adsabs/SciX_UAT_keywords huggingface dataset:
Circumstellar Disk Accretion Across the Lagoon Nebula: The Influence of Environment and Stellar Mass

Pre-main-sequence disk accretion is pivotal for determining the final stellar properties and the early conditions for close-in planets. We aim to establish the impact of internal (stellar mass) and external (radiation field) parameters on the disk evolution in the Lagoon Nebula massive star-forming region. We employ simultaneous u, g, r, i, Hα time-series photometry, archival infrared data, and high-precision K2 light curves to derive the stellar, disk, and accretion properties for 1012 Lagoon Nebula members. We estimate that of all young stars in the Lagoon Nebula, 34%–37% have inner disks traceable down to ∼12 μm, while 38%–41% are actively accreting. We detect disks ∼1.5 times more frequently around G, K, and M stars than around higher-mass stars, which appear to deplete their inner disks on shorter timescales. We find tentative evidence for a faster disk evolution in the central regions of the Lagoon Nebula, where the bulk of the O/B population is located. Conversely, disks appear to last longer at the nebula outskirts, where the measured fraction of disk-bearing stars tends to exceed that of accreting and disk-free stars. The derived mass accretion rates show a nonuniform dependence on stellar mass between ∼0.2 and 5 M ⊙. In addition, the typical accretion rates appear to differ across the Lagoon Nebula extension, with values twice lower in the core region than at its periphery. Finally, we detect tentative radial density gradients in the surface accretion shocks, leading to lags in the appearance of light curve brightness features as a function of wavelength that can amount to ∼7%–30% of the rotation period.

Keywords: stellar accretion disks; young stellar objects; star forming regions; t tauri stars; herbig ae/be stars; variable stars; light curves; multi-color photometry
Kinematics of Parsec-scale Jets of Gamma-Ray Blazars at 43 GHz during 10 yr of the VLBA-BU-BLAZAR Program

We analyze the parsec-scale jet kinematics from 2007 June to 2018 December of a sample of γ-ray bright blazars monitored roughly monthly with the Very Long Baseline Array (VLBA) at 43 GHz under the VLBA-BU-BLAZAR program. We implement a novel piecewise linear fitting method to derive the kinematics of 521 distinct emission knots from a total of 3705 total intensity images in 22 quasars, 13 BL Lacertae objects, and 3 radio galaxies. Apparent speeds of these components range from 0.01c to 78c, and 18.6% of knots (other than the "core") are quasi-stationary. One-fifth of moving knots exhibit nonballistic motion, with acceleration along the jet within 5 pc of the core (projected) and deceleration farther out. These accelerations occur mainly at locations coincident with quasi-stationary features. We calculate the physical parameters of 273 knots with statistically significant motion, including their Doppler factors, Lorentz factors, and viewing angles. We determine the typical values of these parameters for each jet and the average for each subclass of active galactic nuclei. We investigate the variability of the position angle of each jet over the 10 yr of monitoring. The fluctuations in position of the quasi-stationary components in radio galaxies tend to be parallel to the jet, while no directional preference is seen in the components of quasars and BL Lacertae objects. We find a connection between γ-ray states of blazars and their parsec-scale jet properties, with blazars with brighter 43 GHz cores typically reaching higher γ-ray maxima during flares.

Keywords: active galaxies; relativistic jets; interferometry; blazars; flat-spectrum radio quasars; bl lacertae objects
Physical Characterization of Main-belt Comet (248370) 2005 QN173

We report results from new and archival observations of the newly discovered active asteroid (248370) 2005 QN173 (also now designated Comet 433P), which has been determined to be a likely main-belt comet based on a subsequent discovery that it is recurrently active near perihelion. From archival data analysis, we estimate $g^{\prime} $ -, $r^{\prime} $ -, $i^{\prime} $ -, and $z^{\prime} $ -band absolute magnitudes for the nucleus of Hg = 16.62 ± 0.13, Hr = 16.12 ± 0.10, Hi = 16.05 ± 0.11, and Hz = 15.93 ± 0.08, corresponding to nucleus colors of $g^{\prime} -r^{\prime} =0.50\pm 0.16$ , $r^{\prime} -i^{\prime} =0.07\pm 0.15$ , and $i^{\prime} -z^{\prime} =0.12\pm 0.14$ ; an equivalent V-band absolute magnitude of HV = 16.32 ± 0.08; and a nucleus radius of rn = 1.6 ± 0.2 km (using a V-band albedo of pV = 0.054 ± 0.012). Meanwhile, we find mean near-nucleus coma colors when 248370 is active of $g^{\prime} -r^{\prime} =0.47\pm 0.03$ , $r^{\prime} -i^{\prime} =0.10\pm 0.04$ , and $i^{\prime} -z^{\prime} =0.05\pm 0.05$ and similar mean dust tail colors, suggesting that no significant gas coma is present. We find approximate ratios between the scattering cross sections of near-nucleus dust (within 5000 km of the nucleus) and the nucleus of Ad/An = 0.7 ± 0.3 on 2016 July 22 and 1.8 < Ad/An < 2.9 in 2021 July and August. During the 2021 observation period, the coma declined in intrinsic brightness by ~0.35 mag (or ~25%) in 37 days, while the surface brightness of the dust tail remained effectively constant over the same period. Constraints derived from the sunward extent of the coma and width of the tail as measured perpendicular to the orbit plane suggest that the terminal velocities of ejected dust grains are extremely slow (~1 m s-1 for 1 μm particles), suggesting that the observed dust emission may be aided by rapid rotation of the nucleus lowering the effective escape velocity.

Keywords: main-belt comets; comets; comet nuclei; comet tails; main belt asteroids; asteroids; small solar system bodies
Detached Shell Carbon Stars: Tracing Thermal Pulses on the Asymptotic Giant Branch

We consider whether the subset of carbon-rich asymptotic giant branch (AGB) stars that exhibit detached, expanding circumstellar shells may reveal the past histories of these stars as having undergone helium shell flashes (thermal pulses) on the AGB. We exploit newly available Gaia parallaxes and photometry, along with archival infrared photometry, to obtain refined estimates of the luminosities of all (12) known detached shell carbon stars. We examine the relationship between these luminosities and the estimated dynamical ages (ejection times) of the detached shells associated with the 12 stars, which range from ~1000 to ~30,000 yr. When arranged according to detached shell dynamical age, the (implied) luminosity evolution of the known detached shell carbon stars closely follows the predicted "light curves" of individual thermal pulses obtained from models of AGB stars. The comparison between data and models suggests that detached shell carbon stars are descended from ~2.5 to 4.0 M⊙ progenitors. We conclude that detached shell carbon stars may serve as effective tracers of the luminosity evolution of AGB thermal pulses.

Keywords: carbon stars; stellar mass loss; late stellar evolution
Spectral Signatures of Population III and Envelope-stripped Stars in Galaxies at the Epoch of Reionization

While most simulations of the epoch of reionization have focused on single-stellar populations in star-forming dwarf galaxies, products of binary evolution are expected to significantly contribute to emissions of hydrogen-ionizing photons. Among these products are stripped stars (or helium stars), which have their envelopes stripped from interactions with binary companions, leaving an exposed helium core. Previous work has suggested these stripped stars can dominate the Lyman Continuum (LyC) photon output of high-redshift, low-luminosity galaxies post-starburst. Other sources of hard radiation in the early universe include zero-metallicity Population III stars, which may have similar spectral energy distribution (SED) properties to galaxies with radiation dominated by stripped-star emissions. Here, we use four metrics (the power-law exponent over wavelength intervals 240-500 Å, 600-900 Å, and 1200-2000 Å, and the ratio of total luminosity in FUV wavelengths to LyC wavelengths) to compare the SEDs of simulated galaxies with only single-stellar evolution, galaxies containing stripped stars, and galaxies containing Population III stars, with four different initial mass functions (IMFs). We find that stripped stars significantly alter SEDs in the LyC range of galaxies at the epoch of reionization. SEDs in galaxies with stripped stars have lower power-law indices in the LyC range and lower FUV to LyC luminosity ratios. These differences in SEDs are present at all considered luminosities ( ${M}_{\mathrm{UV}}\gt -15$ , AB system), and are most pronounced for lower-luminosity galaxies. Intrinsic SEDs as well as those with interstellar medium absorption of galaxies with stripped stars and Population III stars are found to be distinct for all tested Population III IMFs.

Keywords: binary stars; stellar evolution; early universe; population iii stars
Dark against Luminous Matter around Isolated Central Galaxies: A Comparative Study between Modern Surveys and IllustrisTNG

Based on independent shear measurements using the Dark Energy Camera Legacy Survey/DR8 imaging data, we measure the weak lensing signals around isolated central galaxies (ICGs) from Sloan Digital Sky Survey/DR7 at z ~ 0.1. The projected stellar mass density profiles of satellite galaxies are further deduced, using photometric sources from the Hyper Suprime-cam survey. The signals of ICGs + their extended stellar halos are taken from Wang et al. All measurements are compared with predictions by the IllustrisTNG300-1 simulation. We find, overall, a good agreement between observation and TNG300. In particular, a correction to the stellar mass of massive observed ICGs is applied based on the calibration of He et al., which brings a much better agreement with TNG300 predicted lensing signals at ${\mathrm{log}}_{10}{M}_{* }/{M}_{\odot }\gt 11.1$ . In real observation, red ICGs are hosted by more massive dark matter halos and have more satellites and more extended stellar halos than blue ICGs at fixed stellar mass. However, in TNG300 there are more satellites around blue ICGs at fixed stellar mass, and the outer stellar halos of red and blue ICGs are similar. The stellar halos of TNG galaxies are more extended compared with real observed galaxies, especially for blue ICGs with ${\mathrm{log}}_{10}{M}_{* }/{M}_{\odot }\gt 10.8$ . We find the same trend for TNG100 galaxies and for true halo central galaxies. The tensions between TNG and real galaxies indicate that satellite disruptions are stronger in TNG. In both TNG300 and observation, satellites approximately trace the underlying dark matter distribution beyond 0.1R 200, but the fraction of total stellar mass in TNG300 does not show the same radial distribution as real galaxies.

Keywords: galaxy stellar halos; hydrodynamical simulations; sky surveys; dark matter; galaxy formation; gravitational lensing shear
Decade-long Timing Study of the Black Widow Millisecond Pulsar J1544+4937

Results from 11 yr of radio timing for the eclipsing black widow millisecond pulsar (MSP) binary J1544+4937 is presented in this paper. We report a phase-connected timing model for this MSP, using observations with the Giant Metrewave Radio Telescope (GMRT) at multiple frequencies and with the Green Bank Telescope. This is the longest-duration timing study of any galactic-field MSP with the GMRT. While extending the timing baseline from the existing 1.5 yr to about a decade we report the first detection for a significant value of proper motion (μ T ~ 10.14(5) mas yr-1) for this pulsar. Temporal variations of dispersion measure (ΔDM ~ 10-3 pc cm-3) manifested by significant determination of first-, second-, and third-order dispersion measure (DM) derivatives are observed along the line of sight to the pulsar. We also noticed frequency-dependent DM variations of the order of 10-3 pc cm-3, which could arise due to spatial electron density variations in the interstellar medium. This study has revealed a secular variation of the orbital period for this MSP for the first time. We investigated possible causes and propose that variation in the gravitational quadrupole moment of the companion could be responsible for the observed temporal changes in the orbital period.

Keywords: binary pulsars; radio pulsars; millisecond pulsars; pulsar timing method
Determining Cosmological-model-independent H 0 with Gravitationally Lensed Supernova Refsdal

The reappearance of supernova Refsdal with detailed modeling of the lens cluster allows us to measure the time-delay distance, which serves as a powerful tool to determine the Hubble constant (H 0). We give a cosmological-model-independent method to estimate H 0 through Gaussian process regression, using time-delay measurements from this lensed supernova in combination with supernova data from the Pantheon+ sample. Using eight mass models for the lens cluster, we infer ${H}_{0}={64.2}_{-4.3}^{+4.4}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ , and using two cluster models most consistent with the observations, we infer ${H}_{0}={66.3}_{-3.6}^{+3.8}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ . Our estimates of the value of H 0 are in 1σ agreement with the results assuming a flat ΛCDM model and the uncertainties are comparable. Our constraint results on H 0 from the eight lens models and the two lens models indicate 2σ and 1.8σ tensions with that estimated by Supernova H0 for the Equation of State, respectively. However, our median values of H 0 from the two sets of lens models show good consistency with H 0 inferred from Planck cosmic microwave background observations assuming a ΛCDM model within 1σ. We also find that our results for H 0 indicate 2σ deviations and 1.7σ deviations from the constraint results of H 0 using six time-delay quasars by H0LiCOW with the same analysis method.

Keywords: hubble constant; gravitational lensing; supernovae
Effects of CO-dark Gas on Measurements of Molecular Cloud Stability and the Size-Linewidth Relationship

Stars form within molecular clouds, so characterizing the physical states of molecular clouds is key to understanding the process of star formation. Cloud structure and stability are frequently assessed using metrics including the virial parameter and Larson scaling relationships between cloud radius, velocity dispersion, and surface density. Departures from the typical Galactic relationships between these quantities have been observed in low-metallicity environments. The amount of H2 gas in cloud envelopes without corresponding CO emission is expected to be high under these conditions; therefore, this CO-dark gas could plausibly be responsible for the observed variations in cloud properties. We derive simple corrections that can be applied to empirical clump properties (mass, radius, velocity dispersion, surface density, and virial parameter) to account for CO-dark gas in clumps following power-law and Plummer mass density profiles. We find that CO-dark gas is not likely to be the cause of departures from Larson's relationships in low-metallicity regions, but that virial parameters may be systematically overestimated. We demonstrate that correcting for CO-dark gas is critical for accurately comparing the dynamical state and evolution of molecular clouds across diverse environments.

Keywords: molecular clouds; interstellar medium
Thermal Equilibrium Solutions of Black Hole Accretion Flows: Outflows versus Advection

Observations and numerical simulations have shown that outflows generally exist in the accretion process. We revisit the thermal equilibrium solutions of black hole accretion flows by including the role of outflows. Our study focuses on the comparison of the cooling rate of outflows with that of advection. Our results show that, except for the inner region, outflows can dominate over advection in a wide range of flows, which is in good agreement with previous numerical simulations. We argue that an advection-dominated inner region together with an outflow-dominated outer region should be a general radial distribution for both super-Eddington accretion flows and optically thin flows with low accretion rates.

Keywords: accretion; high energy astrophysics; black holes; hydrodynamics
Explosive Nucleosynthesis in Core-collapse Type II Supernovae: Insights from New C, N, Si, and Al-Mg Isotopic Compositions of Presolar Grains

We report C, N, Si, and Al-Mg isotope data for 39 presolar X silicon carbide (SiC) and four silicon nitride grains-a group of presolar grains that condensed in the remnants of core-collapse Type II supernovae (CCSNe)-isolated from the Murchison meteorite. Energy dispersive X-ray data were used to determine the Mg and Al contents of the X SiC grains for comparison with the Mg/Al ratios determined by secondary ion mass spectroscopy (SIMS). Previous SIMS studies have used O-rich standards in the absence of alternatives. In this study, the correlated isotopic and elemental data of the X SiC grains enabled accurate determination of the initial 26Al/27Al ratios for the grains. Our new grain data suggest that (i) the literature data for X grains are affected to varying degrees by asteroidal/terrestrial contamination, and (ii) the Al/Mg ratios in SiC are a factor of 2 (with ±6% 1σ uncertainties) lower than estimated based on the SIMS analyses that used O-rich standards. The lowered Al/Mg ratios result in proportionally higher inferred initial 26Al/27Al ratios for presolar SiC grains. In addition, the suppression of asteroidal/terrestrial contamination in this study leads to the observation of negative trends for 12C/13C-30Si/28Si and 26Al/27Al-30Si/28Si among our CCSN grains. We discuss these isotope trends in the light of explosive CCSN nucleosynthesis models, based on which we provide new insights into several nontraditional CCSN nucleosynthesis processes, including explosive H burning, the existence of a C/Si zone in the outer regions of CCSNe, and neutrino-nucleus reactions in deep CCSN regions.

Keywords: circumstellar matter; stellar astronomy; circumstellar dust; nucleosynthesis; type ii supernovae
The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). IV. Star Formation Signatures in G023.477

With a mass of ~1000 M ⊙ and a surface density of ~0.5 g cm-2, G023.477+0.114, also known as IRDC 18310-4, is an infrared dark cloud (IRDC) that has the potential to form high-mass stars and has been recognized as a promising prestellar clump candidate. To characterize the early stages of high-mass star formation, we have observed G023.477+0.114 as part of the Atacama Large Millimeter/submillimeter Array (ALMA) Survey of 70 μm Dark High-mass Clumps in Early Stages. We have conducted ~1.″2 resolution observations with ALMA at 1.3 mm in dust continuum and molecular line emission. We have identified 11 cores, whose masses range from 1.1 to 19.0 M ⊙. Ignoring magnetic fields, the virial parameters of the cores are below unity, implying that the cores are gravitationally bound. However, when magnetic fields are included, the prestellar cores are close to virial equilibrium, while the protostellar cores remain sub-virialized. Star formation activity has already started in this clump. Four collimated outflows are detected in CO and SiO. H2CO and CH3OH emission coincide with the high-velocity components seen in the CO and SiO emission. The outflows are randomly oriented for the natal filament and the magnetic field. The position-velocity diagrams suggest that episodic mass ejection has already begun even in this very early phase of protostellar formation. The masses of the identified cores are comparable to the expected maximum stellar mass that this IRDC could form (8-19 M ⊙). We explore two possibilities on how IRDC G023.477+0.114 could eventually form high-mass stars in the context of theoretical scenarios.

Keywords: infrared dark clouds; star formation; star forming regions; massive stars; interstellar line emission
JWST-TST High Contrast: Asymmetries, Dust Populations, and Hints of a Collision in the β Pictoris Disk with NIRCam and MIRI

We present the first JWST Mid-Infrared Instrument (MIRI) and Near Infrared Camera (NIRCam) observations of the prominent debris disk around β Pictoris. Coronagraphic observations in eight filters spanning from 1.8 to 23 μm provide an unprecedentedly clear view of the disk at these wavelengths. The objectives of the observing program were to investigate the dust composition and distribution and to investigate the presence of planets in the system. In this paper, we focus on the disk components, providing surface brightness measurements for all images and a detailed investigation of the asymmetries observed. A companion paper by Kammerer et al. will focus on the planets in this system using the same data. We report for the first time the presence of an extended secondary disk in thermal emission, with a curved extension bent away from the plane of the disk. This feature, which we refer to as the "cat's tail," seems to be connected with the previously reported CO clump, mid-infrared asymmetry detected on the southwest side of the disk, and the warp observed in scattered light. We present a model of this secondary disk sporadically producing dust that broadly reproduces the morphology, flux, and color of the cat's tail, as well as other features observed in the disk, and which suggests the secondary disk is composed largely of porous, organic refractory dust grains.

Keywords: debris disks; circumstellar disks; planetesimals
ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): Detection of Extremely High-density Compact Structure of Prestellar Cores and Multiple Substructures Within

Prestellar cores are self-gravitating dense and cold structures within molecular clouds where future stars are born. They are expected, at the stage of transitioning to the protostellar phase, to harbor centrally concentrated dense (sub)structures that will seed the formation of a new star or the binary/multiple stellar systems. Characterizing this critical stage of evolution is key to our understanding of star formation. In this work, we report the detection of high-density (sub)structures on the thousand-astronomical-unit (au) scale in a sample of dense prestellar cores. Through our recent ALMA observations toward the Orion Planck Galactic Cold Clumps, we have found five extremely dense prestellar cores, which have centrally concentrated regions of ∼2000 au in size, and several 107 cm-3 in average density. Masses of these centrally dense regions are in the range of 0.30 to 6.89 M⊙. For the first time, our higher resolution observations (0.8″ ∼ 320 au) further reveal that one of the cores shows clear signatures of fragmentation; such individual substructures/fragments have sizes of 800-1700 au, masses of 0.08 to 0.84 M⊙, densities of 2 - 8 × 107 cm-3, and separations of ∼1200 au. The substructures are massive enough (≳0.1 M⊙) to form young stellar objects and are likely examples of the earliest stage of stellar embryos that can lead to widely (∼1200 au) separated multiple systems.

Keywords: molecular clouds; collapsing clouds; star formation; protostars