adsabs/SciX_UAT_keywords huggingface dataset:
Classification of Astronomical Spectra Based on Multiscale Partial Convolution

The automated and efficient classification of astronomical spectra is an important research issue in the era of large sky surveys. Most current studies on automatic spectral classification primarily focus on specific data sets and demonstrate outstanding performance. However, the diversity in spectra poses formidable challenges for these classification models, as they exhibit limited capability to generalize across more comprehensive data sets. In response to these challenges, we pioneer a method called the multiscale partial convolution net (MSPC-Net), which amalgamates partial, large kernel, and grouped convolution to facilitate multilabel spectral classification. By harnessing the capabilities of partial convolution, MSPC-Net can effectively reduce the number of model parameters, accelerate the training process, and mitigate the overfitting issue. Integrating large kernel and grouped convolution empowers the model to capture local and global features simultaneously, enhancing its overall classification efficacy. To rigorously evaluate the model's performance, we generate ten different data sets sourced from the Sloan Digital Sky Survey and Large Sky Area Multi-Object Spectroscopic Telescope. These data sets encompass stellar class, stellar subclass, and full classification, providing a comprehensive assessment across various application scenarios. The experimental results reveal that MSPC-Net consistently outperforms the other models across different data sets, especially demonstrating superior performance in the last two data sets with full classification. Consequently, MSPC-Net is poised to find extensive applications in the detailed classification for large-scale sky survey projects. This work not only addresses the challenges of generalization in spectral classification but also contributes significantly to the advancement of robust models for astronomical research.

Keywords: convolutional neural networks; classification systems; astronomy data analysis; surveys
Connection between Polytropic Index and Heating

The paper derives the one-to-one connecting relationships between plasma heating and its polytropic index, and addresses the consequences through the transport equation of temperature. Thermodynamic polytropic processes are classified in accordance to their polytropic index, the exponent of the power-law relationship of thermal pressure expressed with respect to density. These processes generalize the adiabatic one, where no heating is exchanged between the system and its environment. We show that, in addition to heating terms, the transport equation of temperature depends on the adiabatic index, instead of a general, nonadiabatic polytropic index, even when the plasma follows nonadiabatic processes. This is because all the information regarding the system's polytropic index is contained in the heating term, even for a nonconstant polytropic index. Moreover, the paper (i) defines the role of the polytropic index in the context of heating; (ii) clarifies the role of the nonadiabatic polytropic index in the transport equation of temperature; (iii) provides an alternative method for deriving the turbulent heating through the comparably simpler polytropic index path; and, finally, (iv) shows a one-component plasma proof-of-concept of this method and discusses the implications of such derived connecting relationships in the solar wind plasma in the heliosphere.

Keywords: space plasmas; polytropes; heliosphere
Toward a General Parameterization of the Warm Dark Matter Halo Mass Function

Studies of flux anomalies statistics and perturbations in stellar streams have the potential to constrain models of warm dark matter (WDM), including sterile neutrinos. Producing these constraints requires a parameterization of the WDM mass function relative to that of the cold dark matter (CDM) equivalent. We use five WDM models with half-mode masses, Mhm = [1.3,35] × 108 ${M}_{\odot }$ , spread across simulations of the Local Group, lensing ellipticals and the z = 2 universe, to generate such a parameterization: we fit parameters to a functional form for the WDM-to-CDM halo mass function ratio, ${n}_{\mathrm{WDM}}({M}_{X})/{n}_{\mathrm{CDM}}({M}_{X})$ , of ${\left(1+{(\alpha {M}_{\mathrm{hm}}/{M}_{X})}^{\beta }\right)}^{\gamma }$ . For MX ≡ virial mass of central halos we obtain α = 2.3, β = 0.8, and γ = -1.0, and this fit is steeper than the extended Press-Schechter formalism predicts. For MX ≡ mass of subhalos we instead obtain α = 4.2, β = 2.5, and γ = -0.2; in both mass definitions the scatter is ∼20%. The second fit typically underestimates the relative abundance of z = 2 WDM subhalos at the tens of percent level. We caution that robust constraints will require bespoke simulations and a careful definition of halo mass, particularly for subhalos of mass <108 ${M}_{\odot }$ .

Keywords: warm dark matter
Ambipolar Heating of Magnetars

Magnetars, neutron stars thought to be with ultrastrong magnetic fields of 1014-15 G, are observed to be much hotter than ordinary pulsars with ~1012 G, and additional heating sources are required. One possibility is heating by the ambipolar diffusion in the stellar core. This scenario is examined by calculating the models using the relativistic thermal evolutionary code without making the isothermal approximation. The results show that this scenario can be consistent with most of the observed magnetar temperature data.

Keywords: magnetars; x-ray stars; degenerate matter; neutron stars
HD 83443c: A Highly Eccentric Giant Planet on a 22 yr Orbit

We report the discovery of a highly eccentric long-period Jovian planet orbiting the hot-Jupiter host HD 83443. By combining radial velocity data from four instruments (AAT/UCLES, Keck/HIRES, HARPS, Minerva-Australis) spanning more than two decades, we find evidence for a planet with m sin $i={1.35}_{-0.06}^{+0.07}$ M J, moving on an orbit with a = 8.0 ± 0.8 au and eccentricity e = 0.76 ± 0.05. We combine our radial velocity analysis with Gaia eDR3 /Hipparcos proper motion anomalies and derive a dynamical mass of ${1.5}_{-0.2}^{+0.5}{M}_{\mathrm{Jup}}$ . We perform a detailed dynamical simulation that reveals locations of stability within the system that may harbor additional planets, including stable regions within the habitable zone of the host star. HD 83443 is a rare example of a system hosting a hot Jupiter and an exterior planetary companion. The high eccentricity of HD 83443c suggests that a scattering event may have sent the hot Jupiter to its close orbit while leaving the outer planet on a wide and eccentric path.

Keywords: planet hosting stars; radial velocity; exoplanet astronomy; exoplanet dynamics; subgiant stars; astrometry
The Detectability of Kiloparsec-scale Dual Active Galactic Nuclei: The Impact of Galactic Structure and Black Hole Orbital Properties

Observational searches for dual active galactic nuclei (dAGNs) at kiloparsec separations are crucial for understanding the role of galaxy mergers in the evolution of galaxies. In addition, kiloparsec-scale dAGNs may serve as the parent population of merging massive black hole (MBH) binaries, an important source of gravitational waves. We use a semi-analytical model to describe the orbital evolution of unequal mass MBH pairs under the influence of stellar and gaseous dynamical friction in post-merger galaxies. We quantify how the detectability of approximately 40,000 kpc-scale dAGNs depends on the structure of their host galaxies and the orbital properties of the MBH pair. Our models indicate that kiloparsec-scale dAGNs are most likely to be detected in gas-rich post-merger galaxies with smaller stellar bulges and relatively massive, rapidly rotating gas disks. The detectability is also increased in systems with MBHs of comparable masses following low eccentricity prograde orbits. In contrast, dAGNs with retrograde, low eccentricity orbits are some of the least detectable systems among our models. The dAGNs in models in which the accreting MBHs are allowed to exhibit radiative feedback are characterized by a significantly lower overall detectability. The suppression in detectability is most pronounced in gas-rich merger remnant galaxies, where radiation feedback is more likely to arise. If so, then large, relatively gas-poor galaxies may be the best candidates for detecting dAGNs.

Keywords: dynamical friction; galaxy evolution; galaxy mergers; supermassive black holes; agn host galaxies
Detection of Dynamical Instability in Titan's Thermospheric Jet

Similar to Earth, Saturn's largest moon, Titan, possesses a system of high-altitude zonal winds (or jets) that encircle the globe. Using the Atacama Large Millimeter/submillimeter Array (ALMA) in 2016 August, Lellouch et al. discovered an equatorial jet at much higher altitudes than previously known, with a surprisingly fast speed of up to ∼340 m s-1; however, the origin of such high velocities is not yet understood. We obtained spectrally and spatially resolved ALMA observations in 2017 May to map Titan's 3D global wind field and compare our results with a re-analysis of the 2016 August data. Doppler wind velocity maps were derived in the altitude range ∼300-1000 km (from the upper stratosphere to the thermosphere). At the highest thermospheric altitudes, a 47% reduction in the equatorial zonal wind speed was measured over the 9 month period (corresponding to Ls = 82°-90° on Titan). This is interpreted as being due to a dramatic slowing and loss of confinement (broadening) of the recently discovered thermospheric equatorial jet, as a result of dynamical instability. These unexpectedly rapid changes in the upper-atmospheric dynamics are consistent with strong variability of the jet's primary driving mechanism.

Keywords: atmospheric circulation; doppler imaging; radio interferometry
Carbon Abundance of Globular Cluster M22 (NGC 6656) and the Surface Carbon Depletion Rates of the Milky Way Globular Clusters

It is well known that metal-poor red giant branch (RGB) stars show variations in some elemental abundances, including carbon, due to the internal mixing accompanied by their own in situ CN cycle in the hydrogen burning shell. With our new photometric carbon abundance measurements of RGB stars in M22 and other globular clusters (GCs) in our previous studies, M5, M3, and M92, we derive the carbon depletion rates against the V magnitude, d[C/Fe]/M V , for individual populations in each GC. We find the metallicity dependence of the carbon depletion rates, d[C/Fe]/M V ∝ -0.25[Fe/H]. Our results also suggest that the carbon depletion rates of the second generation (SG) of stars are larger than those of the first generation (FG) of stars in our sample GCs, most likely due to different internal temperature profiles with different initial helium abundances between the FG and SG. Our results can provide critical constraints both on understanding the mixing efficiency in the theoretical models, which is largely unknown, and on interpretation of the observational carbon abundance evolution of the bright halo RGB stars.

Keywords: stellar populations; population ii stars; globular star clusters; hertzsprung russell diagram; chemical abundances; stellar evolution; red giant branch; carbon-nitrogen cycle
A Pipeline for Modeling Rapidly Rotating Stars

Recent stellar intensity interferometry observations of stars at 416 nm complement Michelson interferometry observations in the near-infrared where stellar surface intensity gradients (e.g., limb darkening) are weaker. Intensity gradients due to gravity darkening in rapidly rotating stars are also expected to show higher contrast at 416 nm relative to the near-infrared. We have created a software pipeline to model stellar photospheres of rapidly rotating stars to compare predictions at these wavelength regions. The pipeline can produce model images, visibility predictions, and synthetic spectra. Here we show examples for the Be star β CMi, which has not been interferometrically imaged. We see higher contrast from gravity darkening at 416 nm in model images for rapid rotators, but only for those stars that are not viewed equator-on.

Keywords: astronomy data modeling; stellar photospheres; long baseline interferometry; stellar rotation; gravity darkening
The Great Dimming of Betelgeuse: A Surface Mass Ejection and Its Consequences

The bright supergiant, Betelgeuse (Alpha Orionis, HD 39801), underwent a historic optical dimming during 2020 January 27-February 13. Many imaging and spectroscopic observations across the electromagnetic spectrum were obtained prior to, during, and subsequent to this dimming event. These observations of Betelgeuse reveal that a substantial surface mass ejection (SME) occurred and moved out through the extended atmosphere of the supergiant. A photospheric shock occurred in 2019 January-March, progressed through the extended atmosphere of the star during the following 11 months and led to dust production in the atmosphere. Resulting from the substantial mass outflow, the stellar photosphere was left with lower temperatures and the chromosphere with a lower density. The mass ejected could represent a significant fraction of the total annual mass-loss rate from the star suggesting that episodic mass-loss events can contribute an amount comparable to that of the stellar wind. Following the SME, Betelgeuse was left with a cooler average photosphere, an unusual short photometric oscillation, reduced velocity excursions, and the disappearance of the ~400 day pulsation in the optical and radial velocity for more than two years following the Great Dimming.

Keywords: m supergiant stars; red supergiant stars; stellar mass loss; stellar chromospheres; stellar atmospheres
Supercatastrophic Disruption of Asteroids in the Context of SOHO Comet, Fireball, and Meteor Observations

Granvik et al. reported an absence of asteroids on orbits with perihelia near the Sun that they attribute to the "supercatastrophic disruption" of these bodies. Here we investigate whether there is evidence for this process among other bodies with similarly low perihelia: near-Earth asteroids, Solar and Heliospheric Observatory (SOHO) comets, and meter- and millimeter-sized meteoroids. We determine that no known near-Earth asteroids have past (last 104 yr) histories residing significantly inside the Granvik et al. limit, indirectly supporting the disruption hypothesis. The exception is asteroid (467372) 2004 LG, which spent 2500 yr within this limit and thus presents a challenge to that theory. Phaethon has a perihelion distance hovering just above the limit and may be undergoing slow disruption, which may be the source of its dust complex. We find that the rate at which ungrouped SOHO comets are observed is consistent with expected rates for the injection of small (25 m) class asteroids into the near-Sun region and suggest that this fraction of the SOHO-observed comet population may in fact be asteroidal in origin. We also find that there is an absence of meter-sized bodies with near-Sun perihelia but an excess of millimeter-sized meteoroids. This implies that if near-Sun asteroids disrupt, they do not simply fragment into meter-sized chunks but ultimately disintegrate into millimeter-sized particles. We propose that the disruption of near-Sun asteroids, as well as the anomalous brightening and destruction processes that affect SOHO comets, occur through meteoroid erosion, that is, the removal of material through impacts by high-speed near-Sun meteoroids.

Keywords: solar system; meteoroids; near-earth objects; comets; kreutz group; asteroids
White-light Continuum Observation of the Off-limb Loops of the SOL2017-09-10 X8.2 Flare: Temporal and Spatial Variations

Observations of the Sun's off-limb white-light (WL) flares offer rare opportunities to study the energy release and transport mechanisms in flare loops. One of the best such events was SOL2017-09-10, an X8.2 flare that occurred near the Sun's west limb on 2017 September 10 and produced a WL loop system lasting more than 60 minutes and reaching an altitude higher than 30 Mm. The event was well observed by a suite of ground- and space-based instruments, including the Solar Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI) that captured its off-limb loops in WL continuum near Fe I 6173 Å, and the Atmospheric Imager Assembly (SDO/AIA) that observed its ultraviolet (UV) and extreme-ultraviolet (EUV) counterparts. We found quasi-periodic pulsations in the WL and UV emissions at the flare loop-top with a period around 8.0 minutes. Each pulsation appears to have an EUV counterpart that occurs earlier in time and higher in altitude. Despite many similarities in the WL and UV images and light curves, the WL flux at the loop-top continues to grow for about 16 minutes while the UV fluxes gradually decay. We discuss the implication of these unprecedented observations on the understanding of the enigmatic off-limb WL flare emission mechanisms.

Keywords: solar activity; solar white-light flares; active solar corona; solar oscillations
Spectrophotometric Modeling and Mapping of (101955) Bennu

Using hyperspectral data collected by OVIRS, the visible and infrared spectrometer on board the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft, we modeled the global average spectrophotometric properties of the carbonaceous asteroid (101955) Bennu and mapped their variations. We restricted our analysis to 0.4-2.5 μm to avoid the wavelengths where thermal emission from the asteroid dominates (>2.5 μm). Bennu has global photometric properties typical of dark asteroids; we found a geometric albedo of 0.046 ± 0.007 and a linear phase slope of 0.024 ± 0.007 mag deg-1 at 0.55 μm. The average spectral slope of Bennu's normal albedo is -0.0030 μm-1, and the phase-reddening parameter is 4.3 × 10-4 μm-1 deg-1, both over the spectral range of 0.5-2.0 μm. We produced normal albedo maps and phase slope maps at all spectral channels, from which we derived spectral slope and phase-reddening maps. Correlation analysis suggests that phase slope variations on Bennu are likely due to photometric roughness variation. A correlation between photometric and thermal roughness is evident, implying that the roughness of Bennu is self-similar on scales from tens of microns to meters. Our analysis reveals latitudinal trends in the spectral color slope and phase reddening on Bennu. The equatorial region appears to be redder than the global average, and the spectral slope decreases toward higher latitudes. Phase reddening on Bennu is relatively weak in the equatorial region and shows an asymmetry between the northern and southern hemispheres. We attributed the latitudinal trend to the geophysical conditions on Bennu that result in a global pattern of mass flow toward the equator.

Keywords: surface photometry; astronomy data analysis; near-earth objects
Optimal Softening for Gravitational Force Calculations in N-body Dynamics

The choice of the optimal value of the softening length (ɛi) of each particle dealing with N-body simulations has a profound impact on error values in the gravitational force calculation. A slight deviation from its exact optimal value may result in a large error in the calculation. In this paper we augment the accuracy of the existing gravitational force calculation methods by providing a new technique to calculate the individual optimal values of ɛi for various configurations of the Plummer density model. We have proposed an expression ${\epsilon }_{\lambda ,i}={\lambda }_{i}{\left(\tfrac{{m}_{i}}{{\rho }_{i}}\right)}^{\tfrac{1}{3}}$ that relates each particle by considering the average characteristic length (λi) and density (ρi), unlike previous studies that considered ɛi as an exclusive function of ρi. We have performed gravitational force calculations for each and every particle from the Plummer density model using compact as well as noncompact gravitational force methods based on smoothed particle hydrodynamics. We have tested our new equation for the entire range of numerical simulations performed during the study. It is found that the errors in our force calculations are not only lower than those estimated from previous studies but also remain flat for various considerations of nearest neighboring particles (Nneigh). The adjusted expression of ɛλ,i in our study has less dependence on Nneigh in the Plummer sphere. Finally, based on the results obtained using the method proposed in this study, we find that it remarkably improves both the accuracy as well as the stability of the gravitational force calculation.

Keywords: newtonian gravitation; hydrodynamical simulations; astrophysical fluid dynamics; n-body problem
Refining the Census of the Upper Scorpius Association with Gaia

We have refined the census of stars and brown dwarfs in the Upper Sco association (∼10 Myr, ∼145 pc) by (1) updating the selection of candidate members from our previous survey to include the high-precision astrometry from the second data release of Gaia, (2) obtaining spectra of a few hundred candidate members to measure their spectral types and verify their youth, and (3) assessing the membership (largely with Gaia astrometry) of 2020 stars toward Upper Sco that show evidence of youth in this work and previous studies. We arrive at a catalog of 1761 objects that are adopted as members of Upper Sco. The distribution of spectral types among the adopted members is similar to those in other nearby star-forming regions, indicating a similar initial mass function. In previous studies, we have compiled mid-infrared photometry from the Wide-field Infrared Survey Explorer and the Spitzer Space Telescope for members of Upper Sco and used those data to identify the stars that show evidence of circumstellar disks; we present the same analysis for our new catalog of members. As in earlier work, we find that the fraction of members with disks increases with lower stellar masses, ranging from ≲10% for >1 M⊙ to ∼22% for 0.01-0.3 M⊙. Finally, we have estimated the relative ages of Upper Sco and other young associations using their sequences of low-mass stars in ${M}_{{G}_{\mathrm{RP}}}$ versus GBP - GRP. This comparison indicates that Upper Sco is a factor of two younger than the β Pic association (21-24 Myr) according to both nonmagnetic and magnetic evolutionary models. * Based on observations made with the Two Micron All Sky Survey, the Gaia mission, the NASA Infrared Telescope Facility, Cerro Tololo Inter-American Observatory, Gemini Observatory, the Magellan Baade Telescope at Las Campanas Observatory, and the Bok Reflector at Steward Observatory.

Keywords: brown dwarfs; protoplanetary disks; ob associations; star formation; circumstellar disks; initial mass function; stellar associations; low mass stars