adsabs/SciX_UAT_keywords huggingface dataset:
Does Modified Gravity Predict Fast Stellar Bars in Spiral Galaxies?

The evolution of disk galaxies in modified gravity is studied by using high-resolution N-body simulations. More specifically, we use the weak field limit of two modified gravity theories, that is, nonlocal gravity and scalar-tensor-vector gravity, known as MOG, and ignore the existence of a dark matter (DM) halo. We construct the same models as in the standard DM model and compare their dynamics with the galactic models in modified gravity. It turns out that there are serious differences between galactic models in these different viewpoints. For example, we explicitly show that the galactic models in modified gravity host faster bars compared to the DM case, but the final stellar bars are weaker in modified gravity. These facts are not new and have already been reported in our previous simulations for exponential galactic models. Therefore, our main purpose is to show that the above-mentioned differences, with an emphasis on the speed of the bars, are independent of the initial density profile of the adopted disk and halo. To do so, we employ different profiles for the disk and halo and show that the results remain qualitatively independent of the initial galactic models. Moreover, a more accurate method has been used to quantify the kinematic properties of the stellar bars. Our results imply that, contrary to the DM models, bars in modified gravity are fast rotators that never leave the fast-bar region until the end of the simulation.

Keywords: spiral galaxies; disk galaxies; galaxy evolution; scalar-tensor-vector gravity; non-standard theories of gravity
PetroFit: A Python Package for Computing Petrosian Radii and Fitting Galaxy Light Profiles

PetroFit is an open-source Python package based on Astropy and Photutils that can calculate Petrosian profiles and fit galaxy images. It offers end-to-end tools for making accurate photometric measurements, estimating morphological properties, and fitting 2D models to galaxy images. Petrosian metric radii can be used for model parameter estimation and aperture photometry to provide accurate total fluxes. Correction tools are provided for improving Petrosian radii estimates affected by galaxy morphology. PetroFit also provides tools for sampling Astropy-based models (including custom profiles and multicomponent models) onto image grids and enables point-spread function convolution to account for the effects of seeing. These capabilities provide a robust means of modeling and fitting galaxy light profiles. We have made the PetroFit package publicly available on GitHub ( PetroFit/petrofit ) and PyPi (pip install petrofit).

Keywords: astronomy software; ccd photometry; regression; galaxies
Internal Structure and CO2 Reservoirs of Habitable Water Worlds

Water worlds are water-rich (>1 wt% H2O) exoplanets. The classical models of water worlds considered layered structures determined by the phase boundaries of pure water. However, water worlds are likely to possess comet-like compositions, with between ∼3 and 30 mol% CO2 relative to water. In this study, we build an interior structure model of habitable (I.e., surface liquid ocean-bearing) water worlds using the latest results from experimental data on the CO2-H2O system to explore the CO2 budget and localize the main CO2 reservoirs inside of these planets. We show that CO2 dissolved in the ocean and trapped inside of a clathrate layer cannot accommodate a cometary amount of CO2 if the planet accretes more than 11 wt% of volatiles (CO2 + H2O) during its formation. If the atmosphere holds more than a negligible amount of the CO2 (>0.01% of the planet mass), the planet will not have a habitable surface temperature. We propose a new, potentially dominant, CO2 reservoir for water worlds: CO2 buried inside of the high-pressure water ice mantle as CO2 ices or (H2CO3 × H2O), the monohydrate of carbonic acid. If insufficient amounts of CO2 are sequestered in either this reservoir or the planet's iron core, habitable-zone water worlds could generically be stalled in their cooling before liquid oceans have a chance to condense.

Keywords: planetary interior; ocean planets; carbon dioxide; habitable planets; exoplanets; ocean-atmosphere interactions; hydrosphere
Multifilter Time-series Observations of Eleven Blue Short-period ATLAS Variable Stars

Eleven periodic variable stars were observed photometrically through two to four filters from the set UBVR C I C . Phase-folded data for each star cover full cycles of variation. Spectral energy distributions, based on absolute photometry extracted from the literature, are used to inform models of the stars. The stars include four eclipsing systems with hot subdwarfs of spectral type O or B (sdO/B). Periods are in the range 1.8-2.2 hr. Four reflection-effect binaries, with amplitudes as large as 0.5 mag in the R C filter were observed; periods range from 1.6 to 2.4 hr. In two of these latter systems, the primary stars are also sdB stars, while two have white-dwarf components. In all eight of these binaries the companion stars are probably M dwarfs. The remaining three stars are pulsators: one large-amplitude δ Scuti star previously misclassified as an eclipsing system; one field SX Phe star near the Galactic plane; and one multiperiodic high-luminosity star of unknown type. The amplitude is usually a strong function of the wavelength in pulsating stars, but this is not the case for the high-luminosity variable. One possible explanation is that the luminous star has a pulsating companion. The SX Phe and high-luminosity star are both heavily reddened (A V > 5 mag).

Keywords: subdwarf stars; close binary stars; variable stars
Constraining the Positive Ion Composition in Saturn's Lower Ionosphere with the Effective Recombination Coefficient

The present study combines Radio and Plasma Wave Science/Langmuir Probe and Ion and Neutral Mass Spectrometer data from Cassini's last four orbits into Saturn's lower ionosphere to constrain the effective recombination coefficient α300 from measured number densities and electron temperatures at a reference electron temperature of 300 K. Previous studies have shown an influx of ring material causes a state of electron depletion due to grain charging, which will subsequently affect the ionospheric chemistry. The requirement to take grain charging into account limits the derivation of α300 to upper limits. Assuming photochemical equilibrium and using an established method to calculate the electron production rate, we derive upper limits for α300 of ≲ 3 × 10-7 cm3 s-1 for altitudes below 2000 km. This suggests that Saturn's ionospheric positive ions are dominated by species with low recombination rate coefficients like HCO+. An ionosphere dominated by water group ions or complex hydrocarbons, as previously suggested, is incompatible with this result, as these species have recombination rate coefficients > 5 × 10-7 cm3 s-1 at an electron temperature of 300 K.

Keywords: planetary science; saturn; space plasmas; recombination
On the Spectral Evolution of Hot White Dwarf Stars. II. Time-dependent Simulations of Element Transport in Evolving White Dwarfs with STELUM

White dwarf stars are subject to various element transport mechanisms that can cause their surface composition to change radically as they cool, a phenomenon known as spectral evolution. In this paper, we undertake a comprehensive theoretical investigation of the spectral evolution of white dwarfs. First, we introduce STELUM, a new implementation of the stellar evolutionary code developed at the Université de Montréal. We provide a thorough description of the physical content and numerical techniques of the code, covering the treatment of both stellar evolution and chemical transport. Then, we present two state-of-the-art numerical simulations of element transport in evolving white dwarfs. Atomic diffusion, convective mixing, and mass loss are considered simultaneously as time-dependent diffusive processes and are fully coupled to the cooling. We first model the PG 1159-DO-DB-DQ evolutionary channel: a helium-, carbon-, and oxygen-rich PG 1159 star transforms into a pure-helium DB white dwarf due to gravitational settling and then into a helium-dominated, carbon-polluted DQ white dwarf through convective dredge-up. We also compute for the first time the full DO-DA-DC evolutionary channel: a helium-rich DO white dwarf harboring residual hydrogen becomes a pure-hydrogen DA star through the float-up process and then a helium-dominated, hydrogen-bearing DC star due to convective mixing. We demonstrate that our results are in excellent agreement with available empirical constraints. In particular, our DO-DA-DC simulation perfectly reproduces the lower branch of the bifurcation observed in the Gaia color-magnitude diagram, which can therefore be interpreted as a signature of spectral evolution.

Keywords: white dwarf stars; stellar diffusion; stellar convection envelopes; stellar evolutionary models; stellar winds
New Ritz Wavelengths and Transition Probabilities of Parity-forbidden [Mn II] Lines of Astrophysical Interest

We report a comprehensive list of accurate Ritz wavelengths and calculated transition probabilities for parity-forbidden [Mn II] lines. Ritz wavelengths have been derived from experimentally established energy level values resulting from an extensive analysis of a high-resolution Fourier-transform emission spectrum of singly ionized manganese. Our analysis includes transitions between all known metastable and other long-lived levels of Mn II giving a total of 1130 [Mn II] Ritz wavelengths. Our entire list of derived Ritz wavelengths for [Mn II] lines ranges between 237 nm and 170 μm (42,125-58 cm-1). The accurate Ritz wavelengths and calculated transition probabilities for forbidden lines in this paper are useful in the study and diagnostics of nebulae and other low-density astrophysical plasmas.

Keywords: atomic data benchmarking; atomic physics; line positions; spectral line lists; line intensities; laboratory astrophysics; theoretical techniques; high resolution spectroscopy; atomic spectroscopy
Evolution of Primordial Magnetic Fields during Large-scale Structure Formation

Primordial magnetic fields (PMFs) could explain the large-scale magnetic fields present in the universe. Inflation and phase transitions in the early universe could give rise to such fields with unique characteristics. We investigate the magnetohydrodynamic evolution of these magnetogenesis scenarios with cosmological simulations. We evolve inflation-generated magnetic fields either as (i) uniform (homogeneous) or as (ii) scale-invariant stochastic fields, and phase-transition-generated ones either as (iii) helical or as (iv) nonhelical fields from the radiation-dominated epoch. We find that the final distribution of magnetic fields in the simulated cosmic web shows a dependence on the initial strength and the topology of the seed field. Thus, the observed field configuration retains information on the initial conditions at the moment of the field generation. If detected, PMF observations would open a new window for indirect probes of the early universe. The differences between the competing models are revealed on the scale of galaxy clusters, bridges, as well as filaments and voids. The distinctive spectral evolution of different seed fields produces imprints on the correlation length today. We discuss how the differences between rotation measures from highly ionized regions can potentially be probed with forthcoming surveys.

Keywords: magnetohydrodynamical simulations; large-scale structure of the universe; intergalactic medium; primordial magnetic fields
High Tide or Riptide on the Cosmic Shoreline? A Water-rich Atmosphere or Stellar Contamination for the Warm Super-Earth GJ 486b from JWST Observations

Planets orbiting M-dwarf stars are prime targets in the search for rocky exoplanet atmospheres. The small size of M dwarfs renders their planets exceptional targets for transmission spectroscopy, facilitating atmospheric characterization. However, it remains unknown whether their host stars' highly variable extreme-UV radiation environments allow atmospheres to persist. With JWST, we have begun to determine whether or not the most favorable rocky worlds orbiting M dwarfs have detectable atmospheres. Here, we present a 2.8-5.2 μm JWST NIRSpec/G395H transmission spectrum of the warm (700 K, 40.3× Earth's insolation) super-Earth GJ 486b (1.3 R ⊕ and 3.0 M ⊕). The measured spectrum from our two transits of GJ 486b deviates from a flat line at 2.2σ - 3.3σ, based on three independent reductions. Through a combination of forward and retrieval models, we determine that GJ 486b either has a water-rich atmosphere (with the most stringent constraint on the retrieved water abundance of H2O > 10% to 2σ) or the transmission spectrum is contaminated by water present in cool unocculted starspots. We also find that the measured stellar spectrum is best fit by a stellar model with cool starspots and hot faculae. While both retrieval scenarios provide equal quality fits ( ${\chi }_{\nu }^{2}=1.0$ ) to our NIRSpec/G395H observations, shorter wavelength observations can break this degeneracy and reveal if GJ 486b sustains a water-rich atmosphere.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; transmission spectroscopy; astronomy data reduction; planetary atmospheres; water vapor; stellar faculae; stellar atmospheres; infrared spectroscopy
A Primordial Origin for the Gas-rich Debris Disks around Intermediate-mass Stars

While most debris disks consist of dust with little or no gas, a fraction have significant amounts of gas detected via emission lines of CO, ionized carbon, and/or atomic oxygen. Almost all such gaseous debris disks known are around A-type stars with ages up to 50 Myr. We show, using semianalytic disk evolution modeling, that this can be understood if the gaseous debris disks are remnant protoplanetary disks that have become depleted of small grains compared to the interstellar medium. Photoelectric heating by the A stars' far-UV (FUV) radiation is then inefficient, while the stars' extreme-UV (EUV) and X-ray emissions are weak owing to a lack of surface convective zones capable of driving magnetic activity. In this picture, it is relatively difficult for stars outside the range of spectral types from A through early B to have such long-lived gas disks. Less-massive stars have stronger magnetic activity in the chromosphere, transition region, and corona with resulting EUV and X-ray emission, while more-massive stars have photospheres hot enough to produce strong EUV radiation. In both cases, primordial disk gas is likely to photoevaporate well before 50 Myr. These results come from 0D disk evolution models where we incorporate internal accretion stresses, MHD winds, and photoevaporation by EUV and X-ray photons with luminosities that are functions of the stellar mass and age. A key issue this work leaves open is how some disks become depleted in small dust so that FUV photoevaporation slows. Candidates include the grains' growth, settling, radial drift, radiation force, and incorporation into planetary systems.

Keywords: protoplanetary disks; debris disks; stellar evolution; extreme ultraviolet astronomy; exoplanet formation; interstellar medium; a stars
Gaia DR2 Color-Temperature Relations Based on Infrared Flux Method Results

The ESA/Gaia mission is providing accurate and precise all-sky photometry. We combined effective temperatures derived, for a sample of dwarf and giant stars, by Gonzalez Hernandez \& Bonifacio (2009) using the Infrared Flux Method, with the photometry available from the second release of the ESA/Gaia mission. We provide colour-temperature relations for the broad-band colours (BP-RP), (BP-G), (G-RP), (G-K), (BP-K), (RP-K). These relations allow the exploitation of the all-sky Gaia DR2 photometry to obtain precise effective temperatures.

Keywords: stellar atmospheres; stellar effective temperatures
The Orbital Eccentricities of Directly Imaged Companions Using Observable-based Priors: Implications for Population-level Distributions

The eccentricity of a substellar companion is an important tracer of its formation history. Directly imaged companions often present poorly constrained eccentricities. A recently developed prior framework for orbit fitting called "observable-based priors" has the advantage of improving biases in derived orbit parameters for objects with minimal phase coverage, which is the case for the majority of directly imaged companions. We use observable-based priors to fit the orbits of 21 exoplanets and brown dwarfs in an effort to obtain the eccentricity distributions with minimized biases. We present the objects' individual posteriors compared to their previously derived distributions, showing in many cases a shift toward lower eccentricities. We analyze the companions' eccentricity distribution at a population level, and compare this to the distributions obtained with the traditional uniform priors. We fit a Beta distribution to our posteriors using observable-based priors, obtaining shape parameters α = ${1.09}_{-0.22}^{+0.30}$ and β = ${1.42}_{-0.25}^{+0.33}$ . This represents an approximately flat distribution of eccentricities. The derived α and β parameters are consistent with the values obtained using uniform priors, though uniform priors lead to a tail at high eccentricities. We find that separating the population into high- and low-mass companions yields different distributions depending on the classification of intermediate-mass objects. We also determine via simulation that the minimal orbit coverage needed to give meaningful posteriors under the assumptions made for directly imaged planets is ≈15% of the inferred period of the orbit.

Keywords: exoplanet formation; brown dwarfs; orbit determination; orbital elements; extrasolar gaseous giant planets; bayesian statistics
On the General Correlation between 3D Solar Wind Speed and Density Model and Solar Proxies

The solar wind (SW) is a supersonic outflow of plasma from the solar corona, with the latitudinal speed and density profiles varying with the solar activity. The SW protons charge exchange with the inflowing interstellar neutral atoms and create energetic neutral atoms (ENAs), which bring information on the physical state of the plasma within the boundary region of the heliosphere. The speed of the ENAs depends on their energies, and consequently observations at different energies provide information on different epochs backward in time. Therefore, understanding the history of the evolution of the SW is important to understand this information. In this paper, we extend the work by Porowski et al., who provided the WawHelioIon 3DSW model of the time evolution of latitudinal profiles of the SW speed and density based on results of analysis of interplanetary scintillations (IPSs). Based on results of principal component analysis, we search for correlation between selected solar proxies and the structure of the SW obtained from IPSs and show that it is possible to reproduce the evolution of the SW structure during the past three solar cycles based on the proxies. With this, we extend the history of the evolution of the SW structure back to 1976, i.e., to the epoch when observations of the key proxies-the inclination of the SW current sheet and the solar polar magnetic fields-became available. We point out the potential of the use of the proxies for forecasting the structure of the SW into the future.

Keywords: fast solar wind; slow solar wind; solar physics; solar wind; solar activity; stellar activity; heliosphere; astrosphere interstellar medium interactions
Digging for Relics of the Past: The Ancient and Obscured Bulge Globular Cluster NGC 6256

We used a set of moderately deep and high-resolution optical observations obtained with the Hubble Space Telescope to investigate the properties of the stellar population in the heavily obscured bulge globular cluster (GC) NGC 6256. The analysis of the color-magnitude diagram (CMD) revealed a stellar population with an extended blue horizontal branch severely affected by differential reddening, which was corrected, taking into account color excess variations up to δE(B - V) ∼ 0.51. We implemented a Monte Carlo Markov Chain technique to perform the isochrone fitting of the observed CMD in order to derive the stellar age, the cluster distance, and the average color excess in the cluster direction. Using three different sets of isochrones we found that NGC 6256 is characterized by a very old stellar age around 13.0 Gyr, with a typical uncertainty of ∼0.5 Gyr. We also found an average color excess of E(B - V) = 1.19 and a distance from the Sun of 6.8 kpc. We then derived the cluster gravitational center and measured its absolute proper motion using the Gaia-DR2 catalog. All this was used to back-integrate the cluster orbit in a Galaxy-like potential and measure its integrals of motion. It turned out that NGC 6256 is currently in a low-eccentricity orbit entirely confined within the bulge and its integrals of motion are fully compatible with a cluster purely belonging to the Galaxy native GC population. All these pieces of evidence suggest that NGC 6256 is an extremely old relic of the past history of the Galaxy, formed during the very first stages of its assembly.

Keywords: globular star clusters; galaxy bulges; milky way galaxy; galactic bulge; milky way evolution; milky way formation; hst photometry; markov chain monte carlo; algorithms; interstellar reddening; interstellar extinction
SKYSURF: Constraints on Zodiacal Light and Extragalactic Background Light through Panchromatic HST All-sky Surface-brightness Measurements. I. Survey Overview and Methods

We give an overview and describe the rationale, methods, and testing of the Hubble Space Telescope (HST) Archival Legacy project "SKYSURF." SKYSURF uses HST's unique capability as an absolute photometer to measure the ~0.2-1.7 μm sky-surface brightness (sky-SB) from 249,861 WFPC2, ACS, and WFC3 exposures in ~1400 independent HST fields. SKYSURF's panchromatic data set is designed to constrain the discrete and diffuse UV to near-IR sky components: Zodiacal Light (ZL), Kuiper Belt Objects (KBOs), Diffuse Galactic Light (DGL), and the discrete plus diffuse Extragalactic Background Light (EBL). We outline SKYSURF's methods to: (1) measure sky-SB levels between detected objects; (2) measure the discrete EBL, most of which comes from AB≃17-22 mag galaxies; and (3) estimate how much truly diffuse light may exist. Simulations of HST WFC3/IR images with known sky values and gradients, realistic cosmic ray (CR) distributions, and star plus galaxy counts were processed with nine different algorithms to measure the "Lowest Estimated Sky-SB" (LES) in each image between the discrete objects. The best algorithms recover the LES values within 0.2% when there are no image gradients, and within 0.2%-0.4% when there are 5%-10% gradients. We provide a proof of concept of our methods from the WFC3/IR F125W images, where any residual diffuse light that HST sees in excess of zodiacal model predictions does not depend on the total object flux that each image contains. This enables us to present our first SKYSURF results on diffuse light in Carleton et al.

Keywords: hubble space telescope; zodiacal cloud; cosmic background radiation; galaxy counts; star counts