adsabs/SciX_UAT_keywords huggingface dataset:
Recommendations for Teaching Introductory Astronomy Online during the Coronavirus Pandemic

Colleges and universities around the world were forced to move their classes online in 2020 March due to the coronavirus pandemic. Because of the rapid transition to remote teaching, instructors received limited professional development to teach online. As the pandemic continues, many classes continue to be offered online. Institutions are providing training in teaching online and designing courses beyond what was given in 2020 March, but it is unlikely to be the formal training given to those planning to teach an online class. In this note, I provide key recommendations to developing and teaching introductory astronomy online during this time of limited professional development. I also briefly describe my experience of teaching during the pandemic in the Spring 2020 term, which motivated me to compile these recommendations.

Keywords: solar system astronomy; stellar astronomy; galactic and extragalactic astronomy; exoplanet astronomy; observational astronomy; astrobiology
The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). VIII. Dynamics of Embedded Dense Cores

We present dynamical properties of 294 cores embedded in twelve IRDCs observed as part of the ASHES Survey. Protostellar cores have higher gas masses, surface densities, column densities, and volume densities than prestellar cores, indicating core mass growth from the prestellar to the protostellar phase. We find that ~80% of cores with virial parameter (α) measurements are gravitationally bound (α < 2). We also find an anticorrelation between the mass and the virial parameter of cores, with massive cores having on average lower virial parameters. Protostellar cores are more gravitationally bound than prestellar cores, with an average virial parameter of 1.2 and 1.5, respectively. The observed nonthermal velocity dispersion (from N2D+ or DCO+) is consistent with simulations in which turbulence is continuously injected, whereas the core-to-core velocity dispersion is neither in agreement with driven nor decaying turbulence simulations. We find a not significant increment in the line velocity dispersion from prestellar to protostellar cores, suggesting that the dense gas within the core traced by these deuterated molecules is not yet severely affected by turbulence injected from outflow activity at the early evolutionary stages traced in ASHES. The most massive cores are strongly self-gravitating and have greater surface density, Mach number, and velocity dispersion than cores with lower masses. Dense cores do not have significant velocity shifts relative to their low-density envelopes, suggesting that dense cores are comoving with their envelopes. We conclude that the observed core properties are more in line with the predictions of clump-fed scenarios rather than with those of core-fed scenarios.

Keywords: infrared dark clouds; star forming regions; star formation; massive stars; protostars; interstellar line emission; interstellar medium; protoclusters
L-band Calibration of the Green Bank Telescope from 2016-2019

Since 2016, the HI-MaNGA survey has been obtaining neutral hydrogen (which emits a radio 21cm line) measurements for nearby galaxies which are part of a survey known as "MaNGA". This has been done using observations at the Green Bank Radio Telescope (GBT). We use calibration data obtained routinely at the start of observing runs during this entire period, as well as an extra set of calibration data obtained in 2019 to check the standard GBT data reduction calibrations at L-band (1.4 GHz, or 20cm). We find an constant offset of 20% in the calibration relative to the standard values given in the GBT data reduction pipeline for data of this type. This correction will be used to improve measurements for HI-MaNGA.

Keywords: flux calibration; radio telescopes; surveys; h i line emission
Search for Extended Sources in the Images from Chandra X-Ray Observatory Advanced CCD Imaging Spectrometer

We present a convenient tool (ChaSES) which allows to search for extended structures in Chandra X-ray Observatory Advanced CCD Imaging Spectrometer images. The tool relies on DBSCAN clustering algorithm to detect regions with overdensity of photons compared to the background. Here we describe the design and functionality of the tool which we make publicly available on GitHub. We also provide online extensive examples of its applications to the real data.

Keywords: astronomy data analysis; astronomy image processing; astronomy data visualization; astronomy data reduction
The Connection between Warm Carbon-chain Chemistry and Interstellar Irradiation of Star-forming Cores

Some observations of warm carbon-chain chemistry (WCCC) cores indicate that they are often located near the edges of molecular clouds. This finding may suggest that WCCC is promoted in star-forming cores exposed to radiation from the interstellar medium. We aim to investigate the chemistry of carbon chains in such a core. A chemical simulation of a gas parcel in a low-mass star-forming core with a full level of irradiation by interstellar photons and cosmic rays was compared to a simulation of a core receiving only 1/10 of such irradiation. In the full irradiation model, the abundances of carbon chains were found to be higher by a factor of a few to a few hundred, compared to the model with low irradiation. Higher carbon-chain abundances in the prestellar stage and, presumably, in the extended circumstellar envelope arise because of irradiation of gas and dust by interstellar photons and cosmic rays. A full standard rate of cosmic-ray-induced ionization is essential for a high carbon-chain abundance peak to occur in the circumstellar envelope, which is heated by the protostar (the "true" WCCC phenomenon). The full irradiation model has lower abundances of complex organic molecules than the low-irradiation model. We conclude that WCCC can be caused by exposure of a star-forming core to interstellar radiation, or even just to cosmic rays. The Appendix describes an updated accurate approach for calculating the rate of cosmic-ray-induced desorption.

Keywords: astrochemistry; collapsing clouds; cosmic rays; interstellar dust processes; interstellar molecules; star formation; dense interstellar clouds
Direct Multipoint Observations Capturing the Reformation of a Supercritical Fast Magnetosonic Shock

Using multipoint Magnetospheric Multiscale (MMS) observations in an unusual string-of-pearls configuration, we examine in detail observations of the reformation of a fast magnetosonic shock observed on the upstream edge of a foreshock transient structure upstream of Earth's bow shock. The four MMS spacecraft were separated by several hundred kilometers, comparable to suprathermal ion gyroradius scales or several ion inertial lengths. At least half of the shock reformation cycle was observed, with a new shock ramp rising up out of the "foot" region of the original shock ramp. Using the multipoint observations, we convert the observed time-series data into distance along the shock normal in the shock's rest frame. That conversion allows for a unique study of the relative spatial scales of the shock's various features, including the shock's growth rate, and how they evolve during the reformation cycle. Analysis indicates that the growth rate increases during reformation, electron-scale physics play an important role in the shock reformation, and energy conversion processes also undergo the same cyclical periodicity as reformation. Strong, thin electron-kinetic-scale current sheets and large-amplitude electrostatic and electromagnetic waves are reported. Results highlight the critical cross-scale coupling between electron-kinetic- and ion-kinetic-scale processes and details of the nature of nonstationarity, shock-front reformation at collisionless, fast magnetosonic shocks.

Keywords: planetary bow shocks; shocks
Large Carbonaceous Chondrite Parent Bodies Favored by Abundance–Volatility Modeling: A Possible Chemical Signature of Pebble Accretion

Primitive meteorite groups such as the Vigarano, Mighei, and Karoonda carbonaceous chondrites have enigmatic patterns of elemental abundances, with moderately volatile elements—those that transition from vapor to condensate between ∼400 and ∼900 K—defining plateaus of subequal abundances despite a wide range in volatility. In detail, each group defines a plateau with distinctive nonmonotonic "chemical fingerprints" that have been attributed to combinations of mixing, vaporization/condensation, and fluid-mediated metasomatism—but the extent to which these processes can reproduce the observed variability has not been quantified. Starting with primitive Ivuna chondrite, a two-stage, two-component equilibrium condensation–vaporization model—with gravity implemented as Jeans escape—can explain large-scale plateaus in these chondrite groups, as well as more complex, nonmonotonic small-scale variations. For all three chondritic meteorite groups, models favor earlier high-temperature fractionation under low-gravity conditions followed by a low-temperature fractionation event that took place on a protoplanet at least as large as Ceres. The second fractionation event may represent the fractionation of incoming materials to the planetesimal during protracted pebble accretion. Models with only thermally driven volatile loss, gravity, and mixing can explain more than 80% of the observed compositional variability in these meteorite groups. In our five-parameter model, using only five randomly selected elements yields uselessly large ranges of planet sizes and temperatures, ranges that converge with increasing numbers of elements. These results suggest that even simple models are prone to generating inaccurate conclusions when constrained by too few observations, a fault likely held by more complex models as well.

Keywords: meteorite composition; meteorites; chondrites; carbonaceous chondrites; planet formation; planetesimals
Full-sky, Arcminute-scale, 3D Models of Galactic Microwave Foreground Dust Emission Based on Filaments

We present the DUSTFILAMENTS code, a full-sky model for the millimeter Galactic emission of thermal dust. Our model, composed of millions of filaments that are imperfectly aligned with the magnetic field, is able to reproduce the main features of the dust angular power spectra at 353 GHz as measured by the Planck mission. Our model is made up of a population of filaments with sizes following a Pareto distribution $\propto {L}_{a}^{-2.445}$ , with an axis ratio between short and long semiaxes ϵ ~ 0.16 and an angle of magnetic field misalignment with a dispersion rms(θ LH) = 10°. On large scales, our model follows a Planck-based template. On small scales, our model produces spectra that behave like power laws up to ℓ ~ 4000 or smaller scales by considering even smaller filaments, limited only by computing power. We can produce any number of Monte Carlo realizations of small-scale Galactic dust. Our model will allow tests of how the small-scale non-Gaussianity affects CMB weak lensing and the consequences for the measurement of primordial gravitational waves or relativistic light relic species. Our model also can generate frequency decorrelation on the modified blackbody spectrum of dust and is freely adjustable to different levels of decorrelation. This can be used to test the performance of component separation methods and the impact of frequency spectrum residuals on primordial B-mode surveys. The filament density we paint in the sky is also able to reproduce the general level of non-Gaussianities measured by Minkowski functionals in the Planck 353 GHz channel map.

Keywords: cosmology; observational cosmology; milky way magnetic fields; astrophysical dust processes
HETDEX Public Source Catalog 1-Stacking 50,000 Lyman Alpha Emitters

We describe the ensemble properties of the 1.9 < z < 3.5 Lyman alpha emitters (LAEs) found in the HETDEX survey's first public data release, HETDEX Public Source Catalog 1. Stacking the low-resolution (R ~ 800) spectra greatly increases the signal-to-noise ratio (S/N), revealing spectral features otherwise hidden by noise, and we show that the stacked spectrum is representative of an average member of the set. The flux-limited, Lyα S/N restricted stack of 50,000 HETDEX LAEs shows the ensemble biweight average z ~ 2.6 LAE to be a blue (UV continuum slope ~ -2.4 and E(B - V) < 0.1), moderately bright (M UV ~ -19.7) star-forming galaxy with strong Lyα emission (log L Lyα ~ 42.8 and W λ (Lyα) ~ 114 Å), and potentially significant leakage of ionizing radiation. The rest-frame UV light is dominated by a young, metal-poor stellar population with an average age of 5-15 Myr and metallicity of 0.2-0.3 Z ⊙. ∗ Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen. The HET is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly.

Keywords: catalogs; emission line galaxies; lyman-alpha galaxies; redshift surveys
Inflated Eccentric Migration of Evolving Gas Giants I - Accelerated Formation and Destruction of Hot and Warm Jupiters

Hot and warm Jupiters (HJs and WJs, correspondingly) are gas giants orbiting their host stars at very short orbital periods (P HJ < 10 days; 10 < P WJ < 200 days). HJs and a significant fraction of WJs are thought to have migrated from initially farther-out birth locations. While such migration processes have been extensively studied, the thermal evolution of gas giants and its coupling with migration processes are usually overlooked. In particular, gas giants end their core accretion phase with large radii, then contract slowly to their final radii. Moreover, intensive heating can slow the contraction at various evolutionary stages. The initial large inflated radii lead to faster tidal migration, due to the strong dependence of tides on the radius. Here, we explore this accelerated migration channel, which we term inflated eccentric migration, using a semi-analytical, self-consistent model of the thermal-dynamical evolution of the migrating gas giants, later validated by our numerical model (see the companion paper, paper II). We demonstrate our model for specific examples and carry out a population synthesis study. Our results provide a general picture of the properties of the formed HJs and WJs via inflated migration, and their dependence on the initial parameters/distributions. We show that the tidal migration of gas giants could occur much more rapidly then previously thought, and could lead to the accelerated destruction and formation of HJs and an enhanced formation rate for WJs. Accounting for the coupled thermal-dynamical evolution is therefore critical to understanding the formation of HJs/WJs, and the evolution and final properties of the population, and it plays a key role in their migration processes.

Keywords: hot jupiters; exoplanets; exoplanet formation; exoplanet dynamics; exoplanet tides; exoplanet migration; exoplanet evolution; exoplanet structure; exoplanet astronomy; extrasolar gaseous planets
Examining the Relationship Between Convective Core Overshoot and Stellar Properties Using Asteroseismology

Core overshoot is a large source of uncertainty in constructing stellar models. Whether the amount of overshoot is constant or mass dependent is not completely known, even though models sometimes assume a mass-based trend. In this work we use asteroseismic data from stars observed by Kepler to investigate the relationship between various stellar properties and the amount of overshoot needed to properly model a given star. We find a strong positive trend between stellar mass and overshoot amount for stars between 1.1 and 1.5 ${\text{}}{M}_{\odot }$ , with a slope of 0.89. Additionally, we investigate how inferred stellar properties change as a function of overshoot. Our model grids show that the inferred stellar mass and radius can vary by as much as 14% and 6%, respectively, depending on the extent of overshoot. This mass spread results in a commensurate spread in the ages.

Keywords: asteroseismology; stellar convective zones; stellar interiors; stellar oscillations
Search for the Birefringence of Gravitational Waves with the Third Observing Run of Advanced LIGO-Virgo

Gravitational waves would attain birefringence during their propagation from distant sources to the Earth, when the charge, parity, and time reversal (CPT) symmetry is broken. If it was sizeable enough, such birefringence could be measured by the Advanced LIGO, Virgo, and KAGRA detector network. In this work, we place constraints on the birefringence of gravitational waves with the third observing run of this network, i.e., two catalogs GWTC-2 and GWTC-3. For the dispersion relation ω 2 = k 2 ± 2ζ k 3, our analysis shows the up-to-date strictest limit on the CPT-violating parameter, i.e., $\zeta ={4.07}_{-5.79}^{+5.91}\times {10}^{-17}{\rm{m}}$ , at 68% confidence level. This limit is stricter by ~5 times when compared to the existing one (~2× 10-16 m) and stands for the first ~10 GeV-scale test of the CPT symmetry in gravitational waves. The results of the Bayes factor strongly disfavor the birefringence scenario of gravitational waves.

Keywords: gravitational wave astronomy; gravitational waves; general relativity
Crossing the Rubicon of Reionization with z 5 QSOs

One of the key open questions in cosmology is the nature of sources that completed cosmological hydrogen reionization at z ~ 5.2. High-z primeval galaxies have been long considered the main drivers of reionization, with a minor role played by high-z active galactic nuclei (AGN). However, in order to confirm this scenario, it is fundamental to measure the photoionization rate produced by active SMBHs close to the Epoch of Reionization. Given the pivotal role played by spectroscopically complete observations of high-z QSOs, in this paper we present the first results of the RUBICON (Reionizing the Universe with Bright Cosmological Nuclei) survey. It consists of a color-selected sample of bona fide z ~ 5 QSO candidates from the Hyper Suprime-Cam Subaru Strategic Survey. Our QSO candidates have been validated both by photometric redshifts based on spectral energy distribution fitting and by spectroscopic redshifts, confirming that they lie at 4.5 < z spec < 5.2. A relatively high space density of QSOs (Φ ~ 1.4 × 10-8 c Mpc-3) is thus confirmed at z ~ 5 and M 1450 ~ -27, consistent with a pure density evolution of the AGN luminosity function from z = 4 to z = 5, with a mild density evolution rate of 0.25 dex. This indicates that AGN could play a nonnegligible role in cosmic reionization. The Rubicon of reionization has been crossed.

Keywords: reionization; surveys; catalogs; quasars; observational cosmology
Transit Light Curves for Exomoons: Analytical Formalism

The photometric transit method has been the most effective method to detect and characterize exoplanets as several ground based as well as space based survey missions have discovered thousands of exoplanets using this method. With the advent of the upcoming next generation large telescopes, the detection of exomoons in a few of these exoplanetary systems is very plausible. In this paper, we present a comprehensive analytical formalism in order to model the transit light curves for such moon-hosting exoplanets. In order to achieve analytical formalism, we have considered circular orbit of the exomoon around the host planet, which is indeed the case for tidally locked moons. The formalism uses the radius and orbital properties of both the host planet and its moon as model parameters. The coalignment or noncoalignment of the orbits of the planet and the moon are parameterized using two angular parameters and thus can be used to model all the possible orbital alignments for a star-planet-moon system. This formalism also provides unique and direct solutions to every possible star-planet-moon three circular body alignment. Using the formula derived, a few representative light curves are also presented.

Keywords: exoplanets; natural satellites (extrasolar); transit photometry
A Large-scale Approach to Modeling Molecular Biosignatures: The Diatomics

This work presents the first steps to modeling synthetic rovibrational spectra for all molecules of astrophysical interest using a new approach implemented in the Prometheus code. The goal is to create a new comprehensive source of first-principles molecular spectra, thus bridging the gap for missing data to help drive future high-resolution studies. Our primary application domain is for molecules identified as signatures of life in planetary atmospheres (biosignatures), but our approach is general and can be applied to other systems. In this work we evaluate the accuracy of our method by studying four diatomic molecules, H2, O2, N2, and CO, all of which have well-known spectra. Prometheus uses the transition-optimised shifted Hermite (TOSH) theory to account for anharmonicity for the fundamental ν = 0 → ν = 1 band, along with thermal-profile modeling for the rotational transitions. To this end, we expand TOSH theory to enable the modeling of rotational constants. We show that our simple model achieves results that are a better approximation of the real spectra than those produced through an harmonic approach. We compare our results with high-resolution HITRAN and ExoMol spectral data. We find that modeling accuracy tends to diminish for rovibrational transition away from the band origin, thus highlighting the need for the theory to be further adapted.

Keywords: biosignatures; astrochemistry
The Jet-disk Boundary Layer in Black Hole Accretion

Magnetic fields lines are trapped in black hole event horizons by accreting plasma. If the trapped field lines are lightly loaded with plasma, then their motion is controlled by their footpoints on the horizon and thus by the spin of the black hole. In this paper, we investigate the boundary layer between lightly loaded polar field lines and a dense, equatorial accretion flow. We present an analytic model for aligned prograde and retrograde accretion systems and argue that there is significant shear across this jet-disk boundary at most radii for all black hole spins. Specializing to retrograde aligned accretion, where the model predicts the strongest shear, we show numerically that the jet-disk boundary is unstable. The resulting mixing layer episodically loads plasma onto trapped field lines where it is heated, forced to rotate with the hole, and permitted to escape outward into the jet. In one case we follow the mass loading in detail using Lagrangian tracer particles and find a time-averaged mass-loading rate $\sim 0.01\,\dot{M}$ .

Keywords: accretion; magnetohydrodynamics; plasma astrophysics