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- ID:
- ivo://CDS.VizieR/J/A+A/281/817
- Title:
- Model atmospheres for Vega
- Short Name:
- J/A+A/281/817
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/ApJ/813/47
- Title:
- Model atmospheres of irradiated exoplanets
- Short Name:
- J/ApJ/813/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Many parameters constraining the spectral appearance of exoplanets are still poorly understood. We therefore study the properties of irradiated exoplanet atmospheres over a wide parameter range including metallicity, C/O ratio and host spectral type. We calculate a grid of 1-d radiative-convective atmospheres and emission spectra. We perform the calculations with our new Pressure-Temperature Iterator and Spectral Emission Calculator for Planetary Atmospheres (PETIT) code, assuming chemical equilibrium. The atmospheric structures and spectra are made available online. We find that atmospheres of planets with C/O ratios ~1 and Teff>~1500K can exhibit inversions due to heating by the alkalis because the main coolants CH_4_, H_2_O and HCN are depleted. Therefore, temperature inversions possibly occur without the presence of additional absorbers like TiO and VO. At low temperatures we find that the pressure level of the photosphere strongly influences whether the atmospheric opacity is dominated by either water (for low C/O) or methane (for high C/O), or both (regardless of the C/O). For hot, carbon-rich objects this pressure level governs whether the atmosphere is dominated by methane or HCN. Further we find that host stars of late spectral type lead to planetary atmospheres which have shallower, more isothermal temperature profiles. In agreement with prior work we find that for planets with Teff<1750K the transition between water or methane dominated spectra occurs at C/O~0.7, instead of ~1, because condensation preferentially removes oxygen.
- ID:
- ivo://CDS.VizieR/J/AcA/41/73
- Title:
- Model atmospheres of X-ray bursting neutron stars
- Short Name:
- J/AcA/41/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- X-ray burst sources represent a class of accreting neutron stars in close binary systems which do not exhibit any traces of the magnetic field. We present the first detailed tables which show the structure of plane--parallel hydrogen-helium atmospheres of bursting neutron stars. Hydrogen-helium models were computed with precise angle-dependent radiative transfer under constrains of radiative and hydrostatic equilibrium. Compton scattering opacity included both the Klein-Nishina corrections and the effects of relativistic Maxwellian thermal motion of scattering electrons. Compton redistribution function allows for large energy exchange between X-ray photons and scattering electrons.
- ID:
- ivo://CDS.VizieR/J/A+A/550/A103
- Title:
- Model 1D (LHD) and 3D (CO5BOLD) spectra
- Short Name:
- J/A+A/550/A103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To derive space velocities of stars along the line of sight from wavelength shifts in stellar spectra requires accounting for a number of second-order effects. For most stars, gravitational redshifts, convective blueshifts, and transverse stellar motion are the dominant contributors. We provide theoretical corrections for the net velocity shifts due to convection expected for the measurements from the Gaia Radial Velocity Spectrometer (RVS). We used a set of three-dimensional time-dependent simulations of stellar surface convection computed with CO5BOLD to calculate spectra of late-type stars in the Gaia RVS range and to infer the net velocity offset that convective motions will induce in radial velocities derived by cross-correlation. The net velocity shifts derived by cross-correlation depend both on the wavelength range and spectral resolution of the observations. Convective shifts for Gaia RVS observations are less than 0.1km/s for late-K-type stars, and they increase with stellar mass, reaching about 0.3km/s or more for early F-type dwarfs. This tendency is the result of an increase with effective temperature in both temperature and velocity fluctuations in the line-forming region. Our simulations also indicate that the net RVS convective shifts can be positive (i.e. redshifts) in some cases. Overall, the blueshifts weaken slightly with increasing surface gravity, and are enhanced at low metallicity. Gravitational redshifts amount up to 0.7km/s and dominate convective blueshifts for dwarfs, but become much weaker for giants.
- ID:
- ivo://CDS.VizieR/J/ApJS/207/7
- Title:
- Modeling Galactic extinction with dust and PAH
- Short Name:
- J/ApJS/207/7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the remarkable apparent variety of galactic extinction curves by modeling extinction profiles with core-mantle grains and a collection of single polycyclic aromatic hydrocarbons. Our aim is to translate a synthetic description of dust into physically well-grounded building blocks through the analysis of a statistically relevant sample of different extinction curves. All different flavors of observed extinction curves, ranging from the average galactic extinction curve to virtually "bumpless" profiles, can be described by the present model. We prove that a mixture of a relatively small number (54 species in 4 charge states each) of polycyclic aromatic hydrocarbons can reproduce the features of the extinction curve in the ultraviolet, dismissing an old objection to the contribution of polycyclic aromatic hydrocarbons to the interstellar extinction curve. Despite the large number of free parameters (at most the 54x4 column densities of each species in each ionization state included in the molecular ensemble plus the 9 parameters defining the physical properties of classical particles), we can strongly constrain some physically relevant properties such as the total number of C atoms in all species and the mean charge of the mixture. Such properties are found to be largely independent of the adopted dust model whose variation provides effects that are orthogonal to those brought about by the molecular component. Finally, the fitting procedure, together with some physical sense, suggests (but does not require) the presence of an additional component of chemically different very small carbonaceous grains.
- ID:
- ivo://CDS.VizieR/J/A+A/624/A108
- Title:
- Modeling interstellar sulfur depletion
- Short Name:
- J/A+A/624/A108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The elemental depletion of interstellar sulfur from the gas phase has been a recurring challenge for astrochemical models. Observations show that sulfur remains relatively non-depleted with respect to its cosmic value throughout the diffuse and translucent stages of an interstellar molecular cloud, but its atomic and molecular gas-phase constituents cannot account for this cosmic value toward lines of sight containing higher-density environments. We have attempted to address this issue by modeling the evolution of an interstellar cloud from its pristine state as a diffuse atomic cloud to a molecular environment of much higher density, using a gas-grain astrochemical code and an enhanced sulfur reaction network. A common gas-grain astrochemical reaction network has been systematically updated and greatly extended based on previous literature and previous sulfur models, with a focus on the grain chemistry and processes. A simple astrochemical model was used to benchmark the resulting network updates, and the results of the model were compared to typical astronomical observations sourced from the literature. Our new gas-grain astrochemical model is able to reproduce the elemental depletion of sulfur, whereby sulfur can be depleted from the gas-phase by two orders of magnitude, and that this process may occur under dark cloud conditions if the cloud has a chemical age of at least 106 years. The resulting mix of sulfur-bearing species on the grain ranges across all the most common chemical elements (H/C/N/O), not dissimilar to the molecules observed in cometary environments. Notably, this mixture is not dominated simply by H2S, unlike all other current astrochemical models. Despite our relatively simple physical model, most of the known gas-phase S-bearing molecular abundances are accurately reproduced under dense conditions, however they are not expected to be the primary molecular sinks of sulfur. Our model predicts that most of the "missing" sulfur is in the form of organo-sulfur species that are trapped on grains.
- ID:
- ivo://CDS.VizieR/J/ApJ/619/755
- Title:
- Modeling starburst SEDs
- Short Name:
- J/ApJ/619/755
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we combine the stellar spectral synthesis code STARBURST99, the nebular modeling code MAPPINGS IIIq, a one-dimensional dynamical evolution model of H II regions around massive clusters of young stars, and a simplified model of synchrotron emissivity to produce purely theoretical self-consistent synthetic spectral energy distributions (SEDs) for (solar metallicity) starbursts lasting ~10^8^yr. These SEDs extend from the Lyman limit to beyond 21cm. We present detailed SED fits to Arp 220 and NGC 6240, and we give the predicted colors for starburst galaxies derived from our models for the IRAS and the Spitzer Space Telescope MIPS and IRAC instruments. Our models reproduce the spread in observed colors of starburst galaxies. Finally, we present absolute calibrations to convert observed fluxes into star formation rates in the UV (GALEX), at optical wavelengths (H), and in the IR (IRAS or Spitzer).
- ID:
- ivo://CDS.VizieR/J/ApJ/732/65
- Title:
- Modeling the local velocity field with SNIa
- Short Name:
- J/ApJ/732/65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We apply statistically rigorous methods of nonparametric risk estimation to the problem of inferring the local peculiar velocity field from nearby Type Ia supernovae (SNIa). We use two nonparametric methods -weighted least squares (WLS) and coefficient unbiased (CU)- both of which employ spherical harmonics to model the field and use the estimated risk to determine at which multipole to truncate the series. We show that if the data are not drawn from a uniform distribution or if there is power beyond the maximum multipole in the regression, a bias is introduced on the coefficients using WLS. CU estimates the coefficients without this bias by including the sampling density making the coefficients more accurate but not necessarily modeling the velocity field more accurately. After applying nonparametric risk estimation to SNIa data, we find that there are not enough data at this time to measure power beyond the dipole. The WLS Local Group bulk flow is moving at 538+/-86km/s toward (l,b)=(258+/-10{deg},36+/-11{deg}) and the CU bulk flow is moving at 446+/-101km/s toward (l,b)=(273+/-11{deg},46+/-8{deg}). We find that the magnitude and direction of these measurements are in agreement with each other and previous results in the literature.
- ID:
- ivo://CDS.VizieR/J/AJ/130/55
- Title:
- Modelled Lick indices for galaxies
- Short Name:
- J/AJ/130/55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Central velocity dispersions and eight line-strength Lick indices have been determined from 1.3{AA} resolution long-slit spectra of 16 elliptical galaxies in Hickson compact groups. These data were used to determine galaxy properties (ages, metallicities, and {alpha}-element enhancements) and allowed a comparison with the parameters determined for a sample of galaxies in lower density environments studied by Gonzalez (1993, Ph.D. thesis, Univ. California, Santa Cruz). The stellar population parameters were derived by comparison to single stellar population models of Thomas et al. (Cat. <J/ApJ/621/673>) and to a new set of simple stellar population models for the indices Mg_2_, Fe5270, and Fe5335 based on synthetic spectra. These models, based on an updated version of the fitting functions presented in Barbuy et al. (Cat. <J/A+A/404/661>), are fully described here.
