adsabs/SciX_UAT_keywords huggingface dataset:
Parameterized Asymmetric Neutral Hydrogen Disk Integrated Spectrum Characterization (PANDISC). I. Introduction to a Physically Motivated H I Model

Modeling the integrated H I spectra of galaxies has been a difficult task, due to their diverse shapes, but more dynamical information is waiting to be explored in H I line profiles. Based on simple assumptions, we construct a physically motivated model for the integrated H I spectra: Parameterized Asymmetric Neutral hydrogen Disk Integrated Spectrum Characterization (PANDISC). The model shows great flexibility in reproducing the diverse H I profiles. We use Monte Carlo Markov Chain for fitting the model to global H I profiles and produce statistically robust quantitative results. Comparing with several samples of H I data available in the literature, we find the model-fitted widths agree with cataloged velocity widths (e.g., W50) down to S/N ≲ 6. While dynamical information can only be extracted reliably from spectra with S/N > 8. The model is also shown to be useful for applications like the baryonic Tully-Fisher relation (BTFR) and profile-based sample control. By comparing the model parameter v r to v flat, we uncover how the H I width is affected by the structure of the rotation curve, following a trend consistent with the difference in the BTFR slope. We also select a sample of spectra with broad wing-like features suggestive of a population of galaxies with unusual gas dynamics. The PANDISC model bears both promise and limitations for potential use beyond H I lines. Further application on the whole ALFALFA sample will enable us to perform large-scale ensemble studies of the H I properties and dynamics in nearby galaxies.

Keywords: h i line emission; astronomy data analysis; galaxy dynamics; galaxy rotation
Effect of Dust Size on the Near-infrared Spectra (1.0-5.0 μm) of Brown Dwarf Atmospheres

In this study, we demonstrate the dependence of atmospheric dust size on the near-infrared spectra of ten L dwarfs, and constrain the sizes of dust grains in each L dwarf atmosphere. In previous studies, by comparing observed and modeled spectra, it was suggested that the deviations of their spectral shapes from theoretical prediction are general characteristics. Here, we focus on the dust size in brown dwarf atmospheres to understand the observed spectra. We confirm that changing the dust size changes the temperature-pressure structure of the atmosphere, with the shape of the spectrum changing accordingly. At the wavelength at which dust is the main absorber of radiation (the dust-dominated regime), a large dust opacity combined with a medium grain size, e.g., 0.1 μm, results in a low photospheric temperature, and thus a small flux. Conversely, for the wavelength at which gas absorption is dominant (the gas-dominated regime), a large dust opacity modifies the temperature-pressure structure, resulting in a high photospheric temperature, which corresponds to large flux emissions. Taking into account the size effect, we compare the model spectral fluxes in the wavelength range 1-5 μm with the observational ones to constrain the main dust size in the atmosphere of each of the ten L dwarfs observed with AKARI and SpeX or CGS4. Ultimately, we reveal that the observed data are reproduced with higher fidelity by models based on a medium dust size of 0.1-3.0 μm for six of these L dwarfs; therefore, we suggest that such atmospheric dust sizes apply to the majority of L dwarfs.

Keywords: brown dwarfs; l dwarfs; stellar atmospheres; stellar photospheres; spectroscopy; molecular spectroscopy; near infrared astronomy
Using Concentration Offset to Analyze the Dependence of Galaxy Quenching on Morphology

Quenching is the process by which a galaxy's star formation ceases and it moves from being a blue star-forming to a red quiescent galaxy. Concentration has been shown to be a good indicator of this process; this paper uses ΔΣ1 (a concentration offset derived below) to observe how quenching differs between galaxy morphologies. We use Sloan Digital Sky Survey data to plot ΔSFR against ΔΣ1, with morphological classifications from Galaxy Zoo 2 and environmental classifications from Yang et al. We find a difference in the distributions of concentration offset between early- and late-types that is not observed with differing environmental conditions and so conclude that separating the two allows more insight into their individual quenching processes. Late-types are shown to follow a process of compaction before then quenching and this is consistent with a picture where they quench slower than the early-types.

Keywords: galaxy quenching
Parametric Survey of Nonaxisymmetric Accretion Disk Instabilities: Magnetorotational Instability to Super-Alfvénic Rotational Instability

Accretion disks are highly unstable to magnetic instabilities driven by shear flow, where classically, the axisymmetric, weak-field magnetorotational instability (MRI) has received much attention through local WKB approximations. In contrast, discrete nonaxisymmetric counterparts require a more involved analysis through a full global approach to deal with the influence of the nearby magnetohydrodynamic (MHD) continua. Recently, rigorous MHD spectroscopy identified a new type of ultralocalized, nonaxisymmetric instability in global disks with super-Alfvénic flow. These super-Alfvénic rotational instabilities (SARIs) fill vast unstable regions in the complex eigenfrequency plane with (near eigen)modes that corotate at the local Doppler velocity and are radially localized between Alfvénic resonances. Unlike discrete modes, they are utterly insensitive to the radial disk boundaries. In this work, we independently confirm the existence of these unprecedented modes using our novel spectral MHD code Legolas, reproducing and extending our earlier study with detailed eigenspectra and eigenfunctions. We calculate the growth rates of SARIs and MRI in a variety of disk equilibria, highlighting the impact of field strength and orientation, and find correspondence with analytical predictions for thin, weakly magnetized disks. We show that nonaxisymmetric modes can significantly extend instability regimes at high mode numbers, with maximal growth rates comparable to those of the MRI. Furthermore, we explicitly show a region filled with quasi-modes whose eigenfunctions are extremely localized in all directions. These modes must be ubiquitous in accretion disks, and play a role in local shearing box simulations. Finally, we revisit recent dispersion relations in the appendix, highlighting their relation to our global framework.

Keywords: galaxy accretion disks; magnetohydrodynamics
Observations of Magnetic Field Line Curvature and Its Role in the Space Plasma Turbulence

Recent numerical simulations of plasma turbulence showed that magnetic field line curvature plays a key role in particle energization. Based on in situ high-resolution data provided by the four Magnetospheric Multiscale spacecraft, we investigate the magnetic field line curvature and its role in the turbulent magnetosheath plasma. Our analysis reveals that the curvature exhibits two power-law distributions: the low curvature follows the scaling as κ0.33, and the large curvature has a scaling as κ-2.16. The curvature is anticorrelated with the magnitude of the magnetic field, but positively related to the normal force, the drift electric current, and the curvature drift acceleration term, indicating that intense energy dissipation due to the curvature drift occurs in the large curvature region. One typical example shows a localized increase of electron temperature that coincides with a peak in the curvature and the curvature drift acceleration term, which supports the role of the latter in local energization of electrons, in agreement with simulation results. These observations allow us to better understand the connection between magnetic field line curvature, energy dissipation, and particle energization in space and astrophysical plasmas.

Keywords: interplanetary turbulence; interplanetary particle acceleration; magnetic fields; high energy astrophysics; space plasmas
Mapping the X-Ray Corona Evolution of IRAS 13224-3809 with the Power Spectral Density

We develop the power spectral density (PSD) model to explain the nature of the X-ray variability in IRAS 13224-3809, including the full effects of the X-ray reverberation due to the lamppost source. We utilize 16 XMM-Newton observations individually as well as group them into three different luminosity bins: low, medium, and high. The soft (0.3-1 keV) and hard (1.2-5 keV) PSD spectra are extracted and simultaneously fitted with the model. We find that the corona height changes from h ~ 3 r g during the lowest luminosity state to ~25 r g during the highest luminosity state. This provides further evidence that the source height from the reverberation data is significantly larger than what is constrained by the spectral analysis. Furthermore, as the corona height increases, the energy spectrum tends to be softer while the observed fractional excess variance, F var, reduces. We find that the PSD normalization is strongly correlated with F var and moderately correlated with the PSD bending index. Therefore, the normalization is dependent on the accretion rate that controls the intrinsic shape of the PSD. While the intrinsic variability of the disk is manifested by the reverberation signals, the disk and corona may evolve independently. Our results suggest that, as the source height increases, the disk itself generates less overall variability power but more high-frequency variability resulting in the PSD spectrum that flattens out (i.e., the inner disk becomes more active). Using the luminosity-bin data, the hint of the Lorentzian component is seen, with the peak appearing at lower frequencies with increasing luminosity.

Keywords: reverberation mapping; x-ray astronomy; active galactic nuclei; black hole physics
Recent Updates to the Gas-phase Chemical Reactions and Molecular Lines in CLOUDY: Their Effects on Millimeter and Submillimeter Molecular Line Predictions

Here, we present our current updates to the gas-phase chemical reaction rates and molecular lines in the spectral synthesis code CLOUDY, and its implications in spectroscopic modeling of various astrophysical environments. We include energy levels, and radiative and collisional rates for HF, CF+, HC3N, ArH+, HCl, HCN, CN, CH, and CH2. Simultaneously, we expand our molecular network involving these molecules. For this purpose, we have added 561 new reactions and have updated the existing 165 molecular reaction rates involving these molecules. As a result, CLOUDY now predicts all the lines arising from these nine molecules. In addition, we also update H2-H2 collisional data up to rotational levels J = 31 for v = 0. We demonstrate spectroscopic simulations of these molecules for a few astrophysical environments. Our existing model for globules in the Crab Nebula successfully predicts the observed column density of ArH+. Our model predicts a detectable amount of HeH+, OH+, and CH+ for the Crab Nebula. We also model the interstellar medium toward HD185418, W31C, and NGC 253, and our predictions match with most of the observed column densities within the observed error bars. Very often molecular lines trace various physical conditions. Hence, this update will be very supportive for spectroscopic modeling of various astrophysical environments, particularly involving submillimeter and mid-infrared observations using the Atacama Large Millimeter/submillimeter Array and the James Webb Space Telescope, respectively.

Keywords: interstellar molecules; interstellar abundances; interstellar clouds
Dynamical Masses for the Hyades Binary System vB 120

We report spectroscopic observations of vB 120 (HD 30712), a 5.7 yr astrometric-spectroscopic binary system in the Hyades cluster. We combine our radial velocities with others from the literature, and with existing speckle interferometry measurements, to derive an improved 3D orbit for the system. We infer component masses of M 1 = 1.065 ± 0.018 M ☉ and M 2 = 1.008 ± 0.016 M ☉, and an orbital parallax of 21.86 ± 0.15 mas, which we show to be more accurate than the parallax from Gaia DR3. This is the ninth binary or multiple system in the Hyades with dynamical mass determinations, and one of the examples with the highest precision. An analysis of its spectral energy distribution yields the absolute radii of the stars, R 1 = 0.968 ± 0.012 R ☉ and R 2 = 0.878 ± 0.013 R ☉, and effective temperatures of 5656 ± 56 K and 5489 ± 60 K for the primary and secondary, respectively. A comparison of these properties with the predictions of current stellar evolution models for the known age and metallicity of the cluster shows only minor differences.

Keywords: astrometric binary stars; binary stars; spectroscopic binary stars; stellar masses; stellar evolutionary models; open star clusters; radial velocity
Nonlinear Color-Metallicity Relations of Globular Clusters. XI. Nonlinearity Effect Revealed by NGC 5128 (Centaurus A) and NGC 4594 (Sombrero) Galaxies

Metallicity distributions (MDs) of globular clusters (GCs) provide crucial clues for the assembly and star formation history of their host galaxies. GC colors, when GCs are old, have been used as a proxy of GC metallicities. Bimodal GC color distributions (CDs) observed in most early-type galaxies have been interpreted as bimodal MDs for decades, suggesting the presence of merely two GC subpopulations within single galaxies. However, the conventional view has been challenged by a new theory that nonlinear metallicity-to-color conversion can cause bimodal CDs from unimodal MDs. The unimodal MDs seem natural given that MDs involved many thousand protogalaxies. The new theory has been tested and corroborated by various observational and theoretical studies. Here we examine the nonlinear nature of GC color-metallicity relations (CMRs) using photometric and spectroscopic GC data of NGC 5128 (Centaurus A) and NGC 4594 (Sombrero), in comparison with stellar population simulations. We find that, with a slight offset in color, the overall shapes of observed and modeled CMRs agree well for all available colors. Diverse color-depending morphologies of GC CDs of the two galaxies are well reproduced based on their observed spectroscopic MDs via our CMR models. The results corroborate the nonlinear CMR interpretation of the GC color bimodality, shedding further light on theories of galaxy formation.

Keywords: globular star clusters; galaxy evolution; stellar populations
Probability Distribution Functions of Sunspot Magnetic Flux

We investigated the probability distributions of sunspot area and magnetic flux by using data from the Royal Greenwich Observatory and USAF/NOAA. We constructed a sample of 2995 regions with maximum-development areas ≥500 MSH (millionths of solar hemisphere), covering 146.7 yr (1874-2020). The data were fitted by a power-law distribution and four two-parameter distributions (tapered-power-law, gamma, lognormal, and Weibull distributions). The power-law model was unfavorable compared to the four models in terms of AIC, and was not acceptable according to the classical Kolmogorov-Smirnov test. The lognormal and Weibull distributions were excluded because their behavior extended to smaller regions (S ≪ 500 MSH) do not connect to previously published results. Therefore, our choices were tapered-power-law and gamma distributions. The power-law portion of the tapered-power-law and gamma distributions was found to have a power exponent of 1.35-1.9. Due to the exponential falloff of these distributions, the expected frequencies of large sunspots are low. The largest sunspot group observed had an area of 6132 MSH, and the frequency of sunspots larger than 104 MSH was estimated to be every 3-8 × 104 yr. We also estimated the distributions of the Sun-as-a-star total sunspot areas. The largest total area covered by sunspots on record was 1.67% of the visible disk, and can be up to 2.7% by artificially increasing the lifetimes of large sunspots in an area evolution model. These values are still smaller than those found on active Sun-like stars.

Keywords: solar activity; solar magnetic fields; solar photosphere; sunspots; starspots
Constraint on \dot{G}/G from Orbital Timing

Constraints on the variation of the gravitational constant G have been obtained by many observers using different methods, the most reliable and stringent being those based on the orbital timing of bodies in the solar system and binary pulsars. We show that the constraints determined from orbital timing are on $\dot{G}/G-3\dot{c}/c$ rather than on $\dot{G}/G$ when the speed of light c is also considered to be varying. Increasingly tighter constraint on $\dot{G}/G$ from these observations are possibly due to $\dot{G}/G-3\dot{c}/c=0$ . This relationship between G and c was determined in a previous work by fitting the supernovae 1a data using the relativistically covariant cosmological model with varying $c,G$ and cosmological constant Λ.

Keywords: dirac cosmology
A Necessary Condition for Supernova Fallback Invading Newborn Neutron-star Magnetosphere

We numerically investigate the dynamics of a supernova fallback accretion confronting with a relativistic wind from a newborn neutron star (NS). The time evolution of the accretion shock in the radial direction is basically characterized by the encounter radius of the flow renc and a dimensionless parameter $\zeta \equiv L/{\dot{M}}_{\mathrm{fb}}{c}^{2}$ , where L is the NS wind luminosity and ${\dot{M}}_{\mathrm{fb}}$ is the fallback mass accretion rate. We find that the critical condition for the fallback matter to reach near the NS surface can be simply described as $\zeta \lt {\zeta }_{\min }\equiv {{GM}}_{* }/{c}^{2}{r}_{\mathrm{enc}}$ or ${r}_{\mathrm{enc}}L/{{GM}}_{* }{\dot{M}}_{\mathrm{fb}}\lt 1$ independent of the wind Lorentz factor, where M* is the NS mass. With combining the condition for the fallback matter to bury the surface magnetic field under the NS crust, we discuss the possibility that the trifurcation of NSs into rotation-powered pulsars, central compact objects, and magnetars can be induced by supernova fallback.

Keywords: neutron stars; hydrodynamics
ACCESS: Confirmation of No Potassium in the Atmosphere of WASP-31b

We present a new optical (400-950 nm) transmission spectrum of the hot Jupiter WASP-31b (M = 0.48 MJ; R = 1.54 RJ; P = 3.41 days), obtained by combining four transit observations. These transits were observed with IMACS on the Magellan Baade Telescope at Las Campanas Observatory as part of the ACCESS project. We investigate the presence of clouds/hazes in the upper atmosphere of this planet, as well as the contribution of stellar activity on the observed features. In addition, we search for absorption features of the alkali elements Na I and K I, with particular focus on K I, for which there have been two previously published disagreeing results. Observations with Hubble Space Telescope (HST)/STIS detected K I, whereas ground-based low- and high-resolution observations did not. We use equilibrium and nonequilibrium chemistry retrievals to explore the planetary and stellar parameter space of the system with our optical data combined with existing near-IR observations. Our best-fit model is that with a scattering slope consistent with a Rayleigh slope ( $\alpha ={5.3}_{-3.1}^{+2.9}$ ), high-altitude clouds at a log cloud top pressure of -3.6 ${}_{-2.1}^{+2.7}$ bars, and possible muted H2O features. We find that our observations support other ground-based claims of no K I. Clouds are likely why signals like H2O are extremely muted and Na or K cannot be detected. We then juxtapose our Magellan/IMACS transmission spectrum with existing VLT/FORS2, HST/WFC3, HST/STIS, and Spitzer observations to further constrain the optical-to-infrared atmospheric features of the planet. We find that a steeper scattering slope (α = 8.3 ± 1.5) is anchored by STIS wavelengths blueward of 400 nm and only the original STIS observations show significant potassium signal.

Keywords: exoplanet atmospheres; observational astronomy; exoplanets; hot jupiters; spectroscopy
Spectroscopic Observations of Obscured Populations in the Inner Galaxy: 2MASS-GC02, Terzan 4, and the 200 km s-1 stellar peak

The interpretation of potentially new and already known stellar structures located at low latitudes is hindered by the presence of dense gas and dust, as observations toward these sight lines are limited. We have identified Apache Point Observatory Galaxy Evolution Experiment (APOGEE) stars belonging to the low-latitude globular clusters 2MASS-GC02 and Terzan 4, presenting the first chemical element abundances of stars residing in these poorly studied clusters. As expected, the signature of multiple populations coexisting in these metal-rich clusters is evident. We redetermine the radial velocity of 2MASS-GC02 to be -87 ± 7 km s-1, finding that this cluster's heliocentric radial velocity is offset by more than 150 km s-1 from the literature value. We investigate a potentially new low-latitude stellar structure and a kiloparsec-scale nuclear disk (or ring) that has been put forward to explain a high-velocity (VGSR ~ 200 km s-1) peak reported in several Galactic bulge fields based on the APOGEE commissioning observations. New radial velocities of field stars at (l, b) = (-6°,0 °) are presented and combined with the APOGEE observations at negative longitudes to carry out this search. Unfortunately no prominent -200 km s-1 peak at negative longitudes along the plane of the Milky Way are apparent, as predicted for the signature of a nuclear feature. The distances and Gaia EDR3 proper motions of the high-VGSR stars do not support the current models of stars on bar-supporting orbits as an explanation of the +200 km s-1 peak. * Based on observations taken by APOGEE.

Keywords: galactic bulge; globular star clusters; galaxy kinematics; proper motions; milky way formation
PHANGS-JWST: Data-processing Pipeline and First Full Public Data Release

The exquisite angular resolution and sensitivity of JWST are opening a new window for our understanding of the Universe. In nearby galaxies, JWST observations are revolutionizing our understanding of the first phases of star formation and the dusty interstellar medium. Nineteen local galaxies spanning a range of properties and morphologies across the star-forming main sequence have been observed as part of the PHANGS-JWST Cycle 1 Treasury program at spatial scales of ∼5–50 pc. Here, we describe pjpipe, an image-processing pipeline developed for the PHANGS-JWST program that wraps around and extends the official JWST pipeline. We release this pipeline to the community as it contains a number of tools generally useful for JWST NIRCam and MIRI observations. Particularly for extended sources, pjpipe products provide significant improvements over mosaics from the MAST archive in terms of removing instrumental noise in NIRCam data, background flux matching, and calibration of relative and absolute astrometry. We show that slightly smoothing F2100W MIRI data to 0.″9 (degrading the resolution by about 30%) reduces the noise by a factor of ≈3. We also present the first public release (DR1.1.0) of the pjpipe processed eight-band 2–21 μm imaging for all 19 galaxies in the PHANGS-JWST Cycle 1 Treasury program. An additional 55 galaxies will soon follow from a new PHANGS-JWST Cycle 2 Treasury program.

Keywords: star formation; spiral galaxies; surveys; astronomy data reduction; young star clusters; interstellar medium; interstellar dust