adsabs/SciX_UAT_keywords huggingface dataset:
Tidally Forced Planetary Waves in the Tachocline of Solar-like Stars

Can atmospheric waves in planet-hosting solar-like stars substantially resonate to tidal forcing, perhaps at a level of impacting the space weather or even being dynamo-relevant? In particular, low-frequency Rossby waves, which have been detected in the solar near-surface layers, are predestined to respond to sunspot cycle-scale perturbations. In this paper, we seek to address these questions as we formulate a forced wave model for the tachocline layer, which is widely considered as the birthplace of several magnetohydrodynamic planetary waves, i.e., Rossby, inertia-gravity (Poincaré), Kelvin, Alfvén, and gravity waves. The tachocline is modeled as a shallow plasma atmosphere with an effective free surface on top that we describe within the Cartesian β-plane approximation. As a novelty to former studies, we equip the governing equations with a conservative tidal potential and a linear friction law to account for viscous dissipation. We combine the linearized governing equations into one decoupled wave equation, which facilitates an easily approachable analysis. Analytical results are presented and discussed within several interesting free, damped, and forced wave limits for both midlatitude and equatorially trapped waves. For the idealized case of a single tide-generating body following a circular orbit, we derive an explicit analytic solution that we apply to our Sun for estimating leading-order responses to Jupiter. Our analysis reveals that Rossby waves resonating to low-frequency perturbations can potentially reach considerable velocity amplitudes on the order of 101-102 cm s-1, which, however, strongly rely on the yet unknown frictional damping parameter.

Keywords: internal waves; astrophysical fluid dynamics; magnetic fields; tidal interaction
Newly Discovered Wolf-Rayet Stars in M31

The evolved massive star populations of the Local Group galaxies are generally thought to be well understood. However, recent work has suggested that the Wolf-Rayet (WR) content of M31 may have been underestimated. We therefore began a pilot project to search for new WRs in M31 and to reexamine the completeness of our previous WR survey, finished almost a decade prior. Our improved imaging data and spectroscopic follow-up confirmed 19 new WRs across three small fields in M31. These newly discovered WRs are generally fainter than the previously known sample due to slightly increased reddening as opposed to intrinsic faintness. From these findings, we estimate that there are another ~60 WRs left to be discovered in M31; however, the overall ratio of WN-type (nitrogen-rich) to WC-type (carbon-rich) WRs remains unchanged with our latest additions to the M31 WR census. We are in the process of extending this pilot WR survey to include the rest of M31, and a more complete population will be detailed in our future work.

Keywords: wolf-rayet stars; massive stars; evolved stars; andromeda galaxy; stellar populations
The Connection between the Intracluster Light and its Host Halo: Formation Time and Contribution from Different Channels

We extend the analysis presented by Contini et al. to higher redshifts, up to z = 2, by focusing on the relation between the intracluster light (ICL) fraction and the halo mass, its dependence on redshift, the role played by the halo concentration, and the formation time, in a large sample of simulated galaxy groups/clusters with $13\lesssim {\rm{log}}({M}_{{\rm{halo}}}/{M}_{\odot })\lesssim 15$ . Moreover, a key focus is to isolate the relative contributions provided by the main channels for the ICL formation to the total amount. The ICL fraction at higher redshift is weakly dependent on halo mass and comparable with that at the present time, in agreement with recent observations. Stellar stripping, mergers, and preprocessing are the major channels responsible for the ICL formation, with stellar stripping accounting for ~90% of the total ICL, regardless of halo mass and redshift. Preprocessing is an important process for clusters to accrete already formed ICL. The diffuse component forms very early, at z ~ 0.6, and its formation depends on both concentration and formation time of the halo, with more concentrated haloes that formed early assembling their ICL earlier than those that formed later. The efficiency of this process is independent of halo mass but increases with decreasing redshift, which implies that stellar stripping becomes more important with time as the concentration increases. This highlights the link between the ICL and the dynamical state of a halo: groups/clusters that have a higher fraction of diffuse light are more concentrated, relaxed, and in an advanced stage of growth.

Keywords: extragalactic astronomy
M-Dwarf Flare Candidates Simultaneously Observed by K2 and TESS

We present results of a study on the identification of M-dwarf flares using K2 and TESS data. Our sample includes objects observed simultaneously by these two missions, so that we can also compare how flares are identified in the two sets of data. We implement two open-source Python packages, Lightkurve and PyVAN, to work in unison to easily access the data and determine variability in the light curves of 39 M-dwarfs. We identified 13 flare detections in the TESS data while K2 did not provide any reliable detections of flares. We describe the shortcomings of the K2 data that prevented these flares from being identified.

Keywords: m dwarf stars; stellar flares; space telescopes
Determining the IBEX Ribbon Transverse Profile from ENA Temporal Variations: A Proof of Concept for IMAP Observations

Since its discovery in 2009, the IBEX energetic neutral atom (ENA) Ribbon has been a subject of numerous studies. It appears at energies ~0.5-6 keV and is most pronounced at ~1-3 keV. It is almost circular, ~20°-40° wide, and its center lies near the pristine local interstellar magnetic field direction, whose field lines are draped around the heliosphere. The Ribbon intensity is enhanced above the more diffuse, globally distributed flux (GDF) and varies on timescales that are delayed compared to the underlying and slowly varying GDF. We present a novel method to infer the Ribbon boundaries and transverse profile of the Ribbon using sequential time variations of ENA fluxes, with minimal modeling assumptions involved. The method utilizes the difference in temporal evolution between the total Ribbon content and GDF fluxes. We then use the inferred Ribbon transverse profile to statistically quantify the GDF contribution to the observed peak Ribbon intensity to be ~32.23% ± 3.15% in 2009-2011. This Ribbon separation method works best during times of gradual changes in solar wind output, and with high angular resolution and ENA counting statistics; results thus provide a proof of concept for the upcoming Interstellar Mapping and Acceleration Probe ENA measurements.

Keywords: heliosphere; heliosheath; pickup ions; interstellar magnetic fields; solar wind; solar cycle
Energy Dissipation in Magnetic Islands Formed during Magnetic Reconnection

Magnetic reconnection converts magnetic energy into particle kinetic energy, and satellite observations have shown that 20%-50% of magnetic energy is channeled into electron kinetic energy. How such a large amount of magnetic energy is dissipated into electron kinetic energy is in debate. In this paper, by performing a large-scale 2D particle-in-cell simulation of magnetic reconnection with a guide field, we find that there exist both ion and electron shear flows in magnetic islands formed during magnetic reconnection, which are unstable to the ion and electron Kelvin-Helmholtz (K-H) instabilities. With the development of the K-H instabilities, the magnetic field lines are twisted in these magnetic islands, and intensified electron-scale current sheets are consequently generated. We quantitatively analyze the energy dissipation during such a process in magnetic islands and find that electrons obtain kinetic energy from the magnetic field while ion kinetic energy is transferred into magnetic energy. At last, it results that about 42% of magnetic energy is dissipated into electron kinetic energy in the whole process of magnetic reconnection. Our results help us better understand why a large amount of magnetic energy can be dissipated into electron kinetic energy.

Keywords: solar magnetic reconnection; space plasmas; solar energetic particles
Machine Learning-based Classification of Variable Stars

The classification of variable stars, essential for revealing information on stellar properties and cosmic distances, traditionally relied on statistical methods and limited data. With the emergence of transformative machine learning methodologies and large stellar surveys, we are able to perform more efficient, accurate, and robust handling of expansive databases. We deploy two different machine learning models—random forest and XGBoost—that effectively classify variable stars identified in the most recent phase of the Optical Gravitational Lensing Experiment using four features: (1) time of minimum brightness, (2) I-band amplitude, (3) mean or maximum I-band magnitude, and (4) period. The two models achieve a cross-correlation score of 99.00%, indicating largely shared classifications. The results produced by the models uncover new insights into the precision of supervised learning models in predicting variable stars with the aid of the most up-to-date survey data.

Keywords: anomalous cepheid variable stars; cepheid variable stars; delta scuti variable stars; eclipsing binary stars; intrinsic variable stars; long period variable stars; rr lyrae variable stars; variable stars; classification; random forests
IceCat-1: The IceCube Event Catalog of Alert Tracks

We present a catalog of likely astrophysical neutrino track-like events from the IceCube Neutrino Observatory. IceCube began reporting likely astrophysical neutrinos in 2016, and this system was updated in 2019. The catalog presented here includes events that were reported in real time since 2019, as well as events identified in archival data samples starting from 2011. We report 275 neutrino events from two selection channels as the first entries in the catalog, the IceCube Event Catalog of Alert Tracks, which will see ongoing extensions with additional alerts. The Gold and Bronze alert channels respectively provide neutrino candidates with a 50% and 30% probability of being astrophysical, on average assuming an astrophysical neutrino power-law energy spectral index of 2.19. For each neutrino alert, we provide the reconstructed energy, direction, false-alarm rate, probability of being astrophysical in origin, and likelihood contours describing the spatial uncertainty in the alert's reconstructed location. We also investigate a directional correlation of these neutrino events with gamma-ray and X-ray catalogs, including 4FGL, 3HWC, TeVCat, and Swift-BAT.

Keywords: neutrino astronomy; astronomical methods; high energy astrophysics
A Detection of Red Noise in PSR J1824-2452A and Projections for PSR B1937+21 Using NICER X-Ray Timing Data

We have used X-ray data from the Neutron Star Interior Composition Explorer (NICER) to search for long-timescale temporal correlations ("red noise") in the pulse times of arrival (TOAs) from the millisecond pulsars PSR J1824-2452A and PSR B1937+21. These data more closely track intrinsic noise because X-rays are unaffected by the radio-frequency-dependent propagation effects of the interstellar medium. Our search yields strong evidence (natural log Bayes factor of 9.634 ± 0.016) for red noise in PSR J1824-2452A, but the search is inconclusive for PSR B1937+21. In the interest of future X-ray missions, we devise and implement a method to simulate longer and higher-precision X-ray data sets to determine the timing baseline necessary to detect red noise. We find that the red noise in PSR B1937+21 can be reliably detected in a 5 yr mission with a TOA error of 2 μs and an observing cadence of 20 observations per month compared to the 5 μs TOA error and 11 observations per month that NICER currently achieves in PSR B1937+21. We investigate detecting red noise in PSR B1937+21 with other combinations of observing cadences and TOA errors. We also find that time-correlated red noise commensurate with an injected stochastic gravitational-wave background having an amplitude of A GWB = 2 × 10-15 and spectral index of timing residuals of γ GWB = 13/3 can be detected in a pulsar with similar TOA precision to PSR B1937+21. This is with no additional red noise in a 10 yr mission that observes the pulsar 15 times per month and has an average TOA error of 1 μs.

Keywords: pulsars; millisecond pulsars; red noise; x-ray astronomy; pulsar timing method
A Magnetar Engine for Short GRBs and Kilonovae

We investigate the influence of magnetic fields on the evolution of binary neutron star (BNS) merger remnants via three-dimensional (3D) dynamical-spacetime general-relativistic magnetohydrodynamic (MHD) simulations. We evolve a post-merger remnant with an initial poloidal magnetic field, resolve the magnetoturbulence driven by shear flows, and include a microphysical finite-temperature equation of state. A neutrino leakage scheme that captures the overall energetics and lepton number exchange is also included. We find that turbulence induced by the magnetorotational instability in the hypermassive neutron star (HMNS) amplifies magnetic field to beyond magnetar strength (1015 G). The ultra-strong toroidal field is able to launch a relativistic jet from the HMNS. We also find a magnetized wind that ejects neutron-rich material with a rate of ${\dot{M}}_{\mathrm{ej}}\simeq 1\times {10}^{-1}\,{M}_{\odot }\,{{\rm{s}}}^{-1}$ . The total ejecta mass in our simulation is 5 × 10-3 M⊙. This makes the ejecta from the HMNS an important component in BNS mergers and a promising source of r-process elements that can power a kilonova. The jet from the HMNS reaches a terminal Lorentz factor of ∼5 in our highest-resolution simulation. The formation of this jet is aided by neutrino cooling preventing the accretion disk from protruding into the polar region. As neutrino pair-annihilation and radiative processes in the jet (which were not included in the simulations) will boost the Lorentz factor in the jet further, our simulations demonstrate that magnetars formed in BNS mergers are a viable engine for short gamma-ray bursts.

Keywords: magnetohydrodynamics; astrophysical fluid dynamics; general relativity; jets; high energy astrophysics
Quantifying the Evidence Against a Mass Gap between Black Holes and Neutron Stars

The lack of objects between 2 and 5 M ⊙ in the joint mass distribution of compact objects has been termed the "mass gap," and attributed mainly to the characteristics of the supernova mechanism precluding their birth. However, recent observations show that a number of candidates reported to lie inside the "gap" may fill it, suggesting instead a paucity that may be real or largely a result of small number statistics. We quantify in this work the individual candidates and evaluate the joint probability of a mass gap. Our results show that an absolute mass gap is not present, to a very high confidence level. It remains to be seen if a relative paucity of objects stands in the future, and how this population can be related to the formation processes, which may include neutron star mergers, the collapse of a neutron star to a black hole, and others.

Keywords: compact objects; black holes; neutron stars; astrophysical black holes; stellar mass black holes
Image Subtraction in Fourier Space

Image subtraction is essential for transient detection in time-domain astronomy. The point-spread function (PSF), photometric scaling, and sky background generally vary with time and across the field of view for imaging data taken with ground-based optical telescopes. Image subtraction algorithms need to match these variations for the detection of flux variability. An algorithm that can be fully parallelized is highly desirable for future time-domain surveys. Here we introduce the saccadic fast Fourier transform (SFFT) algorithm we developed for image differencing. SFFT uses a δ-function basis for kernel decomposition, and the image subtraction is performed in Fourier space. This brings about a remarkable improvement in computational performance of about an order of magnitude compared to other published image subtraction codes. SFFT can accommodate the spatial variations in wide-field imaging data, including PSF, photometric scaling, and sky background. However, the flexibility of the δ-function basis may also make it more prone to overfitting. The algorithm has been tested extensively on real astronomical data taken by a variety of telescopes. Moreover, the SFFT code allows for the spatial variations of the PSF and sky background to be fitted by spline functions.

Keywords: astronomy software; transient detection
Surface Heterogeneity, Physical, and Shape Model of Near-Earth Asteroid (52768) 1998 OR2

On 2020 April 29, the near-Earth object (52768) 1998 OR2 experienced a close approach to Earth at a distance of 16.4 lunar distances (LD). 1998 OR2 is a potentially hazardous asteroid of absolute magnitude H = 16.04 that can currently come as close to Earth as 3.4 LD. We report here observations of this object in polarimetry, photometry, and radar. Our observations show that the physical characteristics of 1998 OR2 are similar to those of both M- and S-type asteroids. Arecibo's radar observations provide a high radar albedo of ${\hat{\sigma }}_{\mathrm{OC}}\,=$ 0.29 ± 0.08, suggesting that metals are present in 1998 OR2 near-surface. We find a circular polarization ratio of μ c = 0.291 ± 0.012, and the delay-Doppler images show that the surface of 1998 OR2 is a top-shape asteroid with large-scale structures such as large craters and concavities. The polarimetric observations display a consistent variation of the polarimetric response as a function of the rotational phase, suggesting that the surface of 1998 OR2 is heterogeneous. Color observations suggest an X-complex taxonomy in the Bus–DeMeo classification. Combining optical polarization, radar, and two epochs from the NEOWISE satellite observations, we derived an equivalent diameter of D = 1.80 ± 0.1 km and a visual albedo p v = 0.21 ± 0.02. Photometric and radar data provide a sidereal rotation period of P = 4.10872 ± 0.00001 hr, a pole orientation of (332.°3 ± 5°, 20.°7 ± 5°), and a shape model with dimensions of

$({2.08}_{-0.10}^{+0.10},{1.93}_{-0.10}^{+0.10},{1.60}_{-0.05}^{+0.05})$ km.

Keywords: near-earth objects; radar observations; polarimetry
Solar Cycle Dependence of the Turbulence Cascade Rate at 1 au

We study the solar cycle dependence of various turbulence cascade rates based on the methodology developed by Adhikari et al. that utilizes Kolmogorov phenomenology. This approach is extended to derive the heating rates for an Iroshnikov–Kriachnan (IK) phenomenology. The observed turbulence cascade rates corresponding to the total turbulence energy, fluctuating magnetic energy density, fluctuating kinetic energy, and the normalized cross helicity are derived from WIND spacecraft plasma and magnetometer data from 1995 through 2020. We find that (i) the turbulence cascade rate derived from a Kolmogorov phenomenology and an IK phenomenology changes with solar cycle, such that the cascade rate is largest during solar maximum and smallest during solar minimum; (ii) the turbulence energy Kolmogorov cascade rate increases from θ UB (angle between mean magnetic field and velocity) = 0° to 90° and peaks near θ UB = 90°, and then decreases as θ UB tends to 180°; (iii) the 2D turbulence heating rate is larger than the slab heating rate; (iv) the 2D and slab fluctuating magnetic energy density cascade rates are larger than the corresponding cascade rates of the fluctuating kinetic energy; and (v) the total turbulence energy cascade rate is positively correlated with the solar wind speed and temperature and the normalized cross-helicity cascade rate. Finally, we find that the total turbulent energy Kolmogorov cascade rate is larger than the IK cascade rate.

Keywords: solar wind; interplanetary turbulence; the sun
Detection of Travel Time Anisotropy from Subsurface Horizontal Magnetic Fields

A time-distance measurement technique is derived to isolate phase travel time anisotropy caused by subsurface horizontal magnetic fields; a method that uses the measured anisotropy to estimate the field's orientation is also derived. A simulation of acoustic waves propagating in a uniform, inclined magnetic field with solar background structure is used to verify the derived technique. Then the procedure is applied to a numerical simulation of a sunspot for which the subsurface state is known to provide context for the results obtained from the study of several sunspots observed by the Helioseismic and Magnetic Imager. Significant anisotropies are detected, on the order of 1 minute, and the subsurface field's azimuth is estimated and compared with the azimuth of the surface magnetic field. In all cases, the subsurface azimuth is found to be well aligned with that of the surface, and the results from the numerical simulation are used to interpret features in the detected travel time anisotropy.

Keywords: helioseismology; solar active region magnetic fields; sunspots
Understanding FRB 200428 in the Synchrotron Maser Shock Model: Consistency and Possible Challenge

Recently, the discovery of Galactic FRB 200428 associated with an X-ray burst (XRB) of SGR 1935+2154 has built a bridge between FRBs and magnetar activities. In this Letter, we assume that the XRB occurs in the magnetar magnetosphere. We show that the observational properties of FRB 200428 and the associated XRB are consistent with the predictions of synchrotron maser emission at ultrarelativistic magnetized shocks, including radiation efficiency, similar energy occurrence frequency distributions, and simultaneous arrive times. It requires that the upstream medium is a mildly relativistic baryonic shell ejected by a previous flare. The energy injection by flares responsible for the radio bursts will produce a magnetar wind nebula, which has been used to explain the persistent radio source associated with FRB 121102. We find that the radio continuum around SGR 1935+2154 can be well understood in the magnetar wind nebula model, by assuming the same energy injection rate $\dot{E}\propto {t}^{-1.37}$ as FRB 121102. The required baryonic mass is also estimated form the observations of FRB 121102 by the Green Bank Telescope and the Five-hundred-meter Aperture Spherical Telescope. By assuming the same radiation efficiency $\eta \sim {10}^{-5}$ , the total baryonic mass ejected from the central magnetar is about 0.005 solar mass. This value is much larger than the typical mass of a magnetar outer crust, but is comparable to the total mass of a magnetar crust.

Keywords: radio transient sources; radio bursts; magnetars; soft gamma-ray repeaters
M31N 2008-12a, the Unique Recurrent Nova in Andromeda: A Quick Look at the 2022 Eruption

M31N 2008-12a, located in the Andromeda galaxy (M31), is the best studied recurrent nova. It presents periodic outbursts with about one year between eruptions. However, the annual eruption date varies from year to year. In order to discover the annual eruption and facilitate the multi-wavelength follow-up, a monitoring campaign with nightly cadence is needed. Perez-Fournon et al. and Reyes-Rodriguez et al. reported the discovery of the 2022 M31N 2008-12a eruption with the Las Cumbres Observatory global telescope network in the framework of a three-month monitoring campaign that included also the IAC80 and Isaac Newton telescopes. Here, we discuss the 2022 light curve based on all reported photometry, as well as ATLAS forced photometry, and compare it with the well-studied 2015 eruption discussed in Darnley et al.

Keywords: novae; recurrent novae; light curves; photometry