adsabs/SciX_UAT_keywords huggingface dataset:
The X-Ray Properties of Eta Carinae During Its 2020 X-Ray Minimum

The massive binary system Eta Carinae is characterized by intense colliding winds that form shocks and emit X-rays. The system is highly eccentric (e ≃ 0.9), resulting in modulated X-ray emission during its 5.54 yr orbit. The X-ray flux increases in the months prior to periastron passage, exhibiting strong flares, then rapidly declines to a flat minimum lasting a few weeks, followed by a gradual recovery. We present the Neutron Star Interior Composition Explorer telescope spectra obtained before, during, and after the 2020 X-ray minimum, and perform spectral analysis to establish the temporal behavior of the X-ray flux and X-ray-absorbing column density (NH(t)) for the 2-10 keV and 5-10 keV energy ranges. The latter range is dominated by the stellar wind-collision region and, therefore, these spectral parameters-in particular, NH(t)-serve as potentially stringent constraints on the binary orientation. We compare the observed NH(t) results to the behavior predicted by a simple geometrical model in an attempt to ascertain which star is closer to us at periastron: the more massive primary (ω ≃ 240°-270°) or the secondary (ω ≃ 90°). We find that the variations in column density, both far from periastron and around periastron passage, support the latter configuration (ω ≃ 90°). The 2020 X-ray minimum showed the fastest recovery among the last five minima, providing additional evidence for a recent weakening of the primary star's wind.

Keywords: massive stars; binary stars; stellar winds; x-ray stars
Estimating Magnetic Filling Factors from Simultaneous Spectroscopy and Photometry: Disentangling Spots, Plage, and Network

State-of-the-art radial velocity (RV) exoplanet searches are limited by the effects of stellar magnetic activity. Magnetically active spots, plage, and network regions each have different impacts on the observed spectral lines and therefore on the apparent stellar RV. Differentiating the relative coverage, or filling factors, of these active regions is thus necessary to differentiate between activity-driven RV signatures and Doppler shifts due to planetary orbits. In this work, we develop a technique to estimate feature-specific magnetic filling factors on stellar targets using only spectroscopic and photometric observations. We demonstrate linear and neural network implementations of our technique using observations from the solar telescope at HARPS-N, the HK Project at the Mt. Wilson Observatory, and the Total Irradiance Monitor onboard SORCE. We then compare the results of each technique to direct observations by the Solar Dynamics Observatory. Both implementations yield filling factor estimates that are highly correlated with the observed values. Modeling the solar RVs using these filling factors reproduces the expected contributions of the suppression of convective blueshift and rotational imbalance due to brightness inhomogeneities. Both implementations of this technique reduce the overall activity-driven rms RVs from 1.64 to 1.02 m s-1, corresponding to a 1.28 m s-1 reduction in the rms variation. The technique provides an additional 0.41 m s-1 reduction in the rms variation compared to traditional activity indicators.

Keywords: exoplanets; radial velocity; exoplanet detection methods; solar activity; solar active regions
Timing Calibration of the NuSTAR X-Ray Telescope

The Nuclear Spectroscopic Telescope Array (NuSTAR) mission is the first focusing X-ray telescope in the hard X-ray (3-79 keV) band. Among the phenomena that can be studied in this energy band, some require high time resolution and stability: rotation-powered and accreting millisecond pulsars, fast variability from black holes and neutron stars, X-ray bursts, and more. Moreover, a good alignment of the timestamps of X-ray photons to UTC is key for multi-instrument studies of fast astrophysical processes. In this paper, we describe the timing calibration of the NuSTAR mission. In particular, we present a method to correct the temperature-dependent frequency response of the on-board temperature-compensated crystal oscillator. Together with measurements of the spacecraft clock offsets obtained during downlinks passes, this allows a precise characterization of the behavior of the oscillator. The calibrated NuSTAR event timestamps for a typical observation are shown to be accurate to a precision of ∼65 μs.

Keywords: pulsar timing method; cross-validation; x-ray detectors; x-ray astronomy; x-ray telescopes; millisecond pulsars
JWST Observations of Starbursts: Polycyclic Aromatic Hydrocarbon Emission at the Base of the M82 Galactic Wind

We present new observations of the central 1 kpc of the M82 starburst obtained with the James Webb Space Telescope near-infrared camera instrument at a resolution θ ∼ 0.″05–0.″1 (∼1–2 pc). The data comprises images in three mostly continuum filters (F140M, F250M, and F360M), and filters that contain [Fe II] (F164N), H2 v = 1 → 0 (F212N), and the 3.3 μm polycyclic aromatic hydrocarbon (PAH) feature (F335M). We find prominent plumes of PAH emission extending outward from the central starburst region, together with a network of complex filamentary substructures and edge-brightened bubble-like features. The structure of the PAH emission closely resembles that of the ionized gas, as revealed in Paschen α and free–free radio emission. We discuss the origin of the structure, and suggest the PAHs are embedded in a combination of neutral, molecular, and photoionized gas.

Keywords: luminous infrared galaxies; galaxy winds; starburst galaxies; dust physics; interstellar medium
High-spectral-resolution Observations of the Optical Filamentary Nebula Surrounding NGC 1275

We present new high-spectral-resolution observations (R = λ/Δλ = 7000) of the filamentary nebula surrounding NGC 1275, the central galaxy of the Perseus cluster. These observations have been obtained with SITELLE, an imaging Fourier transform spectrometer installed on the Canada–France–Hawai Telescope with a field of view of $11^{\prime} \times 11^{\prime} $ , encapsulating the entire filamentary structure of ionized gas despite its large size of 80 kpc × 50 kpc. Here, we present renewed fluxes, velocities, and velocity dispersion maps that show in great detail the kinematics of the optical nebula at [S II] λ6716, [S II] λ6731, [N II] λ6584, Hα (6563 Å), and [N II] λ6548. These maps reveal the existence of a bright flattened disk-shaped structure in the core extending to r ∼10 kpc and dominated by a chaotic velocity field. This structure is located in the wake of X-ray cavities and characterized by a high mean velocity dispersion of 134 km s‑1. The disk-shaped structure is surrounded by an extended array of filaments spread out to r ∼ 50 kpc that are 10 times fainter in flux, remarkably quiescent, and have a uniform mean velocity dispersion of 44 km s‑1. This stability is puzzling given that the cluster core exhibits several energetic phenomena. Based on these results, we argue that there are two mechanisms that form multiphase gas in clusters of galaxies: a first triggered in the wake of X-ray cavities leading to more turbulent multiphase gas and a second, distinct mechanism, that is gentle and leads to large-scale multiphase gas spreading throughout the core.

Keywords: agn host galaxies; active galaxies; brightest cluster galaxies; filamentary nebulae; perseus cluster
Time-dependent Photoionization Modeling of Warm Absorbers: High-resolution Spectra and Response to Flaring Light Curves

Time-dependent photoionization modeling of warm absorber (WA) outflows in active galactic nuclei can play an important role in understanding the interaction between WAs and the central black hole. The WA may be out of the equilibrium state because of the variable nature of the central continuum. In this paper, with the help of time dependent photoionization modeling, we study how the WA gas properties change with time and how it reacts to changing radiation fields. Incorporating a flaring incident light curve, we investigate the behavior of WAs using a photoionization code that simultaneously and consistently solves the time-dependent equations of level population, heating and cooling, and radiative transfer. We simulate the physical processes in the gas clouds, such as ionization, recombination, heating, cooling, and the transfer of ionizing radiation through the cloud and present high-resolution time-resolved absorption spectra. We demonstrate that time-dependent radiative transfer is important and the calculations that omit this effect quantitatively and systematically underestimate the absorption. Time-dependent photoionization models provide crucial insights into the characteristics of WAs and can be used to constrain their density and spatial distribution.

Keywords: astrophysicists; warm ionized medium; x-ray quasars; time domain astronomy; quasars
Investigation of Nulling and Subpulse-drifting Properties of PSR J1649+2533 with FAST

We report the nulling and subpulse-drifting properties of PSR J1649+2533 with observations of the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). The FAST observations reveal that the nulling fraction of this pulsar is about 20.9% ± 0.8% at 1250 MHz. The statistical study of the durations of the nulling and burst states shows that the burst states can persist for extended pulse periods, exceeding 100 periods in some cases, while the shortest lasts only a few pulse periods. The null states have a much shorter duration, with a maximum duration of less than 30 pulse periods. A comparative study between the pulse profiles of the first active pulse (FAP) and the last active pulse (LAP) shows that the pulse profiles of LAPs are stronger and wider than those of FAPs. An analysis of the two-dimensional fluctuation spectrum for the single-pulse stack indicates that the pulsar exhibits clear amplitude modulation and subpulse drifting. The periods are a P 3 = 2.5 ± 0.1 spin period and P 2 = 17.°0 ± 0.°5 at 1250 MHz, respectively. In addition, the multiband investigation shows that P 2 seems to increase with the increase of the observing frequency, i.e., P 2 ∝ ν 0.8±0.1. This seems to be caused by the increasing pulse-profile width with the frequency. The high-sensitivity FAST observations will enable a detailed understanding of the emission of this pulsar and provide important clues for theoretical studies of the radiation mechanism.

Keywords: radio pulsars; pulsars; neutron stars; non-thermal radiation sources
Photometric Monitoring of the ZZ Ceti Star PG 1541+651

The Kepler and K2 missions discovered multiple ZZ Ceti white dwarf pulsators that exhibit recurrent outbursts. These outbursting white dwarfs are near the red edge of the ZZ Ceti instability strip, suggesting that the phenomenon is physically related to the cessation of pulsations. We present multi-day ground-based monitoring of the poorly studied red-edge ZZ Ceti pulsator PG 1541+651. We do not detect any outbursts in our data. We do find that this pulsator has a very rich and time-variable spectrum of modes in its periodogram. The white dwarf lies in the northern continuous viewing zone of TESS; therefore, it has extensive archival light curves ripe for a detailed asteroseismic analysis of this star.

Keywords: white dwarf stars; zz ceti stars; multi-periodic variable stars
Sun-as-a-star Analysis of Hα Spectra of a Solar Flare Observed by SMART/SDDI: Time Evolution of Red Asymmetry and Line Broadening

Stellar flares sometimes show red/blue asymmetries of the Hα line, which can indicate chromospheric dynamics and prominence activations. However, the origin of asymmetries is not completely understood. For a deeper understanding of stellar data, we performed a Sun-as-a-star analysis of Hα line profiles of an M4.2-class solar flare showing dominant emissions from flare ribbons by using the data of the Solar Dynamics Doppler Imager on board the Solar Magnetic Activity Research Telescope at the Hida Observatory. Sun-as-a-star Hα spectra of the flare show red asymmetry of up to ~95 km s-1 and line broadening of up to ~7.5 Å. The Sun-as-a-star Hα profiles are consistent with spectra from flare regions with weak intensity, but they take smaller redshift velocities and line widths by a factor of ~2 than those with strong intensity. The redshift velocities, as well as line widths, peak out and decay more rapidly than the Hα equivalent widths, which is consistent with the chromospheric condensation model and spatially resolved flare spectra. This suggests that as a result of superposition, the nature of chromospheric condensation is observable even from stellar flare spectra. The time evolution of redshift velocities is found to be similar to that of luminosities of near-ultraviolet rays (1600 Å), while the time evolution of line broadening is similar to that of optical white lights. These Hα spectral behaviors in Sun-as-a-star view could be helpful to distinguish whether the origin of Hα red asymmetry of stellar flares is a flare ribbon or other phenomena.

Keywords: solar flares; solar flare spectra; flare stars; stellar flares; optical flares
NY Bootes: An Active Deep and Low-mass-ratio Contact Binary with a Cool Companion in a Hierarchical Triple System

The first detailed photometric and spectroscopic study of G-type short-period binary NY Boo is presented. The radial velocity curve was obtained by the cross-correlation function (CCF) method based on LAMOST and SDSS spectra, which derived its mass ratio as q = 0.139(1/7.2). The CCF profiles of the SDSS spectra clearly show the existence of a cool third component, which is supported by the results of the orbital period investigation. The period study based on the O-C analysis indicates that besides a long-term decrease, the orbital period has a periodic oscillation due to the light-travel time effect caused by a third body. When the third light contribution is consistent with the CCF results, the orbit of the third body and the inner pair are non-coplanar with m 3 = 0.31 M ⊙. Combining with the TESS light curves, it is found that the target is a deep and low-mass-ratio contact binary (DLMRCB) with a fill-out factor of f = 73%. The notable asymmetry in light curves was detected and explained by the spot model very well. The spectroscopic profiles, the cyclic variation in the O-C diagram, and the radial velocity curve and light-curve solutions all suggest that NY Boo is a hierarchical triple system with a cool tertiary component orbiting around an active DLMRCB. With the orbital period shrinking, the binary may eventually merge. The period of NY Boo decreases faster than other shrinking DLMRCB, together with active inner pair and non-coplanar tertiary component, making NY Boo an important target for studying the late evolution of binaries.

Keywords: close binary stars; binary stars; eclipsing binary stars
Multiepoch Detections of the Extended Atmosphere and Transmission Spectra of KELT-9b with a 1.5 m Telescope

Irradiated Jovian atmospheres are complex and dynamic and can undergo temporal variations due to the close proximity of their parent stars. Of the Jovian planets that have been cataloged to date, KELT-9b is the hottest gas giant known, with an equilibrium temperature of 4050 K. We probe the temporal variability of transmission spectroscopic signatures from KELT-9b via a set of archival multiyear ground-based transit observations, performed with the TRES facility on the 1.5 m reflector at the Fred Lawrence Whipple Observatory. Our observations confirm past detections of Fe I, Fe II, and Mg I over multiple epochs, in addition to excess absorption at Hα, which is an indicator for ongoing mass loss. From our multiyear data set, the Hα light curve consistently deviates from a standard transit and follows a "W" shape that is deeper near ingress and egress and shallower midtransit. To search for and quantify any seasonal variations that may be present, we parameterize a "cometary tail" model to fit for the Hα transit. We find no detectable variations between the different observed epochs. Though a "cometary tail" describes the Hα flux variations well, we note that such a scenario requires a high density of neutral hydrogen in the n = 2 excited state far beyond the planetary atmosphere. Other scenarios, such as center-to-limb variations larger than that expected from 1D atmosphere models, may also contribute to the observed Hα transit shape. These multiepoch observations highlight the capabilities of small telescopes to provide temporal monitoring of the dynamics of exoplanet atmospheres.

Keywords: exoplanets; hot jupiters; exoplanet atmospheric composition; exoplanet atmospheric variability; exoplanet evolution
Probing the Nucleosynthetic Contribution of Low-metallicity, Low-mass Star Companions of CEMP Stars

The observed abundance diversities among CEMP stars can shed light on the formation and evolution of elements in the early Galaxy. In this work, we present results obtained from a detailed abundance analysis of a sample of seven extrinsic carbon stars. The analysis is based on high-resolution spectra obtained with HCT/HESP (R~60,000) and SUBARU/HDS (R~50,000). We present, for the first time, the elemental abundance results for the objects BD-19 132, BD-19 290, HE 1304-2111, HE 1354-2257, and BD+19 3109. Abundances of a few elements are available in the literature for HE 1157-0518 and HD 202851; we present an update on the abundances of these elements along with new abundance estimates for several other elements. Our analysis confirms the object HD 202851 to be a CH star. While BD-19 132, HE 1354-2257, and BD+19 3109 are found to be CEMP-s stars, the objects BD-19 290, HE 1157-0518, and HE 1304-2111 are found to belong to CEMP-r/s group. The observed abundance patterns of the three CEMP-r/s stars are well reproduced with the i-process model predictions. While the objects BD+19 3109 and HD 202851 are confirmed binaries, the binary status of the remaining objects is not known. Analysis based on different elemental abundance ratios confirms low-mass former AGB companions for all the objects. Kinematic analysis shows that BD-19 290, HE 1157-0518, HE 1354-2257, and BD+19 3109 belong to the Galactic halo, whereas BD-19 132, HE 1304-2111, and HD 202851 are members of Galactic thin disk. * Based on data collected using HCT/HESP and SUBARU/HDS.

Keywords: population ii stars
Probing Elastic Quark Phases in Hybrid Stars with Radius Measurements

The internal composition of neutron stars is currently largely unknown. Due to the possibility of phase transitions in quantum chromodynamics, stars could be hybrid and have quark cores. We investigate some imprints of elastic quark phases (only when perturbed) on the dynamical stability of hybrid stars. We show that they increase the dynamical stability window of hybrid stars in the sense that the onset of instabilities happens at larger central densities than the ones for maximum masses. In particular, when the shear modulus of a crystalline quark phase is taken at face value, the relative radius differences between elastic and perfect-fluid hybrid stars with null radial frequencies (onset of instability) would be up to 1%-2%. Roughly, this would imply a maximum relative radius dispersion (on top of the perfect-fluid predictions) of 2%-4% for stars in a given mass range exclusively due to the elasticity of the quark phase. In the more agnostic approach where the estimates for the quark shear modulus only suggest its possible order of magnitude (due to the many approximations taken in its calculation), the relative radius dispersion uniquely due to a quark phase elasticity might be as large as 5%-10%. Finally, we discuss possible implications of the above dispersion of radii for the constraint of the elasticity of a quark phase with electromagnetic missions such as NICER, eXTP, and ATHENA.

Keywords: general relativity; neutron stars; stellar oscillations
JWST PEARLS. Prime Extragalactic Areas for Reionization and Lensing Science: Project Overview and First Results

We give an overview and describe the rationale, methods, and first results from NIRCam images of the JWST "Prime Extragalactic Areas for Reionization and Lensing Science" (PEARLS) project. PEARLS uses up to eight NIRCam filters to survey several prime extragalactic survey areas: two fields at the North Ecliptic Pole (NEP); seven gravitationally lensing clusters; two high redshift protoclusters; and the iconic backlit VV 191 galaxy system to map its dust attenuation. PEARLS also includes NIRISS spectra for one of the NEP fields and NIRSpec spectra of two high-redshift quasars. The main goal of PEARLS is to study the epoch of galaxy assembly, active galactic nucleus (AGN) growth, and First Light. Five fields-the JWST NEP Time-Domain Field (TDF), IRAC Dark Field, and three lensing clusters-will be observed in up to four epochs over a year. The cadence and sensitivity of the imaging data are ideally suited to find faint variable objects such as weak AGN, high-redshift supernovae, and cluster caustic transits. Both NEP fields have sightlines through our Galaxy, providing significant numbers of very faint brown dwarfs whose proper motions can be studied. Observations from the first spoke in the NEP TDF are public. This paper presents our first PEARLS observations, their NIRCam data reduction and analysis, our first object catalogs, the 0.9-4.5 μm galaxy counts and Integrated Galaxy Light. We assess the JWST sky brightness in 13 NIRCam filters, yielding our first constraints to diffuse light at 0.9-4.5 μm. PEARLS is designed to be of lasting benefit to the community.

Keywords: james webb space telescope; zodiacal cloud; star counts; galaxy counts; cosmic background radiation
Reinvestigating the Gamow Factor of Reactions on Light Nuclei

We present a modified Gamow factor by reinvestigating the conventional assumptions used in its derivation. The conventional Gamow factor, factorized from the total cross section, effectively describes the penetration probabilities (PPs) in low-energy nuclear reactions under the assumption of particle energies significantly lower than the Coulomb barrier. However, we find that the assumption is invalid for light nuclei, resulting in PPs that depend on the nuclear potential depth for such nuclei. By adopting a potential depth fitted to experimental fusion cross sections, we demonstrate that PPs for light nuclei (D+D, D+T, D+3He, p+D, p+6Li, and p+7Li) become higher than those predicted by the conventional form near the Coulomb barrier. This reduces the Gamow peak energy by a factor of 5.3 maximally compared to the conventional form. Furthermore, we show that the enhancement factor due to the Debye screening effects in the solar core can be reduced by approximately 5%-10% due to the modified PP. Our findings hold implications for evaluating the available energy region in low-energy reaction experiments based on the Gamow peak energy region and for understanding electron screening effects in typical astrophysical environments.

Keywords: nuclear reaction cross sections; nuclear astrophysics; nuclear physics