adsabs/SciX_UAT_keywords huggingface dataset:
Automated Photometry of γ Cassiopeiae: The Last Roundup

γ Cassiopeiae (B0.5IVe) is the noted prototype of a subgroup of classical Be stars exhibiting hard thermal X-ray emission. This paper reports results from a 23 yr optical campaign on this star with an automated photometric telescope (APT). A series of unstable long cycles of length 56-91 days has nearly ceased over the last decade. Also, we revise the frequency of the dominant coherent signal at 0.82238 days-1. This signal's amplitude has nearly disappeared in the last 15 yr but has somewhat recovered its former strength. We confirm the presence of secondary nonradial pulsation signals found by other authors at frequencies 1.24, 2.48, and 5.03 days-1. The APT data from intensively monitored nights reveal rapidly variable amplitudes among these frequencies. We show that peculiarities in the 0.82 days-1 waveform exist that can vary even over several days. Although the 0.82 days-1 frequency is near the star's presumed rotational frequency, because of its phase slippage with respect to a dip pattern in its far-UV light curve, it is preferable to consider the UV pattern, not the 0.82 days-1 signal, as associated with rotational modulation. We also find hints of the UV dip pattern in periodograms of seasonal data early in our program.

Keywords: b stars
Multiwavelength Sun-as-a-star Analysis of the M8.7 Flare on 2022 October 2 Using Hα and EUV Spectra Taken by SMART/SDDI and SDO/EVE

This paper presents a multiwavelength Sun-as-a-star analysis of the M8.7 flare on 2022 October 2, which was associated with a filament eruption and the subsequent coronal mass ejection. The Sun-as-a-star analysis was performed using Hα data taken by Solar Dynamics Doppler Imager on board the Solar Magnetic Activity Research Telescope at Hida Observatory, Kyoto University, and full-disk integrated extreme ultraviolet (EUV) spectra taken by the Extreme ultraviolet Variability Experiment (EVE) on board the Solar Dynamics Observatory. The Sun-as-a-star Hα spectra showed blueshifted absorption corresponding to the filament eruption. Furthermore, the EVE O V 629.7 Å spectra showed blueshifted brightening, which can also be attributed to the filament eruption. Even when the blueshifted absorption became almost invisible in the Sun-as-a-star Hα spectra, the O V blueshifted brightening up to ‑400 km s‑1 was still clearly visible. This result indicates that even when the shifted components—which are expected to originate from stellar eruptions—become almost invisible in the spatially integrated stellar Hα spectra, the erupting materials may still be present and observable in EUV spectra. Additionally, the Sun-as-a-star Hα and O V spectra exhibited redshifted absorption and brightening, respectively, during the decay phase of the flare. These components probably originate from the post-flare loops, providing clues to the multitemperature nature of the post-flare loops in the spatially integrated observation. Our Sun-as-a-star results suggest that the combination of Hα and EUV lines allows the investigation of the multitemperature structure and temporal development of stellar active phenomena even in spatially integrated spectra.

Keywords: solar flares; stellar flares; solar filament eruptions; solar prominences; solar coronal mass ejections; solar chromosphere
Revealing the Progenitor of SN 2021zby through Analysis of the TESS Shock-cooling Light Curve

We present early observations and analysis of the double-peaked Type IIb supernova (SN IIb) SN 2021zby. TESS captured the prominent early shock-cooling peak of SN 2021zby within the first ~10 days after explosion with a 30 minute cadence. We present optical and near-infrared spectral series of SN 2021zby, including three spectra during the shock-cooling phase. Using a multiband model fit, we find that the inferred properties of its progenitor are consistent with a red supergiant or yellow supergiant, with an envelope mass of ~0.30-0.65 M ⊙ and an envelope radius of ~120-300 R ⊙. These inferred progenitor properties are similar to those of other SNe IIb with a double-peaked feature, such as SNe 1993J, 2011dh, 2016gkg, and 2017jgh. This study further validates the importance of the high cadence and early coverage in resolving the shape of the shock-cooling light curve, while the multiband observations, particularly UV, are also necessary to fully constrain the progenitor properties.

Keywords: core-collapse supernovae; supernovae
An Observational Signature of Sub-equipartition Magnetic Fields in the Spectra of Black Hole Binaries

A common assumption used in the study of accretion disks is that the magnetic energy density and the kinetic energy density should be in equipartition. This assumption relies on the faster growth rate of the magnetic field strength against the kinetic energy of the particles in the flow, for decreasing radius, combined with a dissipation mechanism that tends toward equipartition. In this paper, we examine this assumption by modeling the radio, millimeter, and optical spectra of several black hole binaries in their quiescent state. We use a standard two-component disk model, consisting of an inner geometrically thick and optically thin disk, emitting thermal synchrotron radiation, along with an outer, thin disk, which radiates as a multicolor blackbody. We find that at the low accretion rates typical of the quiescent state, the spectral shape is qualitatively reproduced using magnetic fields that are between 0.1% and 1% of the equipartition value, considerably smaller than previously thought. We discuss our findings in view of (1) the launching of jets in these objects, which is commonly believed to rely on the presence of a strong magnetic field in the central region of the disk, and (2) the role of magnetic dissipation in the structure of the inflow.

Keywords: x-ray binary stars; jets; magnetic fields; stellar mass black holes
Quasiperiodic Microjets Driven by Granular Advection as Observed With High-resolution Imaging at He I 10830 Å

With high-resolution narrowband He I 10830 Å filtergrams from Goode Solar Telescope, we give an extensive analysis for four granule-sized microeruptions which appear as the gentle ejection of material in He I 10830 Å band. The analysis was aided with the EUV data from Atmospheric Imaging Assembly and line-of-sight magnetograms from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. The microeruptions are situated on magnetic polarity inversion lines (PILs), and their roots are accurately traced down to intergranular lanes. Their durations are different: two microeruptions are repetitive microjets, lasting ~50 and 27 minutes respectively, while the other two events are singular, lasting ~5 minutes. For the two microjets, they are continuous and recurrent in the He I 10830 Å band, and the recurrence is quasiperiodic with a period of ~5 minutes. We found that only transient cospatial EUV brightenings are observed for the longer duration microjets and EUV brightenings are absent for the two singular microeruptions. What is essential to the longer duration microjets is that granules with the concentration of a positive magnetic field persistently transport the magnetic field to the PILs, canceling the opposite magnetic flux and making the base of the two microjets and the underlying granules migrate with the speed of ~0.25 and 1.0 km s-1. The observations support the scenario of magnetic reconnection for the quasiperiodic microjets and further show that the reconnection continuously generates multitemperature components, especially the cool component with chromospheric temperature. In addition, the ongoing reconnection is modulated by p-mode oscillations inside the Sun.

Keywords: solar mottles; solar magnetic reconnection
Dynamical Evolution of an Active-region Filament Driven by Magnetic Reconnection

Studying solar filament dynamical evolutions is an important approach to reveal the driving mechanism of solar eruptions, which seriously impact on the Sun-Earth system and could cause disastrous space weather. To better understand the evolution process of solar filaments, here we investigate an active-region filament by employing observations from the New Vacuum Solar Telescope (NVST), Solar Dynamics Observatory, and Interface Region Imaging Spectrograph. The high-resolution NVST Hα images show that the northern footpoint of the filament gradually moved northward. Near the northern footpoint, there is an arch filament system (AFS). Between adjacent footpoints of the filament and the AFS, transient brightening, underlying magnetic cancellation, and bidirectional flows were detected, which jointly imply that it could be the magnetic reconnection between the filament and the AFS that changes the connection of filament threads and drives its footpoint to move northward. In addition, during the footpoint evolution, the filament with highly twisted structure underwent several untwisting motions. Meanwhile, transient brightenings were also observed and appeared as bright knots around several positions where filament threads might braid with each other. And some bright blobs were also detected to propagate outward from the brightening region. These observations suggest that magnetic reconnection might be responsible for the untwisting motion. This work exposes us to a dynamical scenario of the filament evolution driven by magnetic reconnection, which will promote our understanding of the formation and eruption of the filaments.

Keywords: solar atmosphere; solar magnetic fields; solar magnetic reconnection; solar active region filaments; solar filament eruptions
Search for Supernova Neutrinos and Constraint on the Galactic Star Formation Rate with the KamLAND Data

We present the results of a search for core-collapse supernova neutrinos, using long-term KamLAND data from 2002 March 9 to 2020 April 25. We focus on the electron antineutrinos emitted from supernovae in the energy range of 1.8-111 MeV. Supernovae will make a neutrino event cluster with the duration of ~10 s in the KamLAND data. We find no neutrino clusters and give the upper limit on the supernova rate to be 0.15 yr-1 with a 90% confidence level. The detectable range, which corresponds to a >95% detection probability, is 40-59 kpc and 65-81 kpc for core-collapse supernovae and failed core-collapse supernovae, respectively. This paper proposes to convert the supernova rate obtained by the neutrino observation to the Galactic star formation rate. Assuming a modified Salpeter-type initial mass function, the upper limit on the Galactic star formation rate is <(17.5-22.7) M ⊙ yr-1 with a 90% confidence level.

Keywords: supernova neutrinos; neutrino astronomy
High-contrast Demonstration of an Apodized Vortex Coronagraph

High-contrast imaging is the primary path to the direct detection and characterization of Earth-like planets around solar-type stars; a cleverly designed internal coronagraph suppresses the light from the star, revealing the elusive circumstellar companions. However, future large-aperture telescopes (>4 m in diameter) will likely have segmented primary mirrors, which cause additional diffraction of unwanted stellar light. Here we present the first high-contrast laboratory demonstration of an apodized vortex coronagraph, in which an apodizer is placed upstream of a vortex focal plane mask to improve its performance with a segmented aperture. The gray-scale apodization is numerically optimized to yield a better sensitivity to faint companions assuming an aperture shape similar to the LUVOIR-B concept. Using wavefront sensing and control over a one-sided dark hole, we achieve a raw contrast of 2 × 10-8 in monochromatic light at 775 nm, and a raw contrast of 4 × 10-8 in a 10% bandwidth. These results open the path to a new family of coronagraph designs, optimally suited for next-generation segmented space telescopes.

Keywords: exoplanets; direct imaging; space telescopes
Stromlo Stellar Tracks: Non-solar-scaled Abundances for Massive Stars

We present the Stromlo Stellar Tracks, a set of stellar evolutionary tracks, computed by modifying the Modules for Experiments in Stellar Astrophysics (MESA) 1D stellar evolution package, to fit the Galactic Concordance abundances for hot (T > 8000 K) massive (≥10 M⊙) main-sequence (MS) stars. Until now, all stellar evolution tracks have been computed at solar, scaled-solar, or α-element-enhanced abundances, and none of these models correctly represent the Galactic Concordance abundances at different metallicities. This paper is the first implementation of Galactic Concordance abundances to the stellar evolution models. The Stromlo tracks cover massive stars (10 ≤ M/M⊙ ≤ 300) with varying rotations (v/vcrit = 0.0, 0.2, 0.4) and a finely sampled grid of metallicities (-2.0 ≤ [Z/H] ≤ +0.5; Δ[Z/H] = 0.1) evolved from the pre-main sequence to the end of 12C burning. We find that the implementation of Galactic Concordance abundances is critical for the evolution of MS, massive hot stars in order to estimate accurate stellar outputs (L, Teff, g), which, in turn, have a significant impact on determining the ionizing photon luminosity budgets. We additionally support prior findings of the importance that rotation plays on the evolution of massive stars and their ionizing budget. The evolutionary tracks for our Galactic Concordance abundance scaling provide a more empirically motivated approach than simple uniform abundance scaling with metallicity for the analysis of H II regions and have considerable implications for determining nebular emission lines and metallicity. Therefore, it is important to refine existing stellar evolutionary models for comprehensive high-redshift extragalactic studies. The Stromlo tracks are available to the astronomical community.

Keywords: stellar evolution; stellar evolutionary tracks; massive stars; stellar rotation; stellar abundances; interstellar abundances; chemical abundances
FAUST. XIV. Probing the Flared Disk in L1527 with Sulfur-bearing Molecules

IRAS04368+2557 in L1527 is a Class 0/I protostar with a clear disk-envelope system revealed by previous Atacama Large Millimeter/submillimeter Array (ALMA) observations. In this paper, we discuss the flared structure of this source with observed sulfur-bearing molecules included in the FAUST ALMA large program. The analyses of molecular distributions and kinematics have shown that CS, SO, and OCS trace different regions of the disk-envelope system. To evaluate the temperature across the disk, we derive rotation temperature with the two observed SO lines. The temperature profile shows a clear, flared "butterfly" structure with the higher temperature being ∼50 K and the central lower temperature region (<30 K) coinciding with the continuum peak, suggesting dynamically originated heating rather than radiation heating from the central protostar. Other physical properties, including column densities, are also estimated and further used to demonstrate the vertical structure of the disk-envelope system. The "warped" disk structure of L1527 is confirmed with our analyses, showing that sulfur-bearing molecules are not only effective material probes but also sufficient for structural studies of protostellar systems.

Keywords: astrochemistry; interstellar medium; interstellar molecules; protostars; star formation
Spitzer Reveals Evidence of Molecular Absorption in the Atmosphere of the Hot Neptune LTT 9779b

Non-rocky sub-Jovian exoplanets in high-irradiation environments are rare. LTT 9779b, also known as Transiting Exoplanet Survey Satellite (TESS) object of interest (TOI) 193.01, is one of the few such planets discovered to date, and the first example of an ultrahot Neptune. The planet&'s bulk density indicates that it has a substantial atmosphere, so to investigate its atmospheric composition and shed further light on its origin, we obtained Spitzer InfraRed Array Camera secondary eclipse observations of LTT 9779b at 3.6 and 4.5 μm. We combined the Spitzer observations with a measurement of the secondary eclipse in the TESS bandpass. The resulting secondary eclipse spectrum strongly prefers a model that includes CO absorption over a blackbody spectrum, incidentally making LTT 9779b the first TESS exoplanet (and the first ultrahot Neptune) with evidence of a spectral feature in its atmosphere. We did not find evidence of a thermal inversion, at odds with expectations based on the atmospheres of similarly irradiated hot Jupiters. We also report a nominal dayside brightness temperature of 2305 ± 141 K (based on the 3.6 μm secondary eclipse measurement), and we constrained the planet&'s orbital eccentricity to e < 0.01 at the 99.7% confidence level. Together with our analysis of LTT 9779b&'s thermal phase curves reported in a companion paper, our results set the stage for similar investigations of a larger sample of exoplanets discovered in the hot-Neptune desert, investigations that are key to uncovering the origin of this population.

Keywords: sky surveys; eclipses; exoplanets; hot neptunes; infrared astronomy; exoplanet atmospheres
Observation of Alfvén Ion Cyclotron Waves in ICME Magnetic Clouds at 1 au

Waves in plasma play an essential role in the energy transfer and plasma-heating processes. This article discusses the in situ observation of Alfvén ion cyclotron (AIC) waves and their characteristics within interplanetary coronal mass ejection (ICME) flux ropes. We analyzed 401 ICME flux ropes, observed by WIND spacecraft from 1995 to 2021 at 1 au. We found only five ICME flux ropes that show an explicit presence of AIC waves; two have normalized magnetic helicity σ m ≤ -0.5, and the remaining three show σ m ≥ 0.5 polarization. The angle between velocity and magnetic field (θ VB) for σ m ≤ -0.5 is <40°, whereas for σ m ≥ 0.5, θ VB > 140°. This result supports the existence of quasi-parallel and quasi-antiparallel left-handed polarized AIC waves within ICME flux ropes. We suggest that AIC waves are possibly triggered by (i) proton temperature anisotropy Tp ⊥/Tp ∥ > 1 driven by cyclotron instability and (ii) low-frequency Alfvén waves through the magnetohydrodynamic turbulent cascade. This study shows evidence of fluid and kinetic scales coupling in the ICME flux rope.

Keywords: magnetohydrodynamics
A Strong X-Ray Polarization Signal from the Magnetar 1RXS J170849.0-400910

Magnetars are the most strongly magnetized neutron stars, and one of the most promising targets for X-ray polarimetric measurements. We present here the first Imaging X-ray Polarimetry Explorer observation of the magnetar 1RXS J170849.0-400910, jointly analyzed with a new Swift observation and archival NICER data. The total (energy- and phase-integrated) emission in the 2-8 keV energy range is linerarly polarized, at a ~35% level. The phase-averaged polarization signal shows a marked increase with energy, ranging from ~20% at 2-3 keV up to ~80% at 6-8 keV, while the polarization angle remains constant. This indicates that radiation is mostly polarized in a single direction. The spectrum is well reproduced by a combination of either two thermal (blackbody) components or a blackbody and a power law. Both the polarization degree and angle also show a variation with the spin phase, and the former is almost anticorrelated with the source counts in the 2-8 and 2-4 keV bands. We discuss the possible implications and interpretations, based on a joint analysis of the spectral, polarization, and pulsation properties of the source. A scenario in which the surface temperature is not homogeneous, with a hotter cap covered by a gaseous atmosphere and a warmer region in a condensed state, provides a satisfactory description of both the phase- and energy-dependent spectro-polarimetric data. The (comparatively) small size of the two emitting regions, required to explain the observed pulsations, does not allow to reach a robust conclusion about the presence of vacuum birefringence effects.

Keywords: polarimetry; magnetars
Studying Postmerger Outflows from Magnetized-neutrino-cooled Accretion Disks

Neutrino-cooled accretion flow around a spinning black hole, produced by a compact binary merger, is a promising scenario for jet formation and launching magnetically driven outflows. Based on GW170817 gravitational wave detection by LIGO and Virgo observatories, followed by electromagnetic counterparts, this model can explain the central engine of the short-duration gamma-ray bursts and kilonova radiations. Using the open-source general relativistic magnetohydrodynamic HARM-COOL code, we evolved several 2D magnetized accretion disk-black hole models with a realistic equation of state in the fixed curved spacetime background. We applied the particle tracer technique to measure the properties of the outflows. The disk and black hole's initial parameters are chosen in a way to represent different possible postmerger scenarios of the merging compact objects. Our simulations show a strong correlation between the black hole's spin and ejected mass. Generally, mergers producing massive disks and rapidly spinning black holes launch stronger outflows. We observed our models generate winds with moderate velocity (v/c ~ 0.1-0.2) and a broad range of electron fractions. We use these results to estimate the luminosity and light curves of possible radioactively powered transients emitted by such systems. We found that the luminosity peaks within the range of 1040-1042 erg s-1, which agrees with previous studies for disk wind outflows.

Keywords: accretion
Upper Field-strength Limit of Fast Radio Bursts

Fast radio bursts (FRBs) are cosmological radio transients with an unclear generation mechanism. Known characteristics such as their luminosity, duration, spectrum, and repetition rate, etc., suggest that FRBs are powerful coherent radio signals at GHz frequencies, but the status of FRBs near the source remains unknown. As an extreme astronomical event, FRBs should be accompanied by energy-comparable or even more powerful X/γ-ray counterparts. Here, particle-in-cell simulations of ultrastrong GHz radio pulse interaction with GeV photons show that at ≳3 × 1012 V cm-1 field strengths, quantum cascade can generate dense pair plasmas, which greatly dampen the radio pulse. Thus, in the presence of GeV photons in the source region, GHz radio pulses stronger than 3 × 1012 V cm-1 cannot escape. This result indicates an upper field-strength limit of FRBs at the source.

Keywords: radio transient sources; radio bursts; plasma astrophysics
Tossing Black Hole Spin Axes

The detection of double black hole (BH+BH) mergers provides a unique possibility to understand their physical properties and origin. To date, the LIGO-Virgo-KAGRA network of high-frequency gravitational-wave observatories has announced the detection of more than 85 BH+BH merger events. An important diagnostic feature that can be extracted from the data is the distribution of effective inspiral spins of the BHs. This distribution is in clear tension with theoretical expectations from both an isolated binary star origin, which traditionally predicts close-to-aligned BH component spins, and formation via dynamical interactions in dense stellar environments that predicts a symmetric distribution of effective inspiral spins. Here it is demonstrated that isolated binary evolution can convincingly explain the observed data if BHs have their spin axis tossed during their formation process in the core collapse of a massive star, similarly to the process evidently acting in newborn neutron stars. BH formation without spin-axis tossing, however, has difficulties reproducing the observed data-even if alignment of spins prior to the second core collapse is disregarded. Based on simulations with only a minimum of assumptions, constraints from empirical data can be made on the spin magnitudes of the first- and second-born BHs, thereby serving to better understand massive binary star evolution prior to the formation of BHs.

Keywords: stellar mass black holes; gravitational wave sources; supernova dynamics; compact binary stars