adsabs/SciX_UAT_keywords huggingface dataset:
Baked before Breaking into Bits: Evidence for Atira-type Asteroid Splits

Current near-Earth asteroid orbital models cannot reproduce the observed populations close to the Sun. Supercatastrophic and tidal disruptions may explain the differences between theoretical models and observational data. Here, we explore the distributions of mutual nodal distances and the angular separation of perihelia of the known Atiras looking for evidence of past splittings. We find a number of pairs, trios, and one quartet of Atiras with mutual nodal distances as short as 0.001 au at the orbits of Mercury and Venus. The smallest of these highly correlated objects is 2023 WK3. Fragmentation or binary disruption may have triggered the recent formation of the unusual pair made of 594913 'Ayló'chaxnim (2020 AV2) and 2012 VE46 with both mutual nodal distance and angular separation of perihelia in the first percentile of the distribution, making 2012 VE46 a robust candidate to being a former moon or piece of 'Ayló'chaxnim.

Keywords: near-earth objects
Abrupt Shrinking of Solar Corona in the Late 1990s

We derive the longest uniform record of rotational intensities solar coronal magnetic field since 1968 and compare it with the heliospheric magnetic field (HMF) observed at the Earth. We scale the Mount Wilson Observatory and Wilcox Solar Observatory observations of the photospheric magnetic field to the level of the Synoptic Optical Long-term Investigations of the Sun/Vector Spectro Magnetograph and apply the potential field source surface model to calculate the coronal magnetic field. We find that the evolution of the coronal magnetic field during the last 50 yr agrees with the HMF observed at the Earth only if the effective coronal size, the distance of the coronal source surface of the HMF, is allowed to change in time. We calculate the optimum source surface distance for each rotation and find that it experienced an abrupt decrease in the late 1990s. The effective volume of the solar corona shrunk to less than one half during a short period of only a few years. We note that this abrupt shrinking coincides with other changes in solar magnetic fields that are likely related to the decrease of the overall solar activity, I.e., the demise of the Grand Modern Maximum.

Keywords: solar corona; solar magnetic fields; heliosphere; solar activity; solar physics; space weather
Transiting Exoplanet Monitoring Project (TEMP). VI. The Homogeneous Refinement of System Parameters for 39 Transiting Hot Jupiters with 127 New Light Curves

We present 127 new transit light curves for 39 hot Jupiter systems, obtained over the span of 5 yr by two ground-based telescopes. A homogeneous analysis of these newly collected light curves together with archived spectroscopic, photometric, and Doppler velocimetric data using EXOFASTv2 leads to a significant improvement in the physical and orbital parameters of each system. All of our stellar radii are constrained to accuracies of better than 3%. The planetary radii for 37 of our 39 targets are determined to accuracies of better than 5%. Compared to our results, the literature eccentricities are preferentially overestimated due to the Lucy-Sweeney bias. Our new photometric observations therefore allow for significant improvement in the orbital ephemerides of each system. Our correction of the future transit window amounts to a change exceeding 10 minutes for 10 targets at the time of James Webb Space Telescope's launch, including a 72 minutes change for WASP-56. The measured transit midtimes for both literature light curves and our new photometry show no significant deviations from the updated linear ephemerides, ruling out in each system the presence of companion planets with masses greater than 0.39-5.0 M⊕, 1.23-14.36 M⊕, 1.65-21.18 M⊕, and 0.69-6.75 M⊕ near the 1:2, 2:3, 3:2, and 2:1 resonances with the hot Jupiters, respectively, at a confidence level of ±1σ. The absence of resonant companion planets in the hot Jupiter systems is inconsistent with the conventional expectation from disk migration.

Keywords: exoplanet astronomy; exoplanet dynamics; exoplanet systems; exoplanets; hot jupiters; planet hosting stars
Relationship between Polytropic Index and Temperature Anisotropy in Space Plasmas

The paper develops a theoretical relationship between the polytropic index and the temperature anisotropy that may characterize space plasmas. The derivation is based on the correlation among the kinetic energies of particles with velocities described by anisotropic kappa distributions. The correlation coefficient depends on the effective dimensionality of the velocity distribution, which is determined by the temperature anisotropy caused by the ambient magnetic field; on the other hand, the effective dimensionality is directly dependent on the polytropic index. This analysis leads to the connection between the correlation coefficient, effective dimensionality of the velocity space, and the polytropic index, with the temperature anisotropy. Moreover, a data and statistical analysis is performed to test the developed model in the solar wind proton plasma near 1 au. The derived theoretical relationship is in good agreement with observations, showing that the lowest and classical value of the adiabatic polytropic index occurs in the isotropic case, while higher values of the adiabatic index characterize more anisotropic plasmas. Finally, possible extensions of the theory considering (i) nonadiabatic polytropic behavior and (ii) more general distributions, are further discussed.

Keywords: astronomy data analysis; space plasmas; plasma astrophysics; solar wind; slow solar wind; heliosphere
Coevolution and Nuclear Structure in the Dwarf Galaxy POX 52 Studied by Multiwavelength Data from Radio to X-Ray

The nearby dwarf galaxy POX 52 at z = 0.021 hosts an active galactic nucleus (AGN) with a black hole (BH) mass of M BH ~ 105-6 M ⊙ and an Eddington ratio of ~0.1-1. This object provides the rare opportunity to study both AGN and host-galaxy properties in a low-mass highly accreting system. To do so, we collected its multiwavelength data from X-ray to radio. First, we construct a spectral energy distribution, and by fitting it with AGN and host-galaxy components, we constrain AGN-disk and dust-torus components. Then, while considering the AGN-disk emission, we decompose optical Hubble Space Telescope images. As a result, it is found that a classical bulge component is probably present, and its mass (M bulge) is consistent with an expected value from a local relation. Lastly, we analyze new quasi-simultaneous X-ray (0.2-30 keV) data obtained by the Nuclear Spectroscopic Telescope Array and XMM-Newton. The X-ray spectrum can be reproduced by multicolor blackbody, warm and hot coronae, and disk and torus reflection components. Based on this, the spin is estimated to be a spin = 0.998-0.814, which could suggest that most of the current BH mass was achieved by prolonged mass accretion. Given the presence of the bulge, POX 52 would have undergone a galaxy merger, while the M BH-M bulge relation and the inferred prolonged accretion could suggest that AGN feedback occurred. Regarding the AGN structure, the spectral slope of the hot corona, its relative strength to the bolometric emission, and the torus structure are found to be consistent with Eddington-ratio dependencies found for nearby AGNs.

Keywords: astrophysical black holes; x-ray active galactic nuclei; active galactic nuclei; agn host galaxies; galaxy evolution; intermediate-mass black holes
Is [Y/Mg] a Reliable Age Diagnostic for FGK Stars?

Current spectroscopic surveys are producing large catalogs of chemical abundances for stars of all types. The yttrium-to-magnesium ratio, [Y/Mg], has emerged as a candidate age indicator for solar twins in the local stellar neighborhood. However, it is unclear whether it is a viable age diagnostic for more diverse stellar types, so we investigate [Y/Mg] as an age indicator for the FGK-type planet host stars observed by Kepler. We find that the [Y/Mg] "Clock" is most precise for solar twins, with a [Y/Mg]/age slope of m = -0.0370 ±0.0071 dex Gyr-1 and σ Age = 2.6 Gyr. We attribute the lower precision compared to literature results to nonsolar twins contaminating our solar twin sample and recommend a 1.5 Gyr systematic uncertainty for stellar ages derived with any [Y/Mg]-Age relation. We also analyzed the [Y/Mg] Clock as a function of T eff, $\mathrm{log}g$ , and metallicity individually and find no strong trends, but we compute statistically significant [Y/Mg]-Age relations for subsamples defined by ranges in T eff, $\mathrm{log}g$ , and metallicity. Finally, we compare [Y/Mg] and rotation ages and find statistically similar trends as for isochrone ages, although we find that rotation ages perform better for GK dwarfs while isochrones perform better for FG subgiants. We conclude that the [Y/Mg] Clock is most precise for solar twins and analogs but is also a useful age diagnostic for FGK stars.

Keywords: stellar evolutionary models; chemical abundances; abundance ratios; stellar properties; stellar ages; stellar rotation; planet hosting stars
State-switching Mechanism of Intermittent Pulsars

The emission feature of intermittent pulsars is significant for understanding the pulsar emission mechanism. Using the observational evidence of radio emissions turning on and off and the corresponding spin-down rates in these two states of an intermittent pulsar, we will examine the polar-cap potential drop, gap height, and curvature radii of a few intermittent pulsars within the regime of the pulsar polar-cap emission theory by applying the current loss and energy flux of particle flow to pulsar braking, which are generally associated with radio emission from the polar cap. It is seen that the polar-cap parameters of the intermittent pulsars are almost equal to their maximum values, which is the main prediction of the pulsar polar-cap theory with respect to the breaking of the radio emission. It is also noticed that the intermittent pulsars are distributed near the dipole death line in the $P\mbox{--}\dot{P}$ diagram, which is consistent with their emission features and the calculated polar-cap parameters. To further confirm the state switching of the intermittent pulsar, the relationships among spin-down rate, gap height, potential drop, and activity duty cycles of PSR B1931+24 are discussed. It is found that the gap height has an anticorrelation with the activity duty cycle, which indicates that the intermittency of the radio emission has a close connection to the gap height, as indicated by the pulsar polar-cap emission theory.

Keywords: pulsars; neutron stars
Hot Extended Galaxy Halos around Local L* Galaxies from Sunyaev-Zeldovich Measurements

Most of the baryons in L* galaxies are unaccounted for and are predicted to lie in hot gaseous halos (T ~ 106.5 K) that may extend beyond R 200. A hot gaseous halo will produce a thermal Sunyaev-Zeldovich signal that is proportional to the product of the gas mass and the mass-weighted temperature. To best detect this signal, we used a Needlet Independent Linear Combination all-sky Planck map that we produced from the most recent Planck data release, also incorporating WMAP data. The sample is 12 L* spiral galaxies with distances of 3-10 Mpc, which are spatially resolved so that contamination from the optical galaxy can be excluded. One galaxy, NGC 891, has a particularly strong SZ signal, and when excluding it, the stack of 11 galaxies is detected at about 4σ (declining with radius) and is extended to at least 250 kpc (≈R 200) at >99% confidence. The gas mass within a spherical volume to a radius of 250 kpc is 9.8 ± 2.8 × 1010 M ⊙, for T avg = 3 × 106 K. This is about 30% of the predicted baryon content of the average galaxy (3.1 × 1011 M ⊙), and about equal to the mass of stars, disk gas, and warm halo gas. The remaining missing baryons (≈1.4 × 1011 M ⊙, 40%-50% of the total baryon content) are likely to be hot and extend to the 400-500 kpc volume, if not beyond. The result is higher than predictions, but within the uncertainties.

Keywords: spiral galaxies; interstellar plasma; sunyaev-zeldovich effect
Secular Dynamics around a Supermassive black hole via Multipole Expansion

In galactic nuclei, the gravitational potential is dominated by the central supermassive black hole, so stars follow quasi-Keplerian orbits. These orbits are distorted by gravitational forces from other stars, leading to long-term orbital relaxation. The direct numerical study of these processes is challenging because the fast orbital motion imposed by the central black hole requires very small timesteps. An alternative approach, pioneered by Gauß, is to use the secular approximation of smearing out N stars over their Keplerian orbits, using K nodes along each orbit. In this study, we propose three novel improvements to this method. First, we reformulate the discretization of the rates of change of the variables describing the orbital states to ensure that all conservation laws are exactly satisfied. Second, we replace the pairwise sum over nodes by a multipole expansion up to order ${{\ell }}_{\max }$ , reducing the overall computational cost from O(N 2 K 2) to $O({NK}{{\ell }}_{\max }^{2})$ . Finally, we show that the averaged dynamical system is equivalent to 2N interacting unit spin vectors and provide two time integrators: a second-order symplectic scheme, and a fourth-order Lie-group Runge-Kutta method, both of which are straightforward to generalize to higher order. These new simulations recover the diffusion coefficients of stellar eccentricities obtained through analytical calculations of the secular dynamics.

Keywords: galactic center; galaxy nuclei; gravitation; celestial mechanics
Metastable Helium Absorptions with 3D Hydrodynamics and Self-consistent Photochemistry. II. WASP-107b, Stellar Wind, Radiation Pressure, and Shear Instability

This paper presents simulations of the metastable helium (He*) observations of WASP-107b, so far the highest signal-to-noise ratio detection that is confirmed by three different instruments. We employ full 3D hydrodynamics coupled with coevolving nonequilibrium thermochemistry and ray-tracing radiation, predicting mass-loss rates, temperature profiles, and synthetic He* line profiles and light curves from first principles. We find that a stellar wind stronger than solar is demanded by the observed heavily blueshifted line profile and asymmetric transit light curve. Radiation pressure can be important for Lyα observations, but not He*. Our model finds that WASP-107b is losing mass at a rate of $\dot{M}\simeq 1.0\times {10}^{-9}\,{M}_{\oplus }\,{\mathrm{yr}}^{-1}$ . Although $\dot{M}$ varies by <1% given constant wind and irradiation from the host, shear instabilities still emerge from wind impacts, producing ~10% fluctuations of He* transit depths over hour-long timescales. The common assumption that He* transit depth indicates the fluctuation of $\dot{M}$ is problematic. The trailing tail is more susceptible than planet adjacency to the shear instabilities; thus, the line profile is more variable in the blueshifted wing, while the transit light curve is more variable after midtransit. We stress that the synergy between Lyα (higher altitudes, lower density) and He* (lower altitudes, higher density) transit observations, particularly simultaneous ones, yields better understanding of planetary outflows and stellar wind properties.

Keywords: exoplanet atmospheres; exoplanet evolution; exoplanet astronomy; astrochemistry; hydrodynamical simulations; astronomical simulations; hydrodynamics
Near K-edge Photoionization and Photoabsorption of Singly, Doubly, and Triply Charged Silicon Ions

Experimental and theoretical results are presented for double, triple, and quadruple photoionization of Si+ and Si2+ ions and for double photoionization of Si3+ ions by a single photon. The experiments employed the photon-ion merged-beams technique at a synchrotron light source. The experimental photon-energy range 1835-1900 eV comprises resonances associated with the excitation of a 1s electron to higher subshells and subsequent autoionization. Energies, widths, and strengths of these resonances are extracted from high-resolution photoionization measurements, and the core-hole lifetime of K-shell ionized neutral silicon is inferred. In addition, theoretical cross sections for photoabsorption and multiple photoionization were obtained from large-scale multiconfiguration Dirac-Hartree-Fock calculations. The present calculations agree with the experiment much better than previously published theoretical results. The importance of an accurate energy calibration of laboratory data is pointed out. The present benchmark results are particularly useful for discriminating between silicon absorption in the gaseous and in the solid component (dust grains) of the interstellar medium.

Keywords: laboratory astrophysics
HCN and HCO+ in Planetary Nebulae: The Next Level

Observations of HCN and HCO+ have been carried out toward 13 planetary nebulae (PNe) using the facilities of the Arizona Radio Observatory (ARO). These nebulae represent a wide range of morphologies and ages (~2000-28,000 yr). For both molecules, the J = 1 → 0 transitions at 88-89 GHz and the J = 3 → 2 lines at 265-267 GHz were measured, together with CO lines (J = 1 → 0, 2 → 1, and 3 → 2, depending on the source), using the ARO 12 m and Submillimeter Telescopes. HCN and HCO+ were detected with at least one transition in 10 nebulae: He 2-459, Hu 1-1, K3-52, K3-65, M1-8, M1-40, M1-59, M2-53, M4-17, and NGC 6445. HCO+ was additionally identified via two transitions in Na 2. Some observed line profiles were complex, with multiple velocity components tracing varied outflows. From radiative transfer modeling, column densities were established for HCN and HCO+: N tot(HCN) = 0.005-1.1 × 1014 and N tot(HCO+) = 0.008-9.5 × 1013 cm-2. Gas densities of n(H2) ~ 105-107 cm-3 were also determined for all PNe. Fractional abundances with respect to H2, calculated using CO as a proxy, are f(HCN) ~ 0.2-1.5 × 10-7 and f(HCO+) ~ 0.3-5.1 × 10-8. The abundances of HCN and HCO+ did not significantly vary with nebular age to 28,000 yr. Combined with previous observations, at least 30 PNe contain HCN and/or HCO+, indicating that polyatomic molecules are common constituents of these objects. The data strongly support a scenario where dense ejecta from PNe seed the interstellar medium with molecular material.

Keywords: astrochemistry; planetary nebulae; radio astronomy; molecular spectroscopy; interstellar molecules
Using Machine Learning to Find Ghostly Damped Lyα Systems in the SDSS DR14

We report the discovery of 59 new ghostly absorbers from the Sloan Digital Sky Survey Data Release 14. These absorbers, with zabs ∼ zQSO, reveal no Lyα absorption, and they are mainly identified through the detection of strong metal absorption lines in the spectra. The number of such previously known systems is 30. The new systems are found with the aid of machine-learning algorithms. The spectra of 41 (out of total of 89) absorbers also cover the Lyβ spectral region. By fitting the damping wings of the Lyβ absorption in the stacked spectrum of 21 (out of 41) absorbers with relatively stronger Lyβ absorption, we measured an H I column density of log N(H I) = 21.50. This column density is 0.5 dex higher than that of the previous work. We also found that the metal absorption lines in the stacked spectrum of the 21 ghostly absorbers with stronger Lyβ absorption have similar properties as those in the stacked spectrum of the remaining systems. This circumstantial evidence strongly suggests that the majority of our ghostly absorbers are indeed DLAs.

Keywords: interstellar absorption; interstellar line absorption; quasars; quasar absorption line spectroscopy; active galactic nuclei; intergalactic medium; circumgalactic medium
Were the Obliquities in DI Herculis Excited by an Unseen Tertiary Companion?

The eclipsing binary DI Herculis has garnered interest for several decades because of an apparent disagreement between the observed and calculated values of the apsidal precession rate. The problem was resolved when both stars were found to have high obliquities, but the reason for the high obliquities is unknown. Here, we investigate the possibility that the obliquities are (or were) excited by an unseen tertiary star. Obliquity excitation in the current orbital configuration can be ruled out with existing data; any tertiary star that is sufficiently close or massive to overcome the strong spin-orbit coupling of the binary would have been detected through various dynamical effects. It remains possible that the orbit of DI Herculis was initially wider and the obliquity was excited during high-eccentricity tidal migration driven by a tertiary companion, but in this scenario it would be difficult to explain why the observed spin rates are much faster than the pseudo-synchronous rate. In addition, inward migration is most likely to arise when the mass of the perturbing star is comparable to the binary mass, and such a bright tertiary would have been detected in imaging or spectroscopic data. Alternative explanations that do not invoke a tertiary star should be sought for the large obliquities in DI Herculis.

Keywords: binary stars; close binary stars; eclipsing binary stars; multiple stars
Global Sky Models can Improve Flux Estimates in Pulsar and FRB Studies

It is commonplace in pulsar and fast radio burst literature to estimate sky temperature by frequency-scaling of the Haslam et al. 408 MHz map. I suggest that this practice should stop, in favor of using readily available global sky models of diffuse foregrounds. This practical change will improve accuracy of pulse flux estimates.

Keywords: pulsars; radio transient sources; calibration; flux calibration
Testing a New Model of Embedded Protostellar Disks against Observations: The Majority of Orion Class 0/I Disks Are Likely Warm, Massive, and Gravitationally Unstable

We formulate a parameterized model of embedded protostellar disks and test its ability to estimate disk properties by fitting dust-continuum observations. The main physical assumptions of our model are motivated by a recent theoretical study of protostellar disk formation; these assumptions include that the disk should be marginally gravitationally unstable, and that the dominant dust heating mechanism is internal accretion heating instead of external protostellar irradiation. These assumptions allow our model to estimate reliably the disk mass even when the observed emission is optically thick and to determine self-consistent disk (dust) temperatures. Using our model to fit multiwavelength observations of 163 disks in the VANDAM Orion survey, we find that the majority (57%) of this sample can be fit well by our model. Using our model, we produce new estimates of Orion protostellar disk properties. We find that these disks are generally warm and massive, with a typical star-to-disk mass ratio ${M}_{{\rm{d}}}/{M}_{\star }={ \mathcal O }(1)$ in Class 0/I. We also discuss why our estimates differ from those in previous studies and the implications of our results on disk evolution and fragmentation.

Keywords: stellar accretion disks; astronomy data modeling; gravitational instability