adsabs/SciX_UAT_keywords huggingface dataset:
Modified Gravity and the Flux-weighted Gravity-Luminosity Relationship of Blue Supergiant Stars

We calculate models of stellar evolution for very massive stars and include the effects of modified gravity to investigate the influence on the physical properties of blue supergiant stars and their use as extragalactic distance indicators. With shielding and fifth force parameters in a similar range as those in previous studies of Cepheid and tip of the red giant branch (TRGB) stars, we find clear effects on stellar luminosity and flux-weighted gravity. The relationship between flux-weighted gravity, gF ≡ g/ ${T}_{\mathrm{eff}}^{4}$ , and bolometric magnitude Mbol, which has been used successfully for accurate distance determinations, is systematically affected. While the stellar evolution of flux-weighted gravity-luminosity relationships (FGLRs) show a systematic offset from the observed relation, we can use the differential shifts between models with Newtonian and modified gravity to estimate the influence on FGLR distance determinations. Modified gravity leads to an increase in distance of 0.05-0.15 magnitudes in distance modulus. These changes are comparable to the ones found for Cepheid stars. We compare observed FGLR and TRGB distances of nine galaxies to constrain the free parameters of modified gravity. Not accounting for systematic differences between TRGB and FGLR distances shielding parameters of 5 × 10-7 and 10-6 and fifth force parameters of 1/3 and 1 can be ruled out with about 90% confidence. Allowing for potential systematic offsets between TRGB and FGLR distances no determination is possible for a shielding parameter of 10-6. For 5 × 10-7 a fifth force parameter of 1 can be ruled out to 92% but 1/3 is unlikely only to 60%.

Keywords: stellar physics; non-standard theories of gravity; distance indicators; galactic and extragalactic astronomy
DIAmante TESS AutoRegressive Planet Search (DTARPS). I. Analysis of 0.9 Million Light Curves

Nearly one million light curves from the TESS Year 1 southern hemisphere extracted from Full Field Images with the DIAmante pipeline are processed through the AutoRegressive Planet Search statistical procedure. ARIMA models remove lingering autocorrelated noise, the Transit Comb Filter identifies the strongest periodic signal in the light curve, and a Random Forest machine-learning classifier is trained and applied to identify the best potential candidates. Classifier training sets are based on injections of planetary transit signals, eclipsing binaries, and other variable stars. The optimized classifier has a True Positive Rate of 92.5% and a False Positive Rate of 0.43% from the labeled training set. The result of this DIAmante TESS autoregressive planet search of the southern ecliptic hemisphere analysis is a list of 7377 potential exoplanet candidates. The classifier had a 64% recall rate for previously confirmed exoplanets and a 78% negative recall rate for known False Positives. The completeness map of the injected planetary signals shows high recall rates for planets with 8–30R ⊕ radii and periods 0.6–13 days and poor completeness for planets with radii <2R ⊕ or periods <1 day. The list has many False Alarms and False Positives that need to be culled with multifaceted vetting operations (Paper II).

Keywords: exoplanet catalogs; exoplanet detection methods; light curve classification; period search; time domain astronomy; transits
Radial Star Formation Histories in 32 Nearby Galaxies

The spatially resolved star formation histories are studied for 32 normal star-forming galaxies drawn from the Spitzer Extended Disk Galaxy Exploration Science survey. At surface brightness sensitivities fainter than 28 mag arcsec-2, the new optical photometry is deep enough to complement archival ultraviolet and infrared imaging and to explore the properties of the emission well beyond the traditional optical extents of these nearby galaxies. Fits to the spectral energy distributions using a delayed star formation history model indicate a subtle but interesting average radial trend for the spiral galaxies: the inner stellar systems decrease in age with increasing radius, consistent with inside-out disk formation, but the trend reverses in the outermost regions with the stellar age nearly as old as the innermost stars. These results suggest an old stellar outer disk population formed through radial migration and/or the cumulative history of minor mergers and accretions of satellite dwarf galaxies. The subset of S0 galaxies studied here show the opposite trend compared to what is inferred for spirals: characteristic stellar ages that are increasingly older with radius for the inner portions of the galaxies, and increasingly younger stellar ages for the outer portions. This result suggests that either S0 galaxies are not well modeled by a delayed-τ model, and/or that S0 galaxies have a more complicated formation history than spiral galaxies.

Keywords: galaxy ages; galaxy evolution; galaxy stellar halos
Influences on Infrared Spectra of Benzene Ices for Titan, Comets, and Beyond: Annealings, Artifacts, and Isosbestic Points

Infrared (IR) spectra are needed for both laboratory and observational studies of extraterrestrial ices, both within the solar system, such as for trans-Neptunian objects, comets, and Titan, and in the interstellar medium. Here we present new transmission-IR measurements on solid benzene (C6H6), the simplest common aromatic compound. Spectra are shown with a greater combination of higher resolutions and temperatures than found in the literature. The influences of both warmings and annealings on amorphous benzene are described, and comparisons are made of the IR spectra of warmed and cooled crystalline benzene. Reversible variations with temperature are noted for several IR bands of crystalline benzene, with a suggestion for their use as a possible thermometer for remote sensing of extraterrestrial environments. Comparisons are made to both recent and older literature results, and an artifact produced by high vapor-phase condensation rates is identified. New density measurements are reported for crystalline benzene and used, along with IR-forbidden transitions, to identify amorphous and crystalline ices. It is suggested that differences in spectra of crystalline benzene ices at the same temperature do not necessarily imply partial crystallization.

Keywords: titan; comets; molecular spectroscopy; laboratory astrophysics; astrochemistry; small molecules; ice spectroscopy; interstellar molecules
Excitation of Polycyclic Aromatic Hydrocarbon Emission: Dependence on Size Distribution, Ionization, and Starlight Spectrum and Intensity

Using physical models, we study the sensitivity of polycyclic aromatic hydrocarbon (PAH) emission spectra to the character of the illuminating starlight, to the PAH size distribution, and to the PAH charge distribution. The starlight models considered range from the emission from a 3 Myr old starburst, rich in far-ultraviolet (FUV) radiation, to the FUV-poor spectrum of the very old population of the M31 bulge. A wide range of starlight intensities is considered. The effects of reddening in dusty clouds are investigated for different starlight spectra. For a fixed PAH abundance parameter qPAH (the fraction of the total dust mass in PAHs with <103 C atoms), the fraction of the infrared power appearing in the PAH emission features can vary by a factor of two as the starlight spectrum varies from FUV-poor (M31 bulge) to FUV-rich (young starburst). We show how qPAH can be measured from the strength of the 7.7 μm emission. The fractional power in the 17 μm feature can be suppressed by high starlight intensities.

Keywords: interstellar dust; interstellar emissions; dust continuum emission
Constraining Extended Teleparallel Gravity via Cosmography: A Model-independent Approach

As a classical approach, the dynamics of the Universe, influenced by its dark components, are unveiled through prior modifications of Einstein's equations. Cosmography, on the other hand, is a highly efficient tool for reconstructing any modified theory in a model-independent manner. By employing kinematic variables, it offers a profound explanation for cosmic expansion. Although the cosmographical approach has been highly successful in several geometric theories in recent years, it has not been extensively explored in coupled gravities. With this in mind, we intend to constrain an extended teleparallel gravity model, , through cosmographic parameters. We utilize Taylor series expansion, assuming a minimally coupled form, to constrain the unknowns involved in the series. To achieve this, we conduct a Markov Chain Monte Carlo (MCMC) analysis using three different data sets (cosmic chronometers, baryon acoustic oscillations, and Pantheon+SH0ES). The constrained results obtained from MCMC are then compared and verified using various cosmological parameters. Finally, we compare the resulting models with three well-known models.

Keywords: dark energy
Dynamical Thermal Instability in Highly Supersonic Outflows

Acceleration can change the ionization of X-ray irradiated gas to the point that the gas becomes thermally unstable. Cloud formation, the expected outcome of thermal instability (TI), will be suppressed in a dynamic flow, however, due to the stretching of fluid elements that accompanies acceleration. It is therefore unlikely that cloud formation occurs during the launching phase of a supersonic outflow. In this paper, we show that the most favorable conditions for dynamical TI in highly supersonic outflows are found at radii beyond the acceleration zone, where the growth rate of entropy modes is set by the linear theory rate for a static plasma. This finding implies that even mildly relativistic outflows can become clumpy, and we explicitly demonstrate this using hydrodynamical simulations of ultrafast outflows. We describe how the continuity and heat equations can be used to appreciate another impediment (beside mode disruption due to the stretching) to making an outflow clumpy: background flow conditions may not allow the plasma to enter a TI zone in the first place. The continuity equation reveals that both impediments are in fact tightly coupled, yet one is easy to overcome. Namely, time variability in the radiation field is found to be a robust means of placing gas in a TI zone. We further show how the ratio of the dynamical and thermal timescales enters linear theory; the heat equation reveals how this ratio depends on the two processes that tend to remove gas from a TI zone: adiabatic cooling and heat advection.

Keywords: active galactic nuclei
The Rise and Fall of the King: The Correlation between FO Aquarii's Low States and the White Dwarf's Spin-down

The intermediate polar FO Aquarii (FO Aqr) experienced its first reported low-accretion states in 2016, 2017, and 2018, and, using newly available photographic plates, we identify prediscovery low states in 1965, 1966, and 1974. The primary focus of our analysis, however, is an extensive set of time-series photometry obtained between 2002 and 2018, with particularly intensive coverage of the 2016-2018 low states. After computing an updated spin ephemeris for the white dwarf (WD), we show that its spin period began to increase in 2014 after having spent 27 yr decreasing; no other intermediate polar has experienced a sign change of its period derivative, but FO Aqr has now done so twice. Our central finding is that the recent low states all occurred shortly after the WD began to spin down, even though no low states were reported in the preceding quarter-century, when it was spinning up. Additionally, the system's mode of accretion is extremely sensitive to the mass-transfer rate, with accretion being almost exclusively disk-fed when FO Aqr is brighter than V ∼ 14 and substantially stream-fed when it is not. Even in the low states, a grazing eclipse remains detectable, confirming the presence of a disklike structure (but not necessarily a Keplerian accretion disk). We relate these various observations to theoretical predictions that during the low state, the system's accretion disk dissipates into a non-Keplerian ring of diamagnetic blobs. Finally, a new XMM-Newton observation from a high state in 2017 reveals an anomalously soft X-ray spectrum and diminished X-ray luminosity compared to pre-2016 observations.

Keywords: dq herculis stars; cataclysmic variable stars; stellar magnetic fields; white dwarf stars
A Quick Guide to Nearby Young Associations

Nearby associations of stars which are coeval are important benchmark laboratories because they provide robust measurements of stellar ages. The study of such coeval groups makes it possible to better understand star formation by studying the initial mass function, the binary fraction or the circumstellar disks of stars, to determine how the initially dense populations of young stars gradually disperse to form the field population, and to shed light on how the properties of stars, exoplanets and substellar objects evolve with distinct snapshots along their lifetime. The advent of large-scale missions such as Gaia is reshaping our understanding or stellar kinematics in the Solar neighborhood and beyond, and offers the opportunity to detect a large number of loose, coeval stellar associations for the first time, which evaded prior detection because of their low density or the faintness of their members. In parallel, advances in detection and characterization of exoplanets and substellar objects are starting to unveil the detailed properties of extrasolar atmospheres, as well as population-level distributions in fundamental exoplanet properties such as radii, masses, and orbital parameters. Accurate ages are still sparsely available to interpret the evolution of both exoplanets and substellar objects, and both fields are now ripe for detailed age investigations because we are starting to uncover ever-closer low-density associations that previously escaped detection, as well as exoplanets and ever lower-mass members of more distant open clusters and star-forming regions. In this paper, we review some recent advances in the identification and characterization of nearby associations, the methods by which stellar ages are measured, and some of the direct applications of the study of young associations such as the emergent field of isolated planetary-mass objects.

Keywords: stellar associations; open star clusters; stellar kinematics
GECAM Localization of High-energy Transients and the Systematic Error

The Gravitational Wave High-energy Electromagnetic Counterpart All-sky Monitor (GECAM) is a pair of microsatellites (i.e., GECAM-A and GECAM-B) dedicated to monitoring gamma-ray transients including the high-energy electromagnetic counterparts of gravitational waves, such as gamma-ray bursts, soft gamma-ray repeaters, solar flares, and terrestrial gamma-ray flashes. Since launch in 2020 December, GECAM-B has detected hundreds of astronomical and terrestrial events. For these bursts, localization is the key for burst identification and classification as well as follow-up observations in multiple wavelengths. Here, we propose a Bayesian localization method with Poisson data with Gaussian background profile likelihood to localize GECAM bursts based on the distribution of burst counts in detectors with different orientations. We demonstrate that this method can work well for all kinds of bursts, especially extremely short ones. In addition, we propose a new method to estimate the systematic error of localization based on a confidence level test, which can overcome some problems of the existing method in the literature. We validate this method by Monte Carlo simulations, and then apply it to a burst sample with accurate location and find that the mean value of the systematic error of GECAM-B localization is ~2.°5. By considering this systematic error, we can obtain a reliable localization probability map for GECAM bursts. Our methods can be applied to other gamma-ray monitors.

Keywords: astronomical methods; observational astronomy; gamma-ray astronomy; time domain astronomy
Evidence of Ultrafaint Radio Frequency Interference in Deep 21 cm Epoch of Reionization Power Spectra with the Murchison Wide-field Array

We present deep upper limits from the 2014 Murchison Widefield Array Phase I observing season, with a particular emphasis on identifying the spectral fingerprints of extremely faint radio frequency interference (RFI) contamination in the 21 cm power spectra (PS). After meticulous RFI excision involving a combination of the SSINS RFI flagger and a series of PS-based jackknife tests, our lowest upper limit on the Epoch of Reionization (EoR) 21 cm PS signal is Δ2 ≤ 1.61 × 104 mK2 at k = 0.258h Mpc-1 at a redshift of 7.1 using 14.7 hr of data. By leveraging our understanding of how even fainter RFI is likely to contaminate the EoR PS, we are able to identify ultrafaint RFI signals in the cylindrical PS. Surprisingly this signature is most obvious in PS formed with less than 1 hr of data, but is potentially subdominant to other systematics in multiple-hour integrations. Since the total RFI budget in a PS detection is quite strict, this nontrivial integration behavior suggests a need to more realistically model coherently integrated ultrafaint RFI in PS measurements so that its potential contribution to a future detection can be diagnosed.

Keywords: cosmology; reionization; radio interferometers; astronomy data analysis; h i line emission
The First Extensive Spectroscopic Study of Young Stars in the North America and Pelican Nebulae

We present a spectroscopic survey of over 3400 potential members in the North America and Pelican Nebulae (NAP) using several low-resolution (R ≈ 1300-2000) spectrographs: Palomar/Norris, WIYN/Hydra, Keck/DEep Imaging Multi-Object Spectrograph (DEIMOS), and the Multiple Mirror Telescope (MMT)/Hectospec. We identify 580 young stars as likely members of the NAP region based on criteria involving infrared excess, Li I 6708 Å absorption, X-ray emission, parallax, and proper motions. The spectral types of individual spectra are derived by fitting them with templates that are either empirical spectra of pre-main-sequence stars or model atmospheres. The templates are artificially veiled, and a best-fit combination of spectral type and veiling parameter is derived for each star. We use the spectral types with archival photometry to derive V-band extinction and stellar luminosity. From the Hertzsprung-Russell diagram, the median age of the young stars is about 1 Myr, with a luminosity dispersion of ∼0.3-0.4 dex. We investigate the photometric variability of the spectroscopic member sample using Zwicky Transient Facility data and conclude that photometric variability, while present, does not significantly contribute to the luminosity dispersion. While larger than the formal errors, the luminosity dispersion is smaller than if veiling were not taken into account in our spectral typing process. The measured ages of the stellar kinematic groups, combined with the inferred ages for embedded stellar populations revealed by Spitzer, suggest a sequential history of star formation in the NAP region.

Keywords: stellar accretion disks; protoplanetary disks; pre-main sequence stars; stellar spectral types; star formation; star forming regions; stellar associations
Properties of Neutron Stars Described by a Relativistic Ab Initio Model

Properties of neutron stars are investigated by an available relativistic ab initio method, the relativistic Brueckner-Hartree-Fock (RBHF) model, with the latest high-precision, relativistic charge-dependent potentials, pvCD-Bonn A, B, C. The neutron star matter is solved within the beta equilibrium and charge neutrality conditions in the framework of the RBHF model. Compared to the conventional treatment, where the chemical potential of leptons was approximately represented by the symmetry energy of nuclear matter, the equation of state of neutron star matter in the present self-consistent calculation with pvCD-Bonn B has a striking difference above the baryon number density nb = 0.55 fm-3. However, these differences influence the global properties of neutron stars only about 1% to 2%. Then, three two-body potentials pvCD-Bonn A, B, C, with different tensor components, are systematically applied in the RBHF model to calculate the properties of neutron stars. It is found that the maximum masses of neutron stars are around 2.21-2.30 M⊙, and the corresponding radii are R = 11.18-11.72 km. The radii of a 1.4 M⊙ neutron star are predicated as R1.4 = 12.34-12.91 km, and their dimensionless tidal deformabilities are Λ1.4 = 485-626. Furthermore, the direct URCA process in neutron star cooling will happen from nb = 0.414 to 0.530 fm-3 with the proton fractions Yp = 0.136-0.138. All of the results obtained from the RBHF model only with two-body pvCD-Bonn potentials completely satisfy various constraints from recent astronomical observations of massive neutron stars, gravitational wave detection (GW170817), and simultaneous mass-radius measurement.

Keywords: nuclear physics; neutron stars; neutron star cores; gravitational waves
The Bulk Properties of Isolated Neutron Stars Inferred from the Gravitational Redshift Measurements

The measurements of the bulk properties of most isolated neutron stars (INSs) are challenging tasks. Tang et al. have developed a new method, based on the equation of state (EoS) of neutron star (NS) material constrained by the observational data, to infer the gravitational masses of a few INSs whose gravitational redshifts are available. However, in that work, the authors only considered the constraints on the EoS from nuclear experiments/theories and the gravitational wave data of GW170817; the possible phase transition has not been taken into account. In this work, we adopt three EoS models (including the one incorporates a first-order strong phase transition) that are constrained by the latest multimessenger NS data, including in particular the recent mass-radius measurements of two NSs by Neutron Star Interior Composition Explorer, to update the estimation of the gravitational masses of RBS 1223, RX J0720.4-3125, and RX J1856.5-3754. In comparison to our previous approach, the new constraints are tighter, and the gravitational masses are larger by about 0.1M ⊙. All the inferred gravitational masses are within the range of the NS masses measured in other ways. We have also calculated the radius, tidal-deformability, and moment of inertia of these sources. The inclusion of the first-order strong phase transition has little influence on modifying the results.

Keywords: single x-ray stars; gravitational waves; neutron stars; neutron star cores
Effects of Radiative Diffusion on Dynamical Corotation Torque in Three-dimensional Protoplanetary Disks

The dynamical corotation torque arising from the deformation of horseshoe orbits, along with the vortensity gradient in the background disk, is important for determining the orbital migration rate and direction of low-mass planets. Previous two-dimensional studies have predicted that the dynamical corotation torque is positive, decelerating inward planet migration. In contrast, recent three-dimensional studies have shown that buoyancy resonance makes the dynamical corotation torque negative, accelerating inward migration. In this paper, we study the dependence of the dynamical corotation torque on thermal transport, using three-dimensional simulations. We first show that our results are consistent with previous three-dimensional studies when the disk is fully adiabatic. In more realistic radiative disks, however, radiative diffusion suppresses buoyancy resonance significantly, especially in high-altitude regions, and yields a positive dynamical corotation torque. This alleviates the issue of rapid migration being caused by the negative dynamical corotation torque in adiabatic disks. Our results suggest that radiative diffusion, together with stellar irradiation and accretion heating, are needed to accurately describe the migration of low-mass planets.

Keywords: planetary migration; planetary-disk interactions; protoplanetary disks; radiative transfer