adsabs/SciX_UAT_keywords huggingface dataset:
Maps of Magnetic Field Strength in the OMC-1 Using HAWC+ FIR Polarimetric Data

Far-infrared dust polarimetry enables the study of interstellar magnetic fields via tracing of the polarized emission from dust grains that are partially aligned with the direction of the field. The advent of high-quality polarimetric data has permitted the use of statistical methods to extract both the direction and magnitude of the magnetic field. In this work, the Davis-Chandrasekhar-Fermi technique is used to make maps of the plane-of-sky (POS) component of the magnetic field in the Orion Molecular Cloud (OMC-1) by combining polarization maps at 53, 89, 154 and 214 μm from HAWC+/SOFIA with maps of density and velocity dispersion. In addition, maps of the local dispersion of polarization angles are used in conjunction with Zeeman measurements to estimate a map of the strength of the line-of-sight (LOS) component of the field. Combining these maps, information about the three-dimensional magnetic field configuration (integrated along the LOS) is inferred over the OMC-1 region. POS magnetic field strengths of up to 2 mG are observed near the BN/KL object, while the OMC-1 bar shows strengths of up to a few hundred μG. These estimates of the magnetic field components are used to produce maps of the mass-to-magnetic-flux ratio (M/Φ)—a metric for probing the conditions for star formation in molecular clouds—and determine regions of sub- and supercriticality in OMC-1. Such maps can provide invaluable input and comparison to MHD simulations of star formation processes in filamentary structures of molecular clouds.

Keywords: molecular clouds; giant molecular clouds; interstellar magnetic fields; far infrared astronomy
Spontaneous Onset of Collisionless Magnetic Reconnection on an Electron Scale

Using particle-in-cell simulations, we investigate the onset of magnetic reconnection from a quiescent Harris current sheet in collisionless plasmas. After the current sheet is destabilized by the collisionless tearing mode instability, it proceeds to onset of reconnection, which manifests spontaneous thinning of current sheet and pileup of upstream magnetic flux. Once the current sheet thins to a critical thickness, about two electron inertial lengths, reconnection begins to grow explosively in this electron current sheet. This study shows that the spontaneous onset of collisionless magnetic reconnection is controlled by electron kinetics.

Keywords: solar magnetic reconnection; plasma physics; heliosphere; planetary magnetospheres
Recombination of Hot Ionized Nebulae: The Old Planetary Nebula around V4334 Sgr (Sakurai's Star)

After becoming ionized, low-density astrophysical plasmas will begin a process of slow recombination. Models for this still have significant uncertainties. Recombination cannot normally be observed in isolation, because the ionization follows the evolutionary timescale of the ionizing source. Laboratory experiments are unable to reach the appropriate conditions because of the very long required timescales. The extended nebula around the very late helium pulse (VLTP) star V4334 Sgr provides a unique laboratory for this kind of study. The sudden loss of the ionizing UV radiation after the VLTP event has allowed the nebula to recombine free from other influences. More than 290 long-slit spectra taken with FORS1/2 at ESO's Very Large Telescope between 2007 and 2022 are used to follow the time evolution of the lines of H, He, N, S, O, and Ar. Hydrogen and helium lines, representing most of the ionized mass, do not show significant changes. A small increase is seen in [N II] (+2.8% yr-1; 2.7σ significance), while we see a decrease in [O III] (-1.96% yr-1; 2.0σ significance). The [S II] lines show a change of +3.0% yr-1 (1.6σ significance). The lines of [S III] and of [Ar III] show no significant changes. For [S III], the measurement differs from the predicted decrease by 4.5σ. A possible explanation is that the fractions of S3+ and higher are larger than expected. Such an effect could provide a potential solution for the sulfur anomaly in planetary nebulae. * This investigation makes use of ESO data from program IDs 077.D-0394, 079.D-0256, 381.D-0117, 383.D-0427, 385.D-0292, 087.D-0223, 089.D-0080, 091.D-0209, 093.D-0195, 095.D-0113, 097.D-0146, 099.D-0045, and 0109.D-0060.

Keywords: astrophysical processes; recombination; interstellar medium
Measuring the Magnetic Origins of Solar Flares, Coronal Mass Ejections, and Space Weather

We take a broad look at the problem of identifying the magnetic solar causes of space weather. With the lackluster performance of extrapolations based upon magnetic field measurements in the photosphere, we identify a region in the near-UV (NUV) part of the spectrum as optimal for studying the development of magnetic free energy over active regions. Using data from SORCE, the Hubble Space Telescope, and SKYLAB, along with 1D computations of the NUV spectrum and numerical experiments based on the MURaM radiation-magnetohydrodynamic and HanleRT radiative transfer codes, we address multiple challenges. These challenges are best met through a combination of NUV lines of bright Mg II, and lines of Fe II and Fe I (mostly within the 4s-4p transition array) which form in the chromosphere up to 2 × 104 K. Both Hanle and Zeeman effects can in principle be used to derive vector magnetic fields. However, for any given spectral line the τ = 1 surfaces are generally geometrically corrugated owing to fine structure such as fibrils and spicules. By using multiple spectral lines spanning different optical depths, magnetic fields across nearly horizontal surfaces can be inferred in regions of low plasma β, from which free energies, magnetic topology, and other quantities can be derived. Based upon the recently reported successful sub-orbital space measurements of magnetic fields with the CLASP2 instrument, we argue that a modest space-borne telescope will be able to make significant advances in the attempts to predict solar eruptions. Difficulties associated with blended lines are shown to be minor in an Appendix.

Keywords: active sun; the sun; space weather; spectropolarimetry; magnetohydrodynamics; solar flares; solar coronal mass ejections; solar chromosphere; solar corona; solar transition region
Characterizing the X-Ray Emission of Intermediate-mass Pre-main-sequence Stars

We use X-ray and infrared observations to study the properties of three classes of young stars in the Carina Nebula: intermediate-mass (2-5 M⊙) pre-main-sequence stars (IMPS; i.e., intermediate-mass T Tauri stars), late-B and A stars on the zero-age main sequence (AB), and lower-mass T Tauri stars (TTS). We divide our sources among these three subclassifications and further identify disk-bearing young stellar objects versus diskless sources with no detectable infrared (IR) excess emission using IR (1-8 μm) spectral energy distribution modeling. We then perform X-ray spectral fitting to determine the hydrogen-absorbing column density (NH), absorption-corrected X-ray luminosity (LX), and coronal plasma temperature (kT) for each source. We find that the X-ray spectra of both IMPS and TTS are characterized by similar kT and NH, and on average LX/Lbol ~ 4 × 10-4. IMPS are systematically more luminous in X-rays (by ~0.3 dex) than all other subclassifications, with median LX = 2.5 × 1031 erg s-1, while AB stars of similar masses have X-ray emission consistent with TTS companions. These lines of evidence converge on a magnetocoronal flaring source for IMPS X-ray emission, a scaled-up version of the TTS emission mechanism. IMPS therefore provide powerful probes of isochronal ages for the first ~10 Myr in the evolution of a massive stellar population, because their intrinsic, coronal X-ray emission decays rapidly after they commence evolving along radiative tracks. We suggest that the most luminous (in both X-rays and IR) IMPS could be used to place empirical constraints on the location of the intermediate-mass stellar birth line.

Keywords: young stellar objects; pre-main sequence stars; t tauri stars; single x-ray stars
Signature of a Massive Rotating Metal-poor Star Imprinted in the Phoenix Stellar Stream

The Phoenix stellar stream has a low intrinsic dispersion in velocity and metallicity that implies the progenitor was probably a low-mass globular cluster. In this work we use Magellan/Magellan Inamori Kyocera Echelle (MIKE) high-dispersion spectroscopy of eight Phoenix stream red giants to confirm this scenario. In particular, we find negligible intrinsic scatter in metallicity ( $\sigma ([\mathrm{Fe}\,{\rm\small{II}}/{\rm{H}}])={0.04}_{-0.03}^{+0.11}$ ) and a large peak-to-peak range in [Na/Fe] and [Al/Fe] abundance ratios, consistent with the light element abundance patterns seen in the most metal-poor globular clusters. However, unlike any other globular cluster, we also find an intrinsic spread in [Sr II/Fe] spanning ~1 dex, while [Ba II/Fe] shows nearly no intrinsic spread ( $\sigma ([\mathrm{Ba}\,{\rm\small{II}}/{\rm{H}}])={0.03}_{-0.02}^{+0.10}$ ). This abundance signature is best interpreted as slow-neutron-capture element production from a massive fast-rotating metal-poor star (15-20 M⊙, vini/vcrit = 0.4, [Fe/H] = -3.8). The low inferred cluster mass suggests the system would have been unable to retain supernovae ejecta, implying that any massive fast-rotating metal-poor star that enriched the interstellar medium must have formed and evolved before the globular cluster formed. Neutron-capture element production from asymptotic giant branch stars or magneto-rotational instabilities in core-collapse supernovae provide poor fits to the observations. We also report one Phoenix stream star to be a lithium-rich giant (A(Li) = 3.1 ± 0.1). At [Fe/H ] = -2.93; it is among the most metal-poor lithium-rich giants known. * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: stellar streams
On the Coevolution of the AGN and Star-forming Galaxy Ultraviolet Luminosity Functions at 3 < z < 9

Studies of the rest-frame ultraviolet (UV) luminosity functions (LFs) typically treat star-forming galaxies and active galactic nuclei (AGNs) separately. However, modern ground-based surveys now probe volumes large enough to discover AGNs at depths sensitive enough for fainter galaxies, bridging these two populations. Using these observations as constraints, we present a methodology to empirically jointly model the evolution of the rest-UV LFs at z = 3-9. Our critical assumptions are that both populations have LFs well described by double power laws modified to allow for a flattening at the faint-end, and that all LF parameters evolve smoothly with redshift. This methodology provides a good fit to the observations and makes predictions to volume densities not yet observed, finding that the volume density of bright (M UV = -28) AGNs rises by ~105 from z = 9 to z = 3, while bright (M UV = -21) star-forming galaxies rise by only ~102 across the same epoch. The observed bright-end flattening of the z = 9 LF is unlikely to be due to AGN activity, and rather is due to a shallowing of the bright-end slope, implying a reduction of feedback in bright galaxies at early times. The intrinsic ionizing emissivity is dominated by star-forming galaxies at z > 3, even after applying a notional escape fraction. We find decent agreement between our AGN LFs and predictions based on different black hole seeding models, though all models underpredict the observed abundance of bright AGNs. We show that the wide-area surveys of the upcoming Euclid and Roman observatories should be capable of discovering AGNs to z ~ 8.

Keywords: galaxy evolution
Exploring the Extremes: Characterizing a New Population of Old and Cold Brown Dwarfs

Mapping out the populations of thick disk and halo brown dwarfs is important for understanding the metallicity dependence of low-temperature atmospheres and the substellar mass function. Recently, a new population of cold and metal-poor brown dwarfs has been discovered, with T eff ≲ 1400 K and metallicity ≲-1 dex. This population includes what may be the first known "extreme T-type subdwarfs" and possibly the first Y-type subdwarf, WISEA J153429.75-104303.3. We have conducted a Gemini YJHK/Ks photometric follow-up campaign targeting potentially metal-poor T and Y dwarfs, utilizing the GNIRS and Flamingos-2 instruments. We present 14 near-infrared photometric detections of eight unique targets: six T subdwarf candidates, one moderately metal-poor Y dwarf candidate, and one Y subdwarf candidate. We have obtained the first-ever ground-based detection of the highly anomalous object WISEA J153429.75-104303.3. The F110W - J color of WISEA J153429.75-104303.3 is significantly bluer than that of other late T and Y dwarfs, indicating that WISEA J153429.75-104303.3 has an unusual spectrum in the 0.9-1.4 μm wavelength range which encompasses the J-band peak. Our J-band detection of WISEA J153429.75-104303.3 and corresponding model comparisons suggest a subsolar metallicity and temperature of 400-550 K for this object. JWST spectroscopic follow-up at near-infrared and mid-infrared wavelengths would allow us to better understand the spectral peculiarities of WISEA J153429.75-104303.3, assess its physical properties, and conclusively determine whether or not it is the first Y-type subdwarf.

Keywords: brown dwarfs; t dwarfs; y dwarfs; metallicity; infrared photometry
Evolution of the Quiescent Disk Surrounding a Superoutburst of the Dwarf Nova TW Virginis

In this paper, we investigate portions of the Kepler K2 Short Cadence light curve of the dwarf nova (DN) TW Vir at quiescence, using light-curve modeling. The light curve was separated into 24 sections, each with a data length of ∼0.93 days, comprising 4 sections before, and 20 after a superoutburst (SO). Due to morphological differences, the quiescent orbital modulation is classified into three types. Using a fixed disk radius and the two component stellar parameters, all 24 synthetic disk models from these sections show a consistent configuration, consisting of a disk and two hotspots: one at the vertical side of the edge of the disk and the other on the surface of the disk. Before the SO, the disk and a ringlike surface-hotspot are suddenly enhanced, triggering a precursor, and then the SO. At the end of the quiescent period following the SO and before the first normal outburst, the edge-hotspot becomes hotter, while the surface-hotspot switches into a "coolspot" with a coverage of nearly half of the disk's surface. During quiescence, the surface-hotspot is always located at the outer part of the disk, with a constant radial width. A flat radial temperature distribution of the disk is found, and appears flatter when approaching the outburst. Like many U Gem-type DN with orbital periods of 3-5 hr, the mass transfer rate is significantly lower than the predictions of the standard/revised models of CV evolution.

Keywords: interacting binary stars; cataclysmic variable stars; dwarf novae; u geminorum stars; accretion; white dwarf stars; light curves
Supernova Siblings: Assessing the Consistency of Properties of Type Ia Supernovae that Share the Same Parent Galaxies

While many studies have shown a correlation between properties of the light curves of SNe Ia and properties of their host galaxies, it remains unclear what is driving these correlations. We introduce a new direct method to study these correlations by analyzing "parent" galaxies that host multiple SNe Ia "siblings." Here, we search the Dark Energy Survey SN sample, one of the largest samples of discovered SNe, and find eight galaxies that hosted two likely SNe Ia. Comparing the light-curve properties of these SNe and recovered distances from the light curves, we find no better agreement between properties of SNe in the same galaxy as any random pair of galaxies, with the exception of the SN light-curve stretch. We show at 2.8σ significance that at least one-half of the intrinsic scatter of SNe Ia distance modulus residuals is not from common host properties. We also discuss the robustness with which we could make this evaluation with LSST, which will find 100× more pairs of galaxies, and pave a new line of study on the consistency of SNe Ia in the same parent galaxies. Finally, we argue that it is unlikely that some of these SNe are actually single, lensed SN with multiple images.

Keywords: observational cosmology
Digging into the Galactic Bulge: Stellar Population and Structure of the Poorly Studied Cluster NGC 6316

High-resolution Hubble Space Telescope optical observations have been used to analyze the stellar population and the structure of the poorly investigated bulge globular cluster NGC 6316. We constructed the first high-resolution reddening map in the cluster direction, which allowed us to correct the evolutionary sequences in the color-magnitude diagram (CMD) for the effects of differential reddening. A comparison between the CMDs of NGC 6316 and 47 Tucanae revealed strikingly similar stellar populations, with the two systems basically sharing the same turnoff, subgiant branch, and horizontal branch morphologies, indicating comparable ages. The red giant branch in NGC 6316 appears slightly bluer than in 47 Tucanae, suggesting a lower metal content. This has been confirmed by the isochrone fitting of the observed CMD, which provided us with updated values of the cluster age, distance, average color excess, and metallicity. We estimated an absolute age of 13.1 ± 0.5 Gyr, consistent with the age of 47 Tucanae, an average color excess E(B - V) = 0.64 ± 0.01, and a true distance modulus (m - M)0 = 15.27 ± 0.03 that sets the cluster distance at 11.3 kpc from the Sun. In addition, the photometric estimate of the cluster metallicity suggests [Fe/H] ≈ -0.9, which is ~0.2 dex smaller than that of 47 Tucanae. We also determined the gravitational center and the density profile of the system from resolved stars. The latter is well reproduced by a King model. Our results confirm that NGC 6316 is another extremely old relic of the assembly history of the Galaxy.

Keywords: globular star clusters; interstellar reddening; galactic bulge; hst photometry; milky way galaxy; markov chain monte carlo
Characteristics of Kepler Eclipsing Binaries Displaying a Significant O'Connell Effect

The O'Connell effect-the presence of unequal maxima in eclipsing binaries-remains an unsolved riddle in the study of close binary systems. The Kepler space telescope produced high-precision photometry of nearly 3000 eclipsing binary systems, providing a unique opportunity to study the O'Connell effect in a large sample and in greater detail than in previous studies. We have characterized the observational properties-including temperature, luminosity, and eclipse depth-of a set of 212 systems (7.3% of Kepler eclipsing binaries) that display a maxima flux difference of at least 1%, representing the largest sample of O'Connell effect systems yet studied. We explored how these characteristics correlate with each other to help understand the O'Connell effect's underlying causes. We also describe some system classes with peculiar light-curve features aside from the O'Connell effect (~24% of our sample), including temporal variation and asymmetric minima. We found that the O'Connell effect size's correlations with period and temperature are inconsistent with Kouzuma's starspot study. Up to 20% of systems display the parabolic eclipse timing variation signal expected for binaries undergoing mass transfer. Most systems displaying the O'Connell effect have the brighter maximum following the primary eclipse, suggesting a fundamental link between which maximum is brighter and the O'Connell effect's physical causes. Most importantly, we find that the O'Connell effect occurs exclusively in systems where the components are close enough to significantly affect each other, suggesting that the interaction between the components is ultimately responsible for causing the O'Connell effect.

Keywords: eclipsing binary stars; close binary stars; interacting binary stars
Star-image Centering with Deep Learning: HST/WFPC2 Images

A deep learning (DL) algorithm is built and tested for its ability to determine centers of star images in HST/WFPC2 exposures, in filters F555W and F814W. These archival observations hold great potential for proper-motion studies, but the undersampling in the camera's detectors presents challenges for conventional centering algorithms. Two exquisite data sets of over 600 exposures of the cluster NGC 104 in these filters are used as a testbed for training and evaluating the DL code. Results indicate a single-measurement standard error from 8.5 to 11 mpix, depending on the detector and filter. This compares favorably to the ~20 mpix achieved with the customary "effective point spread function (PSF)" centering procedure for WFPC2 images. Importantly, the pixel-phase error is largely eliminated when using the DL method. The current tests are limited to the central portion of each detector; in future studies, the DL code will be modified to allow for the known variation of the PSF across the detectors.

Keywords: astrometry; hubble space telescope; space astrometry; convolutional neural networks; algorithms; neural networks
Relationship between Current Filaments and Turbulence During a Turbulent Reconnection

Both magnetic reconnection and turbulence can play crucial roles in space plasmas. The current layers, developing during magnetic reconnection, can collapse into various small-scale coherent structures, such as current filaments. These current filaments can significantly modulate the kinetic-scale turbulence. However, the quantitative correlation between the current filaments and turbulence remains unknown so far. In this study, we statistically analyze such a relation during a turbulent reconnection in the magnetotail. We find that the kinetic-scale turbulence has a good correlation with the current-density variation ≤ft({J}{\prime }=≤ft|\tfrac{{dJ}}{{dt}}\right|\right). Specifically, (1) the slope of the kinetic-scale power spectral density (PSD), denoted as S PSD, decreases with J‧, exhibiting an empirical relation S PSD = -0.54ln(J‧) - 1.36; (2) the correlation between turbulence intensity (PSD) and J‧ is best at the frequency range 0.02-0.32 ω ce (electron cyclotron frequency); (3) the turbulence intensity (PSD) increases with J‧, exhibiting an empirical relation PSD = J‧ k • e b ; and (4) the k of these fitting functions roughly decreases with frequency. These results can advance our understanding of the interplay between magnetic reconnection and turbulence.

Keywords: interplanetary turbulence; space plasmas; plasma jets
Constraints on Compact Dark Matter with Fast Radio Burst Observations

Fast radio bursts (FRBs) are bright radio transients with millisecond duration at cosmological distances. Since compact dark matter/objects (COs) could act as lenses and cause splitting of these kinds of very short duration signals, Muñoz et al. have proposed a novel method to probe COs with lensing of FRBs. In this Letter, we for the first time apply this method to real data and give constraints of the nature of COs with currently available FRB observations. We emphasize that the information from dynamic spectra of FRBs is quite necessary for identifying any lensed signals and find no echoes in the existing data. The null search gives a constraint comparable to that from galactic wide binaries, though the methods of redshift inference from the dispersion measure would impact a little. Furthermore, we make an improved forecast based on the distributions of real data for the ongoing and upcoming telescopes. Finally, we discuss the situation where one or more lensed signals will be detected. In such a case, the parameter space of COs can be pinned down very well since the lens mass can be directly determined through the observed flux ratio and time delay between split images.

Keywords: gravitational lensing; dark matter