adsabs/SciX_UAT_keywords huggingface dataset:
Clustering of Fast Coronal Mass Ejections during Solar Cycles 23 and 24 and the Implications for CME-CME Interactions

We study the clustering properties of fast coronal mass ejections (CMEs) that occurred during solar cycles 23 and 24. We apply two methods: the Max Spectrum method can detect the predominant clusters, and the declustering threshold time method provides details on the typical clustering properties and timescales. Our analysis shows that during the different phases of solar cycles 23 and 24, CMEs with speeds ≥1000 km s-1 preferentially occur as isolated events and in clusters with, on average, two members. However, clusters with more members appear, particularly during the maximum phases of the solar cycles. Over the total period and in the maximum phases of solar cycles 23 and 24, about 50% are isolated events, 18% (12%) occur in clusters with two (three) members, and another 20% in larger clusters ≥4, whereas in a solar minimum, fast CMEs tend to occur more frequently as isolated events (62%). During different solar cycle phases, the typical declustering timescales of fast CMEs are τc = 28-32 hr, irrespective of the very different occurrence frequencies of CMEs during a solar minimum and maximum. These findings suggest that τc for extreme events may reflect the characteristic energy build-up time for large flare and CME-prolific active regions. Statistically associating the clustering properties of fast CMEs with the disturbance storm time index at Earth suggests that fast CMEs occurring in clusters tend to produce larger geomagnetic storms than isolated fast CMEs. This may be related to CME-CME interaction producing a more complex and stronger interaction with Earth's magnetosphere.

Keywords: solar coronal mass ejections; solar corona
Extension of HOPS out to 500 pc (eHOPS). I. Identification and Modeling of Protostars in the Aquila Molecular Clouds

We present a Spitzer/Herschel focused survey of the Aquila molecular clouds (d ~ 436 pc) as part of the eHOPS (extension of the Herschel orion protostar survey, or HOPS, Out to 500 ParSecs) census of nearby protostars. For every source detected in the Herschel/PACS bands, the eHOPS-Aquila catalog contains 1-850 μm SEDs assembled from the Two Micron All Sky Survey, Spitzer, Herschel, the Wide-field Infrared Survey Explorer, and James Clerk Maxwell Telescope/SCUBA-2 data. Using a newly developed set of criteria, we classify objects by their SEDs as protostars, pre-main-sequence stars with disks, and galaxies. A total of 172 protostars are found in Aquila, tightly concentrated in the molecular filaments that thread the clouds. Of these, 71 (42%) are Class 0 protostars, 54 (31%) are Class I protostars, 43 (25%) are flat-spectrum protostars, and four (2%) are Class II sources. Ten of the Class 0 protostars are young PACS bright red sources similar to those discovered in Orion. We compare the SEDs to a grid of radiative transfer models to constrain the luminosities, envelope densities, and envelope masses of the protostars. A comparison of the eHOPS-Aquila to the HOPS protostars in Orion finds that the protostellar luminosity functions in the two star-forming regions are statistically indistinguishable, the bolometric temperatures/envelope masses of eHOPS-Aquila protostars are shifted to cooler temperatures/higher masses, and the eHOPS-Aquila protostars do not show the decline in luminosity with evolution found in Orion. We briefly discuss whether these differences are due to biases between the samples, diverging star formation histories, or the influence of environment on protostellar evolution. * HOPS: Herschel Orion Protostar Survey.

Keywords: star formation; protostars; molecular clouds; infrared astronomy; young stellar objects; astronomy data modeling; far infrared astronomy; pre-main sequence stars; catalogs; surveys
Modeling Extinction and Reddening Effects by Circumstellar Dust in the Betelgeuse Envelope in the Presence of Radiative Torque Disruption

Circumstellar dust forms and evolves within the envelope of evolved stars, including asymptotic giant branch (AGB) and red supergiant (RSG) stars. The extinction of stellar light by circumstellar dust is vital for interpreting RSG/AGB observations and determining high-mass RSG progenitors of core-collapse supernovae. However, circumstellar dust properties are not well understood. Modern understanding of dust evolution suggests that intense stellar radiation can radically change dust properties across the circumstellar envelope through the RAdiative Torque Disruption (RAT-D) mechanism. In this paper, we study the impacts of RAT-D on the grain size distribution (GSD) of circumstellar dust and model its effects on photometric observations of α Orionis (Betelgeuse). Due to the RAT-D effects, large grains formed in the dust formation zone are disrupted into smaller species of size a < 0.5 μm. Using the GSD constrained by the RAT-D effects, we model the visual extinction of background stars and Betelgeuse. We find that the extinction decreases at near-UV, optical, and IR wavelengths while increasing at far-UV wavelengths. The resulting flux potentially reproduces the observation from the near-UV to the near-IR range. Our results can be used to explain dust extinction and photometric observations of other RSG/AGB stars.

Keywords: red supergiant stars; circumstellar dust; circumstellar envelopes; circumstellar matter; extinction
First Sodium Laser Guide Star Asterism Launching Platform in China on the 1.8 m Telescope at Gaomeigu Observatory

The application of a sodium laser guide star is the key difference between a modern adaptive optics system and traditional adaptive optics system. Especially in system such as multiconjugate adaptive optics, a sodium laser guide star asterism that is formed by several laser guide stars in a certain pattern is required to probe more atmospheric turbulence in different directions. To achieve this, a sodium laser guide star asterism launching platform is required. In this paper, we introduce the sodium laser guide star asterism launching platform built and tested on the 1.8 m telescope of Gaomeigu Observatory. The platform has two functions: one function is to compare the performance of sodium laser guide stars generated by different lasers at the same place, and the other function is to generate a sodium laser guide star asterism with an adjustable shape. The field test results at the beginning of 2021 verified the important role of the platform, which is also the first time that a sodium laser guide star asterism was realized in China.

Keywords: laser guide stars; ground telescopes; astronomical instrumentation
Thermonuclear Reaction Rates and Primordial Nucleosynthesis

Assuming the best numerical value for the cosmic baryonic density and the existence of three neutrino flavors, standard Big Bang nucleosynthesis is a parameter-free model. It is important to assess if the observed primordial abundances can be reproduced by simulations. Numerous studies have shown that the simulations overpredict the primordial 7Li abundance by a factor of $\approx 3$ compared to the observations. The discrepancy may be caused by unknown systematics in 7Li observations, poorly understood depletion of lithium in stars, errors in thermonuclear rates that take part in the lithium and beryllium synthesis, or physics beyond the standard model. Here, we focus on the likelihood of a nuclear physics solution. The status of the key nuclear reaction rates is summarized. Big Bang nucleosynthesis simulations are performed with the most recent reaction rates, and the uncertainties of the predicted abundances are established using a Monte Carlo technique. Correlations between abundances and reaction rates are investigated based on the metric of mutual information. The rates of four reactions impact the primordial 7Li abundance: 3He(α,γ)7Be, d(p,γ)3He, 7Be(d,p)2α, and 7Be(n,p)7Li. We employ a genetic algorithm to search for simultaneous rate changes in these four reactions that may account for all observed primordial abundances. When the search is performed for reaction rate ranges that are much wider than recently reported uncertainties, no acceptable solutions are found. Based on the currently available evidence, we conclude that it is highly unlikely for the cosmological lithium problem to have a nuclear physics solution.

Keywords: big bang nucleosynthesis; reaction rates; nuclear astrophysics; nuclear reaction cross sections; cosmic abundances
Determining the Orbital Period and Wind Geometry in GRO J1655-40

During the course of its 2005 outburst, the black hole X-ray binary GRO J1655-40 launched an accretion disk wind associated with deep X-ray absorption lines and strong Compton scattering. Little is known about this apparently super-Eddington wind, but previous works have discovered optical/infrared (OIR) emission from the wind that varies on the orbital period-a possible clue to its origin and geometry. However, there is significant uncertainty in the orbital phases, and a more precise value of the orbital period is needed to accurately phase fold the wind emission. We present our analysis of the I-band photometry from observations taken with the Small and Medium Aperture Research Telescope System 1.3 m telescope between 2006 and 2016. We have implemented two methods-data-driven and model-based-to determine the orbital period, which we report as 2.62193 ± 0.00002 days from the data-driven method and 2.621928 ± 0.000004 days from the model-based method, a significant (25×) increase in precision over prior measurements. We discuss the possible existence of a period derivative, implications of a peculiar deep minimum in the outburst lightcurve of the system, and connections between OIR variability and the geometry of the super-Eddington wind.

Keywords: accretion; black hole physics; x-ray binary stars; stellar winds
Systematic KMTNet Planetary Anomaly Search. XI. Complete Sample of 2016 Subprime Field Planets

Following Shin et al. (2023b), which is a part of the "Systematic KMTNet Planetary Anomaly Search" series (i.e., a search for planets in the 2016 KMTNet prime fields), we conduct a systematic search of the 2016 KMTNet subprime fields using a semi-machine-based algorithm to identify hidden anomalous events missed by the conventional by-eye search. We find four new planets and seven planet candidates that were buried in the KMTNet archive. The new planets are OGLE-2016-BLG-1598Lb, OGLE-2016-BLG-1800Lb, MOA-2016-BLG-526Lb, and KMT-2016-BLG-2321Lb, which show typical properties of microlensing planets, i.e., giant planets orbit M-dwarf host stars beyond their snow lines. For the planet candidates, we find planet/binary or 2L1S/1L2S degeneracies, which are an obstacle to firmly claiming planet detections. By combining the results of Shin et al. (2023b) and this work, we find a total of nine hidden planets, which is about half the number of planets discovered by eye in 2016. With this work, we have met the goal of the systematic search series for 2016, which is to build a complete microlensing planet sample. We also show that our systematic searches significantly contribute to completing the planet sample, especially for planet/host mass ratios smaller than 10‑3, which were incomplete in previous by-eye searches of the KMTNet archive.

Keywords: gravitational microlensing exoplanet detection
The Einstein Ring GAL-CLUS-022058s: a Lensed Ultrabright Submillimeter Galaxy at z = 1.4796

We report an ultrabright lensed submillimeter galaxy at zspec = 1.4796, identified as a result of a full-sky cross-correlation of the AllWISE and Planck compact source catalogs aimed at searching for bright submillimeter galaxies at z ~ 1.5-2.8. Atacama Pathfinder Experiment (APEX)/LABOCA observations of the candidate galaxy reveal a source with flux S870μm = 54 ± 8 mJy. The position of the APEX source coincides with the position of the AllWISE mid-IR source and with the Einstein ring GAL-CLUS-022058s, observed with the Hubble Space Telescope. Archival VLT/FORS observations reveal the redshift of this Einstein ring, zspec = 1.4796, and the detection of the CO(5-4) line at zspec = 1.4802 with APEX/nFLASH230 confirms the redshift of the submillimeter emission. The lensed source appears to be gravitationally magnified by a massive foreground galaxy cluster lens at z = 0.36. We use Lenstool to model the gravitational lensing, which is close to a "fold arc" configuration for an elliptical mass distribution of the central halo, where four images of the lensed galaxy are seen; the mean magnification is μL = 18 ± 4. We have determined an intrinsic rest-frame infrared luminosity of LIR ≈1012L⊙ and a likely star formation rate of ~70-170 M⊙yr-1. The molecular gas mass is Mmol ~ 2.6 × 1010M⊙ and the gas fraction is f = 0.34 ± 0.07. We also obtain a stellar mass log (M*/M⊙) = 10.7 ± 0.1 and a specific star formation rate log (sSFR/Gyr-1) = 0.15 ± 0.03. This galaxy lies on the so-called main sequence of star-forming galaxies at this redshift.

Keywords: ultraluminous infrared galaxies; starburst galaxies; strong gravitational lensing; galaxy clusters; high-redshift galaxies; submillimeter astronomy
Five Massive Contact Binaries with Twin Components in LMC

Massive contact binaries refer to the close binary systems in which the components have filled their respective Roche lobes and share a common envelope with early-type spectra. Twin binaries are a special type of binary system characterized by two components with nearly equal masses. The Magellanic Cloud, comprising the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud, is a fascinating galaxy that is distinct from the Milky Way. With its low metallicity, it serves as an ideal test bed for studying the formation and evolution of massive binaries and testing theoretical models. In this work, based on long-term observations with Optical Gravitational Lensing Experiment and MAssive Compact Halo Object in the LMC, we identified and performed comprehensive analyses of five massive twin contact binaries via the method of the light travel time effect and Wilson-Devinney code. The results show that all of these twin binaries are accompanied by low-mass third bodies. The third bodies have minimum masses ranging from 0.33 to 1.46 M ⊙. Their orbital periods range from 4.34 to 12.03 yr. The maximum distances between the third bodies and the central binary systems range from 6.7 to 11.4 au. Remarkably, four out of the five massive twins have evolved into deep-contact binaries, which indicates that all of them may have originated from Case A mass transfer. These results strongly suggest the significant influence of the third body in the formation and evolution of massive contact binaries and may hold the key to unraveling the origins of massive binaries.

Keywords: multiple stars; eclipsing binary stars; early stellar evolution; early-type stars
Discrepant Approaches to Modeling Stellar Tides and the Blurring of Pseudosynchronization

We examine the reasons for discrepancies between two alternative approaches to modeling small-amplitude tides in binary systems. The direct solution (DS) approach solves the governing differential equations and boundary conditions directly, while the modal decomposition (MD) approach relies on a normal-mode expansion. Applied to a model for the primary star in the heartbeat system KOI-54, the two approaches predict quite different behavior of the secular tidal torque. The MD approach exhibits the pseudosynchronization phenomenon, where the torque due to the equilibrium tide changes sign at a single, well-defined, and theoretically predicted stellar rotation rate. The DS approach instead shows "blurred" pseudosynchronization, where positive and negative torques intermingle over a range of rotation rates. We trace a major source of these differences to an incorrect damping coefficient in the profile functions describing the frequency dependence of the MD expansion coefficients. With this error corrected, some differences between the approaches remain; however, both are in agreement that pseudosynchronization is blurred in the KOI-54 system. Our findings generalize to any type of star for which the tidal damping depends explicitly or implicitly on the forcing frequency.

Keywords: binary stars; tides; stellar oscillations; orbital evolution; theoretical techniques
No Impact of Core-scale Magnetic Field, Turbulence, or Velocity Gradient on Sizes of Protostellar Disks in Orion A

We compared the sizes and fluxes of a sample of protostellar disks in Orion A measured with the Atacama Large Millimeter/submillimeter Array 0.87 mm continuum data from the VLA/ALMA Nascent Disk and Multiplicity survey with the physical properties of their ambient environments on the core scale of 0.6 pc estimated with the Green Bank Ammonia Survey data and the legacy catalog datasets of the polarimeter for the Submillimeter Common-User Bolometer Array. We did not find any significant dependence of the disk radii and continuum fluxes on a single parameter on the core scale, such as nonthermal line width, magnetic field orientation and strength, or magnitude and orientation of the velocity gradient. Among these parameters, we only found a positive correlation between the magnitude of the velocity gradient and the nonthermal line width. Thus, the observed velocity gradients are more likely related to turbulent motion but not large-scale rotation. Our results of no clear dependence of the disk radii on these parameters are more consistent with the expectation from nonideal MHD simulations of disk formation in collapsing cores, where the disk size is self-regulated by magnetic braking and diffusion, compared to other simulations that only include turbulence and/or a magnetic field misaligned with the rotational axis. Therefore, our results could hint that the nonideal MHD effects play a more important role in the disk formation. Nevertheless, we cannot exclude the influences on the observed disk size distribution by dynamical interaction in a stellar cluster or amounts of angular momentum on the core scale, which cannot be probed with the current data.

Keywords: star formation; interstellar magnetic fields; protostars; circumstellar disks
Probing the C IV Continuum Size–Luminosity Relation in Active Galactic Nuclei with Photometric Reverberation Mapping

Reverberation mapping accurately determines virial black hole masses only for redshifts z < 0.2 by utilizing the relationship between the Hβ broad-line region (BLR) size and the 5100 Å continuum luminosity established with ∼200 active galactic nuclei. For quasars at z ∼ 2–3 determining the BLR size is time-consuming and limited by seasonal gaps, requiring, e.g., ∼20 yr of monitoring of the C IV emission lines. In this work, we demonstrate that an efficient alternative is to use a continuum size–luminosity relation, which can be obtained up to 150 times faster than BLR sizes using photometric reverberation mapping (PRM). We outline the method and its feasibility based on simulations and propose an observational strategy that can be carried out with meter-class telescopes. In particular, we focus on the ESO La Silla 2.2 m telescope as it is suitable for an efficient PRM campaign. These observations will provide the scaling factor between the accretion disk and the BLR size (for C IV-1350 Å), which is crucial for estimating the masses of black holes at higher redshifts (z ≳ 2–3).

Keywords: active galactic nuclei; quasars; high-luminosity active galactic nuclei; high-redshift galaxies; medium band photometry; near infrared astronomy; reverberation mapping; time domain astronomy; time series analysis
MeerKAT Observations of the Reversing Drifting Subpulses in PSR J1750-3503

We present an analysis of the subpulse drift in PSR J1750-3503, which is characterized by abrupt transitions of drift direction. As the pulsar does not exhibit other mode changes or clear nulling, it is an ideal candidate system for studying the phenomenon of drift direction change. For ~80% of the time, the subpulses are characterized by positive drift-from early to later longitudes-while the drift direction is negative in the other ~20%. The subpulse separation for single pulses with positive drift, P 2 = (18.8 ± 0.1)°, is higher than for single pulses with negative drift, P 2 = (17.5 ± 0.2)°. When the drift is stable, the measured repetition time of the drift pattern is P 3 obs = (43.5 ± 0.4)P, where P is the pulsar period. We show that the observed data can be reproduced by a carousel models with subpulse rotation around the magnetic axis using a purely dipolar configuration of the surface magnetic field. The observed drift characteristics can be modeled assuming that the actual repetition time P 3 < 2P, such that we observe its aliased value. A small variation in P 3, of the order of 6% (or less assuming higher alias orders), is enough to reproduce the characteristic drift direction changes we observe.

Keywords: radio pulsars
The Peculiar X-Ray Transient Swift J0840.7-3516: An Unusual Low-mass X-Ray Binary or a Tidal Disruption Event?

We report on the X-ray properties of the new transient Swift J0840.7-3516, discovered with Swift/BAT in 2020 February, using extensive data from Swift, MAXI, NICER, and NuSTAR. The source flux increased for ∼103 s after the discovery, decayed rapidly over ∼5 orders of magnitude in five days, and then remained almost constant over nine months. Large-amplitude short-term variations on timescales of 1-104 s were observed throughout the decay. In the initial flux rise, the source showed a hard power-law-shaped spectrum with a photon index of ∼1.0 extending up to ∼30 keV, above which an exponential cutoff was present. The photon index increased in the following rapid decay and became ∼2 at the end of the decay. A spectral absorption feature at 3-4 keV was detected in the decay. It is not straightforward to explain all the observed properties by any known class of X-ray sources. We discuss the possible nature of the source, including a Galactic low-mass X-ray binary with multiple extreme properties and a tidal disruption event by a supermassive black hole or a Galactic neutron star.

Keywords: x-ray transient sources; low-mass x-ray binary stars; tidal disruption
Explosions in Roche-lobe Distorted Stars: Relativistic Bullets in Binaries

State-of-the-art surveys reveal that most massive stars in the Universe evolve in close binaries. Massive stars in such systems are expected to develop aspherical envelopes due to tidal interactions and/or rotational effects. Recently, it was shown that point explosions in oblate stars can produce relativistic equatorial ring-like outflows. Moreover, since stripped-envelope stars in binaries can expand enough to fill their Roche lobes anew, it is likely that these stars die with a greater degree of asphericity than the oblate spheroid geometry previously studied. We investigate the effects of this asymmetry by studying the gas dynamics of axisymmetric point explosions in stars in various stages of filling their Roche lobes. We find that point explosions in these pear-shaped stars produce transrelativistic ejecta that coalesce into bullets pointed both toward and away from the binary companion. We present this result and comment on key morphological differences between core-collapse explosions in spherical versus distorted stars in binary systems, effects on gravitational wave sources, and observational signatures that could be used to glean these explosion geometries from current and future surveys.

Keywords: relativistic fluid dynamics; binary stars; supernovae; radio transient sources; roche lobe