adsabs/SciX_UAT_keywords huggingface dataset:
Connections between the Transient Polar Warming and Solstitial Pause on Mars

Observations show two different transient atmospheric events around the northern winter solstice on Mars: a warming of the polar lower atmosphere (100-10 Pa) and a reduction in the near-surface wave activity. Here we examine the cause of, and connections between, these two events, and how their occurrence may have changed in past climates using a suite of Mars general circulation model simulations. These simulations show that the polar warming and pause in wave activity are connected, and they occur when there are sufficiently large dust heating rates in the southern (summer) high latitudes, which drive an expansion of the downwelling branch of the Hadley cell into the northern polar region. This causes a poleward shift and weakening of the jet, a warming of the polar lower atmosphere, and reduced baroclinic instability and waves near the surface. The occurrence and strength of the polar warming and wave activity pause increase with obliquity and dust optical depth, with a stronger dependence on obliquity. In past climates with low obliquity the warming and pause are unlikely to occur, or will be very weak, whereas during times of high obliquity they will likely be strong and occur every winter, unless the atmosphere is nearly free of dust.

Keywords: planetary atmospheres; planetary science; atmospheric science; planetary climates; mars
Metamorphosis of a Dwarf Halo Density Profile under Dark Matter Decay

We have studied the density profile of a dwarf halo in the decaying dark matter (DDM) cosmology, using a new algorithm that resolves halo density profiles down to the innermost 700 pc robustly with high efficiency. Following Schwarzschild's orbit-based method, we have also developed a simplified model to calculate the DDM halo density profiles, which agree remarkably well with those from N-body simulations. Both zoom-in simulations and the simplified model reveal that dark matter decay leads to the flattening of the central density and an overall reduction of the density in dwarf halos, and the underlying physics mechanisms are well illustrated by the simplified model. The slowly rising scaled rotation curves of DDM dwarf halos agree with the observations of local dwarf galaxies. Our results suggest that DDM holds great potential for resolving the small-scale problems faced by the cold dark matter model.

Keywords: dark matter; n-body simulations; dwarf galaxies; cosmology; stellar dynamics
Gas Dynamics and Star Formation in NGC 6822

We present H I gas kinematics and star formation activities of NGC 6822, a dwarf galaxy located in the Local Group at a distance of ~490 kpc. We perform profile decomposition of line-of-sight velocity profiles of the H I data cube (42.4″ × 12.0″ spatial, corresponding to ~100 pc; 1.6 km s-1 spectral) taken with the Australia Telescope Compact Array. For this, we use a new tool, the so-called BAYGAUD, which is based on Bayesian analysis techniques, allowing us to decompose a line-of-sight velocity profile into an optimal number of Gaussian components in a quantitative manner. We classify the decomposed H I gas components of NGC 6822 into cool-bulk, warm-bulk, cool-non-bulk, and warm-non-bulk motions with respect to their centroid velocities and velocity dispersions. We correlate their gas surface densities with corresponding star formation rate densities derived using both the GALEX far-ultraviolet and WISE 22 μm data to examine the resolved Kennicutt-Schmidt (K-S) law for NGC 6822. Of the decomposed H I gas components, the cool-bulk component is likely to better follow the linear extension of the K-S law for molecular hydrogen (H2) at low gas surface densities where H I is not saturated.

Keywords: interstellar medium; local group; dwarf irregular galaxies; star formation; galaxy kinematics
A Numerical Approach Using a Finite Element Model to Constrain the Possible Interior Layout of (16) Psyche

Asteroid (16) Psyche (278 × 238 × 171 km in size) is notable for the largest M-type asteroid and has the high radar albedo (0.34 ± 0.08) among the main-belt asteroids. The object is likely a mixture of metal and silicates because of its lower bulk density (~4.0 g cm-3) than metallic materials (~7.5 g cm-3) and observations inferring the existence of silicate materials on the surface. Here, we numerically investigate the interior layout when the structure of Psyche consists of a spherical iron core and two types of the silicate-rich layers (compressed and uncompressed ones) resulting from the compaction process (later known as a three-layer model). We develop an inverse problem algorithm to determine the layout distribution by combining a finite element model approach that accounts for density variations and constrains pressure-based crushing conditions. The results show that, given the crushing limit of 10 MPa, the smallest core size likely reaches 72 km in radius, and the silicate-rich layer, consisting of both compressed and uncompressed regions, has a thickness ranging up to 68 km. To support the localized metal concentration at the crater-like region detected in the recent radar observation, we give more constraints on the minimum core size, which takes up to 34%-40% of the entire size of Psyche. Our study also addresses that the ferrovolcanic surface eruptions could still be a source of metal-rich materials. Finally, while the differentiated structure having a spherical core condition is just part of potential scenarios, the present study infers that the core and compressed layer conditions likely control the surface condition. Further investigations will provide key information for observable properties on NASA's Psyche mission to provide insight into its evolution history.

Keywords: main belt asteroids; asteroids
Variability Catalog of Stars Observed during the TESS Prime Mission

During its 2 yr Prime Mission, TESS observed over 232,000 stars at a 2 minute cadence across ~70% of the sky. These data provide a record of photometric variability across a range of astrophysically interesting timescales, probing stellar rotation, stellar binarity, and pulsations. We have analyzed the TESS 2 minute light curves to identify periodic variability on timescales of 0.01-13 days, and explored the results across various stellar properties. We have identified over 46,000 periodic variables with high confidence, and another 38,000 with moderate confidence. These light curves show differences in variability type across the Hertzsprung-Russell diagram, with distinct groupings of rotational, eclipsing, and pulsational variables. We also see interesting patterns across period-luminosity space, with clear correlations between period and luminosity for high-mass pulsators, evolved stars, and contact binary systems, a discontinuity corresponding to the Kraft break, and a lower occurrence of periodic variability in main-sequence stars on timescales of 1.5-2 days. The variable stars identified in this work are cross-identified with several other variability catalogs, from which we find good agreement between the measured periods of variability. There are ~65,000 variable stars that are newly identified in this work, which includes the rotation rates of low-mass stars, high-frequency pulsation periods for high-mass stars, and a variety of giant star variability.

Keywords: periodic variable stars; light curves; time series analysis; stellar activity; catalogs; hertzsprung russell diagram
Gravitational Wave in f(R) Gravity: Possible Signature of Sub- and Super-Chandrasekhar Limiting-mass White Dwarfs

After the prediction of many sub- and super-Chandrasekhar (at least a dozen for the latter) limiting-mass white dwarfs (WDs), hence apparently a peculiar class of WDs, from the observations of luminosity of Type Ia supernovae, researchers have proposed various models to explain these two classes of WD separately. We earlier showed that these two peculiar classes of WD, along with the regular WD, can be explained by a single form of the f(R) gravity, whose effect is significant only in the high-density regime, and it almost vanishes in the low-density regime. However, since there is no direct detection of such a WD, it is difficult to single out one specific theory from the zoo of modified theories of gravity. We discuss the possibility of direct detection of such a WD in gravitational wave (GW) astronomy. It is well known that in f(R) gravity more than two polarization modes are present. We estimate the amplitudes of all the relevant modes for the peculiar and the regular WD. We further discuss the possibility of their detections through future-based GW detectors, such as LISA, ALIA, DECIGO, BBO, or the Einstein Telescope, and thereby put constraints on or rule out various modified theories of gravity. This exploration links the theory with possible observations through GW in f(R) gravity.

Keywords: white dwarf stars; gravitational waves; scalar-tensor-vector gravity; chandrasekhar limit; rotation powered pulsars; stellar magnetic fields; stellar surfaces
Thermal Models of Asteroids with Two-band Combinations of Wide-field Infrared Survey Explorer Cryogenic Data

We used the reparameterized Near-Earth Asteroid Thermal Model to model observations of a curated set of over 4000 asteroids from the Wide-field Infrared Survey Explorer in two wavelength bands (W2-3 or W3-4) and compared the results to previous results from all four wavelength bands (W1-4). This comparison was done with the goal of elucidating unique aspects of modeling two-band observations so that any potential biases or shortcomings for planned two-band surveys (e.g., the NASA Near-Earth Object Surveyor Mission) can be anticipated and quantified. The W2-3 two-band fits usually yielded slightly smaller diameters than the four-band fits, with a median diameter difference of -10%, with the 5% and 95% quantiles of the distribution at -32% and -1.5%, respectively. We conducted similar comparisons for W3-4, in part because the longest wavelength bands are expected to provide the best two-band results. We found that the W3-4 two-band diameters are slightly larger than the four-band results, with a median diameter difference of 11% and the 5% and 95% quantiles of the distribution at -2.1% and 26%, respectively. The diameter uncertainty, obtained with bootstrap analysis, is larger by 30% and 35% (median values) for the W2-3 and W3-4 fits, respectively, than for the corresponding four-band fits. Using 23 high-quality stellar occultation diameters as a benchmark, we found that the median errors of W2-3 and W3-4 diameter estimates are -15% and +12%, respectively, whereas the median error of the four-band fits is 9.3%. Although the W2-3 and W3-4 diameters appear to have greater systematic errors and uncertainties than their four-band counterparts, two-band estimates remain useful because they improve upon diameter estimates obtained from visible photometry alone.

Keywords: asteroids; main belt asteroids; near-earth objects; sky surveys; small solar system bodies
The Detection of Possible γ-Ray Quasi-periodic Modulation with 600 days from the Blazar S2 0109+22

In this work, we analyzed the long-term γ-ray data by a Fermi Large Area Telescope of blazar S2 0109+22, ranging from 2008 to 2023. The quasi-periodic oscillations (QPOs) of blazars aided in investigating the physical properties of internal supermassive black holes, the nature of variability, and the underlying radiation mechanism. We employed four different methods-Weighted Wavelet Z-transform, Lomb-Scargle periodogram, REDFIT and phase folded light curve analysis, for searching QPO signals. Our analysis identified a possible QPO behavior with a periodicity of ~600 days in 2013 November-2023 January at a significance level of ~3.5σ. This QPO signal sustained ~9 yr, corresponding to 5.6 cycles, which was in good agreement with the previously observed periodicity of ~657 days in radio. We explained this phenomenon based on the accretion model and the lighthouse effect, in a binary black hole system.

Keywords: active galactic nuclei; bl lacertae objects; galaxy jets; gamma-rays
GJ 357 d: Potentially Habitable World or Agent of Chaos?

Multiplanet systems provide important laboratories for exploring dynamical interactions within the range of known exoplanetary system architectures. One such system is GJ 357, consisting of a low-mass host star and three orbiting planets, the outermost (planet d) of which does not transit but lies within the habitable zone (HZ) of the host star. The minimum mass of planet d causes its nature to be unknown, both in terms of whether it is truly terrestrial and if it is a candidate for harboring surface liquid water. Here, we use three sectors of photometry from the Transiting Exoplanet Survey Satellite to show that planets c and d do not transit the host star, and therefore may have masses higher than the derived minimum masses. We present the results for a suite of dynamical simulations that inject an Earth-mass planet within the HZ of the system for three different orbital and mass configurations of planet d. These results show that planet d, rather than being a potentially habitable planet, is likely a source of significant orbital instability for other potential terrestrial planets within the HZ. We find that relatively small eccentricities of planet d cause a majority of the HZ to be unstable for an Earth-mass planet. These results highlight the importance of dynamical stability for systems that are prioritized in the context of planetary habitability.

Keywords: exoplanets; exoplanet astronomy; exoplanet dynamics; exoplanet systems; astrobiology; habitable planets; orbital evolution
Prospects for the Observation of Continuous Gravitational Waves from Spinning Neutron Stars Lensed by the Galactic Supermassive Black Hole

We study the prospects of detecting continuous gravitational waves (CGWs) from spinning neutron stars (NSs), gravitationally lensed by the galactic supermassive black hole. Assuming various astrophysically motivated spatial distributions of galactic NSs, we find that CGW signals from a few (~0-6) neutron stars should be strongly lensed. Lensing will produce two copies of the signal (with time delays of seconds to minutes) that will interfere with each other. The relative motion of the NS with respect to the lensing optical axis will change the interference pattern, which will help us to identify a lensed signal. Accounting for the magnifications and time delays of the lensed signals, we investigate their detectability by ground-based detectors. Modeling the spin distribution of NSs based on that of known pulsars and assuming an ellipticity of ϵ = 10-7, lensed CGWs are unlikely to be detectable by LIGO and Virgo in realistic searches involving ${ \mathcal O }({10}^{12})$ templates. However, third-generation detectors have a ~2%-51% probability of detecting at least one lensed CGW signal. For an ellipticity of ϵ = 10-8, the detection probability reduces to ~0%-18%. Though rare, such an observation will enable interesting probes of the supermassive black hole and its environment.

Keywords: strong gravitational lensing; gravitational waves; general relativity; gravitational wave astronomy; gravitational wave sources; neutron stars
Dependence of Solar Wind Proton Temperature on the Polarization Properties of Alfvénic Fluctuations at Ion-kinetic Scales

We use fluctuating magnetic helicity to investigate the polarization properties of Alfvénic fluctuations at ion-kinetic scales in the solar wind as a function of βp, the ratio of proton thermal pressure to magnetic pressure, and θvB, the angle between the proton flow and local mean magnetic field, B0. Using almost 15 yr of Wind observations, we separate the contributions to helicity from fluctuations with wavevectors, k, quasi-parallel and oblique to B0, finding that the helicity of Alfvénic fluctuations is consistent with predictions from linear Vlasov theory. This result suggests that the nonlinear turbulent fluctuations at these scales share at least some polarization properties with Alfvén waves. We also investigate the dependence of proton temperature in the βp-θvB plane to probe for possible signatures of turbulent dissipation, finding that it correlates with θvB. The proton temperature parallel to B0 is higher in the parameter space where we measure the helicity of right-handed Alfvénic fluctuations, and the temperature perpendicular to B0 is higher where we measure left-handed fluctuations. This finding is inconsistent with the general assumption that by sampling different θvB in the solar wind we can analyze the dependence of the turbulence distribution on θkB, the angle between k and B0. After ruling out both instrumental and expansion effects, we conclude that our results provide new evidence for the importance of local kinetic processes that depend on θvB in determining proton temperature in the solar wind.

Keywords: heliosphere; solar wind; space plasmas; plasma physics; interplanetary turbulence; alfven waves; magnetic fields; the sun
Real-time Flare Prediction Based on Distinctions between Flaring and Non-flaring Active Region Spectra

With machine learning entering into the awareness of the heliophysics community, solar flare prediction has become a topic of increased interest. Although machine-learning models have advanced with each successive publication, the input data has remained largely fixed on magnetic features. Despite this increased model complexity, results seem to indicate that photospheric magnetic field data alone may not be a wholly sufficient source of data for flare prediction. For the first time, we have extended the study of flare prediction to spectral data. In this work, we use Deep Neural Networks to monitor the changes of several features derived from the strong resonant Mg II h and k lines observed by the Interface Region Imaging Spectrograph. The features in descending order of predictive capability are: the triplet emission at 2798.77 Å, line core intensity, total continuum emission between the h and k line cores, the k/h ratio, line width, followed by several other line features such as asymmetry and line center. Regions that are about to flare generate spectra that are distinguishable from non-flaring active region spectra. Our algorithm can correctly identify pre-flare spectra approximately 35 minutes before the start of the flare, with an AUC of 86% and an accuracy, precision, and recall of 80%. The accuracy and AUC monotonically increase to 90% and 97%, respectively, as we move closer in time to the start of the flare. Our study indicates that spectral data alone can lead to good predictive models and should be considered an additional source of information alongside photospheric magnetograms.

Keywords: dimensionality reduction; neural networks; solar flare spectra; support vector machine; solar flares
3D Radiative Transfer Simulations of the Atmospheric Environment of the Carbon-rich AGB Star RU Vir

We report the preliminary near- and mid-infrared 3D radiative transfer simulations of the carbon-rich AGB star RU Vir using the 3D radiative transfer code RADMC-3D. We found that the inclusion of molecular and dust species reproduces the extended atmosphere of this star well. This study is the beginning of an in-progress effort toward a more systematic 3D radiative transfer modeling of RU Vir's extended atmosphere, and other AGB stars. These efforts aim at constraining the stars' stellar parameters, and as preparatory work for the first multi-wavelength imaging of carbon-rich AGB stars with the newest VLTI/MATISSE interferometric instrument.

Keywords: asymptotic giant branch stars; radiative transfer; optical interferometry; stellar mass loss; evolved stars; stellar winds; interstellar medium; astronomical models
Early Planet Formation in Embedded Disks (eDisk). VI. Kinematic Structures around the Very-low-mass Protostar IRAS 16253-2429

Precise estimates of protostellar masses are crucial to characterize the formation of stars of low masses down to brown dwarfs (BDs; M * < 0.08 M ☉). The most accurate estimation of protostellar mass uses the Keplerian rotation in the circumstellar disk around the protostar. To apply the Keplerian rotation method to a protostar at the low-mass end, we have observed the Class 0 protostar IRAS 16253-2429 using the Atacama Large Millimeter/submillimeter Array (ALMA) in the 1.3 mm continuum at an angular resolution of 0.″07 (10 au), and in the 12CO, C18O, 13CO (J = 2-1), and SO (J N = 65-54) molecular lines, as part of the ALMA Large Program Early Planet Formation in Embedded Disks project. The continuum emission traces a nonaxisymmetric, disk-like structure perpendicular to the associated 12CO outflow. The position-velocity (PV) diagrams in the C18O and 13CO lines can be interpreted as infalling and rotating motions. In contrast, the PV diagram along the major axis of the disk-like structure in the 12CO line allows us to identify Keplerian rotation. The central stellar mass and the disk radius are estimated to be ~0.12-0.17 M ☉ and ~13-19 au, respectively. The SO line suggests the existence of an accretion shock at a ring (r ~ 28 au) surrounding the disk and a streamer from the eastern side of the envelope. IRAS 16253-2429 is not a proto-BD but has a central stellar mass close to the BD mass regime, and our results provide a typical picture of such very-low-mass protostars.

Keywords: circumstellar disks; protostars; low mass stars
Contrasting the Mechanisms of Reconnection-driven Electron Acceleration with In Situ Observations from MMS in the Terrestrial Magnetotail

The question of how magnetic reconnection accelerates particles is a long-standing problem in space physics and astrophysics. Earth's magnetosphere is an ideal laboratory for investigating this issue via in situ satellite observations. This article presents a statistical study of the electron acceleration produced by different mechanisms in the near-Earth magnetotail using the unique measurement capabilities of the Magnetospheric Multiscale mission. We find that the average acceleration rates and occurrence rates of large acceleration tend to be higher in outflows with greater speeds. Betatron and first-order Fermi accelerations are intensified near the neutral sheet, while the acceleration from E ∣∣ is not only intensified in the neutral sheet but also significant far away from it, likely in the separatrix region. In contrast to previous studies suggesting that the acceleration and energy conversion predominantly occur in the outflow region, we find that the acceleration rate near the X line is comparable to that in the outflow.

Keywords: plasma physics; space plasmas; planetary magnetospheres