adsabs/SciX_UAT_keywords huggingface dataset:
Two-flavor Color Superconducting Quark Stars May Not Exist

Large uncertainties in the determinations of the equation of state of dense stellar matter allow for the intriguing possibility that the bulk quark matter in beta equilibrium might be the true ground state of the matter at zero pressure. Also, quarks will form Cooper pairs very readily since the dominant interaction between quarks is attractive in some channels. As a result, quark matter will generically exhibit color superconductivity, with the favored pairing pattern at intermediately high densities being two-flavor pairing. In the light of several possible candidates for such self-bound quark stars, including the very low-mass central compact object in supernova remnant HESS J1731-347 reported recently, we carry out a one-field theoretic model, the Nambu–Jona–Lasinio model, to investigate the stability of the beta-stable two-flavor color superconducting (2SC) phase of quark matter, but find no physically allowed parameter space for the existence of 2SC quark stars.

Keywords: compact objects; high energy astrophysics
TESS Spots a Super-puff: The Remarkably Low Density of TOI-1420b

We present the discovery of TOI-1420b, an exceptionally low-density (ρ = 0.08 ± 0.02 g cm-3) transiting planet in a P = 6.96 days orbit around a late G-dwarf star. Using transit observations from TESS, LCOGT, Observatoire Privé du Mont, Whitin, Wendelstein, OAUV, Ca l'Ou, and KeplerCam, along with radial velocity observations from HARPS-N and NEID, we find that the planet has a radius of R p = 11.9 ± 0.3R ⊕ and a mass of M p = 25.1 ± 3.8M ⊕. TOI-1420b is the largest known planet with a mass less than 50M ⊕, indicating that it contains a sizeable envelope of hydrogen and helium. We determine TOI-1420b's envelope mass fraction to be ${f}_{\mathrm{env}}={82}_{-6}^{+7} \% $ , suggesting that runaway gas accretion occurred when its core was at most four to five times the mass of the Earth. TOI-1420b is similar to the planet WASP-107b in mass, radius, density, and orbital period, so a comparison of these two systems may help reveal the origins of close-in low-density planets. With an atmospheric scale height of 1950 km, a transmission spectroscopy metric of 580, and a predicted Rossiter-McLaughlin amplitude of about 17 m s-1, TOI-1420b is an excellent target for future atmospheric and dynamical characterization.

Keywords: exoplanets; transits; exoplanet structure
Detection of the Diffuse H I Emission in the Circumgalactic Medium of NGC 891 and NGC 4565

We present detections of 21 cm emission from neutral hydrogen (H I) in the circumgalactic medium (CGM) of the local edge-on galaxies NGC 891 and NGC 4565 using the Robert C. Byrd Green Bank Telescope (GBT). With our 5σ sensitivity of $8.2\times {10}^{16}$ cm-2 calculated over a 20 km s-1 channel, we achieve $\gt 5\sigma $ detections out to $90\mbox{--}120\,\mathrm{kpc}$ along the minor axes. The velocity width of the CGM emission is as large as that of the disk $\approx 500$ km s-1, indicating the existence of a diffuse component permeating the halo. We compare our GBT measurements with interferometric data from the Westerbork Synthesis Radio Telescope (WSRT). The WSRT maps the H I emission from the disk at high signal-to-noise ratio but has limited surface brightness sensitivity at the angular scales probed with the GBT. After convolving the WSRT data to the spatial resolution of the GBT (FWHM = 9'1), we find that the emission detected by the WSRT accounts for ${48}_{-25}^{+15}$ % ( ${58}_{-18}^{+4}$ %) of the total flux recovered by the GBT from the CGM of NGC 891 (NGC 4565). The existence of significant GBT-only flux suggests the presence of a large amount of diffuse, low column density H I emission in the CGM. For reasonable assumptions, the extended diffuse H I could account for 5.2 ± 0.9% and 2.0 ± 0.8% of the total H I emission of NGC 891 and NGC 4565.

Keywords: circumgalactic medium; extragalactic astronomy; h i line emission; radio spectroscopy; single-dish antennas; diffuse radiation; extended radiation sources
The Complexity of Emerging Magnetic Flux during the Lifetime of Solar Ephemeral Regions

As a relatively active region, the ephemeral region (ER) exhibits a highly complex pattern of magnetic flux emergence. We aim to study in detail the secondary flux emergences (SFEs), which we define as bipoles that appear close to ERs and finally coalesce with ERs after a period of time. We study SFEs during the whole process, from the emergence to the decay of five ERs observed by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. The maximum unsigned magnetic flux for each ER is around 1020 Mx. Each ER has tens of SFEs with an average emerging magnetic flux of approximately 5 × 1018 Mx. The frequency of normalized magnetic flux for all the SFEs follows a power-law distribution with an index of ‑2.08. The majority of SFEs occur between the positive and negative polarities of an ER, and their growth time is concentrated within 1 hr. The magnetic axis of SFE is found to exhibit a random distribution in the five ERs. We suggest that the relationship between SFEs and ERs can be understood by regarding the photospheric magnetic field observations as cross sections of an emerging magnetic structure. Tracking the evolution of ERs, we propose that these SFEs in ERs may have emerged consequentially from the bundle of flux tubes of ERs and that SFEs are partially emerged Ω-loops.

Keywords: solar photosphere; solar physics; solar observatories; solar magnetic flux emergence; solar magnetic fields
Measurements of Titan's Stratospheric Winds during the 2009 Equinox with the eSMA

Saturn's moon Titan possesses stratospheric zonal winds that places it among a sparse class of planetary bodies known to have superrotation in their atmospheres. Few measurements have been made of these speeds in the upper stratosphere, leaving their seasonal variations still not well understood. We examined observations made with the extended Submillimeter Array in 2009 March (L s = 355°) and 2010 February (L s = 5°), shortly before and after Titan's northern spring equinox. Cassini observations and atmospheric models find equinoctial periods to be especially dynamic. Zonal wind calculations, derived from the Doppler frequency shift of CH3CN near 349.4 GHz, yielded speeds of 128 ± 27 m s‑1 in 2009 and 209 ± 48 m s‑1 in 2010. We estimated the measured emission to originate from vertical altitudes of ${336}_{-88}^{+112}$ km, equivalent to pressures of ${3.8}_{-3.4}^{+19.2}$ Pa, commensurate with Titan's upper stratosphere/lower mesosphere. This suggests a possible increase in zonal speeds during this period. The results are then compared to those from previous Cassini-inferred and direct-interferometric observations of winds, as well as general circulation model simulations, to form a more complete picture of the seasonal cycle of stratospheric zonal winds.

Keywords: titan; saturnian satellites; submillimeter astronomy; radio astronomy; natural satellite atmospheres; planetary science; atmospheric dynamics; atmospheric variability; planetary atmospheres
An Ap Star Catalog Based on LAMOST DR9

We present a sample of 2700 Ap stars in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) DR9 catalog. The candidates are first selected to be in a temperature range typical of Ap stars by using the BP - RP color index from Gaia DR3. Then the 5200 Å flux depression features characteristic of Ap stars are visually checked in LAMOST DR9 spectra. The detailed spectral features are given by applying a modified spectral classification program, MKCLASS. The stellar parameters of these Ap stars, such as the T eff, $\mathrm{log}g$ , [Fe/H], [Si/H], and $v\sin i$ , are either extracted from a hot star catalog or derived through empirical relations and then a statistical analysis is carried out. The evolutionary stages are also discussed. Finally, we discuss the rotation and pulsation features of those that have TESS or Kepler light curves. Among these Ap stars, we find seven new rotation variables, one new roAp star, and a new δ Scuti pulsation of a previously known roAp star.

Keywords: chemically peculiar stars; ap stars; chemical abundances; astronomy data analysis; variable stars
Shock Synthesis of Organic Molecules by Meteoroids in the Atmosphere of Titan

Thermochemical modeling and shock-tube experiments show that shocks applied to N2/CH4 gas mixtures can synthesize organic molecules. Sufficiently large, hypersonic meteoroids entering the atmosphere of Saturn's moon Titan should therefore drive organic chemistry. To do so meteoroids must be sufficiently large compared to the atmospheric mean free path at a given altitude to generate shocks, and deposit enough energy per path length to produce temperatures high enough to excite and dissociate the relevant molecules. The Cassini spacecraft imaged multiple meteoroid impacts on Saturn's rings, allowing for the first time an empirical estimate to be made of the flux and size-frequency distributions of meteoroids in the millimeter-to-meter size range. We combine these results with an atmospheric entry model and thermochemical and experimental shock production efficiencies for N2/CH4 atmospheres and calculate the shock production rates for HCN, C2H2, and C2H4 as well as the resulting H2 generation. We find that meteoroids may be producing these molecules at as much as ~1% the production rate of photochemistry driven by UV photons, and may be depositing more energy than magnetospheric ions and 90-100 nm UV photons. Moreover, these meteoroids produce these organic molecules hundreds of kilometers lower in Titan's atmosphere than the relevant UV photons and magnetospheric ions penetrate, with peak production occurring between 200 and 500 km altitudes, i.e., at the observed haze layer. Meteoroid-driven shock generation of molecules may therefore be crucial to understanding Titan's atmospheric chemistry.

Keywords: titan; natural satellite atmospheres
Differences between the Pierre Auger Observatory and Telescope Array Spectra: Systematic Effects or Indication of a Local Source of Ultra-high-energy Cosmic Rays?

The Pierre Auger Observatory (PAO) and Telescope Array (TA) collaborations report significant differences in the observed energy spectra of ultra-high-energy cosmic rays (UHECRs) above 30 EeV. In this work we present a joint fit of TA and PAO data using the rigidity-dependent maximum energy model, including a full marginalization over all relevant parameters. We test two possible scenarios to explain these differences. One is that they are due to complex energy-dependent experimental systematics; the other is the presence of a local astrophysical source in the Northern Hemisphere, which is only visible by the TA experiment. We show that the astrophysical and systematic scenarios improve the explanation of the data equally well, compared to the scenario where both experiments observe the same UHECR flux from a cosmological source distribution and have energy-independent systematics. We test different mass compositions emitted from the local source and conclude that the data are best described by a source lying at a distance below 26 Mpc that emits cosmic rays dominated by the silicon mass group. We also discuss possible source candidates and the possible role of the putative local UHECR source in the observed TA anisotropy and in the differences in TA spectral data from different decl. bands.

Keywords: high energy astrophysics; neutrino astronomy; cosmic rays
2FHL J1745.1–3035: A Newly Discovered, Powerful Pulsar Wind Nebula Candidate

We present a multi-epoch, multi-observatory X-ray analysis for 2FHL J1745.1–3035, a newly discovered very high-energy Galactic source detected by the Fermi Large Area Telescope (LAT) located in close proximity to the Galactic Center (l = 358.°5319; b = ‑0.°7760). The source shows a very hard γ-ray photon index above 50 GeV, Γ γ = 1.2 ± 0.4, and is found to be a TeV emitter by the Fermi–LAT. We conduct a joint XMM-Newton, Chandra, and NuSTAR observing campaign, combining archival XMM-Newton observations, to study the X-ray spectral properties of 2FHL J1745.1–3035 over a time span of over 20 yr. The joint X-ray spectrum is best fitted as a broken-power-law model with break energy E b ∼ 7 keV: the source is very hard at energies below 10 keV, with Γ1 ∼ 0.6, and significantly softer in the higher energy range measured by NuSTAR with Γ2 ∼ 1.9. We also perform a spatially resolved X-ray analysis with Chandra, finding evidence for marginal extension (up to an angular size r ∼ 5″), a result that supports a compact pulsar wind nebula scenario. Based on the X-ray and γ-ray properties, 2FHL J1745.1–3035 is a powerful pulsar wind nebula candidate. Given its nature as an extreme TeV emitter, further supported by the detection of a coincident TeV extended source HESS J1745-303, 2FHL J1745.1–3035 is an ideal candidate for a follow up with the upcoming Cherenkov Telescope Array.

Keywords: pulsar wind nebulae; supernova remnants; high energy astrophysics; gamma-ray astronomy; x-ray identification
Energy Transfer, Discontinuities, and Heating in the Inner Heliosphere Measured with a Weak and Local Formulation of the Politano-Pouquet Law

The solar wind is a highly turbulent plasma for which the mean rate of energy transfer ɛ has been measured for a long time using the Politano-Pouquet (PP98) exact law. However, this law assumes statistical homogeneity that can be violated by the presence of discontinuities. Here, we introduce a new method based on the inertial dissipation ${{ \mathcal D }}_{{\rm{I}}}^{\sigma }$ whose analytical form is derived from incompressible magnetohydrodynamics; it can be considered as a weak and local (in space) formulation of the PP98 law whose expression is recovered after integration in space. We used ${{ \mathcal D }}_{{\rm{I}}}^{\sigma }$ to estimate the local energy transfer rate at scale σ from the THEMIS-B and Parker Solar Probe data taken in the solar wind at different heliospheric distances. Our study reveals that discontinuities near the Sun lead to a strong energy transfer that affects a wide range of scales σ. We also observe that switchbacks seem to be characterized by a singular behavior with an energy transfer varying as σ -3/4, which slightly differs from classical discontinuities characterized by a σ -1 scaling. A comparison between the measurements of ɛ and ${{ \mathcal D }}_{{\rm{I}}}^{\sigma }$ shows that in general the latter is significantly larger than the former.

Keywords: interplanetary turbulence; space plasmas; solar wind
Constraining the White-dwarf Mass and Magnetic Field Strength of a New Intermediate Polar through X-Ray Observations

We report timing and broadband spectral analysis of a Galactic X-ray source, CXOGBS J174517.0-321356 (J1745), with a 614 s periodicity. Chandra discovered the source in the direction of the Galactic Bulge. Gong proposed that J1745 was either an intermediate polar (IP) with a mass of ~1 M ⊙, or an ultracompact X-ray binary (UCXB). To confirm J1745's nature, we jointly fit XMM-Newton and NuSTAR spectra, ruling out a UCXB origin. We have developed a physically realistic model that considers a finite magnetosphere radius, X-ray absorption from the preshock region, and reflection from the white-dwarf (WD) surface to properly determine the IP properties, especially its WD mass. To assess systematic errors on the WD mass measurement, we consider a broad range of specific accretion rates ( $\dot{m}=0.6\mbox{--}44$ g cm-2 s-1) based on the uncertain source distance (d = 3-8 kpc) and fractional accretion area (f = 0.001-0.025). Our model properly implements the fitted accretion column height in the X-ray reflection model and accounts for the underestimated mass accretion rate due to the (unobserved) soft X-ray blackbody and cyclotron cooling emissions. We found that the lowest accretion rate of $\dot{m}$ = 0.6 g cm-2 s-1, which corresponds to the nearest source distance and maximum f value, yields a WD mass of (0.92 ± 0.08)M ⊙. On the other hand, as long as the accretion rate is $\dot{m}\gtrsim 3$ g cm-2 s-1, the WD mass is robustly measured to be (0.81 ± 0.06)M ⊙, nearly independent of $\dot{m}$ . The derived WD mass range is consistent with the mean WD mass of nearby IPs. Assuming spin equilibrium between the WD and accretion disk, we constrained the WD magnetic field to B ≳ 7 MG, indicating that it could be a highly magnetized IP. Our analysis presents the most comprehensive methodology for constraining the WD mass and B field of an IP by consolidating the effects of cyclotron cooling, finite magnetospheric radius, and accretion column height.

Keywords: x-ray binary stars; cataclysmic variable stars; dq herculis stars
Juno's JunoCam Images of Europa

On 2022 September 29 the Juno spacecraft passed Europa at 355 km, the first close pass since the Galileo flyby in 2000. Juno's visible-light imager, JunoCam, collected four images, enabling cartographic, topographic, and surface geology analysis. The topography along the terminator is consistent with previously reported features that may indicate true polar wander. A bright band was discovered, and indicates global symmetry in the stress field that forms bright bands on Europa. The named feature Gwern is shown not to be an impact crater. Surface change detection shows no changes in 22 yr, although this is a difficult task considering differences between the JunoCam and Galileo imagers and very different viewing geometries. No active eruptions were detected.

Keywords: europa
Hydrodynamic Properties of the Sun's Giant Cellular Flows

Measurements of the large cellular flows on the Sun were made by local correlation tracking of features (supergranules) seen in full-disk Doppler images obtained by the Helioseismic and Magnetic Imager (HMI) instrument on the NASA Solar Dynamics Observatory (SDO) satellite. Several improvements made to the local correlation tracking method allowed for more precise measurements of these flows. Measurements were made hourly over the nearly ten years of the mission-to-date. A four-hour time-lag between images was determined to give the best results as a compromise between increased feature displacement and decreased feature evolution. The hourly measurements were averaged over the 34 days that it takes to observe all longitudes at all latitudes to produce daily maps of the latitudinal and longitudinal velocities. Analyses of these flow maps reveal many interesting characteristics of these large cellular flows. While flows at all latitudes are largely in the form of vortices with left-handed helicity in the north and right-handed helicity in the south, there are key distinctions between the low-latitude and high-latitude cells. The low-latitude cells have roughly circular shapes, lifetimes of about one month, rotate nearly rigidly, do not drift in latitude, and do not exhibit any correlation between longitudinal and latitudinal flow. The high-latitude cells have long extensions that spiral inward toward the poles and can wrap nearly completely around the Sun. They have lifetimes of several months, rotate differentially with latitude, drift poleward at speeds approaching 2 m s-1, and have a strong correlation between prograde and equatorward flows. Spherical harmonic spectral analyses of maps of the divergence and curl of the flows confirm that the flows are dominated by the curl component with rms velocities of about 12 m s-1 at wavenumber ℓ = 10. Fourier transforms in time over 1024 daily records of the spherical harmonic spectra indicate two notable components—an m = ±ℓ feature representing the low-latitude component and an m = ±1 feature representing the high-latitude component. The dispersion relation for the low-latitude component is well represented by that derived for Rossby waves or r-modes. The high-latitude component has a constant temporal frequency for all ℓ indicating features advected by differential rotation at rates representative of the base of the convection zone high latitudes. The poleward motions of these features further suggest that the high-latitude meridional flow at the base of the convection zone is poleward—not equatorward.

Keywords: solar convective zone; solar interior; solar differential rotation; solar meridional circulation
Over 500 Days in the Life of the Photosphere of the Type Iax Supernova SN 2014dt

Type Iax supernovae (SNe Iax) are the largest known class of peculiar white dwarf SNe, distinct from normal Type Ia supernovae (SNe Ia). The unique properties of SNe Iax, especially their strong photospheric lines out to extremely late times, allow us to model their optical spectra and derive the physical parameters of the long-lasting photosphere. We present an extensive spectral timeseries, including 21 new spectra, of SN Iax 2014dt from +11 to +562 days after maximum light. We are able to reproduce the entire timeseries with a self-consistent, nearly unaltered deflagration explosion model from Fink et al. using TARDIS, an open source radiative-transfer code. We find that the photospheric velocity of SN 2014dt slows its evolution between +64 and +148 days, which closely overlaps the phase when we see SN 2014dt diverge from the normal spectral evolution of SNe Ia (+90 to +150 days). The photospheric velocity at these epochs, ~400-1000 km s-1, may demarcate a boundary within the ejecta below which the physics of SNe Iax and normal SNe Ia differ. Our results suggest that SN 2014dt is consistent with a weak deflagration explosion model that leaves behind a bound remnant and drives an optically thick, quasi-steady-state wind creating the photospheric lines at late times. The data also suggest that this wind may weaken at epochs past +450 days, perhaps indicating a radioactive power source that has decayed away.

Keywords: supernovae; type ia supernovae; radiative transfer; radiative transfer simulations; supernova dynamics
Split Invariant Curves in Rotating Bar Potentials

Invariant curves are generally closed curves in Poincaré's surface of section. Here we study an interesting dynamical phenomenon, first discovered by Binney et al. in a rotating Kepler potential, where an invariant curve of the surface of section can split into two disconnected line segments under certain conditions, which is distinctively different from the islands of resonant orbits. We first demonstrate the existence of split invariant curves in the Freeman bar model, where all orbits can be described analytically. We find that the split phenomenon occurs when orbits are nearly tangent to the minor/major axis of the bar potential. Moreover, the split phenomenon seems "necessary" to avoid invariant curves intersecting with each other. Such a phenomenon appears only in rotating potentials, and we demonstrate its universal existence in other general rotating bar potentials. It also implies that actions are no longer proportional to the area bounded by an invariant curve if the split occurs, but they can still be computed by other means.

Keywords: barred spiral galaxies; galaxy dynamics; orbits
The Final Fates of Close Hot Subdwarf-White Dwarf Binaries: Mergers Involving He/C/O White Dwarfs and the Formation of Unusual Giant Stars with C/O-Dominated Envelopes

Recently, a class of Roche-lobe-filling binary systems consisting of hot subdwarf stars and white dwarfs (WDs) with sub-hour periods has been discovered. At present, the hot subdwarf is in a shell He-burning phase and is transferring some of its remaining thin H envelope to its WD companion. As the evolution of the hot subdwarf continues, it is expected to detach, leaving behind a low-mass C/O-core WD secondary with a thick He layer. Then, on a timescale of ~10 Myr, gravitational wave radiation will again bring the systems into contact. If the mass transfer is unstable and results in a merger and a catastrophic thermonuclear explosion is not triggered, it creates a remnant with a C/O-dominated envelope, but one still rich enough in He to support an R Corona Borealis-like shell-burning phase. We present evolutionary calculations of this phase and discuss its potential impact on the cooling of the remnant WD.

Keywords: white dwarf stars; subdwarf stars; stellar mergers; r coronae borealis variable stars