adsabs/SciX_UAT_keywords huggingface dataset:
Historical Fermi All-sky Variability Analysis of Galactic Flares

The Fermi All-sky Variability Analysis (FAVA) provides a photometric alternative for identifying week-long gamma-ray flares across the entire sky while being independent of any diffuse Galactic or isotropic emission model. We reviewed 779 weeks of Fermi Large Area Telescope data analyzed by FAVA to estimate the rate and origin of Galactic gamma-ray flares, and to search for new variable Galactic gamma-ray transients. We report an estimated yearly rate of ∼8.5 Galactic gamma-ray flares yr–1, with ∼1 flare yr–1 coming from unknown sources. Out of the known gamma-ray sources that are spatially coincident with these detected flares, we report gamma-ray flares for six of them for the first time. All six are classified as pulsars, or a source of unknown nature but which positionally overlaps with known supernova remnants or pulsar wind nebulae (PWNe). This potentially means these sites are tentative candidates to be the second known site of a variable gamma-ray PWN, after the famous Crab Nebula's PWN. Additionally, we identify nine unassociated flares that are unlikely to have originated from known gamma-ray sources.

Keywords: gamma-ray transient sources; pulsar wind nebulae; supernova remnants; high mass x-ray binary stars; millisecond pulsars; pulsars; gamma-ray astronomy; transient sources; high energy astrophysics
Evidence of Continuous Reconnection along a Helmet Streamer Current Sheet Observed by WISPR on Parker Solar Probe

Parker Solar Probe's second solar encounter from 2019 March 30 to April 11 occurred during a period when the corona had a simple magnetic structure and relatively flat heliospheric current sheet (HCS), which was in the field of view of the Wide-field Imager for Solar Probe (WISPR) throughout. The images show an almost continual flow of transient density enhancements (streamer blobs) of various sizes near the latitude of the HCS during the entire 11 day encounter period. The high resolution and sensitivity of WISPR reveal the structure of some of the individual blobs not seen in observations from 1 au. Many of the blobs show dark central cores, suggesting that they are magnetic flux ropes. The 3D trajectories and sizes of four representative streamer blobs have been determined using the tracking and fitting technique of Liewer et al. (2020). Comparison of the location of these blobs with synoptic white-light maps for this time period, created using data from the Large Angle and Spectrometric Coronagraph (Brueckner et al. 1995) on board the Solar and Heliospheric Observatory, confirms that the blobs are at the location of the helmet streamer associated with the HCS. The blobs were observed in the region beyond 15 R ☉. The continual flow of blobs, the confirmation of their location at the HCS, and their flux-rope-like appearance provide strong evidence that the process of reconnection across the current sheet dominates the slow wind near the HCS.

Keywords: solar k corona; solar coronal streamers
Depletion of 13C in CO in the Atmosphere of Mars Suggested by ExoMars-TGO/NOMAD Observations

The atmosphere of Mars is mainly composed by carbon dioxide (CO2). It has been predicted that photodissociation of CO2 depletes 13C in carbon monoxide (CO). We present the carbon 13C/12C isotopic ratio in CO at 30-50 km altitude from the analysis of the solar occultation measurements taken by the instrument Nadir and Occultation for Mars Discovery on board the ExoMars Trace Gas Orbiter (ExoMars-TGO). We retrieve 12C16O, 13C16O, and 12C18O volume mixing ratios from the spectra taken at 4112-4213 cm-1, where multiple CO isotope lines with similar intensities are available. The intensities of the 12C16O lines in this spectral range are particularly sensitive to temperature, thus we derive the atmospheric temperature by retrieving CO2 density with simultaneously measured spectra at 2966-2990 cm-1. The mean δ 13C value obtained from the 13C16O/12C16O ratios is -263‰, and the standard deviation and standard error of the mean are 132‰ and 4‰, respectively. The relatively large standard deviation is due to the strong temperature dependences in the 12C16O lines. We also examine the 13C16O/12C18O ratio, whose lines are less sensitive to temperature. The mean δ value obtained with 12C18O instead of 12C16O is -82‰ with smaller standard deviation, 60‰. These results suggest that CO is depleted in 13C when compared to CO2 in the Martian atmosphere as measured by the Curiosity rover. This depletion of 13C in CO is consistent with the CO2 photolysis-induced fractionation, which might support a CO-based photochemical origin of organics in Martian sediments.

Keywords: planetary atmospheres
A Core Mass Function Indistinguishable from the Salpeter Stellar Initial Mass Function Using 1000 au Resolution ALMA Observations

We present the core mass function (CMF) of the massive star-forming clump G33.92 + 0.11 using 1.3 mm observations obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). With a resolution of 1000 au, this is one of the highest resolution CMF measurements to date. The CMF is corrected by flux and number incompleteness to obtain a sample that is complete for gas masses M ≳ 2.0 M⊙. The resulting CMF is well represented by a power-law function ( ${dN}/d\mathrm{log}M\propto {M}^{{\rm{\Gamma }}}$ ), whose slope is determined using two different approaches: (i) by least-squares fitting of power-law functions to the flux- and number-corrected CMF, and (ii) by comparing the observed CMF to simulated samples with similar incompleteness. We provide a prescription to quantify and correct a flattening bias affecting the slope fits in the first approach, which is caused by small-sample or edge effects when the data are represented by either classical histograms or a kernel density estimate, respectively. The resulting slopes from both approaches are in good agreement each other, with ${\rm{\Gamma }}=-{1.11}_{-0.11}^{+0.12}$ being our adopted value. Although this slope appears to be slightly flatter than the Salpeter slope Γ = -1.35 for the stellar initial mass function (IMF), we find from Monte Carlo simulations that the CMF in G33.92 + 0.11 is statistically indistinguishable from the Salpeter representation of the stellar IMF. Our results are consistent with the idea that the form of the IMF is inherited from the CMF, at least at high masses and when the latter is observed at high enough resolution.

Keywords: initial mass function; protostars
Low-J Transitions in {\tilde{A}}(2) {\Pi }(0,0,0)-{\tilde{X}}(2) {{\Sigma }}(+) (0,0,0) Band of Buffer-gas-cooled CaOH

Calcium monohydroxide radical (CaOH) is receiving an increasing amount of attention from the astrophysics community as it is expected to be present in the atmospheres of hot rocky super-Earth exoplanets as well as interstellar and circumstellar environments. Here, we report the high-resolution laboratory absorption spectroscopy on low-J transitions in ${\tilde{A}}^{2}{\rm{\Pi }}(0,0,0)-{\tilde{X}}^{2}{{\rm{\Sigma }}}^{+}(0,0,0)$ band of buffer-gas-cooled CaOH. In total, 40 transitions out of the low-J states were assigned, including 27 transitions that have not been reported in previous literature. The determined rotational constants for both ground and excited states are in excellent agreement with previous literature, and the measurement uncertainty for the absolute transition frequencies was improved by more than a factor of 3. This will aid future interstellar, circumstellar, and atmospheric identifications of CaOH. The buffer-gas-cooling method employed here is a particularly powerful method to probe low-J transitions and is easily applicable to other astrophysical molecules.

Keywords: molecular spectroscopy; high resolution spectroscopy; laboratory astrophysics; experimental techniques; spectral line lists; line positions
Searching for Spectroscopic Signatures of Ongoing Quenching in SDSS Galaxies

In this paper, we estimate the "star formation change parameter," SFR79, which characterizes the current SFR relative to the average during the last 800 Myr, for ~300,000 galaxies selected from the Sloan Digital Sky Survey (SDSS). The goals are to examine, in a much larger and independent sample, the trends previously reported in a sample of star-forming (SF) MaNGA galaxies and also to search for spectroscopic signatures of ongoing quenching in the so-called "Green Valley," which is generally believed to contain galaxies that are migrating from the SF population to the quenched population of galaxies. Measuring SFR79 for our large sample of SDSS galaxies, we first confirm the basic results of SF galaxies published by Wang & Lilly. We then discuss in detail the calibration and meaning of SFR79 for galaxies that are well below the SFMS and establish the expected statistical signature of systematic ongoing quenching from modeling the z ~ 0 quenching rate of the SF population. We conclude that it is not possible at present to establish unambiguous observational evidence for systematic ongoing quenching processes, due to limitations both in the noise of the observational data, in particular in the measurements of Hδ absorption, and in the calibration of SFR79, as well as biases introduced by the necessity of selecting objects with significant Hα emission. We do however see plausible indications of ongoing quenching, which are quantitatively consistent with expectations from "growth+quenching" models of galaxy evolution and a typical e-folding timescale for quenching of ~500 Myr.

Keywords: galaxy quenching; galaxy evolution; star formation; green valley galaxies; galaxies; galaxy spectroscopy
Detection of a Planet in 2M1938+4603 Revisited

The Observed-minus-Calculated diagram shows a stability of a period being analyzed. In case of binary system, any nonlinear O - C variation indicates an orbital period variation that can be caused by e.g., mass loss or mass transfer between components (physical change), additional component(s) to the system (apparent change only). Baran et al. reported a sinusoidal variation of the O - C of 2M 1938+4603 and interpreted it as a circumbinary planet. We analyzed the newest and most reliable release of the Kepler data of 2M 1938+4603 and by using our newest approach we removed two main sources that could cause the variation not to be intrinsic to 2M 1938+4603. We removed significant signal not associated with binarity and folded eclipses to increase their cadences. Consequently, we lowered rms of the O - C diagram by a factor of six confirming the sinusoidal variation reported by Baran et al. and making it even more convincing now.

Keywords: exoplanet detection methods; space observatories; pulsating variable stars; b subdwarf stars; eclipsing binary minima timing method
Substructures in the Disk-forming Region of the Class 0 Low-mass Protostellar Source IRAS 16293-2422 Source A on a 10 au Scale

We have observed the Class 0 protostellar source IRAS 16293-2422 A in the C17O and H2CS lines as well as the 1.3 mm dust continuum with the Atacama Large Millimeter/submillimeter Array at an angular resolution of ∼0"1 (14 au). The continuum emission of the binary component, Source A, reveals the substructure consisting of five intensity peaks within 100 au from the protostar. The C17O emission mainly traces the circummultiple structure on a 300 au scale centered at the intensity centroid of the continuum, while it is very weak within a radius of 50 au from the centroid. The H2CS emission, by contrast, traces the rotating disk structure around one of the continuum peaks (A1). Therefore, it seems that the rotation centroid of the circummultiple structure is slightly different from that of the disk around A1. We derive the rotation temperature by using the multiple lines of H2CS. Approaching the protostar A1, the rotation temperature steeply rises up to 300 K or higher at the radius of 50 au from the protostar. It is likely due to a local accretion shock and/or the preferential protostellar heating of the transition zone from the circummultiple structure to the disk around A1. This position corresponds to the place where the organic molecular lines are reported to be enhanced. Since the rise of the rotation temperature of H2CS most likely represents the rise of the gas and dust temperatures, it would be related to the chemical characteristics of this prototypical hot corino.

Keywords: interstellar medium; protostars; interstellar molecules; interstellar emissions; interstellar dynamics
LIMFAST. II. Line Intensity Mapping as a Probe of High-redshift Galaxy Formation

The epoch of reionization (EoR) offers a unique window into the dawn of galaxy formation, through which high-redshift galaxies can be studied by observations of both themselves and their impact on the intergalactic medium. Line intensity mapping (LIM) promises to explore cosmic reionization and its driving sources by measuring intensity fluctuations of emission lines tracing the cosmic gas in varying phases. Using LIMFAST, a novel seminumerical tool designed to self-consistently simulate LIM signals of multiple EoR probes, we investigate how building blocks of galaxy formation and evolution theory, such as feedback-regulated star formation and chemical enrichment, might be studied with multitracer LIM during the EoR. On galaxy scales, we show that the star formation law and the feedback associated with star formation can be indicated by both the shape and redshift evolution of LIM power spectra. For a baseline model of metal production that traces star formation, we find that lines highly sensitive to metallicity are generally better probes of galaxy formation models. On larger scales, we demonstrate that inferring ionized bubble sizes from cross-correlations between tracers of ionized and neutral gas requires a detailed understanding of the astrophysics that shape the line luminosity-halo mass relation. Despite various modeling and observational challenges, wide-area, multitracer LIM surveys will provide important high-redshift tests for the fundamentals of galaxy formation theory, especially the interplay between star formation and feedback by accessing statistically the entire low-mass population of galaxies as ideal laboratories, complementary to upcoming surveys of individual sources by new-generation telescopes.

Keywords: reionization; galaxy formation; astronomical simulations; galaxy evolution; large-scale structure of the universe; observational cosmology; cosmic background radiation
The Complexity of the Cetus Stream Unveiled from the Fusion of STREAMFINDER and StarGO

We combine the power of two stream-searching tools, STREAMFINDER and StarGO applied to the Gaia EDR3 data, to detect stellar debris belonging to the Cetus stream system that forms a complex, nearly polar structure around the Milky Way. In this work, we find the southern extensions of the northern Cetus stream as the Palca stream and a new southern stream, which overlap on the sky but have different distances. These two stream wraps extend over more than ~100° on the sky (-60° < δ < +40°). The current N-body model of the system reproduces both as two wraps in the trailing arm. We also show that the Cetus system is confidently associated with the Triangulum/Pisces, Willka Yaku, and the recently discovered C-20 streams. The association with the ATLAS-Aliqa Uma stream is much weaker. All of these stellar debris are very metal-poor, comparable to the average metallicity of the southern Cetus stream with [Fe/H] = -2.17 ± 0.20. The estimated stellar mass of the Cetus progenitor is at least 105.6 M ⊙, compatible with Ursa Minor or Draco dwarf galaxies. The associated globular cluster with similar stellar mass, NGC 5824 very possibly was accreted in the same group infall. The multi-wrap Cetus stream is a perfect example of a dwarf galaxy that has undergone several periods of stripping, leaving behind debris at multiple locations in the halo. The full characterization of such systems is crucial to unravel the history of the assembly of the Milky Way, and importantly, to provide nearby fossils to study ancient low-mass dwarf galaxies.

Keywords: galactic archaeology; stellar streams; dwarf galaxies; n-body simulations
Testing Disk Identification Methods through Numerical Simulations of Protostellar Evolution

We test whether the radii of circumstellar disks can be reliably determined in observations by applying the results of a numerical simulation. First, we execute a core-collapse simulation, which starts from a rotating magnetized spherical core, and continue the calculation until the protostellar mass reaches 0.5 M⊙. Then, for each set of simulation data, we calculate the radiative transfer to generate the data cube for the synthetic observation. The spatial and velocity resolutions of the synthetic observation are 0"15 (20 au) and 0.1 km s-1, respectively. We define seven different disk radii. Four radii are estimated from the synthetic observation, using the continuum image, continuum visibility, C18O channel map, and C18O position-velocity (PV) diagram. The other three radii are taken from the simulation and use the disk rotation, infall motion, and density contrast around the protostar to identify the disk. Finally, we compare the disk radii estimated from the systemic observation with those from the simulation. We find that the disk radius defined using the PV diagram can reliably trace the Keplerian disk when the protostellar mass is larger than M* ≳ 0.2 M⊙, independent of the inclination angle to the line of sight. In addition, the PV diagram provides an accurate estimate of the central stellar mass through the whole protostellar evolution. The simulation also indicates that the circumstellar disk is massive enough to be gravitationally unstable through the evolution. Such an unstable disk can show either a circular or spiral morphology on a similar timescale.

Keywords: magnetohydrodynamical simulations; protoplanetary disks; low mass stars; protostars
Estimating the Effective Lifetime of the z 6 Quasar Population from the Composite Proximity Zone Profile

The lifetime of quasars can be estimated by means of their proximity zone sizes, which are regions of enhanced flux blueward of the Lyα emission line observed in the rest-frame UV spectra of high-redshift quasars because the intergalactic gas has a finite response time to the quasars' radiation. We estimate the effective lifetime of the high-redshift quasar population from the composite transmitted flux profile within the proximity zone region of a sample of 15 quasars at 5.8 ≤ z ≤ 6.6 with precise systemic redshifts, and similar luminosities, i.e., -27.6 ≤ M1450 ≤ -26.4, and thus a similar instantaneous ionizing power. We develop a Bayesian method to infer the effective lifetime from the composite spectrum, including robust estimates of various sources of uncertainty on the spectrum. We estimate an effective lifetime of the quasar population as a whole of ${\mathrm{log}}_{10}({t}_{{\rm{Q}}}/\mathrm{yr})={5.7}_{-0.3(-0.5)}^{+0.5(+0.8)}$ given by the median and 68th (95th) percentile of the posterior probability distribution. While our result is consistent with previous quasar lifetime studies, it poses significant challenges on the current model for the growth of supermassive black holes located in the center of the quasars' host galaxies, which requires that quasar lifetimes are more than an order of magnitude longer.

Keywords: supermassive black holes; quasars; high-redshift galaxies; early universe; astronomy data analysis
How Magnetic Reconnection May Affect the Coherence of Interplanetary Coronal Mass Ejections

On 2020 April 19-20, a solar ejection was seen by spacecraft in a radial alignment that included Solar Orbiter and Wind. The ejection contained a magnetic flux rope where magnetic field and plasma parameters were well correlated between spacecraft. This structure is called an "unperturbed magnetic flux rope" (UMFR). Ahead of the UMFR is a portion of the ejection (not sheath) that is referred to as "upstream" (US). We focus on the US and inquire why the correlation is so much weaker there. Specifically, we analyze data collected by Solar Orbiter at 0.81 au and Wind at L1. We show that a plausible cause for the lack of coherence in the US is a combination of front erosion and internal reconnection occurring there. Front erosion is inferred from an analysis of azimuthal magnetic flux balance in the UMFR. In the present case, we contend that the US, rather than the UMFR, is the source of the eroded field lines. The presence of erosion is supported further by a direct comparison of the magnetic field data at both spacecraft that shows, in particular, a massive shrinkage of the front portion of the US. Internal reconnection is also happening at thin current sheets inside the US. Strong nonradial flows are reconfiguring the structure. As a result of these reconnection processes, a whole section of the US is disrupted and field lines move down the flanks of the ejection and out of view of Wind.

Keywords: solar coronal mass ejections; interplanetary magnetic fields; solar wind
Beyond the Local Volume. II. Population Scaleheights and Ages of Ultracool Dwarfs in Deep HST/WFC3 Parallel Fields

Ultracool dwarfs (UCDs) represent a significant proportion of stars in the Milky Way, and deep samples of these sources have the potential to constrain the formation history and evolution of low-mass objects in the Galaxy. Until recently, spectral samples have been limited to the local volume (d < 100 pc). Here, we analyze a sample of 164 spectroscopically characterized UCDs identified by Aganze et al. in the Hubble Space Telescope (HST) WFC3 Infrared Spectroscopic Parallel Survey (WISPS) and 3D-HST. We model the observed luminosity function using population simulations to place constraints on scaleheights, vertical velocity dispersions, and population ages as a function of spectral type. Our star counts are consistent with a power-law mass function and constant star formation history for UCDs, with vertical scaleheights of 249 ${}_{-61}^{+48}$ pc for late-M dwarfs, 153 ${}_{-30}^{+56}$ pc for L dwarfs, and 175 ${}_{-56}^{+149}$ pc for T dwarfs. Using spatial and velocity dispersion relations, these scaleheights correspond to disk population ages of 3.6 ${}_{-1.0}^{+0.8}$ Gyr for late-M dwarfs, 2.1 ${}_{-0.5}^{+0.9}$ Gyr for L dwarfs, and 2.4 ${}_{-0.8}^{+2.4}$ Gyr for T dwarfs, which are consistent with prior simulations that predict that L-type dwarfs are on average a younger and less dispersed population. There is an additional 1-2 Gyr systematic uncertainty on these ages due to variances in age-velocity relations. We use our population simulations to predict the UCD yield in the James Webb Space Telescope PASSAGES survey, a similar and deeper survey to WISPS and 3D-HST, and find that it will produce a comparably sized UCD sample, albeit dominated by thick disk and halo sources.

Keywords: brown dwarfs; l dwarfs; t dwarfs; y dwarfs; galactic archaeology; hubble space telescope; stellar ages