adsabs/SciX_UAT_keywords huggingface dataset:
Composition Effects on Kilonova Spectra and Light Curves. I

The merger of neutron star binaries is believed to eject a wide range of heavy elements into the universe. By observing the emission from this ejecta, scientists can probe the ejecta properties (mass, velocity, and composition distributions). The emission (a.k.a. kilonova) is powered by the radioactive decay of the heavy isotopes produced in the merger and this emission is reprocessed by atomic opacities to optical and infrared wavelengths. Understanding the ejecta properties requires calculating the dependence of this emission on these opacities. The strong lines in the optical and infrared in lanthanide opacities have been shown to significantly alter the light curves and spectra in these wavelength bands, arguing that the emission in these wavelengths can probe the composition of this ejecta. Here we study variations in the kilonova emission by varying individual lanthanide (and the actinide uranium) concentrations in the ejecta. The broad forest of lanthanide lines makes it difficult to determine the exact fraction of individual lanthanides. Nd is an exception. Its opacities above 1 μm are higher than other lanthanides and observations of kilonovae can potentially probe increased abundances of Nd. Similarly, at early times when the ejecta is still hot (first day), the U opacity is strong in the 0.2-1 μm wavelength range and kilonova observations may also be able to constrain these abundances.

Keywords: compact binary stars; interacting binary stars; stellar mergers; neutron stars; stellar atmospheric opacity; r-process
The Sparkler: Evolved High-redshift Globular Cluster Candidates Captured by JWST

Using data from JWST, we analyse the compact sources ("sparkles") located around a remarkable z spec = 1.378 galaxy (the 'Sparkler) that is strongly gravitationally lensed by the z = 0.39 galaxy cluster SMACS J0723.3-7327. Several of these compact sources can be cross-identified in multiple images, making it clear that they are associated with the host galaxy. Combining data from JWSTs Near-Infrared Camera (NIRCam) with archival data from the Hubble Space Telescope (HST), we perform 0.4-4.4 μm photometry on these objects, finding several of them to be very red and consistent with the colors of quenched, old stellar systems. Morphological fits confirm that these red sources are spatially unresolved even in the strongly magnified JWST/NIRCam images, while the JWST/NIRISS spectra show [OIII] λ5007 emission in the body of the Sparkler but no indication of star formation in the red compact sparkles. The most natural interpretation of these compact red companions to the Sparkler is that they are evolved globular clusters seen at z = 1.378. Applying DENSE BASIS spectral energy distribution fitting to the sample, we infer formation redshifts of z form ~ 7-11 for these globular cluster candidates, corresponding to ages of ~3.9-4.1 Gyr at the epoch of observation and a formation time just ~0.5 Gyr after the Big Bang. If confirmed with additional spectroscopy, these red, compact sparkles represent the first evolved globular clusters found at high redshift, which could be among the earliest observed objects to have quenched their star formation in the universe, and may open a new window into understanding globular cluster formation. Data and code to reproduce our results will be made available at http://canucs-jwst.com/sparkler.html.

Keywords: globular star clusters; james webb space telescope; galaxy evolution; galaxy clusters; gravitational lensing
A Flexible Bayesian Framework for Assessing Habitability with Joint Observational and Model Constraints

The catalog of stellar evolution tracks discussed in our previous work is meant to help characterize exoplanet host stars of interest for follow-up observations with future missions like the James Webb Space Telescope. However, the utility of the catalog has been predicated on the assumption that we would precisely know the age of the particular host star in question; in reality, it is unlikely that we will be able to accurately estimate the age of a given system. Stellar age is relatively straightforward to calculate for stellar clusters, but it is difficult to accurately measure the age of an individual star to high precision. Unfortunately, this is the kind of information we should consider as we attempt to constrain the long-term habitability potential of a given planetary system of interest. This is ultimately why we must rely on predictions of accurate stellar evolution models, as well a consideration of what we can observably measure (stellar mass, composition, orbital radius of an exoplanet) in order to create a statistical framework wherein we can identify the best candidate systems for follow-up characterization. In this paper we discuss a statistical approach to constrain long-term planetary habitability by evaluating the likelihood that at a given time of observation, a star would have a planet in the 2 Gy continuously habitable zone (CHZ2). Additionally, we will discuss how we can use existing observational data (i.e., data assembled in the Hypatia catalog and the Kepler exoplanet host star database) for a robust comparison to the catalog of theoretical stellar models.

Keywords: interdisciplinary astronomy; stellar properties; habitable planets; catalogs; exoplanets; habitable zone; stellar evolutionary tracks; stellar evolutionary models; stellar evolution; astrobiology
Radio Emission from Ultra-stripped Supernovae as Diagnostics for Properties of the Remnant Double Neutron Star Binaries

An ultra-stripped supernova (SN) is an explosion of a helium or C+O star whose outer envelope has been stripped away by a companion neutron star. A double neutron star (DNS) binary is believed to be left after the explosion, which will emit the gravitational wave later at the coalescence. Recent detections of a few candidates for the ultra-stripped SN have constrained the properties of the explosion and the progenitor, but little information is given as to whether the remnant DNS binary will merge within the cosmic age. A large fraction of the material stripped away from the helium star through the binary interaction is expected to escape from the system and form circumstellar material (CSM). The CSM should be traced by radio emission induced by the collision with the SN ejecta. Based on the stellar evolution models previously developed, we calculate the expected radio luminosities from ultra-stripped SNe. We find that high radio luminosity at its maximum can be an indicator of small separation of a DNS binary leading to its merger within the cosmic age. Our results can be used to optimize the strategy for the radio follow-up observations such as observational epochs and frequencies.

Keywords: supernovae; gravitational wave sources
Giant Planet Swaps during Close Stellar Encounters

The discovery of planetary systems outside of the solar system has challenged some of the tenets of planetary formation. Among the difficult-to-explain observations are systems with a giant planet orbiting a very low mass star, such as the recently discovered GJ 3512b planetary system, where a Jupiter-like planet orbits an M star in a tight and eccentric orbit. Systems such as this one are not predicted by the core accretion theory of planet formation. Here we suggest a novel mechanism, in which the giant planet is born around a more typical Sun-like star (M_{*,1}), but is subsequently exchanged during a dynamical interaction with a flyby low-mass star (M_{*,2}). We perform state-of-the-art N-body simulations with M_{*,1}=1 M_{⊙} and M_{*,2}=0.1 M_{⊙} to study the statistical outcomes of this interaction, and show that exchanges result in high eccentricities for the new orbit around the low-mass star, while about half of the outcomes result in tighter orbits than the planet had around its birth star. We numerically compute the cross section for planet exchange, and show that an upper limit for the probability per planetary system to have undergone such an event is Γ ∼ 4.4(M_{c}/100M_{⊙})-2 (a_{p}/au)(σ/1 km s-1)5 Gyr-1, where ap is the planet semimajor axis around the birth star, σ the velocity dispersion of the star cluster, and Mc the total mass of the star cluster. Hence these planet exchanges could be relatively common for stars born in open clusters and groups, should already be observed in the exoplanet database, and provide new avenues to create unexpected planetary architectures.

Keywords: exoplanet astronomy; exoplanet dynamics; stellar dynamics; n-body simulations
Supernova 2020wnt: An Atypical Superluminous Supernova with a Hidden Central Engine

We present observations of a peculiar hydrogen- and helium-poor stripped-envelope (SE) supernova (SN) 2020wnt, primarily in the optical and near-infrared (near-IR). Its peak absolute bolometric magnitude of -20.9 mag (L bol, peak = (6.8 ± 0.3) × 1043 erg s-1) and a rise time of 69 days are reminiscent of hydrogen-poor superluminous SNe (SLSNe I), luminous transients potentially powered by spinning-down magnetars. Before the main peak, there is a brief peak lasting <10 days post explosion, likely caused by interaction with circumstellar medium (CSM) ejected ~years before the SN explosion. The optical spectra near peak lack a hot continuum and O II absorptions, which are signs of heating from a central engine; they quantitatively resemble those of radioactivity-powered hydrogen/helium-poor Type Ic SESNe. At ~1 yr after peak, nebular spectra reveal a blue pseudo-continuum and narrow O I recombination lines associated with magnetar heating. Radio observations rule out strong CSM interactions as the dominant energy source at +266 days post peak. Near-IR observations at +200-300 days reveal carbon monoxide and dust formation, which causes a dramatic optical light-curve dip. Pair-instability explosion models predict slow light curve and spectral features incompatible with observations. SN 2020wnt is best explained as a magnetar-powered core-collapse explosion of a 28 M ⊙ pre-SN star. The explosion kinetic energy is significantly larger than the magnetar energy at peak, effectively concealing the magnetar-heated inner ejecta until well after peak. SN 2020wnt falls into a continuum between normal SNe Ic and SLSNe I, and demonstrates that optical spectra at peak alone cannot rule out the presence of a central engine.

Keywords: core-collapse supernovae; massive stars; dust formation
Archival VLBA Observations of the Cygnus A Nuclear Radio Transient (Cyg A-2) Strengthen the Tidal Disruption Event Interpretation

We have analyzed archival Very Long Baseline Array (VLBA) data for Cygnus A between 2002 and 2013, to search for radio emission from the transient discovered in 2015 by Perley et al. approximately 0"4 from the nucleus of Cygnus A (Cyg A-2). Perley et al. use Very Large Array and VLBA archival data (between 1989 and 1997) to show that the transient rises in flux density by a factor of at least 5 in less than approximately 20 yr. With the additional data presented here, we revise the rise time to between approximately 4 and 6 yr, based on a new detection of the source at 15.4 GHz from 2011 October. Our results strengthen the interpretation of Cyg A-2 as the result of a tidal disruption event (TDE), as we can identify the location of the compact object responsible for the TDE and can estimate the angular expansion speed of the resulting radio-emitting structures, equivalent to an apparent expansion speed of <0.9c. While our results are consistent with recent X-ray analyses, we can rule out a previously suggested date of early 2013 for the timing of the TDE. We favor a timing between early 2009 and late 2011. Applying the model of Nakar & Piran, we suggest a TDE causing a mildly relativistic outflow with a (density-dependent) total energy >1049 erg. Due to the improved temporal coverage of our archival measurements, we find that it is unlikely that Cyg A-2 has previously been in a high luminosity radio state over the last 30 yr.

Keywords: active galaxies; extragalactic radio sources; experimental techniques
Reaching the Oldest Stars beyond the Local Group: Ancient Star Formation in UGC 4483

We present new WFC3/UVIS observations of UGC 4483, the closest example of a metal-poor blue compact dwarf galaxy, with a metallicity of Z ≃ 1/15 Z⊙ and located at a distance of D ≃ 3.4 Mpc. The extremely high quality of our new data allows us to clearly resolve the multiple stellar evolutionary phases populating the color-magnitude diagram (CMD), to reach more than 4 mag deeper than the tip of the red giant branch, and to detect for the first time core He-burning stars with masses ≲2 M⊙, populating the red clump and possibly the horizontal branch (HB) of the galaxy. By applying the synthetic CMD method to our observations, we determine an average star formation rate over the whole Hubble time of at least $(7.01\pm 0.44)\times {10}^{-4}$ ${M}_{\odot }\,{{yr}}^{-1}$ , corresponding to a total astrated stellar mass of $(9.60\pm 0.61)\times {10}^{6}$ M⊙, 87% of which went into stars at epochs earlier than 1 Gyr ago. With our star formation history recovery method we find the best fit with a distance modulus of DM = 27.45 ± 0.10, slightly lower than previous estimates. Finally, we find strong evidence of an old (≳10 Gyr) stellar population in UGC 4483 thanks to the detection of an HB phase and the identification of six candidate RR Lyrae variable stars. * Based on observations obtained with the NASA/ESA Hubble Space Telescope at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy under NASA Contract NAS 5-26555.

Keywords: blue compact dwarf galaxies; star formation; galaxy evolution; galaxy stellar content; stellar populations
Sunquakes of Solar Cycle 24

The paper presents results of a search for helioseismic events (sunquakes) produced by M-X class solar flares during Solar Cycle 24. The search is performed by analyzing photospheric Dopplergrams from the Helioseismic Magnetic Imager. Among the total number of 500 M-X class flares, 94 helioseismic events were detected. Our analysis has shown that many strong sunquakes were produced by solar flares of low M class (M1-M5), while in some powerful X-class flares helioseismic waves were not observed or were weak. Our study has also revealed that only several active regions were characterized by the most efficient generation of helioseismic waves during flares. We found that the sunquake power correlates with the maximum value of the soft X-ray flux time derivative better than with the X-ray class, indicating that the sunquake mechanism is associated with high-energy particles. We also show that the seismically active flares are more impulsive than the flares without helioseismic perturbations. We present a new catalog of helioseismic solar flares, which opens opportunities for performing statistical studies to better understand the physics of sunquakes as well as the flare-energy release and transport.

Keywords: solar flares; helioseismology; solar x-ray flares; optical flares
A Multibranch Deep Neural Network for the Superresolution of Solar Magnetograms

The existing superresolution (SR) models for solar magnetograms are mostly borrowed from the SR models for natural images. They are less effective for processing solar magnetograms with a very large dynamic range and very rich image features. In this paper, a multibranch superresolution (MBSR) model is specially designed for solar magnetograms. First, we split a low-resolution magnetogram into a group of overlapping image patches, and classify them into three categories according to magnetic flux intensity, namely simple, medium, and complex. Then, image patches of each category are fed into the corresponding branch of the MBSR network, the lightweight branch for simple image patches and the heavyweight one for complex image patches. The advantage of such a strategy is twofold. On the one hand, active regions are allocated more computational resources to train a heavyweight branch more fully, while quiet regions are allocated fewer computational resources to train a lightweight branch for saving computational resources. On the other hand, a lightweight network with a simple nonlinear function is preferable to simple regions, while a heavyweight one may be underfitting. Additionally, to verify the effectiveness of the proposed model, a magnetic field structure similarity metric is proposed to measure the artifacts of the generated high-resolution (HR) magnetograms. Experimental results show that the proposed MBSR model generates HR magnetograms highly consistent with the HMI ones, and achieves the best performance over five objective metrics, including peak signal-to-noise ratio and structure similarity, etc.

Keywords: astronomy image processing; astronomy data modeling; solar physics; astronomical techniques
Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES): Data Release I

We present the first Data Release (DR1) from the Hubble Space Telescope (HST) Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES) program, a Director's Discretionary program devoting approximately 1000 HST orbits to the production of an ultraviolet spectroscopic library of young high- and low-mass stars in the local universe. The science products in this release are combined from individual, extracted and calibrated spectra obtained with the COS and STIS instruments aboard HST. Products are made using both archival HST data and new HST observations obtained through the ULLYSES program. DR1 acts as the first step toward completing a goal of generating a fully public data set for the purpose of enabling, supporting, and stimulating a broad range of transformative astrophysical research.

Keywords: o stars; wolf-rayet stars; b stars; ultraviolet surveys
Beginning a Journey Across the Universe: The Discovery of Extragalactic Neutrino Factories

Neutrinos are the most elusive particles in the universe, capable of traveling nearly unimpeded across it. Despite the vast amount of data collected, a long-standing and unsolved issue is still the association of high-energy neutrinos with the astrophysical sources that originate them. Among the candidate sources of neutrinos, there are blazars, a class of extragalactic sources powered by supermassive black holes that feed highly relativistic jets, pointed toward Earth. Previous studies appear controversial, with several efforts claiming a tentative link between high-energy neutrino events and individual blazars, and others putting into question such relation. In this work, we show that blazars are unambiguously associated with high-energy astrophysical neutrinos at an unprecedented level of confidence, i.e., a chance probability of 6 × 10-7. Our statistical analysis provides the observational evidence that blazars are astrophysical neutrino factories and hence, extragalactic cosmic-ray accelerators.

Keywords: neutrino astronomy; neutrino telescopes; blazars; supermassive black holes; relativistic jets; cosmic ray astronomy
Relation of Gravity, Winds, and the Moment of Inertia of Jupiter and Saturn

We study the relationship of zonal gravity coefficients, J 2n , zonal winds, and axial moment of inertia (MoI) by constructing models for the interiors of giant planets. We employ the nonperturbative concentric Maclaurin spheroid method to construct both physical (realistic equation of state and barotropes) and abstract (small number of constant-density spheroids) interior models. We find that accurate gravity measurements of Jupiter's and Saturn's J 2, J 4, and J 6 by the Juno and Cassini spacecraft do not uniquely determine the MoI of either planet but do constrain it to better than 1%. Zonal winds (or differential rotation (DR)) then emerge as the leading source of uncertainty. For Saturn they are predicted to decrease the MoI by 0.4% because they reach a depth of ~9000 km, while on Jupiter they appear to reach only ~3000 km. We thus predict DR to affect Jupiter's MoI by only 0.01%, too small by one order of magnitude to be detectable by the Juno spacecraft. We find that winds primarily affect the MoI indirectly via the gravity harmonic J 6, while direct contributions are much smaller because the effects of pro- and retrograde winds cancel. DR contributes +6% and -0.8% to Saturn's and Jupiter's J 6 value, respectively. This changes the J 6 contribution that comes from the uniformly rotating bulk of the planet that correlates most strongly with the predicted MoI. With our physical models, we predict Jupiter's MoI to be 0.26393 ± 0.00001. For Saturn, we predict 0.2181 ± 0.0002, assuming a rotation period of 10:33:34 hr that matches the observed polar radius.

Keywords: planetary interior; jupiter; saturn
High-energy (>40 MeV) Proton Intensity Enhancements Associated with the Passage of Interplanetary Shocks at 1 au

We analyze periods with elevated >40 MeV proton intensities observed near Earth over a time span of 43 yr (1973-2016) that coincide with the passage of interplanetary (IP) shocks. Typically, elevated proton intensities result from large solar energetic particle (SEP) events. The IP shocks observed during these elevated-intensity periods may or may not be related to the origin of the SEP events. By choosing those cases when the shocks can be confidently associated with the solar eruption that generated the SEP event, we analyze the components of these SEP events that are localized in the vicinity of the shock (so-called "energetic storm particles", ESPs), focusing on those events where the ESP component exceeds 40 MeV. We examine the interdependence of these high-energy ESPs with (i) the properties of the solar eruptions that generated the shocks and the SEP events, and (ii) the parameters of the shocks at their arrival at 1 au. The solar eruptions at the origin of the shocks producing >40 MeV proton ESP intensity enhancements are within ±50° longitude of central meridian and are associated with fast coronal mass ejections (plane-of-sky speeds ≳1000 km s-1). The ESP events with the largest >40 MeV proton intensity increases tend to occur when there are structures such as intervening IP coronal mass ejections and other unrelated shocks present in the solar wind through which the shock is propagating. Among the various local shock parameters considered, only the shock speed shows a certain degree of correlation with the observed ESP intensity increase.

Keywords: solar energetic particles; interplanetary shocks; interplanetary particle acceleration
VLA Imaging of H I-bearing Ultra-diffuse Galaxies from the ALFALFA Survey

Ultra-diffuse galaxies have generated significant interest due to their large optical extents and low optical surface brightnesses, which challenge galaxy formation models. Here we present resolved synthesis observations of 12 H I-bearing ultra-diffuse galaxies (HUDs) from the Karl G. Jansky Very Large Array, as well as deep optical imaging from the WIYN 3.5 m telescope at Kitt Peak National Observatory. We present the data processing and images, including total intensity H I maps and H I velocity fields. The HUDs show ordered gas distributions and evidence of rotation, important prerequisites for the detailed kinematic models of Mancera Piña et al. We compare the H I and stellar alignment and extent, and find that H I extends beyond the already extended stellar component and the H I disk is often misaligned with respect to the stellar one, emphasizing the importance of caution when approaching inclination measurements for these extreme sources. We explore the H I mass-diameter scaling relation, and find that, although the HUDs have diffuse stellar populations, they fall along the relation with typical global H I surface densities. This resolved sample forms an important basis for more detailed study of the H I distribution in this extreme extragalactic population.

Keywords: galaxies; galaxy evolution; radio astronomy; radio spectroscopy