adsabs/SciX_UAT_keywords huggingface dataset:
Temporal Evolution of the Inverse Evershed Flow

The inverse Evershed flow (IEF) is an inflow of material into the penumbra of sunspots in the solar chromosphere that occurs along dark, elongated super-penumbral fibrils extending from about the outer edge of the moat cell to the sunspot. The IEF channels exhibit brightenings in the penumbra, where the supersonic IEF descends to the photosphere causing shock fronts with localized heating. We used an 1 hr time series of spectroscopic observations of the chromospheric spectral lines of Ca II IR at 854 nm and Hα at 656 nm taken with the Interferometric Bidimensional Spectrometer at the Dunn Solar Telescope to investigate the temporal evolution of IEF channels. Complementary information on the photospheric magnetic field was obtained from observations with the Facility Infrared Spectropolarimeter at 1083 nm and the Helioseismic and Magnetic Imager. We find that individual IEF channels are long-lived (10-60 minutes) and only show minor changes in position and flow speed during their lifetime. Initiation and termination of IEF channels takes several minutes. The IEF channels with line-of-sight velocities of about 10 km s-1 show no lasting impact from transient or oscillatory phenomena with maximal velocity amplitudes of only about 1 km s-1 that run along them. We could not detect any clear correlation of the location and evolution of IEF channels to local magnetic field properties in the photosphere in the penumbra or moving magnetic features in the sunspot moat. Our results support a picture of the IEF as a field-aligned siphon flow along arched loops. From our data we cannot determine if their evolution is controlled by events at the outer end in the moat or at the inner end in the penumbra.

Keywords: sunspots; solar chromosphere; solar photosphere
Uncertainty and Bias of Cosmology and Astrophysical Population Model from Statistical Dark Sirens

Gravitational-wave (GW) radiation from a coalescing compact binary is a standard siren, as the luminosity distance of each event can be directly measured from the amplitude of the signal. One possibility to constrain cosmology using the GW siren is to perform statistical inference on a population of binary black hole (BBH) events. In essence, this statistical method can be viewed as follows. We can modify the shape of the distribution of observed BBH events by changing the cosmological parameters until it eventually matches the distribution constructed from an astrophysical population model, thereby allowing us to determine the cosmological parameters. In this work, we derive the Cramér-Rao bound for both cosmological parameters and those governing the astrophysical population model from this statistical dark siren method by examining the Fisher information contained in the event distribution. Our study provides analytical insights and enables fast yet accurate estimations of the statistical accuracy of dark siren cosmology. Furthermore, we consider the bias in cosmology due to unmodeled substructures in the merger rate and mass distribution. We find that a 1% deviation in the astrophysical model can lead to a more than 1% error in the Hubble constant. This could limit the accuracy of dark siren cosmology when there are more than 104 BBH events detected.

Keywords: cosmological parameters; hubble constant; gravitational wave sources; stellar mass black holes
Disk Wind Feedback from High-mass Protostars. III. Synthetic CO Line Emission

To test theoretical models of massive star formation it is important to compare their predictions with observed systems. To this end, we conduct CO molecular line radiative transfer post-processing of 3D magnetohydrodynamic simulations of various stages in the evolutionary sequence of a massive protostellar core, including its infall envelope and disk wind outflow. Synthetic position–position–velocity cubes of various transitions of 12CO, 13CO, and C18O emission are generated. We also carry out simulated Atacama Large Millimeter/submillimeter Array (ALMA) observations of this emission. We compare the mass, momentum, and kinetic energy estimates obtained from molecular lines to the true values, finding that the mass and momentum estimates can have uncertainties of up to a factor of 4. However, the kinetic energy estimated from molecular lines is more significantly underestimated. Additionally, we compare the mass outflow rate and momentum outflow rate obtained from the synthetic spectra with the true values. Finally, we compare the synthetic spectra with real examples of ALMA-observed protostars and determine the best-fitting protostellar masses and outflow inclination angles. We then calculate the mass outflow rate and momentum outflow rate for these sources, finding that both rates agree with theoretical protostellar evolutionary tracks.

Keywords: interstellar medium; molecular clouds; radiative transfer; stellar jets; stellar winds; magnetohydrodynamics
Discovery of a New Redback Millisecond Pulsar Candidate: 4FGL J0940.3-7610

We have discovered a new candidate redback millisecond pulsar binary near the center of the error ellipse of the bright unassociated Fermi-LAT γ-ray source 4FGL J0940.3-7610. The candidate counterpart is a variable optical source that also shows faint X-ray emission. Optical photometric and spectroscopic monitoring with the SOAR telescope indicates that the companion is a low-mass star in a 6.5 hr orbit around an invisible primary, showing both ellipsoidal variations and irradiation and consistent with the properties of known redback millisecond pulsar binaries. Given the orbital parameters, preliminary modeling of the optical light curves suggests an edge-on inclination and a low-mass (∼1.2-1.4 M⊙) neutron star, along with a secondary mass somewhat more massive than the typical ≳0.4 M⊙. This combination of inclination and secondary properties could make radio eclipses more likely for this system, explaining its previous nondiscovery in radio pulsation searches. Hence, 4FGL J0940.3-7610 may be a strong candidate for a focused search for γ-ray pulsations to enable the future detection of a millisecond pulsar.

Keywords: neutron stars; x-ray binary stars; millisecond pulsars; gamma-ray sources
Spectral Lag Transition of 32 Fermi Gamma-Ray Bursts and Their Application on Constraining Lorentz Invariance Violation

The positive-to-negative transition of spectral lag is an uncommon feature reported in a small number of gamma-ray bursts (GRBs). An application of such a feature has been made to constrain the critical quantum gravity energy (E QG) of the light photons under the hypothesis that the Lorentz invariance might be violated. Motivated by previous case studies, this paper systematically examined the up-to-date GRB sample observed by Fermi Gamma-ray Burst Monitor for the lag transition feature to establish a comprehensive physical limit on the Lorentz invariance violation (LIV). This search resulted in 32 GRBs with redshift available, which exhibit the lag transition phenomenon. We first fit each of the lag-E relations of the 32 GRBs with an empirical smoothly broken power-law function, and found that the lag transition occurs typically at about 400 keV. We then implemented the LIV effect into the fit, which enabled us to constrain the lower limit of the linear and quadratic values of E QG, which are typically distributed at 1.5 × 1014 and 8 × 105 GeV, respectively.

Keywords: gamma-ray bursts; gravitation; quantum gravity
Two Complete Spectral Transitions of Swift J0243.6+6124 Observed by Insight-HXMT

We performed the broadband (1-100 keV) spectral analysis of the first Galactic Be ultraluminous X-ray pulsar (BeULX) Swift J0243.6+6124 observed by Insight-HXMT during the 2017-2018 outburst. The results show spectral transitions at two typical luminosities, roughly consistently with those reported previously via pure timing analysis. We find that the spectrum evolves and becomes softer and has higher cutoff energies until the luminosity reaches L1 (∼1.5 × 1038 erg s-1). Afterwards the spectrum becomes harder with lower cutoff energies until the luminosity increases to L2 (∼4.4 × 1038 erg s-1), around which the second spectral transition occurs. Beyond L2, the spectrum softens again and has larger cutoff energies. Similar behaviors were observed previously in other high-mass X-ray binary systems (HMXBs), especially for the second transition at higher luminosities, which is believed to have a correlation with the magnetic field of the harbored neutron star. Accordingly, we speculate that Swift J0243.6+6124 owns a neutron star with magnetic field strength >1013 G. The spectral transition at around L1 of Swift J0243.6+6124 is first observed thoroughly for any HMXB outburst characterized by strong evolution of the thermal component: the temperature of the blackbody drops sharply accompanied by a sudden increase of the blackbody radius. These spectral transitions can in principle be understood in a general scenario of balancing the emission patterns between the pencil and the fan beams at the magnetic pole, for which the extreme brightness of Swift J0243.6+6124 may provide an almost unique lab to probe the details.

Keywords: accretion; stellar accretion disks; binary pulsars; magnetic fields; neutron stars; x-ray binary stars; x-ray astronomy
Fitting Rotational Frequency of Polytropes as a Function of their Oblateness

Giving a simple functional relationship between the rotational frequency and the centrifugal deformation for compressible stellar models is useful both in observational and theoretical astrophysics. Here I present simple Padé approximants for the rotational frequency of polytropic stars (index N = 1, 1.5, 3) as a function of the oblateness, which are valid at the order of ${ \mathcal O }[{10}^{-2}]$ percent for the speed of rotation up to the mass-shedding limit.

Keywords: stellar rotation
Near-infrared and Optical Nebular-phase Spectra of Type Ia Supernovae SN 2013aa and SN 2017cbv in NGC 5643

We present multiwavelength time-series spectroscopy of SN 2013aa and SN 2017cbv, two Type Ia supernovae (SNe Ia) on the outskirts of the same host galaxy, NGC 5643. This work utilizes new nebular-phase near-infrared (NIR) spectra obtained by the Carnegie Supernova Project-II, in addition to previously published optical and NIR spectra. Using nebular-phase [Fe II] lines in the optical and NIR, we examine the explosion kinematics and test the efficacy of several common emission-line-fitting techniques. The NIR [Fe II] 1.644 μm line provides the most robust velocity measurements against variations due to the choice of the fit method and line blending. The resulting effects on velocity measurements due to choosing different fit methods, initial fit parameters, continuum and line profile functions, and fit region boundaries were also investigated. The NIR [Fe II] velocities yield the same radial shift direction as velocities measured using the optical [Fe II] λ7155 line, but the sizes of the shifts are consistently and substantially lower, pointing to a potential issue in optical studies. The NIR [Fe II] 1.644 μm emission profile shows a lack of significant asymmetry in both SNe, and the observed low velocities elevate the importance for correcting for any velocity contribution from the host galaxy's rotation. The low [Fe II] velocities measured in the NIR at nebular phases disfavor progenitor scenarios in close double-degenerate systems for both SN 2013aa and SN 2017cbv. The time evolution of the NIR [Fe II] 1.644 μm line also indicates moderately high progenitor white dwarf central density and potentially high magnetic fields.

Keywords: type ia supernovae; spectroscopy
Mapping Stellar Surfaces. I. Degeneracies in the Rotational Light-curve Problem

Thanks to missions like Kepler and TESS, we now have access to tens of thousands of high-precision, fast-cadence, and long-baseline stellar photometric observations. In principle, these light curves encode a vast amount of information about stellar variability and, in particular, the distribution of starspots and other features on their surfaces. Unfortunately, the problem of inferring stellar surface properties from a rotational light curve is famously ill-posed, as it often does not admit a unique solution. Inferences about the number, size, contrast, and location of spots can therefore depend very strongly on the assumptions of the model, the regularization scheme, or the prior. The goal of this paper is twofold: (1) to explore the various degeneracies affecting the stellar light-curve "inversion" problem and their effect on what can and cannot be learned from a stellar surface, given unresolved photometric measurements, and (2) to motivate ensemble analyses of the light curves of many stars at once as a powerful data-driven alternative to common priors adopted in the literature. We further derive novel results on the dependence of the null space on stellar inclination and limb darkening and show that single-band photometric measurements cannot uniquely constrain quantities like the total spot coverage without the use of strong priors. This is the first in a series of papers devoted to the development of novel algorithms and tools for the analysis of stellar light curves and spectral time series, with the explicit goal of enabling statistically robust inferences about their surface properties.

Keywords: time series analysis; light curves; stellar surfaces; starspots
Influence of Coronal Holes on CME Deflections: Numerical Study

The understanding of the causes that produce the deflection of coronal mass ejections (CMEs) is essential for the space weather forecast. We study the effects on CME trajectories produced by the different properties of a coronal hole (CH), close to the ejection area. We perform ideal magnetohydrodynamics simulations emulating the early rising of the CME in the presence of a CH. We find that, the stronger the magnetic field and the wider the CH area, the larger the CME deflection. The deflection reduces as the CH moves away from the ejection region. To quantify the deflection we propose a dimensionless parameter that depends on the CH properties. We show that a minimum magnetic energy region, responsible for the deflection, is associated with the presence of the CH near the CME. We establish a relationship between the CH properties, the location of the minimum magnetic region, and the CME deflection.

Keywords: solar physics; solar coronal holes; solar coronal mass ejections; solar magnetic fields; space weather; magnetohydrodynamical simulations; magnetohydrodynamics
Investigating Protoplanetary Disk Cooling through Kinematics: Analytical GI Wiggle

It is likely that young protostellar disks undergo a self-gravitating phase. Such systems are characterized by the presence of a spiral pattern that can be either in a quasi-steady state or in a nonlinear unstable condition. This spiral wave affects both the gas dynamics and kinematics, resulting in deviations from the Keplerian rotation. Recently, a lot of attention has been devoted to kinematic studies of planet-forming environments, and we are now able to measure even small perturbations of velocity field (≲1% of the Keplerian speed) thanks to high spatial and spectral resolution observations of protostellar disks. In this work, we investigate the kinematic signatures of gravitational instability: we perform an analytical study of the linear response of a self-gravitating disk to a spiral-like perturbation, focusing our attention on the velocity field perturbations. We show that unstable disks have clear kinematic imprints into the gas component across the entire disk extent, due to the GI spiral wave perturbation, resulting in deviations from Keplerian rotation. The shape of these signatures depends on several parameters, but they are significantly affected by the cooling factor: by detecting these features, we can put constraints on protoplanetary disk cooling.

Keywords: astrophysical fluid dynamics; stellar accretion disks; gravitational instability
Intensity Distribution in the Heads of Comets

In optical wavelengths, the light emitted by comets consists of sunlight, reflected by dust, and the emission features of atoms and molecules. In his paper from 1957, L. Haser develops the mathematical framework to describe the density distribution of cometary comas. When comet scientists refer to the Haser model, they mostly point to the density distribution of parent and fragment molecules in the coma. However, in his paper, Haser (1957) presented the analytic solution over the line of sight (column density) and considers two particular observation configurations of a nonhomogeneous coma. This translation of the paper, originally in French, stays as close to the source as possible, including using the original figures. Minor typesetting corrections were introduced and are annotated in the text. The Haser model is foundational in cometary atmosphere science, but Haser's paper was not widely read due to language barriers and a lack of digital availability. This translation is presented in an effort to make Haser's work accessible to the wider community. We would like to thank Drs Emmanuel Jehin (Univ. Liège) and Kumar Venkataramani (Auburn Univ.) for critically reading this translation.

Keywords: comets; comet volatiles; history of astronomy
Counting on Short Gamma-Ray Bursts: Gravitational-wave Constraints of Jet Geometry

The detections of GW170817 and GRB 170817A revealed that at least some short gamma-ray bursts (sGRB) are associated with the merger of neutron-star compact binaries. The gamma-rays are thought to result from the formation of collimated jets, but the details of this process continue to elude us. One important feature of gamma-ray bursts is the emission profile of the jet as a function of viewing angle. We present two related methods to measure the effective angular width, ${\theta }_{B}$ , of sGRB jets using gravitational-wave (GW) and gamma-ray data, assuming all sGRBs have the same angular dependence for their luminosities. The first is a counting experiment that requires minimal knowledge about each event, beyond whether or not they were detected in gamma-rays. The second method uses GW and electromagnetic data to estimate parameters of the source. We additionally outline a model-independent method to infer the full jet structure of sGRBs using a nonparametric approach. Applying our methods to GW170817 and GW190425, we find weak constraints on the sGRB luminosity profile. We project that with 5 and 100 binary neutron star detections, the counting method would constrain the relative uncertainty in ${\theta }_{B}$ to within $51 \% $ and $12 \% $ , respectively. Incorporating GW parameter estimation provides only marginal improvements. We conclude that the majority of the information about jet structure comes from the relative sensitivities of GW and gamma-ray detectors as encoded in simple counting experiments.

Keywords: neutron stars; gamma-ray bursts; gravitational waves
MHD Simulations of Dense Core Collision

We investigated the effect of magnetic fields on the collision process between dense molecular cores. We performed three-dimensional magnetohydrodynamic simulations of collisions between two self-gravitating cores using the Enzo adaptive mesh refinement code. The core was modeled as a stable isothermal Bonnor-Ebert (BE) sphere immersed in uniform magnetic fields. Collisions were characterized by the offset parameter b, Mach number of the initial core ${ \mathcal M }$ , magnetic field strength B 0, and angle θ between the initial magnetic field and collision axis. For head-on (b = 0) collisions, one protostar was formed in the compressed layer. The higher the magnetic field strength, the lower the accretion rate. For models with b = 0 and θ = 90°, the accretion rate was more dependent on the initial magnetic field strength compared with b = 0 and θ = 0° models. For off-center (b = 1) collisions, the higher specific angular momentum increased; therefore, the gas motion was complicated. In models with b = 1 and ${ \mathcal M }=1$ , the number of protostars and gas motion highly depended on B 0 and θ. For models with b = 1 and ${ \mathcal M }=3$ , no significant shock-compressed layer was formed and star formation was not triggered.

Keywords: molecular gas; star formation; magnetic fields; magnetohydrodynamical simulations
Validation of a Third Planet in the LHS 1678 System

The nearby LHS 1678 (TOI-696) system contains two confirmed planets and a wide-orbit, likely brown-dwarf companion, which orbit an M2 dwarf with a unique evolutionary history. The host star occupies a narrow "gap" in the Hertzsprung–Russell diagram lower main sequence, associated with the M dwarf fully convective boundary and long-term luminosity fluctuations. This system is one of only about a dozen M dwarf multiplanet systems to date that hosts an ultra-short-period planet (USP). Here we validate and characterize a third planet in the LHS 1678 system using TESS Cycle 1 and 3 data and a new ensemble of ground-based light curves. LHS 1678 d is a 0.98 ± 0.07 R ⊕ planet in a 4.97 day orbit, with an insolation flux of ${9.1}_{-0.8}^{+0.9}\,{S}_{\oplus }$ . These properties place it near 4:3 mean motion resonance with LHS 1678 c and in company with LHS 1678 c in the Venus zone. LHS 1678 c and d are also twins in size and predicted mass, making them a powerful duo for comparative exoplanet studies. LHS 1678 d joins its siblings as another compelling candidate for atmospheric measurements with the JWST and mass measurements using high-precision radial velocity techniques. Additionally, USP LHS 1678 b breaks the "peas-in-a-pod" trend in this system although additional planets could fill in the "pod" beyond its orbit. LHS 1678's unique combination of system properties and their relative rarity among the ubiquity of compact multiplanet systems around M dwarfs makes the system a valuable benchmark for testing theories of planet formation and evolution.

Keywords: exoplanet systems; transit photometry; transit timing variation method; m dwarf stars
Nonthermal Particle Acceleration at Highly Oblique Nonrelativistic Shocks

The nonthermal acceleration of electrons and ions at an oblique, nonrelativistic shock is studied using large-scale particle-in-cell simulations in one spatial dimension. Physical parameters are selected to highlight the role of electron preheating in injection and subsequent acceleration of particles at high Mach number shocks. Simulation results show evidence for the early onset of the diffusive shock acceleration process for both electrons and ions at a highly oblique subluminal shock. Ion acceleration efficiencies of ≲5% are measured at late times, though this is not the saturated value.

Keywords: shocks; galactic cosmic rays; plasma astrophysics