adsabs/SciX_UAT_keywords huggingface dataset:
The Large-scale Magnetic Field Advected in the Corona of a Thin Accretion Disk

Large-scale magnetic field is believed to play a key role in launching and collimating jets/outflows. It was found that advection of the external field by a geometrically thin disk is rather inefficient, while the external weak field may be dragged inwards by fast radially moving tenuous and/or hot gas above the thin disk. We investigate the field advection in a thin (cold) accretion disk covered with hot corona, in which turbulence is responsible for the angular momentum transfer of the gas in the disk and corona. The radial velocity of the gas in the corona is significantly higher than that in the thin disk. Our calculations show that the external magnetic flux is efficiently transported inwards by the corona, and the field line is strongly inclined toward the disk surface, which helps to launch outflows. The field configurations are consistent with those observed in the numerical simulations. The strength of the field is substantially enhanced in the inner region of the disk (usually several orders of magnitude higher than the external field strength), which is able to drive a fraction of gas in the corona into outflows. This mechanism may be useful in explaining the observational features in X-ray binaries and active galactic nuclei. Our results may help in understanding the physics of the magnetohydrodynamic simulations.

Keywords: galaxy jets; galaxy accretion disks; accretion; magnetic fields
Magnetic Braking of Accreting T Tauri Stars: Effects of Mass Accretion Rate, Rotation, and Dipolar Field Strength

The rotational evolution of an accreting pre-main-sequence star is influenced by its magnetic interaction with its surrounding circumstellar disk. Using the PLUTO code, we perform 2.5D magnetohydrodynamic, axisymmetric, time-dependent simulations of star-disk interaction—with an initial dipolar magnetic field structure, and a viscous and resistive accretion disk—in order to model the three mechanisms that contribute to the net stellar torque: accretion flow, stellar wind, and magnetospheric ejections (periodic inflation and reconnection events). We investigate how changes in the stellar magnetic field strength, rotation rate, and mass accretion rate (changing the initial disk density) affect the net stellar torque. All simulations are in a net spin-up regime. We fit semi-analytic functions for the three stellar torque contributions, allowing for the prediction of the net stellar torque for our parameter regime, as well as the possibility of investigating spin evolution using 1D stellar evolution codes. The presence of an accretion disk appears to increase the efficiency of stellar torques compared to isolated stars, for cases with outflow rates much smaller than accretion rates, because the star-disk interaction opens more of the stellar magnetic flux compared to that from isolated stars. In our parameter regime, a stellar wind with a mass-loss rate of ≈1% of the mass accretion rate is capable of extracting ≲50% of the accreting angular momentum. These simulations suggest that achieving spin equilibrium in a representative T Tauri case within our parameter regime, e.g., BP Tau, would require a wind mass-loss rate of ≈25% of the mass accretion rate.

Keywords: stellar winds; stellar evolution; stellar magnetic fields; stellar rotation; magnetohydrodynamical simulations; pre-main sequence stars; stellar accretion; classical t tauri stars; stellar accretion disks
Precise Mass, Orbital Motion, and Stellar Properties of the M-dwarf Binary LP 349‑25AB

LP 349‑25 is a well-studied close stellar binary system comprised of two late M dwarf stars, where both stars are close to the limit between star and brown dwarf. This system was previously identified as a source of gigahertz radio emission. We observed LP 349‑25AB over 11 epochs in 2020–2022, detecting both components in this nearby binary system using the Very Long Baseline Array (VLBA). We fit simultaneously the VLBA absolute astrometric positions together with existing relative astrometric observations derived from optical/infrared observations with a set of algorithms that use nonlinear least-squares, genetic algorithm, and Markov Chain Monte Carlo methods to determine the orbital parameters of the two components. We find the masses of the primary and secondary components to be 0.08188 ± 0.00061 M ⊙ and 0.06411 ± 0.00049 M ⊙, respectively, representing one of the most precise mass estimates of any ultracool dwarf (UCD) to date. The primary is a UCD of 85.71 ± 0.64 M Jup, while the secondary has a mass consistent with being a brown dwarf of 67.11 ± 0.51 M Jup. This is one of the very few direct detections of a brown dwarf with VLBA observations. We also find a distance to the binary system of 14.122 ± 0.057 pc. Using stellar evolutionary models, we find the model-derived stellar parameters of both stars. In particular, we obtain a model-derived age of 262 Myr for the system, which indicates that LP 349‑25AB is composed of two pre–main-sequence stars. In addition, we find that the secondary star is significantly less evolved than the primary star.

Keywords: m stars; binary stars; brown dwarfs; radio astrometry
wdwarfdate: A Python Package to Derive Bayesian Ages of White Dwarfs

White dwarfs have been successfully used as cosmochronometers in the literature; however, their reach has been limited in comparison to their potential. We present wdwarfdate, a publicly available Python package to derive the Bayesian age of a white dwarf, based on its effective temperature (T eff) and surface gravity (log g). We make this software easy to use with the goal of transforming the usage of white dwarfs as cosmochronometers into an accessible tool. The code estimates the mass and cooling age of the white dwarf, as well as the mass and main-sequence age of the progenitor star, allowing for a determination of the total age of the object. We test the reliability of the method by estimating the parameters of white dwarfs from previous studies and find agreement with the literature within measurement errors. In addition, we use wdwarfdate to infer the total age of 18 white dwarfs that are in possible wide binaries with M dwarfs; this leads to an additional set of age-calibrated low-mass stars. By analyzing the limitation of the code we find a typical uncertainty of 10% on the total age when both input parameters have uncertainties of 1%, and an uncertainty of 25% on the total age when T eff has an uncertainty of 10% and log g of 1%. Furthermore, wdwarfdate assumes single-star evolution and can be applied to calculate the total age of a white dwarf with parameters in the range 1500 ≲ T eff ≲ 90,000 K and 7.9 ≲ log g ≲ 9.3. Finally, the code assumes a uniform mixture of C/O in the core and single-star evolution, which is reliable in the range of white dwarf masses 0.45-1.1 M ⊙(7.73 ≲ log g ≲ 8.8).

Keywords: white dwarf stars; fundamental parameters of stars; stellar ages; bayesian statistics; open source software
Uncertainty Estimation in Exoplanet System Parameters

The NASA Exoplanet Archive contains published data for various stellar and planetary parameters, based on the combined work of hundreds of research teams. For cases where a parameter has been estimated multiple times, the opportunity exists to compare the variance in an estimated parameter value with the reported uncertainties. This study focuses on eleven system parameters that are needed for interpreting transit spectroscopy observations and finds evidence for systematic overestimation of uncertainties occurring in seven cases and systematic underestimation of uncertainties occurring in two cases. The fact that the systematic over/under estimation of uncertainties appears to be correlated with specific system parameters is identified as an area of interest for potential future inquiry.

Keywords: exoplanets; exoplanet astronomy
Weather on Other Worlds. V. The Three Most Rapidly Rotating Ultra-cool Dwarfs

We present the discovery of rapid photometric variability in three ultra-cool dwarfs from long-duration monitoring with the Spitzer Space Telescope. The T7, L3.5, and L8 dwarfs have the shortest photometric periods known to date: ${1.080}_{-0.005}^{+0.004}$ hr, ${1.14}_{-0.01}^{+0.03}$ hr, and ${1.23}_{-0.01}^{+0.01}$ hr, respectively. We confirm the rapid rotation through moderate-resolution infrared spectroscopy, which reveals projected rotational velocities between 79 and 104 km s-1. We compare the near-infrared spectra to photospheric models to determine the objects' fundamental parameters and radial velocities. We find that the equatorial rotational velocities for all three objects are ≳100 km s-1. The three L and T dwarfs reported here are the most rapidly spinning and likely the most oblate field ultra-cool dwarfs known to date. Correspondingly, all three are excellent candidates for seeking auroral radio emission and net optical/infrared polarization. As of this writing, 78 L-, T-, and Y-dwarf rotation periods have now been measured. The clustering of the shortest rotation periods near 1 hr suggests that brown dwarfs are unlikely to spin much faster.

Keywords: brown dwarfs; stellar rotation; variable stars; infrared photometry; spectroscopy
High Mass but Low Spin: An Exclusion Region to Rule Out Hierarchical Black Hole Mergers as a Mechanism to Populate the Pair-instability Mass Gap

The occurrence of pair-instability supernovae is predicted to prevent the formation of black holes with masses ≳50 M⊙. Recent gravitational-wave detections in this mass range require an explanation beyond that of standard stellar collapse. Current modeling strategies include the hierarchical assembly of previous generations of black hole mergers as well as other mechanisms of astrophysical nature (lowered nuclear-reaction rates, envelope retention, stellar mergers, accretion, dredge-up episodes). In this paper, we point out the occurrence of an exclusion region that cannot be easily populated by hierarchical black hole mergers. A future gravitational-wave detection of a black hole with mass ≳50 M⊙ and spin ≲0.2 will indicate that the pair-instability mass gap is polluted in some other way. Such a putative outlier can be explained using hierarchical mergers only with considerable fine-tuning of both mass ratio and spins of the preceding black hole merger-an assumption that can then be cross-checked against the bulk of the gravitational-wave catalog.

Keywords: stellar mass black holes; gravitational waves; core-collapse supernovae; ligo
Examinations of CO Completeness Based on Three Independent CO Surveys

We report the global properties recovered by an ongoing CO survey of the Milky Way Imaging Scroll Painting (MWISP) toward the Galactic outskirts. Our results are also compared to those extracted by a uniform decomposition method from the CfA 1.2 m CO survey and the FCRAO 14 m outer Galaxy survey (OGS). We find that more extended and unseen structures are present in the MWISP data. The total flux across the disk recovered by the MWISP survey is 1.6 times larger than those recovered by the CfA survey and OGS in the case of the same resolution. The discrepancies are scaling with distance. For example, in the outermost Outer Scutum-Centaurus arm, the flux ratios for MWISP to CfA and MWISP to OGS increase up to 43.8 and 7.4, respectively. Nonetheless, the census of molecular gas in our Galaxy is still far from complete by the MWISP, with flux completeness of <58%. The total mass ratios of the tabulated molecular clouds between different surveys are similar to the CO flux ratio. The application of these ratios to the total H2 mass of our Galaxy yields a correction factor of at least 1.4, meaning that the H2 mass of our Galaxy should be at least 40% more massive than previously determined. Including the completeness correction, an even more significant fraction of the matter should be contributed by baryonic matter. The mass spectrum in the outer Galactic plane is better described by a nontruncating power law with γ = -1.83 ± 0.05 and an upper mass of M0 = (1.3 ± 0.5) × 106 M⊙.

Keywords: interstellar medium; co line emission; molecular clouds
Ho'oleilana: An Individual Baryon Acoustic Oscillation?

Theory of the physics of the early hot universe leads to a prediction of baryon acoustic oscillations (BAOs) that has received confirmation from the pairwise separations of galaxies in samples of hundreds of thousands of objects. Evidence is presented here for the discovery of a remarkably strong individual contribution to the BAO signal at z = 0.068, an entity that is given the name Ho'oleilana. The radius of the 3D structure is $155\,{{\rm{h}}}_{75}^{-1}$ Mpc. At its core is the Boötes supercluster. The Sloan Great Wall, Center for Astrophysics Great Wall, and Hercules complex all lie within the BAO shell. The interpretation of Ho'oleilana as a BAO structure with our preferred analysis implies a value of the Hubble constant of ${76.9}_{-4.8}^{+8.2}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}.$

Keywords: large-scale structure of the universe
Photometric and Spectroscopic Analysis of V583 Lyrae, an Algol with a g-mode Pulsating Primary and Accretion Disk

V583 Lyr is an extremely low-mass-ratio Algol-type binary with an orbital period of 11.2580 days. We determined an effective temperature of T eff1 = 9000 ± 350 K from newly observed spectra, which might be an underestimate due to binary mass transfer. The binary mass ratio q = 0.1 ± 0.004 and the orbital inclination i = 85.°5 are determined based on the assumption that the secondary fills its Roche lobe and rotates synchronously. The radial velocity curve is obtained from time series spectra, allowing for improved estimation of stellar masses and radii: M 1 = 3.56 ± 0.5 M ⊙, R 1 = 2.4 ± 0.2 R ⊙; and M 2 = 0.36 ± 0.02 M ⊙, R 2 = 6.9 ± 0.4 R ⊙. The variations in the double-peaked Hα emission indicate the formation of a stable disk during mass transfer. V583 Lyr appears to be a post-mass-reversal system, according to the mass transfer estimated using O ‑ C period analysis. Its orbital period is slowly increasing, from which the rate of mass accretion by the primary star is estimated to be $\dot{{M}_{1}}=3.384$ × 10‑8 M ⊙ yr‑1. The pulsation analysis was conducted on the residuals of the light curve. The primary component was found to be a g-mode pulsating star with 26 frequencies extracted lower than 9 day‑1. The frequency groups and rotational splitting properties of the g mode were studied in detail. This study provides compelling evidence for an accretion disk surrounding the g-mode pulsating primary.

Keywords: eclipsing binary stars; stellar pulsations; radial velocity; spectroscopy
Electron Acceleration from Expanding Magnetic Vortices During Reconnection with a Guide Field

Magnetic reconnection is believed to be responsible for the acceleration of energetic electrons with a power-law spectrum in the solar wind and solar flares. However, recent studies of the leading mechanism of electron acceleration in reconnection, namely the acceleration by tearing instability induced multi-islands, demonstrates that this mechanism suffers from an "injection problem" for mildly relativistic reconnection acceleration. In this paper, we investigate a new type of reconnection acceleration in which an electron Kelvin-Helmholtz instability (EKHI) is driven as the current sheet reaches electron inertial length scales during magnetic reconnection with a strong guide field. Electrons are accelerated by stochastic electric fields, induced by the EKHI generated vortices that expand rapidly, and a power-law electron energy spectrum $f(W)\propto {W}^{-\alpha }$ with index α ∼ 3.5 is produced (W is the electron kinetic energy and f(W) is the energy distribution function). We show that the mechanism is a second-order Fermi acceleration process, and the index $\alpha =(1+4{a}^{2}D/R)/2$ where a = Bg/B0, which is determined by the ratio of the spatial scale of the inductive electric field D to that of vortices R and the ratio of guide field Bg to asymptotic magnetic field B0.

Keywords: solar energetic particles; solar magnetic reconnection; solar flares
Observation of Photons above 300 TeV Associated with a High-energy Neutrino from the Cygnus Region

Galactic sites of acceleration of cosmic rays to energies of order 1015 eV and higher, dubbed PeVatrons, reveal themselves by recently discovered gamma radiation of energies above 100 TeV. However, joint gamma-ray and neutrino production, which marks unambiguously cosmic-ray interactions with ambient matter and radiation, was not observed until now. In 2020 November, the IceCube neutrino observatory reported an ~150 TeV neutrino event from the direction of one of the most promising Galactic PeVatrons, the Cygnus Cocoon. Here we report on the observation of a 3.1σ (post-trial) excess of atmospheric air showers from the same direction, observed by the Carpet-2 experiment and consistent with a few months flare in photons above 300 TeV, in temporal coincidence with the neutrino event. The fluence of the gamma-ray flare is of the same order as that expected from the neutrino observation, assuming the standard mechanism of neutrino production. This is the first evidence for the joint production of high-energy neutrinos and gamma-rays in a Galactic source.

Keywords: neutrino astronomy; gamma-rays
Static Thin Disks with Power-law Density Profiles

The task of finding the potential of a thin circular disk with power-law radial density profile is revisited. The result, given in terms of infinite Legendre-type series in the above reference, has now been obtained in closed form thanks to the method of Conway employing Bessel functions. Starting from a closed-form expression for the potential generated by the elementary density term ρ 2l , we cover more generic-finite solid or infinite annular-thin disks using superposition and/or inversion with respect to the rim. We check several specific cases against the series-expansion form by numerical evaluation at particular locations. Finally, we add a method to obtain a closed-form solution for finite annular disks whose density is of "bump" radial shape, as modeled by a suitable combination of several powers of radius. Density and azimuthal pressure of the disks are illustrated on several plots, together with radial profiles of free circular velocity. * Dedicated to our teacher, Professor Jiří Bičák, on the occasion of his 80th birthday. For O.S., Jiří's interest in thin disks was, 30 yr ago (Bičák et al. ), the first motivation to study the topic.

Keywords: relativistic disks; black holes
What are the Composition and Power of the Jet in Cyg X-1?

We calculate the electron-positron pair production rate at the base of the jet of Cyg X-1 by collisions of photons from its hot accretion flow using the measurement of its average soft gamma-ray spectra by the Compton Gamma Ray Observatory and INTEGRAL satellites. We have found that this rate approximately equals the flow rate of the leptons emitting the observed synchrotron radio-to-IR spectrum of the jet, calculated using an extended jet model following that of Blandford & Königl. This coincidence shows the jet composition is likely to be pair dominated. The same coincidences were found before in the microquasar MAXI J1820+070 and in the radio galaxy 3C 120, which shows that the considered mechanism can be universal for at least some classes of relativistic jets. Furthermore, we recalculate the jet power of Cyg X-1. The presence of pairs can strongly reduce the power in the bulk motion of ions, which then limits the parameter space at which the jet can power the ~5 pc nebular structure present in its vicinity.

Keywords: relativistic jets; non-thermal radiation sources; accretion; x-ray binary stars
Probing Ultralate Reionization: Direct Measurements of the Mean Free Path over 5 < z < 6

The mean free path of ionizing photons, λ mfp, is a critical parameter for modeling the intergalactic medium (IGM) both during and after reionization. We present direct measurements of λ mfp from QSO spectra over the redshift range 5 < z < 6, including the first measurements at z ≃ 5.3 and 5.6. Our sample includes data from the XQR-30 VLT large program, as well as new Keck/ESI observations of QSOs near z ~ 5.5, for which we also acquire new [C II] 158 μm redshifts with ALMA. By measuring the Lyman continuum transmission profile in stacked QSO spectra, we find ${\lambda }_{\mathrm{mfp}}={9.33}_{-1.80}^{+2.06}$ , ${5.40}_{-1.40}^{+1.47}$ , ${3.31}_{-1.34}^{+2.74}$ , and ${0.81}_{-0.48}^{+0.73}$ pMpc at z = 5.08, 5.31, 5.65, and 5.93, respectively. Our results demonstrate that λ mfp increases steadily and rapidly with time over 5 < z < 6. Notably, we find that λ mfp deviates significantly from predictions based on a fully ionized and relaxed IGM as late as z = 5.3. By comparing our results to model predictions and indirect λ mfp constraints based on IGM Lyα opacity, we find that the evolution of λ mfp is consistent with scenarios wherein the IGM is still undergoing reionization and/or retains large fluctuations in the ionizing UV background well below redshift 6.

Keywords: reionization; intergalactic medium; quasar absorption line spectroscopy; high-redshift galaxies
Inertial Waves in a Nonlinear Simulation of the Sun's Convection Zone and Radiative Interior

Recent observations of Rossby waves and other more exotic forms of inertial oscillations in the Sun's convection zone have kindled the hope that such waves might be used as a seismic probe of the Sun's interior. Here, we present a 3D numerical simulation in spherical geometry that models the Sun's convection zone and upper radiative interior. This model features a wide variety of inertial oscillations, including both sectoral and tesseral equatorial Rossby waves, retrograde mixed inertial modes, prograde thermal Rossby waves, the recently observed high-frequency retrograde (HFR) vorticity modes, and what may be latitudinal overtones of these HFR modes. With this model, we demonstrate that sectoral and tesseral Rossby waves are ubiquitous within the radiative interior as well as within the convection zone. We suggest that there are two different Rossby-wave families in this simulation that live in different wave cavities: one in the radiative interior and one in the convection zone. Finally, we suggest that many of the retrograde inertial waves that appear in the convection zone, including the HFR modes, are in fact all related, being latitudinal overtones that are mixed modes with the prograde thermal Rossby waves.

Keywords: solar interior; internal waves; solar oscillations; astrophysical fluid dynamics; solar physics