adsabs/SciX_UAT_keywords huggingface dataset:
Assessing the Stellar Population and the Environment of an H II Region on the Far Side of the Galaxy

We have investigated the stellar and interstellar content of the distant star formation region IRAS 17591-2228 (WISE H II region GAL 007.47+0.06). It is associated with a water maser, whose parallax distance is $d={20.4}_{-2.2}^{+2.8}$ kpc, supported by independent measurements of proper motion and radial velocity. It is projected in the same direction as an extremely red (J-KS ∼ 6 mag) group of stars, and a shell of mid-infrared emission. We qualify the group of stars as a cluster candidate, VVV CL177. Its radius spans between 0'45 and 1' and contains at least two young stellar objects with an extreme extinction near ${A}_{{\rm{V}}}\sim 40$ mag. Yet more analysis will be required to determine if it is a real single cluster associated with the water maser. The 13CO emissions at the radial velocity of the maser corresponds to the mid-infrared emission. * Refers As VVV CL177.

Keywords: star clusters; open star clusters; young massive clusters; young stellar objects
Dynamics in the Transition Region beneath Active Region Upflows Viewed by IRIS

Coronal upflows at the edges of active regions (ARs), which are a possible source of slow solar wind, have been found to connect with dynamics in the transition region. To infer at what scale transition region dynamics connect to AR upflows, we investigate the statistical properties of the small-scale dynamics in the transition region underneath the upflows at the edge of NOAA Active Region 11934. With observations from the Interface Region Imaging Spectrograph (IRIS), we found that the Si IV 1403 Å Doppler map consists of numerous blueshifted and redshifted patches mostly with sizes less than 1 Mm2. The blueshifted structures in the transition region tend to be brighter than the redshifted ones, but their nonthermal velocities have no significant difference. With the SWAMIS feature-tracking procedure, we found in IRIS slit-jaw 1400 Å images that dynamic bright dots with an average size of about 0.3 Mm2 and lifetimes of mostly less than 200 s were spread all over the region. Most of the bright dots appear to be localized, without a clear signature of plasma propagation to a long distance on the projection plane. Surge-like motions with speeds of about 15 km s-1 could be seen in some events at the boundaries of the upflow region, where the magnetic field appeared to be inclined. We conclude that the transition region dynamics connecting to coronal upflows should occur in at a very fine scale, suggesting that the corresponding coronal upflows should also be highly structured. It is also plausible that the transition region dynamics might just act as stimulation at the coronal base, which then drives the upflows in the corona.

Keywords: solar active regions; solar transition region; slow solar wind; doppler shift; solar corona; solar atmosphere; solar active region velocity fields; solar coronal transients
A Refined Model of Convectively Driven Flicker in Kepler Light Curves

Light curves produced by the Kepler mission demonstrate stochastic brightness fluctuations (or flicker) of stellar origin which contribute to the noise floor, limiting the sensitivity of exoplanet detection and characterization methods. In stars with surface convection, the primary driver of these variations on short (sub-eight-hour) timescales is believed to be convective granulation. In this work, we improve existing models of this granular flicker amplitude, or F8, by including the effect of the Kepler bandpass on measured flicker, by incorporating metallicity in determining convective Mach numbers, and by using scaling relations from a wider set of numerical simulations. To motivate and validate these changes, we use a recent database of convective flicker measurements in Kepler stars, which allows us to more fully detail the remaining model-prediction error. Our model improvements reduce the typical misprediction of flicker amplitude from a factor of 2.5-2. We rule out rotation period and strong magnetic activity as possible explanations for the remaining model error, and we show that binary companions may affect convective flicker. We also introduce an envelope model that predicts a range of flicker amplitudes for any one star to account for some of the spread in numerical simulations, and we find that this range covers 78% of observed stars. We note that the solar granular flicker amplitude is lower than most Sun-like stars. This improved model of convective flicker amplitude can better characterize this source of noise in exoplanet studies as well as better inform models and simulations of stellar granulation.

Keywords: stellar granulation; transit photometry; solar granulation
The Reliability of Accretion Disk Inclination Derived from X-Ray Spectroscopy of Active Galaxies

The inclination angle of substructures in active galaxies gives insights into physical components from scales of the vicinity of the central black hole to the entire host galaxy. We use the self-consistent reflection spectral model RELXILL to measure the inclination of the inner region of accretion disks with broadband (0.3–78 keV) X-ray observations, systematically studying the reliability of this methodology. To test the capability of the model to return statistically consistent results, we analyze multiepoch joint XMM-Newton and NuSTAR data of the narrow-line Seyfert 1 galaxy I Zwicky 1 and the broad-line radio galaxy 3C 382, which exhibit different degrees of spectral complexity and reflection features. As expected, we find that adding more data for analysis narrows the confidence interval and that multiepoch joint observations return optimal measurements; however, even single-epoch data can be well fitted if the reflection component is sufficiently dominant. Mock spectra are used to test the capability of RELXILL to recover input parameters from typical single-epoch joint observations. We find that inclination is well recovered at 90% confidence, with improved constraints at higher reflection fraction and higher inclination. Higher iron abundance and corona temperature tighten the constraints as well, but the effect is not as significant as a higher reflection fraction. The spin, however, has little effect in reflection-based inclination measurements. We conclude that broadband reflection spectroscopy can reliably measure inner accretion disk inclination.

Keywords: accretion; active galaxies; x-ray active galactic nuclei; supermassive black holes
Star-crossed Lovers DI Tau A and B: Orbit Characterization and Physical Properties Determination

The stellar companion to the weak-line T Tauri star DI Tau A was first discovered by the lunar occultation technique in 1989 and was subsequently confirmed by a speckle imaging observation in 1991. It has not been detected since, despite being targeted by five different studies that used a variety of methods and spanned more than 20 yr. Here, we report the serendipitous rediscovery of DI Tau B during our Young Exoplanets Spectroscopic Survey (YESS). Using radial velocity data from YESS spanning 17 yr, new adaptive optics observations from Keck II, and a variety of other data from the literature, we derive a preliminary orbital solution for the system that effectively explains the detection and (almost all of the) non-detection history of DI Tau B. We estimate the dynamical masses of both components, finding that the large mass difference (q ~ 0.17) and long orbital period (≳35 yr) make the DI Tau system a noteworthy and valuable addition to studies of stellar evolution and pre-main-sequence models. With a long orbital period and a small flux ratio (f2/f1) between DI Tau A and B, additional measurements are needed for a better comparison between these observational results and pre-main-sequence models. Finally, we report an average surface magnetic field strength ( $\bar{B}$ ) for DI Tau A, of ~0.55 kG, which is unusually low in the context of young active stars.

Keywords: binary stars; visual binary stars; pre-main sequence stars; radial velocity; high angular resolution; fundamental parameters of stars
Testing Short-term Variability and Sampling of Primary Volatiles in Comet 46P/Wirtanen

The exceptionally favorable close approach of Jupiter-family comet 46P/Wirtanen in 2018 December enabled characterization of its primary volatile composition with exceptionally high spatial resolution and sensitivities using the iSHELL spectrograph at the NASA Infrared Telescope Facility on Maunakea, H. We sampled emissions from H2O, HCN, C2H2, NH3, C2H6, and CH3OH on UT 2018 December 21 using two instrumental settings that spanned the 2.9-3.6 μm spectral region. We also obtained a sensitive 3σ upper limit for H2CO and for the rarely studied molecule HC3N. We report rotational temperatures, production rates, and mixing ratios (relative to H2O as well as to C2H6). We place our results in context by comparing them with other comets observed at near-IR wavelengths. We also compare our results with those obtained using the NIRSPEC-2 spectrograph on Keck II on UT December 17 and 18 and with results obtained from iSHELL on other dates during the same apparition. Within 1-2σ uncertainty, production rates obtained for all molecules in this work were consistent with those obtained using NIRSPEC-2 except H2O, indicating low-level variability on a timescale of days. Mixing ratios with respect to H2O in 46P/Wirtanen were consistent with corresponding values from NIRSPEC-2 within the uncertainty with the exception of CH3OH, which yielded a higher ratio on December 21. Our measurements afforded a high temporal resolution that spanned ∼2/3 of the rotational period of 46P/Wirtanen, enabling us to test short-term variability in the production rates of H2O and HCN due to rotational effects. Both H2O and HCN production rates showed similar temporal variability, resulting in nearly constant HCN/H2O.

Keywords: comet volatiles; near infrared astronomy; molecular spectroscopy; comets; high resolution spectroscopy; comae
The Kinematic Evolution of Erupting Structures in Confined Solar Flares

In this Letter, we study the kinematic properties of ascending hot blobs associated with confined flares. Taking advantage of high-cadence extreme-ultraviolet images provided by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we find that for the 26 events selected here, the hot blobs are first impulsively accelerated outward, but then quickly slow down to motionlessness. Their velocity evolution is basically synchronous with the temporal variation of the Geostationary Operational Environmental Satellite soft X-ray flux of the associated flares, except that the velocity peak precedes the soft X-ray peak by minutes. Moreover, the duration of the acceleration phase of the erupting blobs is moderately correlated with that of the flare rise phase. For nine of the 26 cases, the erupting blobs even appear minutes prior to the onset of the associated flares. Our results show that a fraction of confined flares also involve the eruption of a magnetic flux rope, which sometimes is formed and heated prior to the flare onset. We suggest that the initiation and development of these confined flares are similar to that of eruptive ones, and the main difference may lie in the background field constraint, which is stronger for the former than for the latter.

Keywords: solar corona; solar activity; solar flares; solar coronal mass ejections
Predicting Short-duration GRB Rates in the Advanced LIGO Volume

Starting with models for the compact object merger event rate, the short-duration gamma-ray burst (sGRB) luminosity function, and the Swift-BAT detector, we calculate the observed Swift sGRB rate and its uncertainty. Our probabilistic sGRB world model reproduces the observed number distributions in redshift and flux for 123 Swift-BAT detected sGRBs and can be used to predict joint sGRB/LIGO detection rates. We discuss the dependence of the rate predictions on the model parameters and explore how they vary with increasing experimental sensitivity. In particular, the number of bursts in the LIGO volume depends strongly on the parameters that govern sGRB beaming. Our results suggest that nearby sGRBs should be observed to have broader jets on average (θ jet ≳ 30°), as compared to the narrowly beamed appearance of cosmological sGRBs due to the detection-selection effect driving the observed jet angle. Assuming all sGRBs are due to compact object mergers, within a D < 200 Mpc aLIGO volume, we predict ${0.18}_{-0.08}^{+0.19}$ sGRB-gravitational wave (GW) associations all sky per year for on-axis events at Swift sensitivities, increasing to ${1.2}_{-0.6}^{+1.9}$ with the inclusion of off-axis events. We explore the consistency of our model with GW170817/GRB 170817A in the context of structured jets. Predictions for future experiments are made.

Keywords: gamma-rays; gamma-ray bursts; gravitational waves; gravitational wave sources; ligo
A VIPA Spectrograph with Ultra-high Resolution and Wavelength Calibration for Astronomical Applications

A prototype spectrograph using a Virtually Imaged Phased Array (VIPA) as the main dispersion element is presented, and its performance is fully examined in our laboratory. The single-mode, fiber-fed spectrograph with simultaneous wavelength calibration possesses a spectral resolution well in excess of $R\approx 1.12\times {10}^{6}$ while the size of the VIPA is several orders of magnitude smaller than that of a conventional échelle with comparable resolution. In laboratory tests, the VIPA-based instrument with a homemade Yb:fiber ring laser frequency comb demonstrates a mode-to-mode tracking stability of 41 cm s-1 over a period of 6 hr. The VIPA spectrograph has promising applications in various astronomical observations in which ultra-high resolution and calibration precision are imperative, such as solar physics research, exoplanet searching with the radial velocity method, and O2 detection in the atmosphere of Earth-like planets. Ultimately, feasible optimizations for night-sky observations under seeing limited conditions are discussed.

Keywords: high resolution spectroscopy; astronomical instrumentation; astronomical methods; astronomical techniques
Khronometric Theories of Modified Newtonian Dynamics

In 2011 Blanchet and Marsat suggested a fully relativistic version of Milgrom's modified Newtonian dynamics in which the dynamical degrees of freedom consist of the spacetime metric and a foliation of spacetime, the khronon field. This theory is simpler than the alternative relativistic formulations. We show that the theory has a consistent nonrelativistic or slow-motion limit. Blanchet and Marsat showed that in the slow motion limit, the theory reproduces stationary solutions of modified Newtonian dynamics. We show that these solutions are stable to khronon perturbations in the low acceleration regime, for the cases of spherical, cylindrical, and planar symmetry. For nonstationary systems in the low acceleration regime, we show that the khronon field generally gives an order unity correction to the modified Newtonian dynamics. In particular, there will be an order unity correction to the MOND version of Kepler's third law, potentially relevant to ongoing efforts to test MOND using GAIA observations of wide binaries.

Keywords: dark matter; galaxy structure; non-standard theories of gravity
A Coronal Mass Ejection Source Region Catalog and Their Associated Properties

The primary objective of this study is to connect coronal mass ejections (CMEs) to their source regions, primarily to create a CME source region catalog, and secondarily to probe the influence that the source regions have on the different statistical properties of CMEs. We create a source region catalog for 3327 CMEs from 1998 to 2017, thus capturing the different phases of cycles 23 and 24. The identified source regions are segregated into three classes-active regions, prominence eruptions, and active prominences-while the CMEs are segregated into slow and fast groups, based on their average projected speeds. We find the contributions of these three source region types to the occurrences of slow and fast CMEs to be different in the above period. A study of the distribution of the average speeds reveals different power laws for CMEs originating from different sources, and the power laws are different during the different phases of cycles 23 and 24. A study of the statistical latitudinal deflections shows equatorward deflections, while the magnitudes of the deflections again bear imprints of the source regions. An east-west asymmetry is also noted, particularly in the rising phase of cycle 23, with the presence of active longitudes for the CMEs, with a preference toward the western part of the Sun. Our results show that different aspects of CME kinematics bear strong imprints of the source regions they originate from, thus indicating the existence of different ejection and/or propagation mechanisms of these CMEs.

Keywords: solar coronal mass ejections; solar cycle
Impact of Nuclear β-decay Half-life Uncertainties on the r-process Simulations

The impact of nuclear β-decay half-life uncertainties on the r-process simulations are investigated in the hot wind r-process scenarios. It is found that the theoretical deviations among various half-life predictions are generally smaller and larger than 1 order of magnitude for the unknown nuclei with N ≲ 126 and N ≳ 126, respectively. This will have a significant impact on the r-process freeze-out time and the neutron-to-seed ratio after the freeze-out time. A universal staggering pattern is observed for the r-process abundances with the use of different half-life models before freeze-out. After the freeze-out, nuclear β-decay half-lives remarkably affect the detailed r-process abundance distributions. It is also found that nuclear β-decay half-lives have a remarkable impact on the abundances of transuranium elements, which play an important role in reproducing the second and the rare-earth peaks of solar r-process abundances, and filling the troughs before them by nuclear fissions.

Keywords: r-process; nucleosynthesis
Quasiperiodic Oscillation in Short Gamma-Ray Bursts from Black Hole-Neutron Star Mergers

Short-duration gamma-ray bursts (sGRBs) are commonly attributed to the mergers of double neutron stars (NSs) or the mergers of a neutron star with a black hole (BH). While the former scenario was confirmed by the event GW170817, the latter remains elusive. Here, we consider the latter scenario in which an NS is tidally disrupted by a fast-spinning low-mass BH and the accretion onto the BH launches a relativistic jet and hence produces an sGRB. The merging binary's orbit is likely misaligned with the BH's spin. Hence, the Lense-Thirring precession around the BH may cause a hyperaccreting thick disk to precess in a solid-body manner. We propose that a jet, initially aligned with the BH spin, is deflected and collimated by the wind from the disk, therefore being forced to precess along with the disk. This would result in a quasiperiodic oscillation or modulation in the gamma-ray light curve of the sGRB, with a quasi-period of ~0.01-0.1 s. The appearance of the modulation may be delayed respective to the triggering of the light curve. This feature, unique to the BH-NS merger, may have already revealed itself in a few observed sGRBs (such as GRB 130310A), and it carries the spin-orbit orientation information of the merging system. Identification of this feature would be a new approach to reveal spin-orbit misaligned merging BH-NS systems, which are likely missed by the current gravitational-wave searching strategy that is principally targeting aligned systems.

Keywords: stellar mass black holes; neutron stars; gravitational wave sources; gamma-ray bursts; relativistic jets
Beyond Gaia: Asteroseismic Distances of M Giants Using Ground-based Transient Surveys

Evolved stars near the tip of the red giant branch show solar-like oscillations with periods spanning hours to months and amplitudes ranging from ∼1 mmag to ∼100 mmag. The systematic detection of the resulting photometric variations with ground-based telescopes would enable the application of asteroseismology to a much larger and more distant sample of stars than is currently accessible with space-based telescopes such as Kepler or the ongoing Transiting Exoplanet Survey Satellite mission. We present an asteroseismic analysis of 493 M giants using data from two ground-based surveys: the Asteroid Terrestrial-impact Last Alert System (ATLAS) and the All-Sky Automated Survey for Supernovae (ASAS-SN). By comparing the extracted frequencies with constraints from Kepler, the Sloan Digital Sky Survey Apache Point Observatory Galaxy Evolution Experiment, and Gaia we demonstrate that ground-based transient surveys allow accurate distance measurements to oscillating M giants with a precision of ∼15%. Using stellar population synthesis models we predict that ATLAS and ASAS-SN can provide asteroseismic distances to ∼2 × 106 galactic M giants out to typical distances of 20-50 kpc, vastly improving the reach of Gaia and providing critical constraints for Galactic archeology and galactic dynamics.

Keywords: stellar distance; asteroseismology; m giant stars; ground-based astronomy
Solar Flare Modified Complex Network

A constructive approach is developed to build the solar flare complex network by utilizing a visibility graph condition alongside the Abe-Suzuki method. Solar flare information such as position, start time, and peak flux is used for this purpose. The obtained characteristics of the topological features (such as the characteristic path length, power-law behavior of the probability distribution function of degrees, and the clustering coefficient) demonstrate the scale-free and small-world properties of the solar flare modified network. To explain the complexity of the constructed network, Omori's law as well as the universal scaling features are investigated. Furthermore, a nonextensive modification of the Gutenberg-Richter law is examined for the solar flare modified network using a q-stretched exponential model. Establishing a two-dimensional map for the configuration of 118 energetic main flares observed between 2006 and 2016, it is found that the main flares are located within the regions consisting of hubs (high-connectivity regions) of the network. A fractal dimension of the solar flare network of about 0.79 is also obtained.

Keywords: solar flares; solar physics; the sun; astronomy data modeling; astronomy databases; astronomy data analysis; time series analysis; neural networks; solar active regions; computational methods; computational astronomy; astronomical simulations
Importance of Angle-dependent Partial Frequency Redistribution in Hyperfine Structure Transitions Under the Incomplete Paschen-Back Effect Regime

Angle-frequency coupling in scattering of polarized light on atoms is represented by the angle-dependent (AD) partial frequency redistribution (PRD) matrices. There are several lines in the linearly polarized solar spectrum, for which PRD combined with quantum interference between hyperfine structure states play a significant role. Here we present the solution of the polarized line transfer equation including the AD-PRD matrix for scattering on a two-level atom with hyperfine structure splitting and an unpolarized lower level. We account for the effects of arbitrary magnetic fields (including the incomplete Paschen-Back effect regime) and elastic collisions. For exploratory purposes we consider a self-emitting isothermal planar atmosphere and use atomic parameters that represent an isolated Na I D2 line. For this case we show that the AD-PRD effects are significant for field strengths below about 30 G, but that the computationally much less demanding approximation of angle-averaged PRD may be used for stronger fields.

Keywords: astrophysical processes; the sun