adsabs/SciX_UAT_keywords huggingface dataset:
A Comparative Study between M30 and M92: M92 is a Merger Remnant with a Large Helium Enhancement

We perform a comparative study of the ex situ second-parameter pair globular clusters (GCs) M30 and M92, having similar metallicities but different horizontal branch morphologies. We obtain similar mean primordial carbon abundances for both clusters. However, M92 shows a large dispersion in carbon due to a more extended C–N anticorrelation, while M30 exhibits a higher primordial nitrogen abundance, suggesting that they have different chemical enrichment histories. Our new results confirm our previous result that M92 is a metal-complex GC showing a bimodal metallicity distribution. We also find that the metal-rich group of stars in M92 shows a helium enhancement as large as ΔY ∼ 0.05 from the red giant branch bump V magnitudes, which can also be supported by (i) a lack of bright red giant branch stars, (ii) synthetic evolutionary horizontal branch population models and (iii) the more extended spatial distribution due to different degree of the diffusion process from their lower masses. We reinterpret the [Eu/Fe] measurements by others, finding that the two metallicity groups of stars in M92 have significantly different [Eu/Fe] abundances with small scatters. This strongly suggests that they formed independently out of well-mixed interstellar media in different environments. We suggest that M92 is a more complex system than a normal GC, most likely a merger remnant of two GCs or an even more complex system. In the Appendix, we address the problems with the recently developed color–temperature relations and the usage of broadband photometry in the populational taggings.

Keywords: stellar populations; population ii stars; hertzsprung russell diagram; globular star clusters; chemical abundances; stellar evolution; red giant branch; red giant bump; horizontal branch
Probing Cosmology with Baryon Acoustic Oscillations Using Gravitational Waves

The third-generation (3G) gravitational wave (GW) detectors such as the Einstein Telescope or Cosmic Explorer are expected to play an important role in cosmology. With the help of 3G detectors, we will be able to probe large-scale structure features such as baryon acoustic oscillations (BAO), galaxy bias, etc. We explore the possibility to do precision cosmology, with the 3G GW detectors by measuring the angular BAO scale using localization volumes of compact binary merger events. Through simulations, we show that with a 3G detector network, by probing the angular BAO scale using purely GW observations, we can constrain the Hubble constant for the standard model of cosmology (ΛCDM) with 90% credible regions as ${H}_{0}={59.4}_{-17.7}^{+33.9}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ . When combined with BAO measurements from galaxy surveys, we show that it can be used to constrain various models of cosmology such as parameterized models for dark energy equations of state. We also show how cosmological constraints using BAO measurements from GW observations in the 3G era will complement the same from spectroscopic surveys.

Keywords: cosmology; gravitational waves; baryon acoustic oscillations; gravitational wave detectors
Low-energy Explosions in a Gravitational Field: Implications for Sub-energetic Supernovae and Fast X-Ray Transients

Observations and theory suggest that core-collapse supernovae can span a range of explosion energies, and when sub-energetic the shockwave initiating the explosion can decelerate to speeds comparable to the escape speed of the progenitor. In these cases, gravity will complicate the explosion hydrodynamics and conceivably cause the shock to stall at large radii within the progenitor star. To understand these unique properties of weak explosions, we develop a perturbative approach for modeling the propagation of an initially strong shock into a time-steady, infalling medium in the gravitational field of a compact object. This method writes the shock position and the post-shock velocity, density, and pressure as series solutions in the (time-dependent) ratio of the freefall speed to the shock speed, and predicts that the shock stalls within the progenitor if the explosion energy is below a critical value. We show that our model agrees very well with hydrodynamic simulations, and accurately predicts (for example) the time-dependent shock position and velocity and the radius at which the shock stalls. Our results have implications for black hole formation and the newly detected class of fast X-ray transients (FXTs). In particular, we propose that a "phantom shock breakout"—where the outer edge of the star falls through a stalled shock—can yield a burst of X-rays without a subsequent optical/UV signature, similar to FXTs. This model predicts the rise time of the X-ray burst, t d, and the mean photon energy, kT, are anticorrelated, approximately as $T\propto {t}_{{\rm{d}}}^{-5/8}$ .

Keywords: analytical mathematics; core-collapse supernovae; hydrodynamics; shocks; x-ray transient sources
The Fermi-LAT Lightcurve Repository

The Fermi Large Area Telescope (LAT) lightcurve repository (LCR) is a publicly available, continually updated library of gamma-ray lightcurves of variable Fermi-LAT sources generated over multiple timescales. The Fermi-LAT LCR aims to provide publication-quality lightcurves binned on timescales of 3, 7, and 30 days for 1525 sources deemed variable in the source catalog of the first 10 yr of Fermi-LAT observations. The repository consists of lightcurves generated through full likelihood analyses that model the sources and the surrounding region, providing fluxes and photon indices for each time bin. The LCR is intended as a resource for the time-domain and multimessenger communities by allowing users to search LAT data quickly to identify correlated variability and flaring emission episodes from gamma-ray sources. We describe the sample selection and analysis employed by the LCR and provide an overview of the associated data access portal. *For any questions about this work, contact in order: M. Negro, D. Kocevski, J. Valverde, A. Brill, S. Garrappa.

Keywords: gamma-ray astronomy; active galactic nuclei; light curves
New SB1s with Spectroscopic Orbits from LAMOST-LRS

The LAMOST Low-Resolution Spectroscopic (LAMOST-LRS) Survey provides radial velocities of 10 million stars. These observations can be used to identify new single-lined spectroscopic binaries (SB1s) with their preliminary spectroscopic orbits. First, we perform a statistical χ 2 test on a subsample of LAMOST-LRS stars with velocity observations sufficient for the present work to obtain a set of 6852 radial velocity variables. Subsequently, we discard 399 astrophysical variables through crossmatching with variable catalogs, resulting in 1297 SB1 candidates. Finally, in order to reliably identify SB1s among these SB1 candidates, we employ a combination of The joker, rvfit, and Levenberg-Marquardt algorithms to give the best-fit solutions. An SB1 is identified if its orbital solution satisfies the criteria of the goodness-of-fit statistic (F2) < 3.1, the signal significance > 10, and the maximum gap in phase (phase_gap_max) < 0.3. Our final catalog of SB1s contains 255 systems, 168 of which are newly discovered ones. Cross validation results indicate that the determined orbital periods are consistent with periods of external catalogs within 1σ uncertainties. The period-eccentricity diagram illustrates that a majority of short-period binaries have small eccentricities. Furthermore, in comparison to the general sample, the SB1 catalog exhibits a relatively higher ratio of dwarfs than giants and a slightly lower metallicity.

Keywords: spectroscopic binary stars; catalogs; radial velocity; orbit determination
A Near-surface Temperature Model of Arrokoth

A near-surface thermal model for Arrokoth is developed based on the recently released 105 facet model of the body. This thermal solution takes into account Arrokoth's surface reradiation back onto itself. The solution method exploits Arrokoth's periodic orbital character to develop a thermal response using a time-asymptotic solution method, which involves a Fourier transform solution of the heat equation, an approach recently used by others. We display detailed thermal solutions assuming that Arrokoth's near-surface material's thermal inertia ${ \mathcal I }\,=\,$ 2.5 W/m-2 K-1 s1/2. We predict that at New Horizons' encounter with Arrokoth, its encounter hemisphere surface temperatures were ~57-59 K in its polar regions, 30-40 K in its equatorial zones, and 11-13 K for its winter hemisphere. Arrokoth's orbitally averaged temperatures are around 30-35 K in its polar regions and closer to 40 K near its equatorial zones. Thermal reradiation from the surrounding surface amounts to less than 5% of the total energy budget, while the total energy ensconced into and exhumed out of Arrokoth's interior via thermal conduction over one orbit is about 0.5% of the total energy budget. As a generalized application of this thermal modeling together with other Kuiper Belt object origins considerations, we favor the interpretation that New Horizons' REX instrument's 29 ± 5 K brightness temperature measurement is consistent with Arrokoth's near-surface material being made of sub-to-few-millimeter-size tholin-coated amorphous H2O ice grains with 1 W/m-2 K-1 s1/2 $\lt \,{ \mathcal I }\,\lt $ 10-20 W/m-2 K-1 s1/2 and which are characterized by an X-band emissivity in the range 0.9 and 1.

Keywords: classical kuiper belt objects; small solar system bodies; natural satellite surfaces; computational methods
The JCMT BISTRO Survey: The Distribution of Magnetic Field Strengths toward the OMC-1 Region

Measurement of magnetic field strengths in a molecular cloud is essential for determining the criticality of magnetic support against gravitational collapse. In this paper, as part of the JCMT BISTRO survey, we suggest a new application of the Davis-Chandrasekhar-Fermi (DCF) method to estimate the distribution of magnetic field strengths in the OMC-1 region. We use observations of dust polarization emission at 450 and 850 μm, and C18O (3-2) spectral line data obtained with the JCMT. We estimate the volume density, the velocity dispersion, and the polarization angle dispersion in a box, 40″ × 40″ (5×5 pixels), which moves over the OMC-1 region. By substituting three quantities in each box with the DCF method, we get magnetic field strengths over the OMC-1 region. We note that there are very large uncertainties in the inferred field strengths, as discussed in detail in this paper. The field strengths vary from 0.8 to 26.4 mG, and their mean value is about 6 mG. Additionally, we obtain maps of the mass-to-flux ratio in units of a critical value and the Alfvén Mach number. The central parts of the BN-KL and South (S) clumps in the OMC-1 region are magnetically supercritical, so the magnetic field cannot support the clumps against gravitational collapse. However, the outer parts of the region are magnetically subcritical. The mean Alfvén Mach number is about 0.4 over the region, which implies that the magnetic pressure exceeds the turbulent pressure in the OMC-1 region.

Keywords: dense interstellar clouds; polarimetry; interstellar magnetic fields
The Earliest Stage of Galactic Star Formation

Using a recently developed technique to estimate gas temperatures (T SF) in star-forming regions from large photometric surveys, we propose a diagram, analogous to the Hertzsprung-Russell diagram for individual stars, to probe the evolution of individual galaxies. On this T SF-sSFR (specific star formation rate) diagram, a small fraction of star-forming galaxies appear to be dominated by different feedback mechanisms than typical star-forming galaxies. These galaxies generically have younger stellar populations and lower stellar masses and increase in relative abundance toward higher redshifts, so we argue that these objects are in an earlier stage of galactic star formation. Further, Hubble observations find that these "core-forming" galaxies also exhibit distinct morphology and that tracks on the T SF-sSFR diagram are also a morphological sequence. Thus, unlike starburst phases which can be triggered environmentally, these earliest core-forming galaxies appear to be a stage that typical galaxies go through early in their star formation history. We therefore argue that most galaxies first go through a core formation stage, then subsequently disk formation, and finally become quiescent.

Keywords: galaxy evolution; star formation; star forming regions; initial mass function; stellar feedback
The High-redshift Clusters Occupied by Bent Radio AGN (COBRA) Survey: Radio Source Properties

The shape of bent, double-lobed radio sources requires a dense gaseous medium. Bent sources can therefore be used to identify galaxy clusters and characterize their evolutionary history. By combining radio observations from the Very Large Array Faint Images of the Radio Sky at Twenty centimeters (VLA FIRST) survey with optical and infrared imaging of 36 red sequence selected cluster candidates from the high-z Clusters Occupied by Bent Radio AGN (COBRA) survey (0.35 < z < 2.2), we find that radio sources with narrower opening angles reside in richer clusters, indicating that the cluster environment impacts radio morphology. Within these clusters, we determine 55.5% of our radio host galaxies are brightest cluster galaxies (BCGs) and that the remainder are associated with other luminous galaxies. The projected separations between the radio sources and cluster centers and the sizes of the opening angles of bent sources follow similar distributions for BCG and non-BCG host populations, suggesting that COBRA host galaxies are either BCGs or galaxies that may evolve into BCGs. By measuring the orientation of the radio sources relative to the cluster centers, we find between 30% and 42% of COBRA bent sources are outgoing and have passed through the cluster center, while between 8% and 58% of COBRA bent sources are infalling. Although these sources typically do not follow directly radial paths, the large population of outgoing sources contrasts what is observed in low-z samples of bent sources and may indicate that the intracluster medium is less dense in these high-z clusters.

Keywords: high-redshift galaxy clusters; galaxy clusters; extragalactic radio sources; fanaroff-riley radio galaxies; galaxy evolution; infrared galaxies; radio galaxies; tailed radio galaxies
Kiloparsec-scale Imaging of the CO(1-0)-traced Cold Molecular Gas Reservoir in a z 3.4 Submillimeter Galaxy

We present a high-resolution study of the cold molecular gas as traced by CO(1-0) in the unlensed z ~ 3.4 submillimeter galaxy SMM J13120+4242, using multiconfiguration observations with the Karl G. Jansky Very Large Array (JVLA). The gas reservoir, imaged on 0.″39 (~3 kpc) scales, is resolved into two components separated by ~11 kpc with a total extent of 16 ± 3 kpc. Despite the large spatial extent of the reservoir, the observations show a CO(1-0) FWHM linewidth of only 267 ± 64 km s-1. We derive a revised line luminosity of ${L}_{\mathrm{CO}(1-0)}^{{\prime} }$ = (10 ± 3) × 1010 K km s-1 pc2 and a molecular gas mass of M gas = (13 ± 3)× 1010 (α CO/1) M ⊙. Despite the presence of a velocity gradient (consistent with previous resolved CO(6-5) imaging), the CO(1-0) imaging shows evidence for significant turbulent motions that are preventing the gas from fully settling into a disk. The system likely represents a merger in an advanced stage. Although the dynamical mass is highly uncertain, we use it to place an upper limit on the CO-to-H2 mass conversion factor α CO of 1.4. We revisit the SED fitting, finding that this galaxy lies on the very massive end of the main sequence at z = 3.4. Based on the low gas fraction, short gas depletion time, and evidence for a central AGN, we propose that SMM J13120 is in a rapid transitional phase between a merger-driven starburst and an unobscured quasar. The case of SMM J13120 highlights how mergers may drive important physical changes in galaxies without pushing them off the main sequence.

Keywords: galaxy evolution; high-redshift galaxies; starburst galaxies; interstellar medium
Nitrogen Dioxide Pollution as a Signature of Extraterrestrial Technology

Nitrogen dioxide (NO2) on Earth today has biogenic and anthropogenic sources. During the Covid-19 pandemic, observations of global NO2 emissions have shown a significant decrease in urban areas. Drawing upon this example of NO2 as an industrial byproduct, we use a one-dimensional photochemical model and synthetic spectral generator to assess the detectability of NO2 as an atmospheric technosignature on exoplanets. We consider cases of an Earth-like planet around Sun-like, K-dwarf, and M-dwarf stars. We find that NO2 concentrations increase on planets around cooler stars because there are fewer short-wavelength photons that can photolyze NO2. In cloud-free results, present Earth-level NO2 on an Earth-like planet around a Sun-like star at 10 pc can be detected with signal-to-noise ratio ∼5 within ∼400 hr with a 15 m LUVOIR-like telescope when observed in the 0.2-0.7 μm range where NO2 has a strong absorption. However, clouds and aerosols can reduce the detectability and could mimic the NO2 feature. Historically, global NO2 levels were 3× higher, indicating the capability of detecting a civilization at the stage where Earth's civilization was 40 yr ago. Transit and direct imaging observations to detect infrared spectral signatures of NO2 on habitable planets around M-dwarfs would need several hundred hours of observation time, both due to weaker NO2 absorption in this region and because of masking features by dominant H2O and CO2 bands in the infrared part of the spectrum. Non-detection at these levels could be used to place upper limits on the prevalence of NO2 as a technosignature.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition
Coronal Densities, Temperatures, and Abundances during the 2019 Total Solar Eclipse: The Role of Multiwavelength Observations in Coronal Plasma Characterization

The Airborne Infrared Spectrometer (AIR-Spec) offers an unprecedented opportunity to explore the near-infrared (NIR) wavelength range. It has been flown at two total solar eclipses, in 2017 and 2019. The wavelength range of the much-improved instrument on the second flight (2019 July 2) was shifted to cover two density-sensitive lines from S XI. In this paper we study detailed diagnostics for temperature, electron density, and elemental abundances by comparing results from AIR-Spec slit positions above the east and west limbs with those from Hinode/EIS, the PolarCam detector, and SDO/AIA. We find very good agreement in the electron densities obtained from the EIS EUV line ratios, those from the NIR S XI ratio, and those obtained from the polarized brightness PolarCam measurements. Electron densities ranged from log N e [cm-3] = 8.4 near the limb to 7.2 at R 0 = 1.3. EIS spectra indicate that the temperature distribution above the west limb is near isothermal at around 1.3 MK, while that on the east has an additional higher-T component. The AIR-Spec radiances in Si X and S XI, as well as the AIA data in the 171, 193, and 211 Å bands, are consistent with the EIS results. EIS and AIR-Spec data indicate that the sulfur abundance (relative to silicon) is photospheric in both regions, confirming our previous results of the 2017 eclipse. The AIA data also indicate that the absolute iron abundance is photospheric. Our analysis confirms the importance of the diagnostic potential of the NIR wavelength range and that this important wavelength range can be used reliably and independently to determine coronal plasma parameters.

Keywords: solar coronal lines; solar corona; solar instruments; total eclipses; spectrometers; solar abundances
Kepler-1656b's Extreme Eccentricity: Signature of a Gentle Giant

Highly eccentric orbits are one of the major surprises of exoplanets relative to the solar system and indicate rich and tumultuous dynamical histories. One system of particular interest is Kepler-1656, which hosts a sub-Jovian planet with an eccentricity of 0.8. Sufficiently eccentric orbits will shrink in the semimajor axis due to tidal dissipation of orbital energy during periastron passage. Here our goal was to assess whether Kepler-1656b is currently undergoing such high-eccentricity migration, and to further understand the system's origins and architecture. We confirm a second planet in the system with M c = 0.40 ± 0.09 M jup and Pc = 1919 ± 27 days. We simulated the dynamical evolution of planet b in the presence of planet c and find a variety of possible outcomes for the system, such as tidal migration and engulfment. The system is consistent with an in situ dynamical origin of planet b followed by subsequent eccentric Kozai-Lidov perturbations that excite Kepler-1656b's eccentricity gently, i.e., without initiating tidal migration. Thus, despite its high eccentricity, we find no evidence that planet b is or has migrated through the high-eccentricity channel. Finally, we predict the outer orbit to be mutually inclined in a nearly perpendicular configuration with respect to the inner planet orbit based on the outcomes of our simulations and make observable predictions for the inner planet's spin-orbit angle. Our methodology can be applied to other eccentric or tidally locked planets to constrain their origins, orbital configurations, and properties of a potential companion.

Keywords: exoplanet astronomy; exoplanet dynamics; extrasolar gaseous giant planets; exoplanet detection methods; exoplanet evolution; exoplanet migration
Radiative Magnetohydrodynamic Simulation of the Confined Eruption of a Magnetic Flux Rope: Unveiling the Driving and Constraining Forces

We analyze the forces that control the dynamic evolution of a flux rope eruption in a three-dimensional radiative magnetohydrodynamic simulation. The confined eruption of the flux rope gives rise to a C8.5 flare. The flux rope rises slowly with an almost constant velocity of a few kilometers per second in the early stage when the gravity and Lorentz force are nearly counterbalanced. After the flux rope rises to the height at which the decay index of the external poloidal field satisfies the torus instability criterion, the significantly enhanced Lorentz force breaks the force balance and drives the rapid acceleration of the flux rope. Fast magnetic reconnection is immediately induced within the current sheet under the erupting flux rope, which provides strong positive feedback to the eruption. The eruption is eventually confined due to the tension force from the strong external toroidal field. Our results suggest that the gravity of plasma plays an important role in sustaining the quasi-static evolution of the preeruptive flux rope. The Lorentz force, which is contributed from both the ideal magnetohydrodynamic instability and magnetic reconnection, dominates the dynamic evolution during the eruption process.

Keywords: radiative magnetohydrodynamics; solar activity; solar magnetic fields; solar active region magnetic fields; solar flares