adsabs/SciX_UAT_keywords huggingface dataset:
On the Occurrence of Type IV Solar Radio Bursts in Solar Cycle 24 and Their Association with Coronal Mass Ejections

Solar activities, in particular coronal mass ejections (CMEs), are often accompanied by bursts of radiation at meter wavelengths. Some of these bursts have a long duration and extend over a wide frequency band, namely, type IV radio bursts. However, the association of type IV bursts with CMEs is still not well understood. In this article, we perform the first statistical study of type IV solar radio bursts in solar cycle 24. Our study includes a total of 446 type IV radio bursts that occurred during this cycle. Our results show that a clear majority, ∼81% of type IV bursts, were accompanied by CMEs, based on a temporal association with white-light CME observations. However, we found that only ∼2.2% of the CMEs are accompanied by type IV radio bursts. We categorized the type IV bursts as moving or stationary based on their spectral characteristics and found that only ∼18% of the total type IV bursts in this study were moving type IV bursts. Our study suggests that type IV bursts can occur with both "Fast" (≥500 km s-1) and "Slow" (<500 km s-1), and also both "Wide" (≥60°) and "Narrow" (<60°), CMEs. However, the moving type IV bursts in our study were mostly associated with "Fast" and "Wide" CMEs (∼52%), similar to type II radio bursts. Contrary to type II bursts, stationary type IV bursts have a more uniform association with all CME types.

Keywords: solar activity; solar corona; solar coronal mass ejections; radio bursts; sunspots
A Selection of 23 Bright Hypervelocity Gaia DR3 Stars

From the Gaia DR3 data twenty three bright hypervelocity stars that have Tycho catalogue numbers are presented. All these stars are of high galactic latitude and some may be galactic halo stars. All of them have accurate Gaia DR3 parallaxes and radial velocities. There is hardly any relevant literature on some of these stars. The Gaia DR3 astrophysical parameters of some of these stars indicate that they are of late spectral types and some are metal-poor. The astrophysical parameters are available for some of these stars in the literature but they differ from the Gaia DR3 results. Detailed chemical composition determination of these stars from an analysis of high resolution spectra is very much needed to further understand the evolutionary status and how these stars acquired such high radial velocities.

Keywords: hypervelocity stars
Apparent Effect of Dust Extinction on the Observed Outflow Velocity of Ionized Gas in Galaxy Mergers

In this study, we examine photoionization outflows during the late stages of galaxy mergers, with a specific focus on the relation between the observed velocity of outflowing gas and the apparent effects of dust extinction. We used the N-body/smoothed particle hydrodynamics code ASURA for galaxy merger simulations. These simulations concentrated on identical galaxy mergers featuring supermassive black holes of 108 M ⊙ and gas fractions of 30% and 10%. From the simulation data, we derived velocity and velocity dispersion diagrams for the active galactic nuclei (AGN)-driven ionized outflowing gas. Our findings show that high-velocity outflows with velocity dispersions of 500 km s-1 or greater can be observed in the late stages of galactic mergers. Particularly, in buried AGNs, both the luminosity-weighted outflow velocity and velocity dispersion increase owing to the apparent effects of dust extinction. Owing to these effects, velocity-velocity dispersion diagrams display a noticeable blue-shifted tilt in models with higher gas fractions. Crucially, this tilt is not influenced by the AGN luminosity but emerges from the observational impacts of dust extinction. Our results imply that the observed high-velocity [O III] λ5007 outflow exceeding 1000 km s-1 in buried AGNs may be linked to the dust extinction that occurs during the late stages of gas-rich galaxy mergers.

Keywords: galactic center; galaxy mergers; active galactic nuclei; high-luminosity active galactic nuclei; hydrodynamical simulations
Nondetection of the Gamma-Ray Burst X-Ray Emission Line: The Down-Comptonization Effect

The detection of the gamma-ray burst (GRB) X-ray emission line is important for studying GRB physics and constraining the GRB redshift. Since the line-like feature in the GRB X-ray spectrum was first reported in 1999, several works on line searching have been published over the past two decades. Even though some observations on the X-ray line-like feature were performed, its significance remains controversial to date. In this paper, we utilize the down-Comptonization mechanism and present the time evolution of the Fe Kα line emitted near the GRB central engine. The line intensity decreases with the evolution time, and the time evolution depends on the electron density and the electron temperature. In addition, the initial line with a larger broadening decreases less over time. For instance, when the emission line penetrates material with an electron density above 1012 cm-3 at 1 keV, it generally becomes insignificant enough after 100 s for it not to be detected . The line-like profile deviates from the Gaussian form, and it finally changes to be similar to a blackbody shape at the time of the thermal equilibrium between the line photons and the surrounding material.

Keywords: gamma-ray bursts; x-ray detectors
Evidence for a Nondichotomous Solution to the Kepler Dichotomy: Mutual Inclinations of Kepler Planetary Systems from Transit Duration Variations

Early analyses of exoplanet statistics from the Kepler mission revealed that a model population of multiplanet systems with low mutual inclinations (~1°-2°) adequately describes the multiple-transiting systems but underpredicts the number of single-transiting systems. This so-called "Kepler dichotomy" signals the existence of a subpopulation of multiplanet systems possessing larger mutual inclinations. However, the details of these inclinations remain uncertain. In this work, we derive constraints on the intrinsic mutual inclination distribution by statistically exploiting transit duration variations (TDVs) of the Kepler planet population. When planetary orbits are mutually inclined, planet-planet interactions cause orbital precession, which can lead to detectable long-term changes in transit durations. These TDV signals are inclination sensitive and have been detected for roughly two dozen Kepler planets. We compare the properties of the Kepler-observed TDV detections to TDV detections of simulated planetary systems constructed from two population models with differing assumptions about the mutual inclination distribution. We find strong evidence for a continuous distribution of relatively low mutual inclinations that is well characterized by a power-law relationship between the median mutual inclination ( ${\tilde{\mu }}_{i,n}$ ) and the intrinsic multiplicity (n): ${\tilde{\mu }}_{i,n}={\tilde{\mu }}_{i,5}{(n/5)}^{\alpha }$ , where ${\tilde{\mu }}_{i,5}={1.10}_{-0.11}^{+0.15}$ and $\alpha =-{1.73}_{-0.08}^{+0.09}$ . These results suggest that late-stage planet assembly and possibly stellar oblateness are the dominant physical origins for the excitation of Kepler planet mutual inclinations.

Keywords: exoplanets; exoplanet systems; exoplanet catalogs; exoplanet detection methods; exoplanet dynamics; transit duration variation method; planetary system formation; exoplanet formation
A Volatile-poor Formation of LHS 3844b Based on Its Lack of Significant Atmosphere

Exoplanet discoveries have reached into the realm of terrestrial planets that are becoming the subject of atmospheric studies. One such discovery is LHS 3844b, a 1.3 Earth radius planet in a 0.46 day orbit around an M4.5-5 dwarf star. Follow-up observations indicate that the planet is largely devoid of substantial atmosphere. This lack of significant atmosphere places astrophysical and geophysical constraints on LHS 3844b, primarily the degree of volatile outgassing and the rate of atmosphere erosion. We estimate the age of the host star as 7.8 ± 1.6 Gyr and find evidence of an active past comparable to that of Proxima Centauri. We use geodynamical models of volcanic outgassing and atmospheric erosion to show that the apparent lack of atmosphere is consistent with a volatile-poor mantle for LHS 3844b. We show the core is unlikely to host enough C to produce a sufficiently volatile-poor mantle, unless the bulk planet is volatile-poor relative to Earth. While we cannot rule out a giant impact stripping LHS 3844b's atmosphere, we show that this mechanism would require significant mantle stripping, potentially leaving LHS 3844b as an Fe-rich "super-Mercury." Atmospheric erosion by smaller impacts is possible, but only if the planet has already begun degassing and is bombarded by 103 impactors of radius 500-1000 km traveling at escape velocity. We discuss formation and migration scenarios that could account for a volatile-poor origin, including the potential for an unobserved massive companion planet. A relatively volatile-poor composition of LHS 3844b suggests that the planet formed interior to the system snow line.

Keywords: exoplanets; stellar activity; exoplanet atmospheres; planetary interior; planet formation
Looking for Astrometric Signals below 20 m s-1: A Jupiter-mass Planet Signature in ɛ Eri

The USNO ground-based astrometric program URAT-Bright in combination with the Hipparcos mission epoch astrometry provides precise proper motions of a thousand bright stars in the southern hemisphere on a time basis of about 25 yr. Small but statistically significant differences between these proper motions and Gaia EDR3 data can reveal long-period exoplanets similar to Jupiter in the nearest star systems. The presence of such a planet orbiting the magnetically active dwarf ɛ Eri is confirmed from both URAT-Hipparcos-EDR3 data and Hipparcos-EDR3 data with a corresponding projected velocity of (+5, +8) and (+6, +13) m s-1, respectively. These signals are formally significant at a 0.989 and 1.0 confidence. We conclude that the newest astrometric results confirm the existence of a long-period exoplanet orbiting ɛ Eri, which was marginally detected from precision radial velocity measurements some 20 yr ago.

Keywords: astrometric exoplanet detection; proper motions
Can Proton Beam Heating Flare Models Explain Sunquakes?

Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI) observations reveal a class of solar flares with substantial energy and momentum impacts in the photosphere, concurrent with white-light emission and helioseismic responses, known as sunquakes. Previous radiative hydrodynamic modeling has demonstrated the challenges of explaining sunquakes in the framework of the standard flare model of "electron beam" heating. One of the possibilities to explain the sunquakes and other signatures of the photospheric impact is to consider additional heating mechanisms involved in solar flares, for example via flare-accelerated protons. In this work, we analyze a set of single-loop Fokker-Planck and radiative hydrodynamics RADYN+FP simulations where the atmosphere is heated by nonthermal power-law-distributed proton beams which can penetrate deeper than the electron beams into the low atmospheric layers. Using the output of the RADYN models, we calculate synthetic Fe I 6173 Å line Stokes profiles and from those the line-of-sight observables of the SDO/HMI instrument, as well as the 3D helioseismic response, and compare them with the corresponding observational characteristics. These initial results show that the models with proton beam heating can produce the enhancement of the HMI continuum observable and explain qualitatively the generation of sunquakes. The continuum observable enhancement is evident in all models but is more prominent in ones with E c ≥ 500 keV. In contrast, the models with E c ≤ 100 keV provide a stronger sunquake-like helioseismic impact according to the 3D acoustic modeling, suggesting that low-energy (deka- and hecto-keV) protons have an important role in the generation of sunquakes.

Keywords: solar white-light flares; helioseismology; hydrodynamical simulations; spectropolarimetry
Reaction Pathway and Rovibrational Analysis of Aluminum Nitride Species as Potential Dust Grain Nucleation Agents

A dust nucleating agent may be present in interstellar or circumstellar media that has gone seemingly undetected and unstudied for decades. Some analyses of the Murchison CM2 meteorite suggest that at least some of the aluminum present within condensed as aluminum nitrides instead of the long-studied, but heretofore undetected suite of aluminum oxides. The present theoretical study utilizes explicitly correlated coupled cluster theory and density functional theory to provide a formation pathway from alane (AlH3) and ammonia to the cyclic structure Al2N2H4, which has the proper Al/N ratio expected of bulk aluminum nitrides. Novel rovibrational spectroscopic constants are computed for alane and the first two formed structures, AlNH6 and AlNH4, along the reaction pathway for use as reference in possible laboratory or observational studies. The ν 8 bending frequency for AlNH6 at 755.7 cm‑1 (13.23 μm) presents a vibrational transition intensity of 515 km mol‑1, more intense than the antisymmetric C‑O stretch of carbon dioxide, and contains a dipole moment of 5.40 D, which is ∼3× larger than that of water. Thus, the present reaction pathway and rovibrational spectroscopic analysis may potentially assist in the astrophysical detection of novel, inorganic species which may be indicative of larger dust grain nucleation.

Keywords: astrochemistry; interdisciplinary astronomy; neutral-neutral reactions; quantum-chemical calculations; molecular spectroscopic constants
Chromospheric Heating by Acoustic Waves Compared to Radiative Cooling. II. Revised Grid of Models

Acoustic and magnetoacoustic waves are considered to be possible agents of chromospheric heating. We present a comparison of deposited acoustic energy flux with total integrated radiative losses in the middle chromosphere of the quiet Sun and a weak plage. The comparison is based on a consistent set of high-resolution observations acquired by the Interferometric Bidimensional Spectrometer instrument in the Ca II 854.2 nm line. The deposited acoustic-flux energy is derived from Doppler velocities observed in the line core and a set of 1737 non-local thermodynamic equilibrium 1D hydrostatic semi-empirical models, which also provide the radiative losses. The models are obtained by scaling the temperature and column mass of five initial models by Vernazza et al. (1981; VAL) B-F to get the best fit of synthetic to observed profiles. We find that the deposited acoustic-flux energy in the quiet-Sun chromosphere balances 30%-50% of the energy released by radiation. In the plage, it contributes by 50%-60% in locations with vertical magnetic field and 70%-90% in regions where the magnetic field is inclined more than 50° to the solar surface normal.

Keywords: solar chromospheric heating; plages; solar chromosphere
Effects of Spectral Resolution on Simple Magnetic Field Diagnostics of the Mg II H and K Lines

We study the effects of finite spectral resolution on the magnetic field values retrieved through the weak-field approximation (WFA) from the cores of the Mg II h and k lines. The retrieval of the line-of-sight component of the magnetic field, B LOS, from synthetic spectra generated in a uniformly magnetized FAL-C atmosphere is accurate when restricted to the inner lobes of Stokes V. As we degrade the spectral resolution, partial redistribution effects, which more prominently affect the outer lobes of Stokes V, are brought into the line core through spectral smearing, degrading the accuracy of the WFA and resulting in an inference bias, which is more pronounced as the resolution becomes poorer. When applied to a diverse set of spectra emerging from a sunspot simulation, we find good accuracy in the retrieved B LOS when comparing it to the model value at the height where the optical depth in the line core is unity. The accuracy is preserved up to field strengths of B ~ 1500 G. Limited spectral resolution results in a small bias toward weaker retrieved fields. The WFA for the transverse component of the magnetic field is also evaluated. Reduced spectral resolution degrades the accuracy of the inferences, because spectral mixing results in the line effectively probing deeper layers of the atmosphere.

Keywords: solar magnetic fields; solar chromosphere; spectropolarimetry
Luminosity Functions and Host-to-host Scatter of Dwarf Satellite Systems in the Local Volume

Low-mass satellites around Milky Way (MW)-like galaxies are important probes of small-scale structure and galaxy formation. However, confirmation of satellite candidates with distance measurements remains a key barrier to fast progress in the Local Volume (LV). We measure the surface brightness fluctuation distances to recently cataloged candidate dwarf satellites around 10 massive hosts within D < 12 Mpc to confirm association. The satellite systems of these hosts are complete and mostly cleaned of contaminants down to Mg ∼ -9 to -10, within the area of the search footprints. Joining this sample with hosts surveyed to comparable or better completeness in the literature, we explore how well cosmological simulations combined with common stellar to halo mass relations (SHMR) match observed satellite luminosity functions in the classical satellite luminosity regime. Adopting an SHMR that matches hydrodynamic simulations, we find that the predicted overall satellite abundance agrees well with the observations. The MW is remarkably typical in its luminosity function among LV hosts. We find that the host-to-host scatter predicted by the model is in close agreement with the scatter between the observed systems, once the different masses of the observed systems are taken into account. However, we find significant evidence that the observed systems have more bright and fewer faint satellites than the SHMR model predicts, possibly necessitating a higher normalization of the SHMR around halo masses of 1011 M⊙ or significantly greater scatter than present in common SHMRs. These results demonstrate the utility of nearby satellite systems in inferring the galaxy-subhalo connection in the low-mass regime.

Keywords: dwarf galaxies; galaxy dark matter halos; galaxy distances; luminosity function
Abundance Patterns of α and Neutron-capture Elements in the Helmi Stream

We identified eight additional stars as members of the Helmi stream (HStr) in the combined GALAH+ DR3 and Gaia EDR3 catalog. By consistently reevaluating claimed members from the literature, we consolidate a sample of 22 HStr stars with parameters determined from high-resolution spectroscopy and spanning a considerably wider (by ∼0.5 dex) metallicity interval (- 2.5 ≲ [Fe/H] < - 1.0) than previously reported. Our study focuses on α (Mg and Ca) and neutron-capture (Ba and Eu) elements. We find that the chemistry of HStr is typical of dwarf spheroidal (dSph) galaxies, in good agreement with previous N-body simulations of this merging event. Stars of HStr constitute a clear declining sequence in [α/Fe] for increasing metallicity up to [Fe/H] ∼ -1.0. Moreover, stars of HStr show a median value of +0.5 dex for [Eu/Fe] with a small dispersion (±0.1 dex). Every star analyzed with [Fe/H] < -1.2 belongs to the r-process enhanced ([Eu/Fe] > +0.3 and [Ba/Eu] < 0.0) metal-poor category, providing remarkable evidence that, at such a low-metallicity regime, stars of HStr experienced enrichment in neutron-capture elements predominantly via r-process nucleosynthesis. Finally, the extended metallicity range also suggests an increase in [Ba/Eu] for higher [Fe/H], in conformity with other surviving dwarf satellite galaxies of the Milky Way.

Keywords: dwarf galaxies; milky way stellar halo; milky way dynamics; milky way evolution; milky way formation; population ii stars; stellar populations; chemical abundances; r-process
The Dispersion Measure and Scattering of Fast Radio Bursts: Contributions from the Intergalactic Medium, Foreground Halos, and Hosts

We investigate the dispersion measure (DM) and scattering of fast radio bursts (FRBs) by the intergalactic medium (IGM), foreground halos, and host halos using cosmological hydrodynamical simulation. We find that the median DM caused by foreground halos is around 30% of that caused by the IGM, but it has a much larger variance. The DM induced by hosts deviates from a log-normal distribution but exhibits an extended distribution in the range of $1\mbox{--}3000\,\mathrm{pc}\,{\mathrm{cm}}^{-3}$ with a median value $\sim 100\,\mathrm{pc}\,{\mathrm{cm}}^{-3}$ . Then we produce mock FRB sources, assuming a uniform distribution in the range $z\sim 0\mbox{--}0.82$ , to consider the propagation effect of IGM, foreground, and host halos on FRB signals simultaneously. The DM distribution of mock sources agrees well with the observation. The fitted DM-redshift relation of the mock sources can provide a rough estimation of the redshifts of observed events with errors $\delta z\lesssim 0.15$ . The distribution of mock sources in the DM scattering time (τ) space can also match the observation, assuming a Kolmogorov turbulence model where the inner and outer scales are 1000 km to 1 au and 0.2-10 pc, respectively. Finally, we estimate the relative importance of these media for DM and τ in our models. The IGM and host halos are the primary and secondary sources for the extragalactic DM ( ${\mathrm{DM}}_{\mathrm{exg}}$ ). Meanwhile, the contribution from foreground halos increases as ${\mathrm{DM}}_{\mathrm{exg}}$ increases. The host and foreground halos may be the most important media for scattering. Statistically, the latter may dominate the scattering of events with ${\mathrm{DM}}_{\mathrm{exg}}\gtrsim 200\,\mathrm{pc}\,{\mathrm{cm}}^{-3}$ .

Keywords: radio transient sources; intergalactic medium; circumgalactic medium; interstellar medium
The Sloan Digital Sky Survey Reverberation Mapping Project: How Broad Emission Line Widths Change When Luminosity Changes

Quasar broad emission lines are largely powered by photoionization from the accretion continuum. Increased central luminosity will enhance line emissivity in more distant clouds, leading to increased average distance of the broad-line-emitting clouds and decreased averaged line width, which is known as the "breathing" broad-line region. However, different lines breathe differently, and some high-ionization lines, such as C IV, can even show "anti-breathing" where the line broadens when luminosity increases. Using multi-year photometric and spectroscopic monitoring data from the Sloan Digital Sky Survey Reverberation Mapping project, we quantify the breathing effect ( ${\rm{\Delta }}\mathrm{log}W=\alpha {\rm{\Delta }}\mathrm{log}L$ ) of broad Hα, Hβ, Mg II, C IV, and C III] for statistical quasar samples over z ≈ 0.1-2.5. We find that Hβ displays the most consistent normal breathing expected from the virial relation (α ∼ -0.25), Mg II and Hα on average show no breathing (α ∼ 0), and C IV (and similarly C III] and Si IV) mostly shows anti-breathing (α > 0). The anti-breathing of C IV can be well understood by the presence of a non-varying core component in addition to a reverberating broad-base component, which is consistent with earlier findings. The deviation from canonical breathing introduces extra scatter (a luminosity-dependent bias) in single-epoch virial BH mass estimates due to intrinsic quasar variability, which underlies the long-argued caveats of C IV single-epoch masses. Using the line dispersion instead of FWHM leads to fewer, albeit still substantial, deviations from canonical breathing in most cases. Our results strengthen the need for reverberation mapping to provide reliable quasar BH masses and to quantify the level of variability-induced bias in single-epoch BH masses based on various lines.

Keywords: reverberation mapping; quasars; supermassive black holes