adsabs/SciX_UAT_keywords huggingface dataset:
A Comparative L-dwarf Sample Exploring the Interplay between Atmospheric Assumptions and Data Properties

Comparisons of atmospheric retrievals can reveal powerful insights on the strengths and limitations of our data and modeling tools. In this paper, we examine a sample of five L dwarfs of similar effective temperature (T eff) or spectral type to compare their pressure-temperature (P-T) profiles. Additionally, we explore the impact of an object's metallicity and the signal-to-noise ratio (S/N) of the observations on the parameters we can retrieve. We present the first atmospheric retrievals: 2MASS J15261405+2043414, 2MASS J05395200-0059019, 2MASS J15394189-0520428, and GD 165B increasing the small but growing number of L dwarfs retrieved. When compared to the atmospheric retrievals of SDSS J141624.08+134826.7, a low-metallicity d/sdL7 primary in a wide L+T binary, we find that similar T eff sources have similar P-T profiles with metallicity differences impacting the relative offset between their P-T profiles in the photosphere. We also find that for near-infrared spectra, when the S/N is ≳80 we are in a regime where model uncertainties dominate over data measurement uncertainties. As such, S/N does not play a role in the retrieval's ability to distinguish between a cloud-free and cloudless model, but may impact the confidence of the retrieved parameters. Lastly, we also discuss how to break cloud model degeneracies and the impact of extraneous gases in a retrieval model.

Keywords: brown dwarfs; exoplanets; atmospheric composition; fundamental parameters of stars; l dwarfs; stellar atmospheres; metallicity
Probing the Full CO Spectral Line Energy Distribution (SLED) in the Nuclear Region of a Quasar-starburst System at z = 6.003

We report Atacama Large Millimeter/submillimeter Array observations of CO(8-7), (9-8), ${{\rm{H}}}_{2}{\rm{O}}({2}_{\mathrm{0,2}}\mbox{--}{1}_{\mathrm{1,1}})$ , and ${\mathrm{OH}}^{+}({1}_{1}\mbox{--}{0}_{1})$ and NOrthern Extended Millimeter Array observations of CO(5-4), (6-5), (12-11), and (13-12) toward the z = 6.003 quasar SDSS J231038.88+185519.7, aiming to probe the physical conditions of the molecular gas content of this source. We present the best sampled CO spectral line energy distribution (SLED) at z = 6.003, and analyzed it with the radiative transfer code MOLPOP-CEP. Fitting the CO SLED to a one-component model indicates a kinetic temperature Tkin = 228 K, molecular gas density $\mathrm{log}(n({{\rm{H}}}_{2})/{\mathrm{cm}}^{-3}$ ) = 4.75, and CO column density $\mathrm{log}(N(\mathrm{CO})/{\mathrm{cm}}^{-2})=17.5$ ; although, a two-component model better fits the data. In either case, the CO SLED is dominated by a "warm" and "dense" component. Compared to samples of local (Ultra) Luminous Infrared Galaxies, starburst galaxies, and high-redshift submillimeter galaxies, J2310+1855 exhibits higher CO excitation at (J ≥ 8), like other high-redshift quasars. The high CO excitation, together with the enhanced ${L}_{{{\rm{H}}}_{2}{\rm{O}}}/{L}_{\mathrm{IR}}$ , ${L}_{{{\rm{H}}}_{2}{\rm{O}}}/{L}_{\mathrm{CO}}$ , and ${L}_{{\mathrm{OH}}^{+}}/{L}_{{{\rm{H}}}_{2}{\rm{O}}}$ ratios, suggests that besides the UV radiation from young massive stars, other mechanisms such as shocks, cosmic-rays, and X-rays might also be responsible for the heating and ionization of the molecular gas. In the nuclear region probed by the molecular emissions lines, any of these mechanisms might be present due to the powerful quasar and the starburst activity.

Keywords: submillimeter astronomy; quasars; starburst galaxies; infrared galaxies; agn host galaxies; high-redshift galaxies; interstellar medium; molecular gas; interstellar phases; early universe
METAL: The Metal Evolution, Transport, and Abundance in the Large Magellanic Cloud Hubble Program. IV. Calibration of Dust Depletions versus Abundance Ratios in the Milky Way and Magellanic Clouds and Application to Damped Lyα Systems

The evolution of the metal content of the universe can be tracked through rest-frame UV spectroscopy of damped Lyα systems (DLAs). Gas-phase abundances in DLAs must be corrected for dust depletion effects, which can be accomplished by calibrating the relation between abundance ratios such as [Zn/Fe] and depletions (the fraction of metals in gas, as opposed to dust). Using samples of gas-phase abundances and depletions in the Milky Way (MW), LMC, and SMC, we demonstrate that the relation between [Zn/Fe] and other abundance ratios does not change significantly between these local galaxies and DLAs, indicating that [Zn/Fe] should trace depletions of heavy elements in those systems. The availability of photospheric abundances in young massive stars, a proxy for the total (gas+dust) metallicity of neutral gas, in the MW, LMC, and SMC allows us to calibrate the relation between [Zn/Fe] and depletions in these nearby galaxies. We apply the local calibrations of depletions to DLAs. We find that the fraction of metals in dust, the dust-to-gas ratio, and total abundances are 2-5 times lower than inferred from previous depletion calibrations based on MW measurements and a different formalism. However, the trend of dust abundance versus metallicity remains only slightly sublinear for all existing depletion calibrations, contrary to what is inferred from far-IR (FIR), 21 cm, and CO emission in nearby galaxies and predicted by chemical evolution models. Observational constraints on the FIR dust opacity and depletions at metallicities lower than 20% solar will be needed to resolve this tension.

Keywords: interstellar medium; interstellar dust processes; galaxy chemical evolution; galaxy abundances; interstellar abundances; damped lyman-alpha systems
No Signature of the Birth Environment of Exoplanets from Their Host Stars' Mahalanobis Phase Space

The architectures of extrasolar planetary systems often deviate considerably from the "standard" model for planet formation, which is largely based on our own solar system. In particular, gas giants on close orbits are not predicted by planet formation theory and so some processes are thought to move the planets closer to their host stars. Recent research has suggested that hot-Jupiter host stars display a different phase space compared to stars that do not host hot Jupiters. This has been attributed to these stars forming in star-forming regions of high stellar density, where dynamical interactions with passing stars have perturbed the planets. We test this hypothesis by quantifying the phase space of planet-hosting stars in dynamical N-body simulations of star-forming regions. We find that stars that retain their planets have a higher phase space than nonhosts, regardless of their initial physical density. This is because an imprint of the kinematic substructure from the regions birth is retained, as these stars have experienced fewer and less disruptive encounters than stars whose planets have been liberated and become free-floating. However, host stars whose planets remain bound but have had their orbits significantly altered by dynamical encounters are also primarily found in high phase space regimes. We therefore corroborate other research in this area that has suggested the high phase space of hot-Jupiter host stars is not caused by dynamical encounters or stellar clustering, but rather reflects an age bias in that these stars are (kinematically) younger than other exoplanet host stars.

Keywords: star forming regions; exoplanet migration; stellar dynamics; n-body simulations
Stratified and Vertically Shearing Streaming Instabilities in Protoplanetary Disks

Under the right conditions, the streaming instability between imperfectly coupled dust and gas is a powerful mechanism for planetesimal formation as it can concentrate dust grains to the point of gravitational collapse. In its simplest form, the streaming instability can be captured by analyzing the linear stability of unstratified disk models, which represent the midplane of protoplanetary disks. We extend such studies by carrying out vertically global linear stability analyses of dust layers in protoplanetary disks. We find that the dominant form of instability in stratified dust layers is the one driven by the vertical gradient in the rotation velocity of the dust-gas mixture, but also requires partial dust-gas coupling. These vertically shearing streaming instabilities grow on orbital timescales and occur on radial length scales ∼ 10-3Hg, where Hg is the local pressure scale height. The classic streaming instability, associated with the relative radial drift between dust and gas, occurs on radial length scales ∼ 10-2Hg, but has much smaller growth rates than vertically shearing streaming instabilities. Including gas viscosity is strongly stabilizing and leads to vertically elongated disturbances. We briefly discuss the potential effects of vertically shearing streaming instabilities on planetesimal formation.

Keywords: protoplanetary disks; hydrodynamics; astrophysical fluid dynamics; planet formation; planetesimals
A Simple but Powerful Method to Reduce Background Noise in Celestial Gamma-Ray Images

Reducing background noise is essential for clear data analysis and signal detection. In this study, we introduce a novel denoising algorithm tailored for gamma-ray astronomical data, utilizing local density sampling techniques. The proposed algorithm preferentially amplifies regions of high local density, which are indicative of potential sources, while diminishing the influence of low-density areas. This selective enhancement significantly bolsters the performance of clustering algorithms in pinpointing point sources, effectively minimizing the interference of high-density noise that could be mistaken for genuine sources. We have implemented this algorithm on Fermi Large Area Telescope data, and our results showcase a marked advancement in the clustering algorithm's capacity to discard false sources.

Keywords: astronomy data analysis; astronomy image processing
PHANGS-JWST First Results: A Combined HST and JWST Analysis of the Nuclear Star Cluster in NGC 628

We combine archival Hubble Space Telescope and new James Webb Space Telescope imaging data covering the ultraviolet to mid-infrared regime to morphologically analyze the nuclear star cluster (NSC) of NGC 628, a grand-design spiral galaxy. The cluster is located in a 200 pc × 400 pc cavity lacking both dust and gas. We find roughly constant values for the effective radius (r eff ~ 5 pc) and ellipticity (ϵ ~ 0.05), while the Sérsic index (n) and position angle (PA) drop from n ~ 3 to ~2 and PA ~ 130° to 90°, respectively. In the mid-infrared, r eff ~ 12 pc, ϵ ~ 0.4, and n ~ 1-1.5, with the same PA ~ 90°. The NSC has a stellar mass of ${\mathrm{log}}_{10}\,({M}_{\star }^{\mathrm{nsc}}/{M}_{\odot })=7.06\pm 0.31$ , as derived through B - V, confirmed when using multiwavelength data, and in agreement with the literature value. Fitting the spectral energy distribution (SED), excluding the mid-infrared data, yields a main stellar population age of (8 ± 3) Gyr with a metallicity of Z = 0.012 ± 0.006. There is no indication of any significant star formation over the last few gigayears. Whether gas and dust were dynamically kept out or evacuated from the central cavity remains unclear. The best fit suggests an excess of flux in the mid-infrared bands, with further indications that the center of the mid-infrared structure is displaced with respect to the optical center of the NSC. We discuss five potential scenarios, none of them fully explaining both the observed photometry and structure.

Keywords: disk galaxies; globular star clusters; hubble space telescope; james webb space telescope
Time Delay of Mg II Emission Response for the Luminous Quasar HE 0435-4312: toward Application of the High-accretor Radius-Luminosity Relation in Cosmology

Using six years of spectroscopic monitoring of the luminous quasar HE 0435-4312 (z = 1.2231) with the Southern African Large Telescope, in combination with photometric data (CATALINA, OGLE, SALTICAM, and BMT), we determined a rest-frame time delay of ${296}_{-14}^{+13}$ days between the Mg II broad-line emission and the ionizing continuum using seven different time-delay inference methods. Time-delay artifact peaks and aliases were mitigated using the bootstrap method and prior weighting probability function, as well as by analyzing unevenly sampled mock light curves. The Mg II emission is considerably variable with a fractional variability of ∼5.4%, which is comparable to the continuum variability (∼4.8%). Because of its high luminosity (L3000 = 1046.4 erg s-1), the source is beneficial for a further reduction of the scatter along the Mg II-based radius-luminosity relation and its extended versions, especially when the highly accreting subsample that has an rms scatter of ∼0.2 dex is considered. This opens up the possibility of using the high-accretor Mg II-based radius-luminosity relation for constraining cosmological parameters. With the current sample of 27 reverberation-mapped sources, the best-fit cosmological parameters (Ωm, ΩΛ) = (0.19; 0.62) are consistent with the standard cosmological model within the 1σ confidence level.

Keywords: accretion; galaxy accretion disks; active galactic nuclei; quasars; emission line galaxies; reverberation mapping; galaxy spectroscopy; galaxy photometry
Spatial Variations of Low-mass Negative Ions in Titan's Upper Atmosphere

Observations with Cassini's Electron Spectrometer discovered negative ions in Titan's ionosphere, at altitudes between 1400 and 950 km. Within the broad mass distribution extending up to several thousand amu, two distinct peaks were identified at 25.8-26.0 and 49.0-50.1 amu/q, corresponding to the carbon chain anions CN- and/or ${{\rm{C}}}_{2}{{\rm{H}}}^{-}$ for the first peak and C3N- and/or C4H- for the second peak. In this study we present the spatial distribution of these low-mass negative ions from 28 Titan flybys with favorable observations between 2004 October 26 and 2012 May 22. We report a trend of lower densities on the night side and increased densities up to twice as high on the day side at small solar zenith angles. To further understand this trend, we compare the negative ion densities to the total electron density measured by Cassini's Langmuir Probe. We find the low-mass negative ion density and the electron density to be proportional to each other on the day side but independent of each other on the night side. This indicates photochemical processes and is in agreement with the primary production route for the low-mass negative ions being initiated by dissociative reactions with suprathermal electron populations produced by photoionisation. We also find the ratio of ${\mathrm{CN}}^{-}/{{\rm{C}}}_{2}{{\rm{H}}}^{-}$ to ${{\rm{C}}}_{3}{{\rm{N}}}^{-}/{{\rm{C}}}_{4}{{\rm{H}}}^{-}$ to be highly constrained on the day side, in agreement with this production channel, but notably displaying large variations on the night side.

Keywords: saturnian satellites
NGC 5128 Globular Cluster Candidates Out to 150 kpc: A Comprehensive Catalog from Gaia and Ground-based Data

We present a new catalog of 40,502 globular cluster (GC) candidates in NGC 5128 out to a projected radius of ~150 kpc based on data from the Panoramic Imaging Survey of Centaurus and Sculptor, the Gaia Data Release 2, and the NOAO Source Catalog. Ranking these candidates based on the likelihood that they are true GCs, we find that approximately 1900 belong to our top two ranking categories and should be the highest priority for spectroscopic follow-up for confirmation. Taking into account our new data and a vetting of previous GC catalogs, we estimate a total GC population of 1450 ± 160 GCs. We show that a substantial number of sources previously argued to be low-velocity GCs are instead foreground stars, reducing the inferred GC velocity dispersion. This work showcases the power of Gaia to identify slightly extended sources at the ~4 Mpc distance of NGC 5128, enabling accurate identification of GCs throughout the entire extended halo, not just the inner regions that have been the focus of most previous work. * This paper includes data gathered with the 6.5 m Magellan Telescope at Las Campanas Observatory, Chile.

Keywords: globular star clusters; optical identification; galaxy evolution
Cosmic-Ray Acceleration in Radio-jet Shear Flows: Scattering Inside and Outside the Jet

A steady-state, analytical model of energetic particle acceleration in radio-jet shear flows due to cosmic-ray viscosity is explored, including particle scattering both into and out of the shear flow acceleration region. This involves solving a mixed Dirichlet-Von Neumann boundary value problem at the edge of the jet. The spectrum of the accelerated particles is harder than the free-escape case from the edge of the jet. The flow velocity u = u(r) ez is along the axis of jet (the z-axis). u is independent of distance z along the jet axis, and u(r) is a monotonically decreasing function of cylindrical radius r from the jet axis. The scattering time $\tau {(r,p)={\tau }_{0}(p/{p}_{0})}^{\alpha }$ where p is the particle momentum in the fluid frame in the shear flow region 0 < r < r2, and $\tau {(r,p)={\tau }_{0}(p/{p}_{0})}^{\alpha }{(r/{r}_{2})}^{s}$ outside the jet (r > r2). Green's functions are obtained for monoenergetic injection of particles with momentum p = p0 at radius r = r1 (0 < r1 < r2). The Green's function and Green's formula are used to determine solutions for a general spectrum of particles at $r=\infty $ . Solutions are obtained corresponding to a monoenergetic spectrum at infinity. We discuss the implications of these results for the acceleration of ultra-high-energy cosmic-rays in active galactic nucleus jet sources. Leaky box models of particle acceleration in shear flows, including synchrotron losses and particle escape, are used to describe the momentum spectrum of accelerated particles. The use of the relativistic telegrapher transport equation model is discussed.

Keywords: cosmic rays; ultra-high-energy cosmic radiation; radio jets; relativistic jets
Discovery of an X-Ray Photoionized Optical Nebula and a Radio Nebula Associated with the ULX NGC 4861 X-1

We have conducted long-slit spectroscopic observations and analyzed archival radio data for the ultraluminous X-ray source (ULX) NGC 4861 X-1. Our spectral line analysis unveils NGC 4861 X-1 as the fourth ULX situated within an X-ray photoionized nebula, following three previous findings made approximately two decades ago. Remarkably, we discover NGC 4861 X-1 also possesses a radio nebula emitting optically thin synchrotron radiation, which contradicts its X-ray photoionization and raises doubts about the four ULXs being a mere coincidence. Instead of gradually accumulating from different bands bit by bit, our multiband discovery is made all at once. Moreover, we tentatively perceive a faint continuum spectrum of the optical nebula. Further observations are needed to ascertain its radio structures and verify the optical continuum.

Keywords: ultraluminous x-ray sources; radio jets; emission nebulae; x-ray binary stars
Accurate and Efficient Photoeccentric Transit Modeling

A planet's orbital eccentricity is fundamental to understanding the present dynamical state of a system and is a relic of its formation history. There is high scientific value in measuring the eccentricities of Kepler and Transiting Exoplanet Survey Satellite (TESS) planets given the sheer size of these samples and the diversity of their planetary systems. However, Kepler and TESS light curves typically only permit robust determinations of the planet-to-star radius ratio r, orbital period P, and transit midpoint t 0. Three other orbital properties, including the impact parameter b, eccentricity e, and argument of periastron ω, are more challenging to measure because they are all encoded in the light curve through subtle effects on a single observable-the transit duration T 14. In Gilbert et al., we showed that a five-parameter transit description {P, t 0, r, b, T 14} naturally yields unbiased measurements of r and b. Here, we build upon our previous work and introduce an accurate and efficient prescription to measure e and ω. We validate this approach through a suite of injection-and-recovery experiments. Our method agrees with previous approaches that use a seven-parameter transit description {P, t 0, r, b, ρ ⋆, e, ω}, which explicitly fits the eccentricity vector and mean stellar density. The five-parameter method is simpler than the seven-parameter method and is "future-proof" in that posterior samples can be quickly reweighted (via importance sampling) to accommodate updated priors and updated stellar properties. This method thus circumvents the need for an expensive reanalysis of the raw photometry, offering a streamlined path toward large-scale population analyses of the eccentricity from transit surveys.

Keywords: exoplanets; transit photometry; bayesian statistics; eccentricity; light curves; astronomy data modeling
Optical Spectrum of the Adamantane Radical Cation

Known for their stable structural and thermal properties, diamondoids and particularly their radical cations are viable candidates as carriers for diffuse interstellar bands. While previous research has mainly focused on neutral diamondoids and their derivatives, little is known about their radical cations, which may form in interstellar environments by ionizing radiation. We report the first experimental optical spectrum of the simplest diamondoid cation, the adamantane radical cation ( ${{\rm{C}}}_{10}{{{\rm{H}}}_{16}}^{+}$ ), obtained via electronic photodissociation spectroscopy of cryogenic ions in the 310-1000 nm range. The main fragmentation channels are H loss at low energies and C3H7 loss at higher energies. The optical spectrum reveals a broad band spanning the range of 420-850 nm, assigned to the D2(2E) ← D0(2A1) transition using time-dependent density functional theory calculations. Despite a vibrational temperature below 20 K, we observe no vibrational structure because of lifetime broadening and/or Franck-Condon congestion. A second band system originating at 345 nm that shows vibrational progressions is attributed to the overlapping D5(2A1)/D6(2E) ← D0(2A1) transitions split by the Jahn-Teller effect. The lifetime deduced from the widths of these vibronic bands is ∼30 fs. Comparison of the spectrum with known diffuse interstellar bands suggests that ${{\rm{C}}}_{10}{{{\rm{H}}}_{16}}^{+}$ is not likely to be a carrier. However, the strong absorption features in the UV to near-IR show promise in the investigation of higher-order diamondoids as potential candidates.

Keywords: astrochemistry; laboratory astrophysics; interstellar medium; molecular spectroscopy; diffuse interstellar bands; electron impact ionization; interstellar molecules
The Dusty Red Supergiant Progenitor and the Local Environment of the Type II SN 2023ixf in M101

As one of the closest supernovae (SNe) in the last decade, SN 2023ixf is an unprecedented target to investigate the progenitor star that exploded. However, there is still significant uncertainty in the reported progenitor properties. In this work, we present a detailed study of SN 2023ixf's progenitor with two independent analyses. We first modeled its spectral energy distribution (SED) based on Hubble Space Telescope optical, Spitzer mid-infrared (IR), and ground-based near-IR data. We find that stellar pulsation and circumstellar extinction have great impacts on SED fitting, and the result suggests a relatively massive red supergiant surrounded by C-rich dust with an initial mass of 16.2-17.4 M ⊙. The corresponding rate of mass loss occurring at least 3 yr before the SN explosion is about 2 × 10-4 M ⊙ yr-1. We also derived the star formation history of the SN environment based on resolved stellar populations, and the most recent star-forming epoch corresponds to a progenitor initial mass of 17-19 M ⊙, in agreement with that from our SED fitting. Therefore, we conclude that the progenitor of SN 2023ixf is close to the high-mass end for Type II SN progenitors.

Keywords: type ii supernovae; circumstellar dust