we observe multiple stability changes for certain models. The equations of state used are piecewise linear functions of the particle energy and provide a rich variety of different equilibria.

Keywords: general relativity; gravitational collapse; gravitational instability; galaxy dynamics
The NANOGrav 12.5 yr Data Set: Polarimetry and Faraday Rotation Measures from Observations of Millisecond Pulsars with the Green Bank Telescope

In this work, we present polarization profiles for 23 millisecond pulsars observed at 820 and 1500 MHz with the Green Bank Telescope as part of the NANOGrav pulsar timing array. We calibrate the data using Mueller matrix solutions calculated from observations of PSRs B1929+10 and J1022+1001. We discuss the polarization profiles, which can be used to constrain pulsar emission geometry, and present both the first published radio polarization profiles for nine pulsars and the discovery of very low-intensity average profile components ("microcomponents") in four pulsars. We obtain the Faraday rotation measures for each pulsar and use them to calculate the Galactic magnetic field parallel to the line of sight for different lines of sight through the interstellar medium. We fit for linear and sinusoidal trends in time in the dispersion measure and Galactic magnetic field and detect magnetic field variations with a period of 1 yr in some pulsars, but overall find that the variations in these parameters are more consistent with a stochastic origin.

Keywords: pulsars; interstellar medium; astronomical techniques