adsabs/SciX_UAT_keywords huggingface dataset:
Small-scale Magnetic Flux Ropes in the First Two Parker Solar Probe Encounters

Small-scale magnetic flux ropes (SFRs) are a type of structure in the solar wind that possess helical magnetic field lines. In a recent report we presented the radial variations of the properties of SFRs from 0.29 to 8 au using in situ measurements from the Helios, Advanced Composition Explorer/WIND (ACE/Wind), Ulysses, and Voyager spacecrafts. With the launch of the Parker Solar Probe (PSP), we extend our previous investigation further into the inner heliosphere. We apply a Grad-Shafranov-based algorithm to identify SFRs during the first two PSP encounters. We find that the number of SFRs detected near the Sun is much less than at larger radial distances, where magnetohydrodynamic (MHD) turbulence may act as the local source to produce these structures. The prevalence of Alfvénic structures significantly suppresses the detection of SFRs at closer distances. We compare the SFR event list with other event identification methods, yielding a dozen well-matched events. The cross-section maps of two selected events confirm the cylindrical magnetic flux-rope configuration. The power-law relation between the SFR magnetic field and heliocentric distances seems to hold down to 0.16 au.

Keywords: solar wind; interplanetary turbulence; magnetohydrodynamics; astronomy data analysis; astronomy databases
Spinning Nanoparticles Impacted by C-shock: Implications for Radio-millimeter Emission from Star-forming Regions

We investigate the impact of anomalous microwave emission (AME) on the radio-millimeter spectral energy distribution for three typical interstellar medium (ISM) conditions surrounding star-forming regions-cold neutral medium, warm neutral medium, and photodissociation regions-by comparing the emissivities of three major contributors: free-free, thermal dust emission, and AME. In particular, for spinning nanoparticles (i.e., potential carriers of AME), we consider a known grain destruction mechanism due to a centrifugal force from spin-up processes caused by collisions between dust grains and supersonic neutral streams in a magnetized shock (C-shock). We demonstrate that, if the ISM in a magnetic field is impacted by a C-shock developed by a supernova explosion in the early phase of massive star formation (≲10 Myr), AME can be significantly or almost entirely suppressed relative to free-free and thermal dust continuum emission if the grain tensile strength is small enough. This study may shed light on explaining the rare observations of AME from extragalactic star-forming regions preferentially observed from massive star clusters and suggest a scenario of "the rise and fall of AME" in accordance with the temporal evolution of star-forming regions.

Keywords: interstellar medium; interstellar dust processes; radiative processes; radio astronomy; millimeter astronomy; interstellar dust; astrophysical dust processes; star forming regions
Splitting of Long-period Comet C/2018 F4 (PANSTARRS)

Long-period comet C/2018 F4 (PANSTARRS) was observed to show duplicity of its inner region in 2020 September, suggestive of a splitting event. We here present analyses of our observations of the comet taken from the LCO Outbursting Objects Key project and the University of Hawaii 2.2 m telescope after the discovery of the splitting. The two fragments Components A and B, estimated to be ~60 m to 4 km in radius, remained highly similar to each other in terms of brightness, color, and dust morphology throughout our observing campaign from 2020 September to 2021 December. Our fragmentation model yielded that the two components split at a relative speed of 3.00 ± 0.18 m s-1 in 2020 late April, implying a specific energy change of $\left(5.3\pm 2.8\right)\times {10}^{3}$ J kg-1, and that Component B was subjected to a stronger nongravitational acceleration than Component A in both the radial and normal directions of the orbit. The obtained splitting time is broadly consistent with the result from the dust morphology analysis, which further suggested that the dominant dust grains were millimeter-sized and ejected at a speed of ~2 m s-1. We postulate that the pre-split nucleus of the comet consisted of two lobes resembling that of 67P, or that the comet used to be a binary system like main-belt comet 288P. Regardless, we highlight the possibility of using observations of split comets as a feasible manner to study the bilobate shape or binarity fraction of cometary nuclei.

Keywords: small solar system bodies; long period comets; comets
LoTSS Jellyfish Galaxies. IV. Enhanced Star Formation on the Leading Half of Cluster Galaxies and Gas Compression in IC3949

With Mapping Nearby Galaxies at APO integral field spectroscopy, we present a resolved analysis of star formation for 29 jellyfish galaxies in nearby clusters, identified from radio continuum imaging taken by the Low Frequency Array. Simulations predict enhanced star formation on the "leading half" (LH) of galaxies undergoing ram pressure stripping, and in this work we report observational evidence for this elevated star formation. The dividing line (through the galaxy center) that maximizes this star formation enhancement is systematically tied to the observed direction of the ram-pressure-stripped tail, suggesting a physical connection between ram pressure and this star formation enhancement. We also present a case study on the distribution of molecular gas in one jellyfish galaxy from our sample, IC3949, using Atacama Large Millimeter/submillimeter Array CO J = 1 - 0, HCN J = 1 - 0, and HCO+ J = 1 - 0 observations from the ALMA MaNGA Quenching and Star Formation Survey. The H2 depletion time (as traced by CO) in IC3949 ranges from ~1 Gyr in the outskirts of the molecular gas disk to ~11 Gyr near the galaxy center. IC3949 shows a clear region of enhanced star formation on the LH of the galaxy where the average depletion time is ~2.7 Gyr, in line with the median value for the galaxy on the whole. Dense gas tracers, HCN and HCO+, are only detected at the galaxy center and on the LH of IC3949. Our results favor a scenario in which ram pressure compresses the interstellar medium, promoting the formation of molecular gas that in turn fuels a localized increase of star formation.

Keywords: galaxy clusters; star formation; ram pressure stripped tails; galaxy quenching; molecular gas
Predicted Masses of Galactic Cepheids in the Gaia Data Release 2

On the basis of recently computed nonlinear convective pulsation models of Galactic Cepheids, spanning wide ranges of input stellar parameters, we derive theoretical mass-dependent Period-Wesenheit relations in the Gaia bands, namely, G, GBP, and GBR, that are found to be almost independent of the assumed efficiency of superadiabatic convection. The application to a selected subsample of the Gaia Data Release 2 Galactic Cepheids database allows us to derive mass-dependent estimates of their individual distances. By imposing their match with the astrometric values inferred from Gaia, we are able to evaluate the individual mass of each pulsator. The inferred mass distribution is peaked around 5.6M⊙ and 5.4M⊙ for the F and FO pulsators, respectively. If the estimated Gaia parallax offset $\langle {\rm{\Delta }}\varpi \rangle =0.046$ mas is applied to Gaia parallaxes before imposing their coincidence with the theoretical ones, the inferred mass distribution is found to shift toward lower masses, namely, ∼5.2M⊙ and 5.1M⊙ for the F and FO pulsators, respectively. The comparison with independent evaluations of the stellar masses, for a subset of binary Cepheids in our sample, seems to support the predictive capability of the current theoretical scenario. By forcing the coincidence of our mass determinations with these literature values we derive an independent estimate of the mean offset to be applied to Gaia DR2 parallaxes, $\langle {\rm{\Delta }}\varpi \rangle =0.053\pm 0.029$ mas, slightly higher but in agreement within the errors with the Riess et al. value.

Keywords: cepheid variable stars; cepheid distance; distance indicators; stellar pulsations; stellar oscillations; stellar evolution
Simulation of the Interplanetary Bz Using a Data-driven Heliospheric Solar Wind Model

Aimed to be ready for the transition from research to operation, we have developed a solar wind model by coupling a data-driven empirical coronal model with a magnetohydrodynamics heliospheric model. We performed a data-driven simulation of the solar wind for a two-year period during the declining and minimum phases of solar cycle 23. Comparisons with OMNI and Ulysses spacecraft data show that the model can reproduce the large-scale variations of the solar wind plasma parameters. The evolution of geocentric solar magnetospheric (GSM) Bx and Bz components are also reasonably duplicated by the model in terms of polarity and strength. Apparent signatures of the Russell-McPherron (R-M) effect are found from both observed data and simulated results, indicating that during the investigated interval the R-M effect is the dominant mechanism that controls the large-scale evolution of the north-south component of the interplanetary magnetic field in the GSM frame. The results demonstrate that the established model can provide valuable space weather information about the solar wind.

Keywords: magnetohydrodynamical simulations; solar wind; interplanetary magnetic fields; space weather
Filamentary Network and Magnetic Field Structures Revealed with BISTRO in the High-mass Star-forming Region NGC 2264: Global Properties and Local Magnetogravitational Configurations

We report 850 μm continuum polarization observations toward the filamentary high-mass star-forming region NGC 2264, taken as part of the B-fields In STar forming Regions Observations large program on the James Clerk Maxwell Telescope. These data reveal a well-structured nonuniform magnetic field in the NGC 2264C and 2264D regions with a prevailing orientation around 30° from north to east. Field strength estimates and a virial analysis of the major clumps indicate that NGC 2264C is globally dominated by gravity, while in 2264D, magnetic, gravitational, and kinetic energies are roughly balanced. We present an analysis scheme that utilizes the locally resolved magnetic field structures, together with the locally measured gravitational vector field and the extracted filamentary network. From this, we infer statistical trends showing that this network consists of two main groups of filaments oriented approximately perpendicular to one another. Additionally, gravity shows one dominating converging direction that is roughly perpendicular to one of the filament orientations, which is suggestive of mass accretion along this direction. Beyond these statistical trends, we identify two types of filaments. The type I filament is perpendicular to the magnetic field with local gravity transitioning from parallel to perpendicular to the magnetic field from the outside to the filament ridge. The type II filament is parallel to the magnetic field and local gravity. We interpret these two types of filaments as originating from the competition between radial collapsing, driven by filament self-gravity, and longitudinal collapsing, driven by the region's global gravity.

Keywords: collapsing clouds; interstellar filaments; molecular clouds; interstellar magnetic fields; interstellar medium; polarimetry; interstellar dynamics; star forming regions; submillimeter astronomy; young massive clusters
Investigation of the Gamma-Ray Bursts Prompt Emission Under the Relativistically Expanding Fireball Scenario

The spectral properties of a composite thermal emission arising from a relativistic expanding fireball can be remarkably different from the Planck function. We perform a detailed study of such a system to explore the features of the prompt emission spectra from gamma-ray bursts (GRBs). In particular, we address the effect of optical opacity and its dependence on the density profile between the expanding gas and the observer. This results in a nontrivial shape of the photospheric radius, which in combination with the constraints derived from the equal arrival time can result in a mild broader spectrum compared to the Planck function. Further, we show the time-integrated spectrum from the expanding fireball deviates significantly from the instantaneous emission and is capable of explaining the observed broad spectral width of GRBs. We also show that the demand of the spectral width of the order of unity, obtained through statistical analysis, is consistent with the scenario where the dynamics of the expanding fireball are governed predominantly by the energy content of the matter.

Keywords: x-ray transient sources; gamma-ray bursts; radiative processes
Rotation Periods of TESS Objects of Interest from the Magellan-TESS Survey with Multiband Photometry from Evryscope and TESS

Stellar radial-velocity (RV) jitter due to surface activity may bias the RV semiamplitude and mass of rocky planets. The amplitude of the jitter may be estimated from the uncertainty in the rotation period, allowing the mass to be more accurately obtained. We find candidate rotation periods for 17 out of 35 TESS Objects of Interest (TOI) hosting <3 R⊕ planets as part of the Magellan-TESS survey, which is the first-ever statistically robust study of exoplanet masses and radii across the photoevaporation gap. Seven periods are ≥3σ detections, two are ≥1.5σ, and eight show plausible variability, but the periods remain unconfirmed. The other 18 TOIs are nondetections. Candidate rotators include the host stars of the confirmed planets L 168-9 b, the HD 21749 system, LTT 1445 A b, TOI 1062 b, and the L 98-59 system. Thirteen candidates have no counterpart in the 1000 TOI rotation catalog of Canto Martins et al. We find periods for G3-M3 dwarfs using combined light curves from TESS and the Evryscope all-sky array of small telescopes, sometimes with longer periods than would be possible with TESS alone. Secure periods range from 1.4 to 26 days with Evryscope-measured photometric amplitudes as small as 2.1 mmag in $g^{\prime} $ . We also apply Monte Carlo sampling and a Gaussian process stellar activity model from exoplanet to the TESS light curves of six TOIs to confirm the Evryscope periods.

Keywords: stellar activity; radial velocity; exoplanet astronomy; sky surveys; starspots
Dust Rings and Cavities in the Protoplanetary Disks around HD 163296 and DoAr 44

We model substructure in the protoplanetary disks around DoAr 44 and HD 163296 in order to better understand the conditions under which planets may form. We match archival millimeter-wavelength thermal emission against models of the disks' structure that are in radiation balance with the starlight heating and in vertical hydrostatic equilibrium, and then we compare to archival polarized scattered near-infrared images of the disks. The millimeter emission arises in the interior, while the scattered near-infrared radiation probes the disks' outer layers. Our best model of the HD 163296 disk has dust masses 81 ± 13 M ⊕ in the inner ring at 68 au and ${82}_{-16}^{+26}$ M ⊕ in the outer ring at 102 au, both falling within the range of estimates from previous studies. Our DoAr 44 model has total dust mass ${84}_{-3.5}^{+7.0}$ M ⊕. Unlike HD 163296, DoAr 44 as of yet has no detected planets. If the central cavity in the DoAr 44 disk is caused by a planet, the planet's mass must be at least 0.5 M J and is unlikely to be greater than 1.6 M J. We demonstrate that the DoAr 44 disk's structure with a bright ring offset within a fainter skirt can be formed by dust particles drifting through a plausible distribution of gas.

Keywords: protoplanetary disks; planet formation; radiative transfer simulations
Eclipsing Binary Populations across the Northern Galactic Plane from the KISOGP Survey

We present a catalog of eclipsing binaries in the northern Galactic plane from the Kiso Wide-Field Camera Intensive Survey of the Galactic Plane (KISOGP). We visually identified 7055 eclipsing binaries spread across ∼330 deg2, including 4197 W Ursa Majoris/EW-type, 1458 β Lyrae/EB-type, and 1400 Algol/EA-type eclipsing binaries. For all systems, I-band light curves were used to obtain accurate system parameters. We derived the distances and extinction values for the EW-type objects from their period-luminosity relation. We also obtained the structure of the thin disk from the distribution of our sample of eclipsing binary systems, combined with those of high-mass star-forming regions and Cepheid tracers. We found that the thin disk is inhomogeneous in number density as a function of Galactic longitude. Using this new set of distance tracers, we constrain the detailed structure of the thin disk. Finally, we report a global parallax zero-point offset of Δπ = -42.1 ± 1.9 (stat.) ± 12.9 (syst.) μas between our carefully calibrated EW-type eclipsing binary positions and those provided by Gaia Early Data Release 3. Implementation of the officially recommended parallax zero-point correction results in a significantly reduced offset. Additionally, we provide a photometric characterization of our EW-type eclipsing binaries that can be applied to further analyses.

Keywords: eclipsing binary stars; w ursae majoris variable stars; distance indicators; milky way disk; catalogs
Lyα Irradiation of Superhydrogenated Coronene Films: Implications for H2 Formation

We present the results of an experimental study of the interaction of Lyα photons with superhydrogenated coronene films. The effects of ultraviolet (UV) irradiation have been analyzed with infrared spectroscopy. The spectral changes provide evidence for UV photodestruction of the C-D bonds of the superhydrogenated coronene with a cross section of 8 ± 2 × 10-20 cm2. The comparison of our experimental result with the prediction from theoretical modeling suggests an extension of the region inside photodissociation regions where superhydrogenated coronene can survive and contribute to H2 formation. H2 formation through abstraction in superhydrogenated coronene dominates over direct H2 loss induced by UV photodestruction.

Keywords: astrochemistry
Revealing Thermal Comptonization of Accretion Disk Photons in IC 4329A with AstroSat

We present five simultaneous UV/X-ray observations of IC 4329A by AstroSat performed over a 5 month period. We utilize the excellent spatial resolution of the Ultra-Violet Imaging Telescope on board AstroSat to reliably separate the intrinsic active galactic nucleus (AGN) flux from the host galaxy emission and correct for the Galactic and internal reddening, as well as the contribution from the narrow- and broad-line regions. We detect large-amplitude UV variability, which is unusual for a large black hole mass AGN like IC 4329A, over such a small period. In fact, the fractional variability amplitude is larger in the UV band than in the X-ray band. This demonstrates that the observed UV variability is intrinsic to the disk and not due to X-ray illumination. The joint X-ray spectral analyses of five sets of Soft X-ray Telescope and Large Area X-ray Proportional Counter spectral data reveal a soft X-ray excess component, a narrow iron line (with no indication of a significant Compton hump), and a steepening power law (ΔΓ ~ 0.21) with increasing X-ray flux. The soft excess component could arise due to thermal Comptonization of the inner disk photons in a warm corona with kTe ~ 0.26 keV. The UV emission we detect acts as the primary seed photons for the hot corona, which produces the broadband X-ray continuum. The X-ray spectral variability is well described by the cooling of this corona from kTe ~ 42 to ~32 keV with increasing UV flux, while the optical depth remains constant at τ ~ 2.3.

Keywords: active galactic nuclei
The Phase-curve Signature of Condensible Water-rich Atmospheres on Slowly Rotating Tidally Locked Exoplanets

We use an idealized three-dimensional general circulation model to study condensible-rich atmospheres with an ineffective cold trap on slowly rotating tidally locked terrestrial planets. In particular, we show the climate dynamics in a thin and temperate atmosphere with condensible water vapor. The similarities between our thin and temperate atmosphere and the warm and thick atmosphere approaching the water vapor runaway greenhouse in previous works are discussed, including the reversal of the thermal emission between the day and night hemispheres. Different from the transit spectroscopy of water vapor that depends on the absolute amount of atmospheric water vapor, the contrast between the dayside and nightside thermal emission provides information regarding the relative ratio of water vapor to the background atmosphere as well as the atmospheric pressure near the substellar tropopause and the emission level on the nightside on potentially habitable worlds.

Keywords: computational methods; atmospheric circulation; extrasolar rocky planets; water vapor; exoplanet atmospheres; exoplanet atmospheric composition
Research on Calibration Method of off-axis Closed-loop Detection System for Multi-target Spectral Telescope

The LAMOST telescope has been operating steadily for more than 10 yr and is currently undergoing an upgrade to its fiber-optic positioning system on the telescope's focal plane. By adding a vision detection system to accurately measure the current position of the optical fibres and carry out closed-loop feedback control, the positioning accuracy of the original optical fiber system is greatly improved. Due to the limitation of the existing optical path of the telescope, to avoid blocking the optical path, the detection system camera cannot be placed on the optical axis of the telescope, which makes the camera and the optical fiber end face at a relatively inclined position. However, the angle between the camera and an object will introduce errors to the polynomial calibration method used in the visual detection system. To address this problem, by analyzing the relationship between the camera imaging principle and the polynomial calibration method, this paper studies the influence of distortion and imaging angle on polynomial calibration results under different angle conditions and proposes an improved high-precision polynomial calibration method. First, the distortion parameters are calculated using Zhang's method, and the image distortion is removed. Then, a mapping model between oblique plane image and nonoblique plane image is established through a homography matrix. The coordinates of all oblique plane feature points are mapped one by one to the nonoblique plane positions on the image space, and a good correction effect is obtained. Finally, the calibration images from different angles are calculated and analyzed through simulation experiments and compared with Zhang's method. The results show that this method has a 10%-40% improvement over Zhang's method.

Keywords: astronomical instrumentation; astronomical techniques; photogrammetry
Chandra HETG X-Ray Spectra and Variability of π Aqr, a γ Cas-type Be Star

High-resolution X-ray spectra of π Aqr, a γ Cas-type star, obtained with the Chandra/HETG spectrometer, revealed emission lines of H-like ions of Mg, Si, S, and Fe; a strong, hard continuum; and a lack of He-like ions, indicating the presence of very hot thermal plasma. The X-ray light curve showed significant fluctuations, with coherent variability at a period of about 3400 s in one observation. The hardness ratio was relatively constant except for one observation in which the spectrum was much harder and more absorbed. We interpret the X-ray emission as arising from accretion onto the secondary, which is likely a magnetic white dwarf, an intermediate polar system.

Keywords: x-ray astronomy; gamma cassiopeiae stars; high resolution spectroscopy; early-type emission stars; white dwarf stars; be stars