adsabs/SciX_UAT_keywords huggingface dataset:
Molecular Gas Properties in Young Stellar Clusters with a Suppressed Star Cluster Wind

In compact and dense star-forming clouds a global star cluster wind could be suppressed. In this case stellar feedback is unable to expel the leftover gas from the cluster. Young massive stars remain embedded in a dense residual gas and stir it by moving in the gravitational well of the system. Here we present a self-consistent model for the molecular gas distribution in such young, enshrouded stellar clusters. It is assumed that the cloud collapse terminates and the star formation ceases when a balance between the turbulent pressure and gravity and between the turbulent energy dissipation and regeneration rates is established. These conditions result in an equation that determines the residual gas density distribution that, in turn, allows one to determine the other characteristics of the leftover gas and the star formation efficiency. It is shown that our model predictions are in good agreement with several observationally determined properties of cloud D1 in the nearby dwarf spheroidal galaxy NGC 5253 and its embedded cluster.

Keywords: star clusters
Probing TYC 3315-1807-1, An sdB+dM Binary Displaying Strong Period Variation and Reflection Effect

Subdwarf (sdB) stars include core helium-burning stars with a very thin hydrogen envelope that lies at the blue end of the horizontal branch (or extreme horizontal branch). Among them, short-period sdB binaries especially with cool companions are significant to test and constrain binary evolution. We discuss one such sdB+dM type binary, TYC 3315-1807-1 (V1), which was first reported by Kawka. Results of the photometric analysis on Transiting Exoplanet Survey Satellite data are being reported. Light variation in the light curve suggests that the system displays a large reflection effect with no eclipses. Spectroscopic observations of the object were also carried out to probe into the nature of secondary companion as well as to understand the post-common-envelope evolution of such objects. The variability in Balmer, He, and Na line profiles as a function of phase, probably caused by observed reflection effect was identified and studied. Period variation study of the object was done using times of minima obtained from the literature and the O - C plot was produced, which points to a decrease in the period (dp/dt = -1.36315 × 10-7 day yr-1), and the possible scenario of evolution is discussed. From the evolutionary models, we constrain the possible mass of the sdB to be 0.274 M ⊙ and that of the secondary is 0.113 M ⊙, and we conclude that V1 may evolve directly as a helium-core white dwarf.

Keywords: binary stars
YMCA-1: A New Remote Star Cluster of the Milky Way?

We report the possible discovery of a new stellar system (YMCA-1), identified during a search for small scale overdensities in the photometric data of the YMCA survey. The object's projected position lies on the periphery of the Large Magellanic Cloud about 13° apart from its center. The most likely interpretation of its color-magnitude diagram, as well as of its integrated properties, is that YMCA-1 may be an old and remote star cluster of the Milky Way at a distance of 100 kpc from the Galactic center. If this scenario could be confirmed, then the cluster would be significantly fainter and more compact than most of the known star clusters residing in the extreme outskirts of the Galactic halo, but quite similar to Laevens 3. However, much deeper photometry is needed to firmly establish the actual nature of the cluster, and the distance to the system. * This work is based on INAF-VST guaranteed observing time under ESO program: 0104.D-0427(A).

Keywords: star clusters; milky way stellar halo; surveys; hertzsprung russell diagram; magellanic clouds
Evidence for Transparency and Clumps in the Circumbinary Ring of the T Tauri Star V582 Mon (KH 15D)

The binary T Tauri star V582 Mon (KH 15D) is surrounded by a tilted and nodally precessing ring of dusty material, which has caused periodic occultations of one or both stars over the last 50 years. Here, we present multi-color time-series photometry (VRIJHK) throughout the 2017/2018 observing season, when the ring was covering the entire orbit of star A and gradually exposing the orbit of star B. We calculate the mean apparent magnitude of star B to be I = 14.08. Besides the periodic eclipses of star B due to its orbital motion, we observed unexpected dips in brightness indicative of partially transparent stellar-sized clumps within the ring. The wavelength dependence of these events is suggestive of extinction by dust grains significantly larger than typical interstellar dust grains. The photometric variability observed while star B is being uncovered by the trailing edge of the ring is not simply the time reversal of the behavior seen when star A was being covered by the leading edge. Whereas the leading edge appeared to be very sharply defined, the trailing edge is "clumpy" and "fuzzy" (transparent), with a more gradual transition in opacity. The clumpiness and transparency of the occulting material provide a unique opportunity to study the properties of dust grains in a likely planet-forming zone.

Keywords: weak-line t tauri stars; t tauri stars; binary stars; protoplanetary disks
Radiation Hydrodynamics Simulations of Protoplanetary Disks: Stellar Mass Dependence of the Disk Photoevaporation Rate

Recent multiwavelength observations suggest that inner parts of protoplanetary disks (PPDs) have shorter lifetimes for heavier host stars. Since PPDs around high-mass stars are irradiated by strong ultraviolet radiation, photoevaporation may provide an explanation for the observed trend. We perform radiation hydrodynamics simulations of photoevaporation of PPDs for a wide range of host star mass of M* = 0.5-7.0 M⊙. We derive disk mass-loss rate $\dot{M}$ , which has strong stellar dependence as $\dot{M}\approx 7.30\times {10}^{-9}{({M}_{* }/{\text{}}{M}_{\odot })}^{2}\,{\text{}}{M}_{\odot }\,{\mathrm{yr}}^{-1}$ . The absolute value of $\dot{M}$ scales with the adopted far-ultraviolet and X-ray luminosities. We derive the surface mass-loss rates and provide polynomial function fits to them. We also develop a semianalytic model that well reproduces the derived mass-loss rates. The estimated inner-disk lifetime decreases as the host star mass increases, in agreement with the observational trend. We thus argue that photoevaporation is a major physical mechanism for PPD dispersal for a wide range of the stellar mass and can account for the observed stellar mass dependence of the inner-disk lifetime.

Keywords: protoplanetary disks; planet formation; hydrodynamical simulations; star formation; interstellar medium
TwO Parameters Semi Empirical Model (TOPSEM): Galaxy Evolution and Bulge/Disk Dicothomy from Two-stage Halo Accretion

In recent years, increasing attention has been devoted to semi-empirical, data-driven models to tackle some aspects of the complex and still largely debated topic of galaxy formation and evolution. We here present a new semi-empirical model whose marking feature is simplicity: it relies on solely two assumptions, one initial condition and two free parameters. Galaxies are connected to evolving dark matter haloes through abundance matching between specific halo accretion rate (sHAR) and specific star formation rate (sSFR). Quenching is treated separately, in a fully empirical way, to marginalize over quiescent galaxies and test our assumption on the sSFR evolution without contaminations from passive objects. Our flexible and transparent model is able to reproduce the observed stellar mass functions up to z ~ 5, giving support to our hypothesis of a monotonic relation between sHAR and sSFR. We then exploit the model to test a hypothesis on morphological evolution of galaxies. We attempt to explain the bulge/disk bimodality in terms of the two halo accretion modes: fast and slow accretion. Specifically, we speculate that bulge/spheroidal components might form during the early phase of fast halo growth, while disks form during the later phase of slow accretion. We find excellent agreement with both the observational bulge and elliptical mass functions.

Keywords: galaxy formation; galaxy evolution; galaxy quenching; galaxy dark matter halos
An Obscured, Seyfert 2-like State of the Stellar-mass Black Hole GRS 1915+105 Caused by Failed Disk Winds

We report on Chandra grating spectra of the stellar-mass black hole GRS 1915+105 obtained during a novel, highly obscured state. As the source entered this state, a dense, massive accretion disk wind was detected through strong absorption lines. Photoionization modeling indicates that it must originate close to the central engine, orders of magnitude from the outer accretion disk. Strong, nearly sinusoidal flux variability in this phase yielded a key insight: the wind is blueshifted when its column density is relatively low, but redshifted as it approaches the Compton-thick threshold. At no point does the wind appear to achieve the local escape velocity; in this sense, it is a "failed wind." Later observations suggest that the disk ultimately fails to keep even the central engine clear of gas, leading to heavily obscured and Compton-thick states characterized by very strong Fe K emission lines. Indeed, these later spectra are successfully described using models developed for obscured active galactic nuclei (AGNs). We discuss our results in terms of the remarkable similarity of GRS 1915+105 deep in its "obscured state" to Seyfert 2 and Compton-thick AGNs, and we explore how our understanding of accretion and obscuration in massive black holes is impacted by our observations.

Keywords: black holes; compact objects; active galactic nuclei; x-ray active galactic nuclei
The Molecular Clouds Associated with the H II Regions/Candidates between L = 207°7 and L = 211°7

Using the PMO-13.7 m millimeter telescope at Delingha in China, we have conducted a large-scale simultaneous survey of 12CO, 13CO, and C18O J = 1 - 0 emission toward the sky region centered at l = 209°7, b = -2°25 with a coverage of 4°0 × 4°5. The majority of the emission in the region comes from the clouds with velocities lying in the range from -3 to 55 km s-1, at kinematic distances from 0.5 to 7.0 kpc. The molecular clouds in the region are concentrated into three velocity ranges. The molecular clouds associated with the 10 H II regions/candidates are identified and their physical properties are presented. Massive stars are found within Sh2-280, Sh2-282, Sh2-283, and BFS54, and we suggest them to be the candidate excitation sources of the H II regions. The distributions of the excitation temperature and line width with the projected distance from the center of H II region/candidate suggest that the majority of the 10 H II regions/candidates and their associated molecular gas are three-dimensional structures, rather than two-dimensional structures.

Keywords: h ii regions; molecular spectroscopy; molecular clouds
New Radio Constraints on the Obscured Star Formation Rates of Massive GRB Hosts at Redshifts 2-3.5

It is not clear whether gamma-ray bursts (GRBs) are unbiased tracers of cosmic star formation at z > 2. Since dusty starburst galaxies are significant contributors to the cosmic star formation at these redshifts, they should form a major part of the GRB host population. However, recent studies at z ≤ 2 have shown that the majority of the star formation activity in GRB hosts is not obscured by dust. Here, we investigate the galaxy-scale dust obscuration in z ∼ 2-3.5 GRB hosts preselected to have high-resolution, high signal-to-noise afterglow spectra in the rest-frame ultraviolet (UV) and thus relatively low line-of-sight dust obscuration. We present new deep Very Large Array observations of four GRB hosts, and compare the radio-based (upper limits on the) total star formation rates (SFRs) to the unobscured SFRs derived from fits to the optical-UV spectral energy distribution. The fraction of the total SFR that is obscured by dust in these galaxies is found to be <90% in general, and ≲50% for GRB 021004 in particular. These observations suggest that z ∼ 2-3.5 GRBs with UV-unobscured sightlines originate in star-forming galaxies with low overall dust obscuration, unlike the dusty starburst population.

Keywords: star formation; interstellar dust extinction; gamma-ray bursts; galaxy properties; galaxy evolution
Radio Spectral Imaging of an M8.4 Eruptive Solar Flare: Possible Evidence of a Termination Shock

Solar flare termination shocks have been suggested as one of the viable mechanisms for accelerating electrons and ions to high energies. Observational evidence of such shocks, however, remains rare. Using radio dynamic spectroscopic imaging of a long-duration C1.9 flare obtained by the Karl G. Jansky Very Large Array (VLA), Chen et al. suggested that a type of coherent radio bursts, referred to as "stochastic spike bursts," were radio signatures of nonthermal electrons interacting with myriad density fluctuations at the front of a flare termination shock. Here we report another stochastic spike burst event recorded during the extended energy release phase of a long-duration M8.4-class eruptive flare on 2012 March 10. VLA radio spectroscopic imaging of the spikes in 1.0-1.6 GHz shows that, similar to the case of Chen et al., the burst centroids form an extended, ∼10″-long structure in the corona. By combining extreme-ultraviolet imaging observations of the flare from two vantage points with hard X-ray and ultraviolet observations of the flare ribbon brightenings, we reconstruct the flare arcade in three dimensions. The results show that the spike source is located at ∼60 Mm above the flare arcade, where a diffuse supra-arcade fan and multitudes of plasma downflows are present. Although the flare arcade and ribbons seen during the impulsive phase do not allow us to clearly understand how the observed spike source location is connected to the flare geometry, the cooling flare arcade observed 2 hr later suggests that the spikes are located in the above-the-loop-top region, where a termination shock presumably forms.

Keywords: solar flares; shocks; solar coronal mass ejections; solar radio emission; solar magnetic reconnection; non-thermal radiation sources; solar radio flares
Nonlinear Density Wave Theory in a Gaseous Disk

A nonlinear solution for the gaseous component of a galactic disk has been derived self-consistently using fluid description and reductive perturbation theory. We show that gas follows a spiral pattern, similarly to the stellar component; but the spirals are slightly separated due to different relevant parameters, as observations suggest. This analytical solution provides an additional contribution to a better understanding of rotation velocity curves of spiral galaxies. Since the proposed approach, and consequently solution, can be used in various astrophysical dynamical systems, we keep as general as possible a form of the calculus. We underline differences between the stellar and gaseous cases, and we apply this solution roughly on the gaseous disk component dynamics pointing out the importance of the nonlinear approach.

Keywords: spiral galaxies; disk galaxies
Dynamical Formation of the GW190814 Merger

We investigate the possible dynamical origin of GW190814, a gravitational wave (GW) source discovered by the LIGO-Virgo-Kagra collaboration (LVC) associated with a merger between a stellar black hole (BH) with mass 23.2 M⊙ and a compact object, either a BH or a neutron star (NS), with mass 2.59 M⊙. Using a database of 240,000 N-body simulations modeling the formation of NS-BH mergers via dynamical encounters in dense clusters, we find that systems like GW190814 are likely to form in young, metal-rich clusters. Our model suggests that a little excess (∼2%-4%) of objects with masses in the range of 2.3-3 M⊙ in the compact remnants' mass spectrum leads to a detection rate for dynamically formed "GW190814 -like" mergers of ΓGW190814 ≃ 1-6 yr-1 Gpc-3, i.e., within the observational constraints set by the GW190814 discovery, ΓLVC ∼ 1-23 yr-1 Gpc-3. Additionally, our model suggests that ∼1.8%-4.8% of dynamical NS-BH mergers are compatible with GW190426_152155, the only confirmed NS-BH merger detected by the LVC. We show that the relative amount of light and heavy NS-BH mergers can provide clues about the environments in which they developed.

Keywords: astrophysical black holes; stellar astronomy; gravitational waves; neutron stars; compact objects; compact radiation sources
Mercury's Lobate Scarps Reveal that Polygonal Impact Craters Form on Contractional Structures

Analysis of polygonal impact craters (PICs) can be used to investigate the presence and orientations of subtle and/or buried faults and fractures across the solar system that may otherwise be unobservable in spacecraft images. Although this technique has been vetted for the analysis of extensional structures, no previous work has investigated if PICs also form on contractional thrust faults. This determination, which we investigated in this work, is critical for accurate tectonic setting interpretations from PICs. Mercury shows an abundance of thrust-fault-related landforms, making it an ideal laboratory to perform this investigation. In this work, we found that Mercury's thrust faults, and their overlying folds and fractures, cause some complex craters ∼20 km or larger to form PICs. However, in most cases, craters form as circular impact craters on these structures. When PIC straight rim segments do form, they parallel the lobate scarp thrust faults and fold hinges. Some PICs likely formed as a result of an impact's interaction with the thrust fault itself, while others may have interacted with fold hinge joints. The parallel relationship between PICs and shortening structures is consistent with the well-established relationship between PICs and extensional structures. Therefore, in addition to extensional fractures, contractional features should also be taken into consideration when utilizing PICs to interpret tectonic settings on bodies across the solar system.

Keywords: planetary science; mercury (planet); tectonics; impact phenomena; craters
A Harsh Test of Far-field Scrambling with the Habitable-zone Planet Finder and the Hobby-Eberly Telescope

The Habitable-zone Planet Finder (HPF) is a fiber-fed precise radial velocity (RV) spectrograph at the 10 m Hobby-Eberly Telescope (HET). Due to its fixed-altitude design, the HET pupil changes appreciably across a track, leading to significant changes of the fiber far-field illumination. HPF's fiber scrambler is designed to suppress the impact of these illumination changes on the RVs—but the residual impact on the RV measurements has yet to be probed on-sky. We use GJ 411, a bright early type (M2) M dwarf to probe the effects of far-field input trends due to these pupil variations on HPF RVs. These large changes (∼2x) in the pupil area and centroid present a harsh test of HPF's far-field scrambling. Our results show that the RVs are effectively decoupled from these extreme far-field input changes due to pupil centroid offsets, attesting to the effectiveness of the scrambler design. This experiment allows us to test the impact of these changes with large pupil variation on-sky, something we would not easily be able to do at a conventional optical telescope. While the pupil and illumination changes expected at these other telescopes are small, scaling from our results enables us to estimate and bound these effects, and show that they are controllable even for the new and next generation of RV instruments in their quest to beat down instrumental noise sources toward the goal of a few $\,\mathrm{cm}\,{{\rm{s}}}^{-1}$ .

Keywords: astronomical instrumentation; astronomical methods; radial velocity; exoplanet detection methods
Chemical Composition of Bright Stars in the Continuous Viewing Zone of the TESS Space Mission

Accurate atmospheric parameters and chemical composition of stars play a vital role in characterizing physical parameters of exoplanetary systems and understanding of their formation. A full asteroseismic characterization of a star is also possible if its main atmospheric parameters are known. The NASA Transiting Exoplanet Survey Satellite (TESS) space telescope will play a very important role in searching of exoplanets around bright stars and stellar asteroseismic variability research. We have observed all 302 bright (V < 8 mag) and cooler than F5 spectral class stars in the northern TESS continuous viewing zone with a 1.65 m telescope at the Molėtai Astronomical Observatory of Vilnius University and the high-resolution Vilnius University Echelle Spectrograph. We uniformly determined the main atmospheric parameters, ages, orbital parameters, velocity components, and precise abundances of 24 chemical species (C(C2), N(CN), [O I], Na I, Mg I, Al I, Si I, Si II, Ca I, Ca II, Sc I, Sc II, Ti I, Ti II, V I, Cr I, Cr II, Mn I, Fe I, Fe II, Co I, Ni I, Cu I, and Zn I) for 277 slowly rotating single stars in the field. About 83% of the sample stars exhibit the Mg/Si ratios greater than 1.0 and may potentially harbor rocky planets in their systems.

Keywords: high resolution spectroscopy; catalogs; chemical abundances
Galaxy and Mass Assembly (GAMA): Stellar-to-dynamical Mass Relation. I. Constraining the Precision of Stellar Mass Estimates

In this empirical work, we aim to quantify the systematic uncertainties in stellar-mass (M ⋆) estimates made from spectral energy distribution (SED) fitting through stellar population synthesis (SPS) for galaxies in the local Universe by using the dynamical mass (M dyn) estimator as an SED-independent check on stellar mass. We first construct a statistical model of the high-dimensional space of galaxy properties; including size (R e ), velocity dispersion (σ e ), surface brightness (I e ), mass-to-light ratio (M ⋆/L), rest-frame color, Sérsic index (n), and dynamical mass (M dyn), and accounting for selection effects and covariant errors. We disentangle the correlations among galaxy properties and find that the variation in M ⋆/M dyn is driven by σ e , Sérsic index and color. We use these parameters to calibrate an SED-independent M ⋆ estimator, ${\hat{M}}_{\star }$ . We find the random scatter of the relation ${M}_{\star }-{\hat{M}}_{\star }$ to be 0.108 dex and 0.147 dex for quiescent and star-forming galaxies, respectively. Finally, we inspect the residuals as a function of SPS parameters (dust, age, metallicity, and star formation rate) and spectral indices (Hα, Hδ, and D n 4000). For quiescent galaxies, ~65% of the scatter can be explained by the uncertainty in SPS parameters, with dust and age being the largest sources of uncertainty. For star-forming galaxies, while age and metallicity are the leading factors, SPS parameters account for only ~13% of the scatter. These results leave us with remaining unmodelled scatters of 0.055 dex and 0.122 dex for quiescent and star-forming galaxies, respectively. This can be interpreted as a conservative limit on the precision in M ⋆ that can be achieved via simple SPS modeling.

Keywords: galaxy masses; galaxy properties; astronomy data modeling; astrostatistics strategies; galaxy stellar content