adsabs/SciX_UAT_keywords huggingface dataset:
The Lifetimes of Star Clusters Born with a Top-heavy IMF

Several observational and theoretical indications suggest that the initial mass function (IMF) becomes increasingly top-heavy (i.e., overabundant in high-mass stars with mass $m\gt 1{M}_{\odot }$ ) with decreasing metallicity and increasing gas density of the forming object. This affects the evolution of globular clusters (GCs) owing to the different mass-loss rates and the number of black holes formed. Previous numerical modeling of GCs usually assumed an invariant canonical IMF. Using the state-of-the-art NBODY6 code, we perform a comprehensive series of direct N-body simulations to study the evolution of star clusters, starting with a top-heavy IMF and undergoing early gas expulsion. Utilizing the embedded cluster mass-radius relation of Marks & Kroupa for initializing the models, and by varying the degree of top-heaviness, we calculate the minimum cluster mass needed for the cluster to survive longer than 12 Gyr. We document how the evolution of different characteristics of star clusters such as the total mass, the final size, the density, the mass-to-light ratio, the population of stellar remnants, and the survival of GCs is influenced by the degree of top-heaviness. We find that the lifetimes of clusters with different IMFs moving on the same orbit are proportional to the relaxation time to a power of x that is in the range of 0.8-1. The observed correlation between concentration and the mass function slope in Galactic GCs can be accounted for excellently in models starting with a top-heavy IMF and undergoing an early phase of rapid gas expulsion.

Keywords: globular star clusters; stellar mass functions; dynamical evolution; n-body simulations
The CO Emission in the Taffy Galaxies (UGC 12914/15) at 60 pc Resolution. I. The Battle for Star Formation in the Turbulent Taffy Bridge

We present Atacama Large Millimeter/submillimeter Array observations at a spatial resolution of 0.″2 (60 pc) of CO emission from the Taffy galaxies (UGC 12914/5). The observations are compared with narrowband Paα, mid-IR, radio continuum and X-ray imaging, plus optical spectroscopy. The galaxies have undergone a recent head-on collision, creating a massive gaseous bridge that is known to be highly turbulent. The bridge contains a complex web of narrow molecular filaments and clumps. The majority of the filaments are devoid of star formation, and fall significantly below the Kennicutt-Schmidt relationship for normal galaxies, especially for the numerous regions undetected in Paα emission. Within the loosely connected filaments and clumps of gas we find regions of high velocity dispersion that appear gravitationally unbound for a wide range of likely values of X CO. Like the "Firecracker" region in the Antennae system, they would require extremely high external dynamical or thermal pressure to stop them dissipating rapidly on short crossing timescales of 2-5 Myr. We suggest that the clouds may be transient structures within a highly turbulent multiphase medium that is strongly suppressing star formation. Despite the overall turbulence in the system, stars seem to have formed in compact hotspots within a kiloparsec-sized extragalactic H II region, where the molecular gas has a lower velocity dispersion than elsewhere, and shows evidence for a collision with an ionized gas cloud. Like the shocked gas in the Stephan's Quintet group, the conditions in the Taffy bridge shows how difficult it is to form stars within a turbulent, multiphase, gas.

Keywords: interacting galaxies
A Magnetogram-matching Method for Energizing Magnetic Flux Ropes Toward Eruption

We propose a new "helicity-pumping" method for energizing coronal equilibria that contain a magnetic flux rope (MFR) toward an eruption. We achieve this in a sequence of magnetohydrodynamics relaxations of small line-tied pulses of magnetic helicity, each of which is simulated by a suitable rescaling of the current-carrying part of the field. The whole procedure is "magnetogram-matching" because it involves no changes to the normal component of the field at the photospheric boundary. The method is illustrated by applying it to an observed force-free configuration whose MFR is modeled with our regularized Biot-Savart law method. We find that, in spite of the bipolar character of the external field, the MFR eruption is sustained by two reconnection processes. The first, which we refer to as breakthrough reconnection, is analogous to breakout reconnection in quadrupolar configurations. It occurs at a quasi-separator inside a current layer that wraps around the erupting MFR and is caused by the photospheric line-tying effect. The second process is the classical flare reconnection, which develops at the second quasi-separator inside a vertical current layer that is formed below the erupting MFR. Both reconnection processes work in tandem with the magnetic forces of the unstable MFR to propel it through the overlying ambient field, and their interplay may also be relevant for the thermal processes occurring in the plasma of solar flares. The considered example suggests that our method will be beneficial for both the modeling of observed eruptive events and theoretical studies of eruptions in idealized magnetic configurations.

Keywords: solar coronal mass ejections; solar filaments; solar prominences; solar flares; solar magnetic fields; solar activity; solar physics
Corrigendum: "Gender Systematics in the NRAO Proposal Review System"(2021, PASP, 133, 115002)

In Hunt et al., we used the Anderson-Darling (AD) two-sample test to evaluate the probability that the observed linear rank distributions for female and male principal investigators are from the same parent sample. We determined the nominal AD p-value, ρ AD(x, y), where x and y are the female and male linear ranks, and estimated the uncertainty by calculating the mean and 68% confidence intervals from the AD p-value bootstrapped distributions, ${\rho }_{\mathrm{AD}}^{\mathrm{boot}}$ . Since the p-value is a measure of probability, and the distribution of p-values is uniform, this method is not appropriate. Here we calculate ${\rho }_{\mathrm{AD}}^{\mathrm{boot}}$ as the proportion of bootstrapped AD test statistics that are greater than or equal to the nominal AD test statistic. We find that the nominal and bootstrapped AD p-values are similar and therefore we do not recommend any changes to the conclusions in Hunt et al.

Keywords: observatories
The Emergence of a Brightest Cluster Galaxy in a Protocluster Core at z = 2.24

We report the detection of a pair of massive quiescent galaxies likely in the process of merging at the center of the spectroscopically confirmed, extremely massive protocluster BOSS1244 at z = 2.24 ± 0.02. These galaxies, BOSS1244-QG1 and BOSS1244-QG2, were detected with Hubble Space Telescope grism slitless spectroscopic observations. These two quiescent galaxies are among the brightest member galaxies, with z = 2.223–2.255 in BOSS1244, and reside at redshifts z = 2.244 and z = 2.242, with a half-light radius of 6.76 ± 0.50 kpc and 2.72 ± 0.16 kpc, respectively. BOSS1244-QG1 and BOSS1244-QG2 are separated by a projected distance of about 70 physical kpc, implying that the two galaxies likely merge to form a massive brightest cluster galaxy (BCG) with size and mass similar to the most massive BCGs in the local Universe. We thus infer that BCG formation through dry major mergers may happen earlier than the full assembly of a cluster core, which broadens our previous understanding of the coevolution of mature galaxy clusters and BCGs in the nearby Universe. Moreover, we find a strong density–star formation relation over a scale of ∼18 comoving Mpc in BOSS1244, i.e., star formation activity decreases as density increases, implying that the quenching of star formation in BCGs and their progenitors is likely governed by environment-related processes before the virialization of the cluster core.

Keywords: protoclusters; brightest cluster galaxies; galaxy formation; galaxy environments; high-redshift galaxies; galaxy evolution
Infrared Properties of Asymptotic Giant Branch Stars in Our Galaxy and the Magellanic Clouds

We investigate the infrared properties of asymptotic giant branch (AGB) stars in our Galaxy and the Magellanic Clouds using various infrared observational data and theoretical models. We use catalogs for the sample of 4996 AGB stars in our Galaxy and about 39,000 AGB stars in the Magellanic Clouds from the available literature. For each object in the sample, we cross-identify the 2MASS, Wide-field Infrared Survey Explorer, and Spitzer counterparts. To compare the physical properties of O- and C-rich AGB stars in our Galaxy and the Magellanic Clouds, we present IR two-color diagrams (2CDs) using various photometric data. We perform radiative transfer model calculations for AGB stars using various possible parameters of central stars and dust shells. Using the dust opacity functions of amorphous silicate and carbon, the theoretical dust shell models can roughly reproduce the observations of AGB stars on various IR 2CDs. Compared with our Galaxy, we find that the Magellanic Clouds are deficient in AGB stars with thick dust shells. Compared with the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC) is more deficient in AGB stars with thick dust shells. This could be because the Magellanic Clouds are more metal-poor than our Galaxy and the LMC is more metal-rich than the SMC. We also present the IR properties of known pulsating variables. Investigating the magnitude distributions at mid-IR (MIR) bands for AGB stars in the Magellanic Clouds, we find that the SMC is more deficient in bright AGB stars at MIR bands compared with the LMC.

Keywords: asymptotic giant branch stars; circumstellar dust; infrared astronomy; radiative transfer
Impacts of Viscous Dissipation on Collisional Growth and Fragmentation of Dust Aggregates

Understanding the collisional behavior of dust aggregates consisting of submicron-sized grains is essential to unveiling how planetesimals formed in protoplanetary disks. It is known that the collisional behavior of individual dust particles strongly depends on the strength of viscous dissipation force; however, impacts of viscous dissipation on the collisional behavior of dust aggregates have not been studied in detail, especially for the cases of oblique collisions. Here we investigated the impacts of viscous dissipation on the collisional behavior of dust aggregates. We performed numerical simulations of collisions between two equal-mass dust aggregates with various collision velocities and impact parameters. We also changed the strength of viscous dissipation force systematically. We found that the threshold collision velocity for the fragmentation of dust aggregates barely depends on the strength of viscous dissipation force when we consider oblique collisions. In contrast, the size distribution of fragments changes significantly when the viscous dissipation force is considered. We obtained the empirical fitting formulae for the size distribution of fragments for the case of strong dissipation, which would be useful to study the evolution of size and spatial distributions of dust aggregates in protoplanetary disks.

Keywords: protoplanetary disks; circumstellar disks; planet formation; planetesimals
Extending a Grid of Hydrodynamic Planetary Upper Atmosphere Models

In this research note, we outline the extension of the grid of upper atmosphere models first presented in Kubyshkina et al. The original grid is based on a 1D hydrodynamic model and consists of about 7000 models covering planets of a size ranging from that of Earth to twice that of Neptune at orbits corresponding to equilibrium temperatures between 300 and 2000 K around solar-like (0.4 to 1.3 solar mass) stars. The extended and revised grid of models consists of 10,235 points and covers a planetary mass range of up to 109 Earth masses, which allows one to outline the transition between low- and high-gravity hot planets in in short period orbits. We prepared the interpolation tool allowing one to use the grid to define the mass-loss of a planet that falls into the parameter range of the grid. We provide a comparison of our results to common analytical models.

Keywords: hydrodynamics; hydrodynamical simulations; exoplanet atmospheres; exoplanet atmospheric variability; upper atmosphere
Orbital Clustering Identifies the Origins of Galactic Stellar Streams

The origins of most stellar streams in the Milky Way are unknown. With improved proper motions provided by Gaia EDR3, we show that the orbits of 23 Galactic stellar streams are highly clustered in orbital phase space. Based on their energies and angular momenta, most streams in our sample can plausibly be associated with a specific (disrupted) dwarf galaxy host that brought them into the Milky Way. For eight streams we also identify likely globular cluster progenitors (four of these associations are reported here for the first time). Some of these stream progenitors are surprisingly far apart, displaced from their tidal debris by a few to tens of degrees. We identify stellar streams that appear spatially distinct, but whose similar orbits indicate they likely originate from the same progenitor. If confirmed as physical discontinuities, they will provide strong constraints on the mass loss from the progenitor. The nearly universal ex situ origin of existing stellar streams makes them valuable tracers of galaxy mergers and dynamical friction within the Galactic halo. Their phase-space clustering can be leveraged to construct a precise global map of dark matter in the Milky Way, while their internal structure may hold clues to the small-scale structure of dark matter in their original host galaxies.

Keywords: milky way stellar halo; tidal tails; galaxy accretion; globular star clusters
Formation of Complex Organic Molecules on Interstellar CO Ices? Insights from Computational Chemistry Simulations

The carbon (3P) atom is a reactive species that, according to laboratory experiments and theoretical calculations, condensates with interstellar ice components. This fact is of uttermost importance for the chemistry in the interstellar medium (ISM) because the condensation reaction is barrierless, and the subsequent species formed are still reactive given their open-shell character. Carbon condensation on CO-rich ices forms the C=C=O (3Σ-) species, which can be easily hydrogenated twice to form ketene (H2CCO). Ketene is very reactive in terrestrial conditions, usually found as an intermediate that is difficult to isolate in chemical synthesis laboratories. These characteristics suggest that ketene can be a good candidate to form interstellar complex organic molecules via a two-step process, i.e., its activation followed by a radical-radical coupling. In this work, reactions between ketene and atomic H and the OH and NH2 radicals on a CO-rich ice model have been explored by means of quantum chemical calculations complemented by kinetic calculations to evaluate if they are favorable in the ISM. Results indicate that the addition of H to ketene (helped by tunneling) to form the acetyl radical (CH3CO) is the most preferred path as the reactions with OH and NH2 possess activation energies (≥9 kJ mol-1) hard to surmount in the ISM conditions unless external processes provide energy to the system. Thus, acetaldehyde (CH3CHO) and, probably, ethanol (CH3CH2OH) formation via further hydrogenations, are the possible unique operating synthetic routes. Moreover, from the computed, relatively large binding energies of OH and NH2 on CO ice, slow diffusion is expected, hampering possible radical-radical couplings with CH3CO. The astrophysical implications of these findings are discussed considering the incoming James Webb Space Telescope observations.

Keywords: astrochemistry; interstellar medium; interstellar molecules; interstellar dust; surface ices; complex organic molecules; reaction rates; computational methods
Investigating Protostellar Accretion-driven Outflows across the Mass Spectrum: JWST NIRSpec Integral Field Unit 3–5 μm Spectral Mapping of Five Young Protostars

Investigating Protostellar Accretion is a Cycle 1 JWST program using the NIRSpec+MIRI integral field units to obtain 2.9–28 μm spectral cubes of five young protostars with luminosities of 0.2–10,000 L ⊙ in their primary accretion phase. This paper introduces the NIRSpec 2.9–5.3 μm data of the inner 840–9000 au with spatial resolutions from 28 to 300 au. The spectra show rising continuum emission; deep ice absorption; emission from H2, H I, and [Fe II]; and the CO fundamental series in emission and absorption. Maps of the continuum emission show scattered light cavities for all five protostars. In the cavities, collimated jets are detected in [Fe II] for the four <320 L ⊙ protostars, two of which are additionally traced in Brα. Knots of [Fe II] emission are detected toward the most luminous protostar, and knots of [Fe II] emission with dynamical times of <30 yr are found in the jets of the others. While only one jet is traced in H2, knots of H2 and CO are detected in the jets of four protostars. H2 is seen extending through the cavities, showing that they are filled by warm molecular gas. Bright H2 emission is seen along the walls of a single cavity, while in three cavities narrow shells of H2 emission are found, one of which has an [Fe II] knot at its apex. These data show cavities containing collimated jets traced in atomic/ionic gas surrounded by warm molecular gas in a wide-angle wind and/or gas accelerated by bow shocks in the jets.

Keywords: star formation; protostars; stellar jets; stellar winds; stellar accretion disks
Magnetic Braking of Accreting T Tauri Stars II: Torque Formulation Spanning Spin-up and Spin-down Regimes

The magnetic interaction between a classical T Tauri star and its surrounding accretion disk is thought to influence its rotational evolution. We use 2.5D magnetohydrodynamic, axisymmetric simulations of star-disk interaction, computed via the PLUTO code, to calculate the net torque acting on these stars. We divide the net torque into three contributions: accretion (spin-up), stellar winds (spin-down), and magnetospheric ejections (MEs) (spin-up or down). In Paper I, we explored interaction regimes in which the stellar magnetosphere truncates the inner disk at a location spinning faster than the star, resulting in a strong net spin-up contribution from accretion and MEs ("steady accretion" regime). In this paper, we investigate interaction regimes in which the truncation radius gets closer to and even exceeds corotation, where it is possible for the disk material to gain angular momentum and be periodically ejected by the centrifugal barrier ("propeller" regime). This reduces the accretion torque, can change the sign of the ME torque, and can result in a net stellar spin-down configuration. These results suggest it is possible to have a net spin-down stellar torque even for truncation radii within the corotation radius (R t ≳ 0.7R co). We fit semi-analytic functions for the truncation radius, and the torque associated with star-disk interaction (i.e., the sum of accretion and ME torques) and stellar wind, allowing for the prediction of the net stellar torque for a parameter regime covering both net spin-up and spin-down configurations, as well as the possibility of investigating rotational evolution via 1D stellar evolution codes.

Keywords: stellar winds; stellar evolution; stellar magnetic fields; stellar rotation; magnetohydrodynamical simulations; pre-main sequence stars; stellar accretion; classical t tauri stars; stellar accretion disks
ELT Imaging of MWC 297 from the 23 m LBTI: Complex Disk Structure and a Companion Candidate

Herbig Ae/Be stars represent the early outcomes of star formation and the initial stages of planet formation at intermediate stellar masses. Understanding both of these processes requires detailed characterization of their disk structures and companion frequencies. We present new 3.7 μm imaging of the Herbig Be star MWC 297 from nonredundant masking observations on the phase-controlled, 23 m Large Binocular Telescope Interferometer. The images reveal complex disk structure on the scales of several au, as well as a companion candidate. We discuss physical interpretations for these features and demonstrate that the imaging results are independent of choices such as priors, regularization hyperparameters, and error-bar estimates. With an angular resolution of ∼17 mas, these data provide the first robust Extremely Large Telescope-resolution view of a distant young star.

Keywords: herbig ae/be stars; circumstellar matter; interferometry; direct imaging
The Rapid Far-ultraviolet Variability of ET And and Its Rotational Period

Evidence is presented that the far-ultraviolet flux of ET And (A0Vp SiSr) recorded by the International Ultraviolet Explorer was variable over a timescale of about one hour on 1979 August 7. In contrast, the spectra taken over 9 hr on 1979 August 3 do not show any flux variability. This behavior is discussed using the light curve of ET And recently acquired with TESS. We also derive a refined rotational period, Prot = 1.618845 ± 0.000006 days, from the detrended TESS light curve.

Keywords: chemically peculiar stars
UOCS-IX. AstroSat/UVIT Study of the Open Cluster NGC 2818: Blue Stragglers, Yellow Stragglers, Planetary Nebula, and their Membership

We present the first far-UV (FUV) imaging results of the intermediate-age Galactic open cluster NGC 2818 that has a planetary nebula (PN) within the field using images taken from the Ultra Violet Imaging Telescope (UVIT) aboard AstroSat. We identify cluster members by combining UVIT-detected sources with Gaia EDR3 data. We detect four bright and hot blue straggler stars (BSSs) and two yellow straggler stars (YSSs) based on their location in optical and FUV-optical color-magnitude diagrams. Based on the parameters estimated using spectral energy distributions, we infer that BSSs are either collisional products or might have undetectable white dwarf (WD) companions. Our photometric analysis of YSSs confirms their binarity, consistent with the spectroscopic results. We find YSSs to be formed through a mass-transfer scenario and the hot components are likely to be A-type subdwarfs. A comparison of the radial velocity, Gaia EDR3 proper motion of the PN with the cluster, and reddening toward the PN and the cluster does not rule out the membership of the PN. Comparing the central star's position with theoretical post‑AGB (pAGB) models suggest that it has already entered the WD cooling phase, and its mass is deduced to be ~0.66 M ⊙. The corresponding progenitor mass turns out to be ~2.1 M ⊙, comparable to the turn-off mass of the cluster, implying that the progenitor could have formed in the cluster. We suggest that the NGC 2818 might be one of the few known clusters to host a PN, providing a unique opportunity to test stellar evolution models.

Keywords: milky way galaxy; open star clusters; blue straggler stars; yellow straggler stars; ultraviolet photometry; ultraviolet observatories; hertzsprung russell diagram; planetary nebulae
No Small-scale Radio Jets Here: Multiepoch Observations of Radio Continuum Structures in NGC 1068 with the VLBA

We present recent Very Long Baseline Array (VLBA) 5 GHz radio observations of the nearby, luminous Seyfert 2 galaxy NGC 1068 for comparison to similar VLBA observations made on 1997 April 26. By cross-correlating the positions of emitting regions across both epochs, we find that spatially resolved extranuclear radio knots in this system have subrelativistic transverse speeds (v ≲0.1c). We discuss sources of the observed knots and how the radio emission relates to additional phases of gas in the central ~150 pc of this system. We suggest that the most likely explanation for the observed emission is synchrotron radiation formed by shocked host media via interactions between active galactic nucleus winds and the host environment.

Keywords: active galactic nuclei; radio astronomy; agn host galaxies