adsabs/SciX_UAT_keywords huggingface dataset:
The Ca II H and K Rotation-Activity Relation in 53 Mid-to-late-type M Dwarfs

In the canonical theory of stellar magnetic dynamo, the tachocline in partially convective stars serves to arrange small-scale fields, generated by stochastic movement of plasma into a coherent large-scale field. Mid-to-late-type M dwarfs, which are fully convective, show more magnetic activity than classical magnetic dynamo theory predicts. However, mid-to-late-type M dwarfs show tight correlations between rotation and magnetic activity, consistent with elements of classical dynamo theory. We use data from the Magellan Inamori Kyocera Echelle Spectrograph to detail the relation between Ca II H and K flux and rotation period for these low-mass stars. We measure ${R}_{\mathrm{HK}}^{{\prime} }$ values for 53 spectroscopically identified M dwarfs selected from the MEarth survey; these stars span spectral classes from M5.0 to M3.5 and have rotation periods ranging from hours to months. We present the rotation-activity relationship as traced through these data. We find power-law and saturated regimes consistent to within 1σ of previously published results and observe a mass dependence in ${R}_{\mathrm{HK}}^{{\prime} }$ .

Keywords: m dwarf stars; stellar activity
Constraining the Time of Gravitational-wave Emission from Core-collapse Supernovae

The advent of sensitive gravitational-wave (GW) detectors, coupled with wide-field, high-cadence optical time-domain surveys, raises the possibility of the first joint GW-electromagnetic detections of core-collapse supernovae (CCSNe). For targeted searches of GWs from CCSNe, optical observations can be used to increase the sensitivity of the search by restricting the relevant time interval, defined here as the GW search window (GSW). The extent of the GSW is a critical factor in determining the achievable false alarm probability for a triggered CCSN search. The ability to constrain the GSW from optical observations depends on how early a CCSN is detected, as well as the ability to model the early optical emission. Here we present several approaches to constrain the GSW, ranging in complexity from model-independent analytical fits of the early light curve, model-dependent fits of the rising or entire light curve, and a new data-driven approach using existing well-sampled CCSN light curves from Kepler and the Transiting Exoplanet Survey Satellite. We use these approaches to determine the time of core-collapse and its associated uncertainty (i.e., the GSW). We apply our methods to two Type II SNe that occurred during LIGO/Virgo Observing Run 3: SN 2019fcn and SN 2019ejj (both in the same galaxy at d = 15.7 Mpc). Our approach shortens the duration of the GSW and improves the robustness of the GSW compared to the techniques used in past GW CCSN searches.

Keywords: core-collapse supernovae; type ii supernovae; gravitational waves; gravitational wave astronomy; high energy astrophysics
Fast Transit Computation Using Tabulated Stellar Intensities

Limb-darkening laws are convenient parameterizations of the stellar intensity center-to-limb variation, and their use is ubiquitous in eclipse and transit modeling. But they are not "laws" in any sense—they are simple approximations of the real intensity variations, and their limitations are becoming more and more apparent as stellar atmosphere models improve and higher precision data become available. When fitting eclipses and transit light curves, one would ideally like to use model intensities that are based on fundamental stellar parameters such as the mass, radius, and effective temperature of the star, rather than a limb-darkening law representation and its coefficients. This is especially true when attempting to detect higher-order effects such as planetary oblateness, rings, satellites, or atmospheres. However, using model intensities requires numerically integrating many small-area "tiles" on the model stellar surface(s), and this has traditionally been too computationally expensive for general use. Here we present a fast technique to compute light curves and the Rossiter-McLaughlin effect that uses tabulated stellar models intensities. This is a step in the development of tools that obviate the need for limb-darkening laws.

Keywords: limb darkening; computational methods; eclipsing binary stars; transits; exoplanets
Ensuring Robustness in Training-set-based Global 21 cm Cosmology Analysis

We present a methodology for ensuring the robustness of our analysis pipeline in separating the global 21 cm hydrogen cosmology signal from large systematics based on singular value decomposition (SVD) of training sets. We show how traditional goodness-of-fit metrics such as the χ2 statistic that assess the fit to the full data may not be able to detect a suboptimal extraction of the 21 cm signal when it is fit alongside one or more additional components owing to significant covariance between them. However, we find that comparing the number of SVD eigenmodes for each component chosen by the pipeline for a given fit to the distribution of eigenmodes chosen for synthetic data realizations created from training set curves can detect when one or more of the training sets is insufficient to optimally extract the signal. Furthermore, this test can distinguish which training set (e.g., foreground, 21 cm signal) needs to be modified in order to better describe the data and improve the quality of the 21 cm signal extraction. We also extend this goodness-of-fit testing to cases where a prior distribution derived from the training sets is applied and find that, in this case, the χ2 statistic and the recently introduced ψ2 statistic are able to detect inadequacies in the training sets due to the increased restrictions imposed by the prior. Crucially, the tests described in this paper can be performed when analyzing any type of observations with our pipeline.

Keywords: astronomy data analysis; reionization; cosmology; observational cosmology; radio astronomy; astronomy data modeling; h i line emission
The Celestial Reference Frame at K Band: Imaging. I. The First 28 Epochs

We present K-band (24 GHz) images of 731 compact extragalactic radio sources with submilliarcsecond resolution, based on radio interferometric observations made with the Very Long Baseline Array of 10 telescopes during 29 day long sessions spanning from 2015 to 2018 and recorded at 2048 Mbps. Many of these sources are imaged with submilliarcsecond resolution for the first time at frequencies above X band (8 GHz). From each of the K-band images, we derive the following source properties: peak brightness, core and total flux density, the ratio of peak and core to total flux (compactness measure), radial source extent, structure index, source size, and jet direction. The vast majority of sources are imaged at multiple epochs, providing insights into their temporal behavior. The use of K band was motivated by the fact that the sources are generally intrinsically more compact at higher frequencies, as well as by the factor of 3 improvement in interferometer resolution relative to the historically standard S/X band (2.3/8.4 GHz) used for a large amount of reference frame and calibrator work. Lastly, as most of the sources imaged here are in the K-band component of the third International Celestial Reference Frame, these images serve to characterize the objects used in that International Astronomical Union standard.

Keywords: very long baseline interferometry; radio astrometry; extragalactic radio sources; observational astronomy; radio continuum emission; radio source catalogs; astronomical coordinate systems; high angular resolution
Raman Scattering by Atomic Hydrogen in Photodissociation Regions: An Alternative to the Polycyclic Aromatic Hydrocarbons Hypothesis

Photodissociation regions (PDRs) illuminated by high temperature (T > 104 K) radiation fields display characteristic optical to midinfrared spectral features: emission bands that cluster around the blue limits of hydrogen series, an extended red emission (ERE) in the vicinity of Hα, and a continuum in the infrared part of the spectrum only. The spectral footprint of ERE and its intensity at maximum unequivocally designate Raman scattering by hydrogen of photons near Lyβ as responsible for the feature, thus suggesting PDR spectra be considered Raman spectra. This finding challenges the currently accepted hypothesis that yet-to-be-identified complex carbonaceous molecules, such as polycyclic aromatic hydrocarbons, are the source of PDRs' unidentified infrared bands. It has, therefore, significant implications for the field of astrochemistry.

Keywords: infrared excess; interstellar emissions
Real-time Likelihood-free Inference of Roman Binary Microlensing Events with Amortized Neural Posterior Estimation

Fast and automated inference of binary-lens, single-source (2L1S) microlensing events with sampling-based Bayesian algorithms (e.g., Markov Chain Monte Carlo, MCMC) is challenged on two fronts: the high computational cost of likelihood evaluations with microlensing simulation codes, and a pathological parameter space where the negative-log-likelihood surface can contain a multitude of local minima that are narrow and deep. Analysis of 2L1S events usually involves grid searches over some parameters to locate approximate solutions as a prerequisite to posterior sampling, an expensive process that often requires human-in-the-loop domain expertise. As the next-generation, space-based microlensing survey with the Roman Space Telescope is expected to yield thousands of binary microlensing events, a new fast and automated method is desirable. Here, we present a likelihood-free inference approach named amortized neural posterior estimation, where a neural density estimator (NDE) learns a surrogate posterior $\hat{p}({\boldsymbol{\theta }}| {\boldsymbol{x}})$ as an observation-parameterized conditional probability distribution, from pre-computed simulations over the full prior space. Trained on 291,012 simulated Roman-like 2L1S simulations, the NDE produces accurate and precise posteriors within seconds for any observation within the prior support without requiring a domain expert in the loop, thus allowing for real-time and automated inference. We show that the NDE also captures expected posterior degeneracies. The NDE posterior could then be refined into the exact posterior with a downstream MCMC sampler with minimal burn-in steps.

Keywords: binary lens microlensing; gravitational microlensing exoplanet detection
Corrections to Estimated Accretion Disk Size due to Color Correction, Disk Truncation, and Disk Wind

We consider three corrections to the disk sizes estimated at a given frequency using accretion models. They are due to a color correction, a disk truncation at an inner radius larger than the innermost stable circular orbit, and disk winds, which we apply to the standard disk model. We apply our results to the estimates of the disk sizes based on microlensing. We find that these three effects combined can explain the long-standing problem of the disk sizes from microlensing being larger than those estimated using the standard disk model (i.e., that without accounting for the above effects). In particular, an increase of the color correction with the increasing temperature can lead to a strong increase of the half-light radius even if this correction is close to unity at the temperature corresponding to an observed frequency. Our proposed formalism for calculating the half-light radius also resolves the long-standing issue of discrepancies between the disk size estimates based on the accretion rate and on the observed flux.

Keywords: accretion; galaxy accretion disks; gravitational microlensing; active galactic nuclei
Monte Carlo Stellar Dynamics near Massive Black Holes: Two-dimensional Fokker–Planck Solutions of Multiple Mass Components

In this study we present a novel Monte Carlo code, referred to as GNC, which enables the investigation of dynamical relaxation in clusters comprising multiple mass components in the vicinity of supermassive black holes at the centers of galaxies. Our method is based on two-dimensional Fokker–Planck equations in the energy and angular momentum space, and allows the evolution of multiple mass components, including stars and compact objects. The code demonstrates remarkable flexibility in incorporating additional complex dynamics. By employing a weighting method, we effectively enhance the statistical accuracy of rare particle results. In this initial publication, we present the fundamental version of our method, focusing on two-body relaxations and loss cone effects. Through comparisons with previous studies, we establish consistent outcomes in terms of relaxation processes, energy and angular momentum distributions, density profiles, and loss cone consumption rates. We consistently observe the development of tangential anisotropy within the cluster, while the outer regions tend to retain near-isotropic characteristics. GNC holds great promise for exploring a wide range of intriguing phenomena within galactic nuclei, including relativistic stellar dynamics, providing detailed and insightful outcomes.

Keywords: stellar dynamics; supermassive black holes; monte carlo methods; galaxy nuclei; gravitation; stellar kinematics
KIC 9028474: A Long-period Eclipsing Binary on a Highly Eccentric Orbit

We present a comprehensive analysis of a very long-period (124.93669 days) eclipsing binary KIC 9028474, which is composed of F9V+G1V components on a highly eccentric (e = 0.82029) orbit. Masses and radii of the primary and the secondary components are M 1 = 1.18 ± 0.04 M ⊙, M 2 = 1.04 ± 0.03 M ⊙, R 1 = 1.52 ± 0.02 R ⊙, and R 2 = 1.11 ± 0.01 R ⊙, respectively. Eclipse time variations show the presence of apsidal motion, which in turn shows the existence of a third body in a relatively close orbit. Simultaneous analysis of infrared spectra and space photometry reveals that the primary component is about to leave the main sequence, indicating an age of 5.2 ± 0.8 Gyr for the system. Theoretical evaluation of the observed eccentricity indicates that the components of KIC 9028474 will end their whole life much before the orbital circularization is achieved. Given the limited resolution of the spectra, we can only place an upper limit on the rotational velocities of each star, thus a theoretical evaluation of the synchronization of the components.

Keywords: eclipsing binary stars; detached binary stars; fundamental parameters of stars; eccentricity
GOALS-JWST: Small Neutral Grains and Enhanced 3.3 μm PAH Emission in the Seyfert Galaxy NGC 7469

We present James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec) integral field spectroscopy of the nearby luminous infrared galaxy NGC 7469. We take advantage of the high spatial/spectral resolution and wavelength coverage of JWST/NIRSpec to study the 3.3 μm neutral polycyclic aromatic hydrocarbon (PAH) grain emission on ~200 pc scales. A clear change in the average grain properties between the star-forming ring and the central AGN is found. Regions in the vicinity of the AGN, with [Ne III]/[Ne II] > 0.25, tend to have larger grain sizes and lower aliphatic-to-aromatic (3.4/3.3) ratios, indicating that smaller grains are preferentially removed by photodestruction in the vicinity of the AGN. PAH emission at the nucleus is weak and shows a low 11.3/3.3 PAH ratio. We find an overall suppression of the total PAH emission relative to the ionized gas in the central 1 kpc region of the AGN in NGC 7469 compared to what has been observed with Spitzer on 3 kpc scales. However, the fractional 3.3 μm-to-total PAH power is enhanced in the starburst ring, possibly due to a variety of physical effects on subkiloparsec scales, including recurrent fluorescence of small grains or multiple photon absorption by large grains. Finally, the IFU data show that while the 3.3 μm PAH-derived star formation rate (SFR) in the ring is 27% higher than that inferred from the [Ne II] and [Ne III] emission lines, the integrated SFR derived from the 3.3 μm feature would be underestimated by a factor of 2 due to the deficit of PAHs around the AGN, as might occur if a composite system like NGC 7469 were to be observed at high redshift.

Keywords: seyfert galaxies; active galactic nuclei; polycyclic aromatic hydrocarbons; starburst galaxies; luminous infrared galaxies
Fishing for Planets: A Comparative Analysis of EPRV Survey Performance in the Presence of Correlated Noise

With dedicated exoplanet surveys underway for multiple extreme-precision radial velocity (EPRV) instruments, the near-future prospects of RV exoplanet science are promising. These surveys' generous time allocations are expected to facilitate the discovery of Earth analogs around bright, nearby Sun-like stars. But survey success will depend critically on the choice of observing strategy, which will determine the survey's ability to mitigate known sources of noise and extract low-amplitude exoplanet signals. Here we present an analysis of the Fisher information content of simulated EPRV surveys, accounting for the most recent advances in our understanding of stellar variability on both short and long timescales (i.e., oscillations and granulation within individual nights, and activity-induced variations across multiple nights). In this analysis, we capture the correlated nature of stellar variability by parameterizing these signals with Gaussian process kernels. We describe the underlying simulation framework and the physical interpretation of the Fisher information content, and we evaluate the efficacy of EPRV survey strategies that have been presented in the literature. We explore and compare strategies for scheduling observations over various timescales, and we make recommendations to optimize survey performance for the detection of Earth-like exoplanets.

Keywords: exoplanet detection methods; radial velocity; surveys; fisher's information; stellar activity
Searching for Anisotropic Stochastic Gravitational-wave Backgrounds with Constellations of Space-based Interferometers

Many recent works have shown that the angular resolution of ground-based detectors is too poor to characterize the anisotropies of the stochastic gravitational-wave background (SGWB). For this reason, we asked ourselves if a constellation of space-based instruments could be more suitable. We consider the Laser Interferometer Space Antenna (LISA), a constellation of multiple LISA-like clusters, and the Deci-hertz Interferometer Gravitational-wave Observatory (DECIGO). Specifically, we test whether these detector constellations can probe the anisotropies of the SGWB. For this scope, we considered the SGWB produced by two astrophysical sources: merging compact binaries, and a recently proposed scenario for massive black hole seed formation through multiple mergers of stellar remnants. We find that measuring the angular power spectrum of the SGWB anisotropies is almost unattainable. However, it turns out that it could be possible to probe the SGWB anisotropies through cross-correlation with the cosmic microwave background (CMB) fluctuations. In particular, we find that a constellation of two LISA-like detectors and CMB-S4 can marginally constrain the cross-correlation between the CMB lensing convergence and the SGWB produced by the black hole seed formation process. Moreover, we find that DECIGO can probe the cross-correlation between the CMB lensing and the SGWB from merging compact binaries.

Keywords: gravitational wave sources; gravitational wave detectors; large-scale structure of the universe; cosmology; black holes
Betelgeuse Fainter in the Submillimeter Too: An Analysis of JCMT and APEX Monitoring during the Recent Optical Minimum

Betelgeuse, the nearest red supergiant star to Earth, underwent an unusually deep minimum at optical wavelengths during its most recent pulsation cycle. We present submillimeter observations taken by the James Clerk Maxwell Telescope and Atacama Pathfinder Experiment over a time span of 13 yr including the optical dimming. We find that Betelgeuse has also dimmed by ∼20% at these longer wavelengths during this optical minimum. Using radiative-transfer models, we show that this is likely due to changes in the photosphere (luminosity) of the star as opposed to the surrounding dust, as was previously suggested in the literature.

Keywords: red supergiant stars; submillimeter astronomy; variable stars; time domain astronomy
The Supersonic Project: The Eccentricity and Rotational Support of SIGOs and DM GHOSts

A supersonic relative velocity between dark matter (DM) and baryons (the stream velocity) at the time of recombination induces the formation of low-mass objects with anomalous properties in the early universe. We widen the scope of the "Supersonic Project" paper series to include objects we term Dark Matter + Gas Halos Offset by Streaming (DM GHOSts)-diffuse, DM-enriched structures formed because of a physical offset between the centers of mass of DM and baryonic overdensities. We present an updated numerical investigation of DM GHOSts and Supersonically Induced Gas Objects (SIGOs), including the effects of molecular cooling, in high-resolution hydrodynamic simulations using the AREPO code. Supplemented by an analytical understanding of their ellipsoidal gravitational potentials, we study the population-level properties of these objects, characterizing their morphology, spin, radial mass, and velocity distributions in comparison to classical structures in non-streaming regions. The stream velocity causes deviations from sphericity in both the gas and DM components and lends greater rotational support to the gas. Low-mass (≲105.5 M ⊙) objects in regions of streaming demonstrate core-like rotation and mass profiles. Anomalies in the rotation and morphology of DM GHOSts could represent an early universe analog to observed ultra-faint dwarf galaxies with variations in DM content and unusual rotation curves.

Keywords: galaxy formation; dwarf galaxies; galaxy rotation curves; high-redshift galaxies
Observational Effects of Banded Repeating FRBs

Recent observations have shown that repeating fast radio bursts (FRBs) exhibit band-limited emission, whose frequency-dependent amplitude can be modeled using a Gaussian function. In this analysis, we show that banded emission of FRBs can lead to incompleteness across the observing band. This biases the detected sample of bursts and can explain the various shapes of cumulative energy distributions seen for repeating FRBs. We assume a Gaussian shape of the burst spectra and use simulations to demonstrate the above bias using an FRB 121102-like example. We recovered energy distributions that showed a break in power law and flattening of power law at low energies, based on the fluence threshold of the observations. We provide recommendations for single-pulse searches and analysis of repeating FRBs to account for this incompleteness. Primarily, we recommend that burst spectra should be modeled to estimate the intrinsic fluence and bandwidth of the burst robustly. Also, bursts that lie mainly within the observing band should be used for analyses of energy distributions. We show that the bimodality reported in the distribution of energies of FRB 121102 by Li et al. disappears when burst bandwidth, instead of the center frequency of the observation, is used to estimate energy. Subbanded searches will also aid in detecting band-limited bursts. All the analysis scripts used in this work are available in a Github repository (https://github.com/KshitijAggarwal/banded_repeater_analysis).

Keywords: radio transient sources; extragalactic radio sources; radio bursts; astronomy data analysis