adsabs/SciX_UAT_keywords huggingface dataset:
Multiwavelength Study of Dark Globule DC 314.8-5.1: Point-source Identification and Diffuse Emission Characterization

We present an analysis of multiwavelength observations of the dark globule DC 314.8-5.1, using data from the Gaia optical, Two Micron All Star Survey near-infrared, and Wide-field Infrared Survey Explorer mid-infrared surveys, dedicated imaging with the Spitzer Space Telescope, and X-ray data obtained with the Swift X-Ray Telescope (XRT). The main goal was to identify possible pre-main-sequence stars (PMSs) and young stellar objects (YSOs) associated with the globule. For this, we studied the infrared colors of all point sources within the boundaries of the cloud. After removing sources with nonstellar spectra, we investigated the Gaia parallaxes for the YSO candidates and found that none are physically related to DC 314.8-5.1. In addition, we searched for X-ray emission from PMSs with Swift-XRT, and found no 0.5-10 keV emission down to a luminosity level ≲1031 erg s-1, typical of a PMS with mass ≥2 M ⊙. Our detailed inspection therefore supports a very young, "prestellar core" evolutionary stage for the cloud. Based on archival Planck and IRAS data, we moreover identify the presence of hot dust, with temperatures ≳100 K, in addition to the dominant dust component at 14 K, originating with the associated reflection nebula.

Keywords: interstellar medium; molecular clouds; young stellar objects; pre-main sequence stars; infrared astronomy; x-ray astronomy
Search for Continuous Gravitational Waves from Scorpius X-1 in LIGO O2 Data

We present the results of a search in LIGO O2 public data for continuous gravitational waves from the neutron star in the low-mass X-ray binary Scorpius X-1. We search for signals with ≈ constant frequency in the range 40-180 Hz. Thanks to the efficiency of our search pipeline we can use a long coherence time and achieve unprecedented sensitivity, significantly improving on existing results. This is the first search that has been able to probe gravitational wave amplitudes that could balance the accretion torque at the neutron star radius. Our search excludes emission at this level between 67.5 and 131.5 Hz, for an inclination angle 44° ± 6° derived from radio observations, and assuming that the spin axis is perpendicular to the orbital plane. If the torque arm is ≈26 km—a conservative estimate of the Alfvén radius—our results are more constraining than the indirect limit across the band. This allows us to exclude certain mass-radius combinations and to place upper limits on the strength of the star's magnetic field with a different probe than ever used before. We also correct a mistake that appears in the literature in the equation that gives the gravitational wave amplitude at the torque balance and we re-interpret the associated latest LIGO/Virgo results in light of this.

Keywords: gravitational waves; neutron stars; low-mass x-ray binary stars
A Comparison of Chemical Models of Exoplanet Atmospheres Enabled by TauREx 3.1

Thermochemical equilibrium is one of the most commonly used assumptions in current exoplanet retrievals. As science operations with the James Webb Space Telescope (JWST) draw near and with the planned launch of Ariel, it is crucial to assess the underlying biases and assumptions made when applying self-consistent chemistry to spectral retrievals. Here we use the flexibility of TauREx 3.1 to cross-compare three state-of-the-art chemical equilibrium codes: ACE, FastChem, and GGchem. We simulate JWST spectra for ACE, FastChem, GGchem, and GGchem+condensation containing only the elements C, H, O, and N and spectra for FastChem, GGchem, and GGchem+condensation with a more extensive range of elements, giving seven simulated JWST spectra in total, and then cross-retrieve, giving a total of 56 retrievals. Our analysis demonstrates that, like-for-like, all chemical codes retrieve the correct parameters to within 1% of the truth. However, in retrievals, where the contained elements do not match the truth, parameters such as metallicity deviate by 20% while maintaining extremely low uncertainties <1%, giving false confidence. This point is of major importance for future analyses on JWST and Ariel, highlighting that self-consistent chemical schemes that do not employ the proper assumptions (missing species, fixed elemental ratios, condensation) are at risk of confidently biasing interpretations. Free chemistry retrievals employing parametric descriptions of the chemical profiles can provide alternative unbiased explorations.

Keywords: open source software; publicly available software; chemical abundances; bayesian statistics; exoplanet atmospheres; exoplanet astronomy; exoplanet atmospheric composition; exoplanets; radiative transfer
On Making Magnetic-flux-rope Ω Loops for Solar Bipolar Magnetic Regions of All Sizes by Convection Cells

We propose that the flux-rope Ω loop that emerges to become any bipolar magnetic region (BMR) is made by a convection cell of the Ω-loop's size from initially horizontal magnetic field ingested through the cell's bottom. This idea is based on (1) observed characteristics of BMRs of all spans (∼1000 to ∼200,000 km), (2) a well-known simulation of the production of a BMR by a supergranule-sized convection cell from horizontal field placed at cell bottom, and (3) a well-known convection-zone simulation. From the observations and simulations, we (1) infer that the strength of the field ingested by the biggest convection cells (giant cells) to make the biggest BMR Ω loops is ∼103 G, (2) plausibly explain why the span and flux of the biggest observed BMRs are ∼200,000 km and ∼1022 Mx, (3) suggest how giant cells might also make "failed-BMR" Ω loops that populate the upper convection zone with horizontal field, from which smaller convection cells make BMR Ω loops of their size, (4) suggest why sunspots observed in a sunspot cycle's declining phase tend to violate the hemispheric helicity rule, and (5) support a previously proposed amended Babcock scenario for the sunspot cycle's dynamo process. Because the proposed convection-based heuristic model for making a sunspot-BMR Ω loop avoids having ∼105 G field in the initial flux rope at the bottom of the convection zone, it is an appealing alternative to the present magnetic-buoyancy-based standard scenario and warrants testing by high-enough-resolution giant-cell magnetoconvection simulations.

Keywords: solar magnetic fields; solar magnetic flux emergence; solar convective zone; solar cycle; solar dynamo
The Evolution of Magellanic-like Galaxy Pairs and the Production of Magellanic Stream Analogs in Simulations with Tides, Ram Pressure, and Stellar Feedback

We present a series of chemodynamical simulations of Magellanic-like systems consisting of two interacting, equal-mass dwarf galaxies orbiting a massive host galaxy, including feedback and star formation, tides, and ram pressure. We study the star formation and chemical enrichment history of the dwarfs and the production of a Magellanic Stream analog. The dwarfs interact with each other through tidal forces, distorting their morphologies and triggering star formation. A stream is naturally produced as outflows, induced by feedback, and interactions are stretched by tidal forces. Counter to some recent simulations, we find that the leading arm persists even in the presence of ram pressure from the host galaxy. Interactions between the dwarfs and the host galaxies produce multiple kinematic components in the stream, as observed. A combination of ongoing star formation and entrained low-metallicity gas causes the stream to have a complex chemical structure, with an average metallicity that is generally lower than that of the dwarfs.

Keywords: magellanic clouds; magellanic stream; galaxy interactions; stellar feedback; circumgalactic medium; galaxy tides; ram pressure stripped tails; hydrodynamical simulations; dwarf galaxies
First Batch of z ≈ 11-20 Candidate Objects Revealed by the James Webb Space Telescope Early Release Observations on SMACS 0723-73

On 2022 July 13, NASA released to the whole world the data obtained by the James Webb Space Telescope (JWST) Early Release Observations (ERO). These are the first set of science-grade data from this long-awaited facility, marking the beginning of a new era in astronomy. In the study of the early universe, JWST will allow us to push far beyond z ≈ 11, the redshift boundary previously imposed by the 1.7 μm red cutoff of the Hubble Space Telescope (HST). In contrast, JWST's NIRCam reaches ~5 μm. Among the JWST ERO targets there is a nearby galaxy cluster SMACS 0723-73, which is a massive cluster and has been long recognized as a potential "cosmic telescope" in amplifying background galaxies. The ERO six-band NIRCam observations on this target have covered an additional flanking field not boosted by gravitational lensing, which also sees far beyond HST. Here we report the result from our search of candidate objects at z > 11 using these ERO data. In total, there are 87 such objects identified by using the standard "dropout" technique. These objects are all detected in multiple bands and therefore cannot be spurious. For most of them, their multiband colors are inconsistent with known types of contaminants. If the detected dropout signature is interpreted as the expected Lyman break, it implies that these objects are at z ≈ 11-20. The large number of such candidate objects at such high redshifts is not expected from the previously favored predictions and demands further investigations. JWST spectroscopy on such objects will be critical.

Keywords: galaxy formation; galaxy evolution; early universe
Estimation of Stellar Ages and Masses Using Gaussian Process Regression

Stellar ages play a crucial role in understanding the formation and evolution of stars and Galaxies, which pose many challenges while determining in practice. In this paper, we have introduced a new machine-learning method, Gaussian process regression (GPR), to estimate the stellar ages, which is different from the traditional isochrone fitting method, which fully utilizes the information provided by previous studies. To demonstrate the performance of our method, we have applied it to the field stars of two important phases of evolution, main-sequence turn-off (MSTO) stars and giants, whose ages and masses are available in the literature. Also, GPR is applied to the red giants of open clusters (e.g., M67). Results showed that the ages given by GPR are in better agreement with those given by isochrone fitting methods. The ages are also estimated from various other machine-learning methods (e.g., support vector regression, neural networks, and random forest) and are compared with GPR, which resulted in GPR outperforming others. In addition to ages, we have applied GPR to estimate the masses of the MSTO stars and red giants and found that the masses predicted by GPR for the red giants are within acceptable uncertainties of masses derived from the asteroseismic scaling relation. We have provided the constraints on the input parameters to GPR, which decides the accuracy of the output ages and masses. Results conclude that the newly introduced GPR is promising to provide a novel approach to estimate stellar ages and masses in the era of big data sets. As a supplement, masses and ages for the MSTO stars and red giants estimated from GPR are provided as a catalog that could be used as a training set for upcoming large data sets with spectroscopic parameters.

Keywords: astronomy data analysis; red giant stars; stellar ages; astronomical methods
Spectral Evolution of Dark Asteroid Surfaces Induced by Space Weathering over a Decade

The surfaces of airless bodies like asteroids in the solar system are known to be affected by space weathering. Experiments simulating space weathering are essential for studying the effects of this process on meteorite samples, but the problem is that the time spent to reproduce space weathering in these experiments is billions of times shorter than the actual phenomenon. In 2010 December, the T-type asteroid 596 Scheila underwent a collision with an impactor a few tens of meters in size. A decade later, there is an opportunity to study how the surface layer of this asteroid is being altered by space weathering after the impact. To do so, we performed visible spectrophotometric and near-infrared spectroscopic observations of 596 Scheila. The acquired spectrum is consistent with those observed shortly after the 2010 impact event within the observational uncertainty range. This indicates that the surface color of dark asteroids is not noticeably changed by space weathering over a 10 yr period. This study is the first to investigate color changes due to space weathering on an actual asteroid surface in the solar system. Considering that fresh layers are regularly created on asteroid surfaces by collisions, we suggest a genetic link between D/T-type and dark (low albedo) X-complex asteroids and very red objects such as 269 Justitia, 732 Tjilaki, and 203 Pompeja. New observations show that 203 Pompeja has an X-type-like surface, with some local surface areas exhibiting a very red spectrum.

Keywords: small solar system bodies; asteroids; main belt asteroids; asteroid surfaces
Phase-dependent Spectral Shape Changes in the Ultraluminous X-Ray Pulsar NGC 5907 ULX1

The discovery of coherent pulsations from several ultraluminous X-ray pulsars (ULXPs) has provided direct evidence of a supercritical accretion flow. However, the geometrical structure of such an accretion flow onto the central neutron star remains poorly understood. NGC 5907 ULX1 is one of the most luminous ULXPs, with a luminosity exceeding 1041 erg s‑1. Here we present a broadband X-ray study of this ULXP using the data from simultaneous observations with XMM-Newton and NuSTAR conducted in 2014 July. The phase-resolved spectra are well reproduced by a model consisting of a multicolor disk blackbody emission with a temperature gradient of p = 0.5 (T ∝ r ‑p ) and a power law with an exponential cutoff. The disk component is phase-invariant and has an innermost temperature of ∼ 0.3 keV. Its normalization suggests a relatively low inclination angle of the disk, in contrast to the previous claims in other literature. The power-law component, attributed to the emission from the accretion flow inside the magnetosphere of the neutron star, indicates phase-dependent spectral shape changes; the spectrum is slightly harder in the pre-peak phase than in the post-peak phase. This implies that the magnetosphere has an asymmetric geometry around the magnetic axis and that hotter regions close to the magnetic pole become visible before the pulse peak.

Keywords: pulsars; ultraluminous x-ray sources; accretion; x-ray binary stars
A Comparative Study of Ionospheric Response to Solar Flares at Earth, Venus, and Mars

It has been widely recognized that the ionosphere of the terrestrial planet responds greatly to the enhanced X-ray and extreme ultraviolet radiation during solar flares. However, little attention has been paid to the comparative study of the ionospheric response between different Earth-like planets. In this work, we investigate the responses of the ionospheres of Earth, Venus, and Mars to the 2017 September 6 solar flares, with self-consistent planetary ionospheric models. The result shows that the electron density increases significantly in the relatively low ionosphere region, and its maximum relative change displays profound differences between planets. The ion temperatures at Earth and Venus share a similar response to flares, but differ from those at Mars, which relates to the background atmospheric conditions. For the electron temperature response to the X9.3 flare, at Earth it increases with a maximum magnitude of 250 K, in contrast to the decrease of ~45 K at Venus and ~40 K at Mars. The vertical plasma velocity at all three planets exhibits enhancement during solar flares. As a result, the upward flux increases by 2.16 × 1012 m-2 s-1 at 800 km of Earth, 3.79 × 1010 m-2 s-1, and 8.45 × 109 m-2 s-1 at 400 km of Venus and Mars. This is the first self-consistent simulation of the flare-induced enhancement of upward plasma flow at Venus and Mars.

Keywords: planetary ionospheres; planetary science; solar flares
Data-driven Stellar Models

We developed a data-driven model to map stellar parameters (Teff, $\mathrm{log}g$ , and $\left[\mathrm{Fe}/{\rm{H}}\right]$ ) accurately and precisely to broadband stellar photometry. This model must, and does, simultaneously constrain the passband-specific dust reddening vector in the Milky Way, R. The model uses a neural network to learn the (de-reddened) absolute magnitude in one band and colors across many bands, given stellar parameters from spectroscopic surveys and parallax constraints from Gaia. To demonstrate the effectiveness of this approach, we train our model on a data set with spectroscopic parameters from LAMOST, APOGEE, and GALAH, Gaia parallaxes, and optical and near-infrared photometry from Gaia, Pan-STARRS 1, Two Micron All Sky Survey and Wide-field Infrared Survey Explorer. Testing the model on these data sets leads to an excellent fit and a precise—and by construction—accurate prediction of the color-magnitude diagrams in many bands. This flexible approach rigorously links spectroscopic and photometric surveys, and also results in an improved, Teff-dependent R. As such, it provides a simple and accurate method for predicting photometry in stellar evolutionary models. Our model will form a basis to infer stellar properties, distances, and dust extinction from photometric data, which should be of great use in 3D mapping of the Milky Way. Our trained model can be obtained at doi:10.5281/zenodo.3902382.

Keywords: astrostatistics; neural networks; stellar photometry; interstellar dust extinction
JWST Transit Spectra. II. Constraining Aerosol Species, Particle-size Distributions, Temperature, and Metallicity for Cloudy Exoplanets

The James Webb Space Telescope (JWST) will provide moderate-resolution transit spectra with continuous wavelength coverage from the optical to the mid-infrared for the first time. In this paper, we illustrate how different aerosol species, size distributions, and spatial distributions encode information in the JWST transit spectra of warm exoplanets. We use the transit spectral modeling code METIS, along with Mie theory and several flexible treatments of aerosol size and spatial distributions to perform parameter sensitivity studies, calculate transit contribution functions, compute Jacobians, and retrieve parameters from simulated data. The broader wavelength coverage of the JWST can encompass enough non-gray aerosol behavior to recover information about the species and size distribution of particles under many feasible aerosol scenarios. Within the JWST wavelength range, the optical and mid-infrared typically provide information about 0.1-1 μm sized aerosols, while the near-infrared to mid-infrared wavelengths usually provide information about gaseous absorption. Strong gaseous absorption features in the infrared can remain visible, even when clouds and hazes are flattening the optical and near-infrared portion of the spectrum that is currently observable. For some combinations of aerosol properties, temperature, and surface gravity, one can make a precise measure of metallicity despite the presence of aerosols, but more often the retrieved metallicity of a cloudy or hazy atmosphere has significantly lower precision than for a clear atmosphere with otherwise similar properties. Future efforts to securely link aerosol properties to atmospheric metallicity and temperature in a physically motivated manner will ultimately enable a robust physical understanding of the processes at play in cloudy, hazy exoplanet atmospheres.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; exoplanets
Nonlinear Alfvén Wave Model of Stellar Coronae and Winds from the Sun to M Dwarfs

An M dwarf's atmosphere and wind are expected to be highly magnetized. The nonlinear propagation of Alfvén waves could play a key role in both heating the stellar atmosphere and driving the stellar wind. Using this Alfvén wave scenario, we carried out a one-dimensional compressive magnetohydrodynamic simulation to examine the nonlinear propagation of Alfvén waves from the M dwarf's photosphere, chromosphere to the corona, and interplanetary space. Based on the simulation results, we developed a semi-empirical method describing the solar and M dwarf's coronal temperature, stellar wind velocity, and wind's mass-loss rate. We find that M dwarfs' coronae tend to be cooler than the solar corona, and that M dwarfs' stellar winds can be characterized as having a faster velocity and much smaller mass-loss rate compared to those of the solar wind.

Keywords: stellar winds; stellar coronae; stellar chromospheres; m dwarf stars; alfven waves; magnetohydrodynamics
Life on Titan May Signal Early Life in the Universe

The temperature of the cosmic microwave background was equal to the surface temperature of Saturn's moon Titan, 94 K, at a redshift z = 33.5, after the first galaxies formed. Titan-like objects would have maintained this surface temperature for tens of Myr irrespective of their distance from a star. Titan has the potential for the chemistry of familiar life in its subsurface water ocean, as well new forms of life in the rivers, lakes and seas of liquid methane and ethane on its surface. The potential future discovery of life on Titan would open the possibility that the earliest lifeforms emerged in metal-rich environments of the earliest galaxies in the universe, merely 100 Myr after the big bang.

Keywords: population iii stars; astrobiology
He I 10830 Å Dimming during Solar Flares. I. The Crucial Role of Nonthermal Collisional Ionizations

While solar flares are predominantly characterized by an intense broadband enhancement to the solar radiative output, certain spectral lines and continua will, in theory, exhibit flare-induced dimmings. Observations of transitions of orthohelium He I λλ 10830 Å and the He I D3 lines have shown evidence of such dimming, usually followed by enhanced emission. It has been suggested that nonthermal collisional ionization of helium by an electron beam, followed by recombinations to orthohelium, is responsible for overpopulating those levels, leading to stronger absorption. However, it has not been possible observationally to preclude the possibility of overpopulating orthohelium via enhanced photoionization of He I by EUV irradiance from the flaring corona followed by recombinations. Here we present radiation hydrodynamics simulations of nonthermal electron-beam-driven flares where (1) both nonthermal collisional ionization of helium and coronal irradiance are included, and (2) only coronal irradiance is included. A grid of simulations covering a range of total energies deposited by the electron beam and a range of nonthermal electron-beam low-energy cutoff values were simulated. In order to obtain flare-induced dimming of the He I 10830 Å line, it was necessary for nonthermal collisional ionization to be present. The effect was more prominent in flares with larger low-energy cutoff values and longer lived in weaker flares and flares with a more gradual energy deposition timescale. These results demonstrate the usefulness of orthohelium line emission as a diagnostic of flare energy transport.

Keywords: active solar chromosphere; solar chromosphere; solar physics; solar flares; solar flare spectra; spectroscopy; radiative transfer simulations; hydrodynamical simulations; solar radiation