adsabs/SciX_UAT_keywords huggingface dataset:
Surface Properties of Near-Sun Asteroids

Near-Earth asteroids (NEAs) with small perihelion distances reach subsolar temperatures of ≥1000 K. They are hypothesized to undergo "supercatastrophic" disruption, potentially caused by near-Sun processes such as thermal cracking, spin-up, meteoroid impacts, and subsurface volatile release, all of which are likely to cause surface alteration, which may change the spectral slope of the surface. We attempted to observe 35 of the 53 known near-Sun asteroids with q ≤ 0.15 au from 2017 January to 2020 March to search for trends related to near-Sun processes. We report the optical colors and spectral slopes of 22 objects that we successfully observed and the measured rotation periods for three objects. We find the distribution of colors to be overall bluer than the color distribution of NEAs, though there is a large overlap. We attribute the large scatter to unknown dynamical histories and compositions for individual objects, as well as competing surface altering processes. We also investigated potential correlations between colors and other properties (e.g., perihelion distance, Tisserand parameter, rotation period) and searched for evidence of activity. Finally, we have compiled all known physical and dynamical properties of these objects, including probabilistic source regions and dwell times with q ≤ 0.15 au.

Keywords: near-earth objects; small solar system bodies; asteroids; solar system astronomy; ground-based astronomy; optical astronomy
Probing Intra-Halo Light with Galaxy Stacking in CIBER Images

We study the stellar halos of 0.2 ≲ z ≲ 0.5 galaxies with stellar masses spanning M* ~ 1010.5 to 1012M⊙ (approximately L* galaxies at this redshift) using imaging data from the Cosmic Infrared Background Experiment (CIBER). A previous CIBER fluctuation analysis suggested that intra-halo light (IHL) contributes a significant portion of the near-infrared extragalactic background light (EBL), the integrated emission from all sources throughout cosmic history. In this work, we carry out a stacking analysis with a sample of ~30,000 Sloan Digital Sky Survey (SDSS) photometric galaxies from CIBER images in two near-infrared bands (1.1 and 1.8 μm) to directly probe the IHL associated with these galaxies. We stack galaxies in five sub-samples split by brightness and detect an extended galaxy profile beyond the instrument point-spread function (PSF) derived by stacking stars. We jointly fit a model for the inherent galaxy light profile plus large-scale one- and two-halo clustering to measure the extended galaxy IHL. We detect nonlinear one-halo clustering in the 1.8 μm band at a level consistent with numerical simulations. By extrapolating the fraction of extended galaxy light we measure to all galaxy mass scales, we find ~30%/15% of the total galaxy light budget from galaxies is at radius r > 10/20 kpc, respectively. These results are new at near-infrared wavelengths at the L* mass scale and suggest that the IHL emission and one-halo clustering could have appreciable contributions to the amplitude of large-scale EBL background fluctuations.

Keywords: diffuse radiation; near infrared astronomy; large-scale structure of the universe; galaxy evolution; cosmic background radiation
Galactic Extinction: How Many Novae Does It Hide and How Does It Affect the Galactic Nova Rate?

There is a long-standing discrepancy between the observed Galactic classical nova rate of ~10 yr-1 and the predicted rate from Galactic models of ~30-50 yr-1. One explanation for this discrepancy is that many novae are hidden by interstellar extinction, but the degree to which dust can obscure novae is poorly constrained. We use newly available all-sky three-dimensional dust maps to compare the brightness and spatial distribution of known novae to that predicted from relatively simple models in which novae trace Galactic stellar mass. We find that only half (53%) of the novae are expected to be easily detectable (g ≲ 15) with current all-sky optical surveys such as the All-Sky Automated Survey for Supernovae (ASAS-SN). This fraction is much lower than previously estimated, showing that dust does substantially affect nova detection in the optical. By comparing complementary survey results from the ASAS-SN, OGLE-IV, and Palomar Gattini IR surveys using our modeling, we find a tentative Galactic nova rate of ~30 yr-1, though this could be as high as ~40 yr-1, depending on the assumed distribution of novae within the Galaxy. These preliminary estimates will be improved in future work through more sophisticated modeling of nova detection in ASAS-SN and other surveys.

Keywords: classical novae; cataclysmic variable stars; novae; white dwarf stars
Emission of Magnetar Bursts and Precursors of Neutron Star Mergers

Magnetar bursts can be emitted by Alfvén waves growing in the outer magnetosphere to nonlinear amplitudes, δB/ B ~ 1, and triggering magnetic reconnection. Similar magnetic flares should occur quasi-periodically in a magnetized neutron star binary nearing merger. In both cases, fast dissipation in the magnetic flare creates optically thick e± plasma, whose heat capacity is negligible compared with the generated radiation energy. Magnetic dissipation then involves photon viscosity and acts through Compton drag on the plasma bulk motions in the reconnection region. The effective temperature of the resulting Comptonization process is self-regulated to tens of keV. The generated X-ray emission is calculated using time-dependent radiative transfer simulations, which follow the creation of e± pairs and the production, Comptonization, and escape of photons. The simulations show how the dissipation region becomes dressed in an e± coat and how the escaping spectrum is shaped by radiative transfer through the coat. The results are compared with observed magnetar bursts, including the recent activity of SGR 1935+2154 accompanied by a fast radio burst. Predictions are made for X-ray precursors of magnetized neutron star mergers.

Keywords: x-ray transient sources; neutron stars; magnetars; radiative processes; radio bursts; plasma astrophysics; radiative transfer
Are the Magnetic Field Directions of Surrounding Loops a Key Parameter for Confining a Solar Filament Eruption?

Using high-resolution Hα data from the 1 m New Vacuum Solar Telescope, combined with multiband Atmospheric Imaging Assembly extreme ultraviolet observations and Helioseismic and Magnetic Imager light-of-sight magnetograms from the Solar Dynamical Observatory, we study a quiet-Sun filament eruption on 2019 November 1. During the erupting process, the filament was blocked by at least three sets of surrounding loops (L1-L3). The magnetic field direction of L2 is opposite to that of the top segment of the erupting filament. While the top segment contacted L2, a current sheet formed between L2 and the top segment. Then, magnetic reconnection took place, resulting in the destruction of L2 and the filament. On the other hand, the magnetic field direction of L1 is the same as that of the left leg of the erupting filament, and that of L3 is the same as that of the right leg. The left leg expanded eastward and met L1, then it stopped. The right leg expanded westward and collided with L3. It rebounded and finally stopped at the interaction region. These observations imply that the magnetic field directions of the surrounding magnetic structures are a key parameter for confining a filament eruption. While the field direction of a surrounding structure is the same as that of an eruptive filament, the filament is confined.

Keywords: solar activity; solar filaments; solar prominences; solar magnetic reconnection; solar magnetic fields
Longevity Is the Key Factor in the Search for Technosignatures

It is well known that the chances of success of the search for extraterrestrial intelligence depend on the longevity of technological civilizations or, more broadly, on the duration of the signs of their existence, or technosignatures. Here, we re-examine this general tenet in more detail, and we show that its broader implications have not been given their proper significance. In particular, an often overlooked aspect is that the duration of a technosignature is in principle almost entirely separable from the age of the civilization that produces it. We propose a classification scheme of technosignatures based on their duration, and we use Monte Carlo simulations to show that, given an initial generic distribution of Galactic technosignatures, only the ones with the longest duration are likely to be detected. This tells us, among other things, that looking for a large number of short-lived technosignatures is a weaker observational strategy than focusing the search on a few long-lived ones. It also suggests abandoning any anthropocentric bias in approaching the question of extraterrestrial intelligence. We finally give some ideas of possible pathways that can lead to the establishment of long-lived technosignatures.

Keywords: astrobiology; search for extraterrestrial intelligence; technosignatures
The Triggering Process of an X-class Solar Flare on a Small Quadrupolar Active Region

The occurrence of X-class solar flares and their potential impact on space weather often receive greater attention than other flares. But predicting when and where an X-class flare will occur is still a challenge. With the multiwavelength observation from the Solar Dynamics Observatory and FengYun-3E satellite, we investigate the triggering of a GOES X1.0 flare occurring in the NOAA active region (AR) 12887. Our results show that this unique X-class flare is bred in a relatively small but complex quadrupolar AR. Before the X-class flare, two filaments (F1 and F2) exist below a null-point topology of the quadrupolar AR. Magnetic field extrapolation and observation reveal that F1 and F2 correspond to two magnetic flux ropes with the same chirality and that their adjacent feet are respectively rooted at nonconjugated opposite polarities. Interestingly, these two polarities collide rapidly, accompanied by photospheric magnetic flux emergence, cancellation, and shear motion in the AR center. Above this site, F1 and F2 subsequently intersect with each other and merge into a longer filament (F3) via a tether-cutting-like reconnection process. As a result, F3 rises and erupts upward, eventually leading to a coronal mass ejection and the X-class flare. This observation suggests that the rapid collision of nonconjugated opposite polarities provides a key condition for the triggering of this X-class flare and also provides a featured case for a flare trigger mechanism and space weather forecasting.

Keywords: space weather; solar active regions; solar magnetic fields; solar filaments; solar flares
The Challenge of Measuring Asteroid Masses with Gaia DR2 Astrometry

The Gaia second data release (DR2) contains high-accuracy astrometric measurements of thousands of solar system bodies. These measurements raise the possibility of determining asteroid masses by modeling scattering events between massive objects observed by Gaia. In this paper, we identify promising encounters between small asteroids that occur during DR2 and quantify the various errors involved in mass determination. We argue that, in the best case, Gaia astrometry can provide constraints as tight as ≈1 km on the positions of asteroids. Further, we find that even with general relativistic corrections, integrations of the solar system accumulate 1 km errors after 700 days. While not a problem for modeling DR2 astrometry, future Gaia data releases may require models accounting for additional effects such as gravitational harmonics of the sun and planets. Additionally, due to suboptimal astrometric uncertainty, the geometry of the observations, and the Gaia observing pattern there are much looser constraints as a result in most cases, with constraints being several orders of magnitude weaker in some cases. This suggests that accurate mass determination for the smallest asteroids will require additional observations, either from future Gaia data releases or from other sources. We provide a list of encounters that are most promising for further investigation.

Keywords: asteroid dynamics; asteroids; main belt asteroids
On the Use of Field RR Lyrae As Galactic Probes: IV. New Insights Into and Around the Oosterhoff Dichotomy

We discuss the largest and most homogeneous spectroscopic data set of field RR Lyrae variables (RRLs) available to date. We estimated abundances using both high-resolution and low-resolution (ΔS method) spectra for fundamental (RRab) and first overtone (RRc) RRLs. The iron abundances for 7941 RRLs were supplemented with similar estimates that are available in the literature, ending up with 9015 RRLs (6150 RRab, 2865 RRc). The metallicity distribution shows a mean value of ⟨[Fe/H]⟩ = -1.51 ± 0.01, and σ(standard deviation) = 0.41 dex with a long metal-poor tail approaching [Fe/H] ≃ - 3 and a sharp metal-rich tail approaching solar iron abundance. The RRab variables are more metal-rich (⟨[Fe/H]⟩ab = -1.48 ± 0.01, σ = 0.41 dex) than RRc variables (⟨[Fe/H]⟩c = -1.58 ± 0.01, σ = 0.40 dex). The relative fraction of RRab variables in the Bailey diagram (visual amplitude versus period) located along the short-period (more metal-rich) and the long-period (more metal-poor) sequences are 80% and 20%, while RRc variables display an opposite trend, namely 30% and 70%, respectively. We found that the pulsation period of both RRab and RRc variables steadily decreases when moving from the metal-poor to the metal-rich regime. The visual amplitude shows the same trend, but RRc amplitudes are almost two times more sensitive than RRab amplitudes to metallicity. We also investigated the dependence of the population ratio (Nc/Ntot) of field RRLs on the metallicity and we found that the distribution is more complex than in globular clusters. The population ratio steadily increases from ~0.25 to ~0.36 in the metal-poor regime, it decreases from ~0.36 to ~0.18 for -1.8 ≤ [Fe/H] ≤ -0.9 and it increases to a value of ~0.3 approaching solar iron abundance. * Based on observations obtained with the du Pont telescope at Las Campanas Observatory, operated by Carnegie Institution for Science. Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. Based partly on data obtained with the STELLA robotic telescopes in Tenerife, an AIP facility jointly operated by AIP and IAC. Some of the observations reported in this paper were obtained with the Southern African Large Telescope (SALT). Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere.

Keywords: rr lyrae variable stars; milky way stellar halo; spectroscopy
Astrophysical Implications on Hyperon Couplings and Hyperon Star Properties with Relativistic Equations of States

Hyperons are essential constituents in the neutron star interior. The poorly known hyperonic interaction is a source of uncertainty for studying laboratory hypernuclei and neutron star observations. In this work, we perform Bayesian inference of phenomenological hyperon-nucleon interactions using the tidal deformability measurement of the GW170817 binary neutron star merger as detected by LIGO/Virgo and the mass-radius measurements of PSR J0030+0541 and PSR J0740+6620 as detected by NICER. The analysis is based on a set of stiff relativistic neutron star matter equation of states with hyperons from the relativistic mean-field theory, naturally fulfilling the causality requirement and empirical nuclear matter properties. We specifically utilize the strong correlation recently deduced between the scalar and vector meson-hyperon couplings, imposed by the measured Λ separation energy in single-Λ hypernuclei, and perform four different tests with or without the strong correlation. We find that the laboratory hypernuclear constraint ensures a large enough Λ-scalar-meson coupling to match the large vector coupling in hyperon star matter. When adopting the current most probable intervals of hyperon couplings from the joint analysis of laboratory and astrophysical data, we find the maximum mass of hyperon stars is at most ${2.176}_{-0.202}^{+0.085}{M}_{\odot }$ (68% credible interval) from the chosen set of stiff equation of states. The reduction of the stellar radius due to hyperons is quantified based on our analysis and various hyperon star properties are provided.

Keywords: neutron star cores; neutron stars; gravitational waves; pulsars
Bayesian Analysis of Neutron-star Properties with Parameterized Equations of State: The Role of the Likelihood Functions

We have investigated the systematic differences introduced when performing a Bayesian-inference analysis of the equation of state (EOS) of neutron stars employing either variable- or constant-likelihood functions. The former has the advantage of retaining the full information on the distributions of the measurements, making exhaustive usage of the data. The latter, on the other hand, has the advantage of a much simpler implementation and reduced computational costs. In both approaches, the EOSs have identical priors and have been built using the sound speed parameterization method so as to satisfy the constraints from X-ray and gravitational waves observations, as well as those from chiral effective theory and perturbative quantum chromodynamics. In all cases, the two approaches lead to very similar results and the 90% confidence levels essentially overlap. Some differences do appear, but in regions where the probability density is extremely small and are mostly due to the sharp cutoff on the binary tidal deformability $\tilde{{\rm{\Lambda }}}\leqslant 720$ set in the constant-likelihood approach. Our analysis has also produced two additional results. First, an inverse correlation between the normalized central number density, n c,TOV/n s , and the radius of a maximally massive star, R TOV. Second, and most importantly, it has confirmed the relation between the chirp mass and the binary tidal deformability. The importance of this result is that it relates ${{ \mathcal M }}_{\mathrm{chirp}}$ , which is measured very accurately, and $\tilde{{\rm{\Lambda }}}$ , which contains important information on the EOS. Hence, when ${{ \mathcal M }}_{\mathrm{chirp}}$ is measured in future detections, our relation can be used to set tight constraints on $\tilde{{\rm{\Lambda }}}$ .

Keywords: neutron star cores; nuclear physics; bayesian statistics
Imaging Spectropolarimetry—A New Observing Mode on the Hubble Space Telescope's Advanced Camera for Surveys

Imaging spectropolarimetry is a new observing mode on the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope (HST) that was commissioned in Cycle 30 and is available to HST observers starting in Cycle 31 (i.e., from 2023). It is a technique that is accessible from ground-based observatories, but the superb spatial resolution afforded by HST/ACS combined with the slitless nature of HST/ACS grism spectroscopy opens up the possibility of studying polarized extended emission in a way that is not currently possible even with Adaptive Optics facilities on the ground. This mode could help to study interesting targets including (but not limited to) QSOs, active galactic nucleus and Radio Galaxies, ISM Dust Properties, Pre-Planetary Nebulae, Proto-Planetary and Debris Disks, Supernovae/Supernova Remnants, and solar system objects. This research note presents the preliminary results from the calibration programs used to calibrate imaging spectropolarimetry on HST/ACS.

Keywords: hubble space telescope; spectropolarimetry; astronomical techniques; polarimetry
Steady Wind-blown Cavities within Infalling Rotating Envelopes: Application to the Broad Velocity Component in Young Protostars

Wind-driven outflows are observed around a broad range of accreting objects throughout the universe, ranging from forming low-mass stars to supermassive black holes. We study the interaction between a central isotropic wind and an infalling, rotating envelope, which determines the steady-state cavity shape formed at their interface under the assumption of weak mixing. The shape of the resulting wind-blown cavity is elongated and self-similar, with a physical size determined by the ratio between wind ram pressure and envelope thermal pressure. We compute the growth of a warm turbulent mixing layer between the shocked wind and the deflected envelope, and calculate the resultant broad-line profile, under the assumption of a linear (Couette-type) velocity profile across the layer. We then test our model against the warm broad velocity component observed in CO J = 16-15 by Herschel/HIFI in the protostar Serpens-Main SMM1. Given independent observational constraints on the temperature and density of the dust envelope around SMM1, we find an excellent match to all its observed properties (line profile, momentum, temperature) and to the SMM1 outflow cavity width for a physically reasonable set of parameters: a ratio of wind to infall mass flux of ≃4%, a wind speed of vw ≃ 30 km s-1, an interstellar abundance of CO and H2, and a turbulent entrainment efficiency consistent with laboratory experiments. The inferred ratio of ejection to disk accretion rate, ≃6%-20%, is in agreement with current disk wind theories. Thus, the model provides a new framework to reconcile the modest outflow cavity widths in protostars with large observed flow velocities. Being self-similar, it is applicable over a broader range of astrophysical contexts as well.

Keywords: stellar jets; stellar winds; protostars; accretion; stellar-interstellar interactions; astrochemistry
Classifying Single Stars and Spectroscopic Binaries Using Optical Stellar Templates

Stellar spectral classification is a fundamental tool of modern astronomy, providing insight into physical characteristics such as effective temperature, surface gravity, and metallicity. Accurate and fast spectral typing is an integral need for large all-sky spectroscopic surveys like the Sloan Digital Sky Survey (SDSS) and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope. Here, we present the next version of PyHammer, a stellar spectral classification software that uses optical spectral templates and spectral line index measurements. PyHammer v2.0 extends the classification power to include dwarf carbon stars, DA white dwarf stars, and also double-lined spectroscopic binaries (SB2). This release also includes a new empirical library of luminosity-normalized spectra that can be used to flux calibrate observed spectra or to create synthetic SB2 spectra. We have generated physically reasonable SB2 combinations as templates, adding the ability to spectrally type SB2s to PyHammer. We test classification success rates on SB2 spectra, generated from the SDSS, across a wide range of spectral types and signal-to-noise ratios. Within the defined range of pairings described, more than 95% of SB2s are correctly classified.

Keywords: astronomy software; stellar classification; spectroscopic binary stars; carbon stars; white dwarf stars