- ID:
- ivo://CDS.VizieR/J/A+A/553/A81
- Title:
- Refraction of corundum, spinel, {alpha}-quartz
- Short Name:
- J/A+A/553/A81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Many cosmic dust species, among them refractory oxides, form at temperatures higher than 300K. Nevertheless, most astrophysical studies are based on the room-temperature optical constants of solids, such as corundum and spinel. A more realistic approach is needed for these materials, especially in the context of modeling late-type stars. We aimed at deriving sets of optical constants of selected, astrophysically relevant oxide dust species with high melting points. A high-temperature, high-pressure cell and a Fourier-transform spectrometer were used to measure reflectance spectra of polished samples. For corundum ({alpha}-Al_2_O_3_), spinel (MgAl_2_O_4_), and {alpha}-quartz (SiO_2_), temperature-dependent optical constants were measured from 300K up to more than 900K. Small particle spectra were also calculated from these data.
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- ID:
- ivo://CDS.VizieR/J/A+A/483/661
- Title:
- Refractive index for silicon carbide (SiC)
- Short Name:
- J/A+A/483/661
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The SiC optical constants are fundamental inputs for radiative transfer (RT) models of astrophysical dust environments. However, previously published values contain errors and do not adequately represent the bulk physical properties of the cubic ({beta}) SiC polytype usually found around carbon stars. We provide new, uncompromised optical constants for {beta}- and {alpha}-SiC derived from single-crystal reflectance spectra and investigate quantitatively (i) whether there is any difference between {alpha}- and {beta}-SiC that can be seen in infrared (IR) spectra and optical functions and (ii) whether weak features from {lambda}~12.5-13.0{mu}m need to be fitted. We measured mid- and far-IR reflectance spectra for two samples of 3C ({beta}-)SiC and four samples of 6H ({alpha}-)SiC. For the latter group, we acquired polarized data (E{perpendicular.to}c, E{parallel.to}c orientations). We calculated the real and imaginary parts of the complex refractive index (n({lambda})+ik({lambda})) and the ideal absorption coefficients via classical dispersion fits to our reflectance spectra.
- ID:
- ivo://CDS.VizieR/J/A+A/540/A2
- Title:
- Refractive index of hydrocarbon solids
- Short Name:
- J/A+A/540/A2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The properties of hydrogenated amorphous carbon (a-C:H) dust are known to evolve in response to the local conditions. We present an adaptable model for the determination of the optical properties of low-temperature, interstellar a-C:H grains that is based on the fundamental physics of their composition.
- ID:
- ivo://CDS.VizieR/J/ApJS/210/21
- Title:
- Refractive indices of grain materials
- Short Name:
- J/ApJS/210/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As small solid grains grow into larger ones in protoplanetary nebulae, or in the cloudy atmospheres of exoplanets, they generally form porous aggregates rather than solid spheres. A number of previous studies have used highly sophisticated schemes to calculate opacity models for irregular, porous particles with sizes much smaller than a wavelength. However, mere growth itself can affect the opacity of the medium in far more significant ways than the detailed compositional and/or structural differences between grain constituents once aggregate particle sizes exceed the relevant wavelengths. This physics is not new; our goal here is to provide a model that provides physical insight and is simple to use in the increasing number of protoplanetary nebula evolution and exoplanet atmosphere models appearing in recent years, yet quantitatively captures the main radiative properties of mixtures of particles of arbitrary size, porosity, and composition. The model is a simple combination of effective medium theory with small-particle closed-form expressions, combined with suitably chosen transitions to geometric optics behavior. Calculations of wavelength-dependent emission and Rosseland mean opacity are shown and compared with Mie theory. The model's fidelity is very good in all comparisons we have made except in cases involving pure metal particles or monochromatic opacities for solid particles with sizes comparable to the wavelength.
- ID:
- ivo://CDS.VizieR/J/A+A/417/827
- Title:
- Relativistic corrections to Sunyaev-Zeldovich effect
- Short Name:
- J/A+A/417/827
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- These tables contain numerical values for the distortion of the spectral intensity {Delta}I/y defined by the equation {Delta}I/y = 1/y * X^3^/(e^X^-1) * {Delta}n(X)/n0(X) = X^3^/(e^X^-1)*F({theta}_e_,X) The spectral intensity is the function of two variables X and {theta}_e_. Here X={omega}/k_B_*T_0_, {omega} being the photon angular frequency and k_B_*T_0_ being the thermal energy of CMB photons, and {theta}_e_=k_B_*Te/m_e_*c^2^, k_B_*Te being the thermal energy of the electrons and m_e_*c^2^ being the electron rest energy (T_0_ is the temperature of the cosmic microwave background radiation). In these tables, the range for X is taken as 0<X<20 and the range for {theta}_e_ is taken as 0.002<{theta}_e_<0.100.
- ID:
- ivo://CDS.VizieR/J/ApJS/197/20
- Title:
- Relativistic EOS for core-collapse SN simulations
- Short Name:
- J/ApJS/197/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We construct the equation of state (EOS) of dense matter covering a wide range of temperature, proton fraction, and density for the use of core-collapse supernova simulations. The study is based on the relativistic mean-field (RMF) theory, which can provide an excellent description of nuclear matter and finite nuclei. The Thomas-Fermi approximation in combination with assumed nucleon distribution functions and a free energy minimization is adopted to describe the non-uniform matter, which is composed of a lattice of heavy nuclei. We treat the uniform matter and non-uniform matter consistently using the same RMF theory. We present two sets of EOS tables, namely EOS2 and EOS3. EOS2 is an update of our earlier work published in 1998 (EOS1; see 1998NuPhA.637..435S and 1998PThPh.100.1013S), where only the nucleon degree of freedom is taken into account. EOS3 includes additional contributions from {Lambda} hyperons. The effect of {Lambda} hyperons on the EOS is negligible in the low-temperature and low-density region, whereas it tends to soften the EOS at high density. In comparison with EOS1, EOS2 and EOS3 have an improved design of ranges and grids, which covers the temperature range T=0.1-10^2.6^MeV with the logarithmic grid spacing {delta}log_10_(T/[MeV])=0.04 (92 points including T=0), the proton fraction range Y_p_=0-0.65 with the linear grid spacing {Delta}Y_p_=0.01 (66 points), and the density range {rho}_B_=10^5.1^-10^16^g/cm^3^ with the logarithmic grid spacing {Delta}log_10_({rho}_B_/[g/cm^3^])=0.1 (110 points).
- ID:
- ivo://CDS.VizieR/J/AJ/156/33
- Title:
- Resonance sticking in the population of scattering TNOs
- Short Name:
- J/AJ/156/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A substantial fraction of our solar system's trans-Neptunian objects (TNOs) are in mean-motion resonance with Neptune. Many of these objects were likely caught into resonances by planetary migration-either smooth or stochastic- approximately 4 Gyr ago. Some, however, gravitationally scattered off of Neptune and became transiently stuck in more recent events. Here we use numerical simulations to predict the number of transiently stuck objects, captured from the current actively scattering population, that occupy 111 resonances at semimajor axes a=30-100 au. Our source population is an observationally constrained model of the currently scattering TNOs. We predict that, integrated across all resonances at these distances, the current transient-sticking population comprises 40% of the total transiently stuck+scattering TNOs, suggesting that these objects should be treated as a single population. We compute the relative distribution of transiently stuck objects across all p:q resonances with 1/6=<q/p=<1, p<40, and q<20, providing predictions for the population of transient objects with H_r_<8.66 in each resonance. We find that the relative populations are approximately proportional to each resonance's libration period and confirm that the importance of transient sticking increases with semimajor axis in the studied range. We calculate the expected distribution of libration amplitudes for stuck objects and demonstrate that observational constraints indicate that both the total number and the amplitude distribution of 5:2 resonant TNOs are inconsistent with a population dominated by transient sticking from the current scattering disk. The 5:2 resonance hence poses a challenge for leading theories of Kuiper Belt sculpting.
- ID:
- ivo://CDS.VizieR/J/A+A/575/A18
- Title:
- Revising the ages of planet-hosting stars
- Short Name:
- J/A+A/575/A18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This article aims to measure the age of stars with planets (SWP) through stellar tracks and isochrones computed with the Padova & Trieste Stellar Evolutionary Code (PARSEC). We developed algorithms based on two different techniques for determining the ages of field stars: isochrone placement and Bayesian estimation. Their application to a synthetic sample of coeval stars shows the intrinsic limits of each method. For instance, the Bayesian computation of the modal age tends to select the extreme age values in the isochrones grid. Therefore, we used the isochrone placement technique to measure the ages of 317 SWP. We found that ~6% of SWP have ages lower than 0.5Gyr. The age distribution peaks in the interval [1.5, 2]Gyr, then it decreases. However, ~7% of the stars are older than 11Gyr. The Sun turns out to be a common star that hosts planets, when considering its evolutionary stage. Our SWP age distribution is less peaked and slightly shifted towards lower ages if compared with ages in the literature and based on the isochrone fit. In particular, there are no ages below 0.5Gyr in the literature.
- ID:
- ivo://CDS.VizieR/J/A+A/590/A9
- Title:
- RGB stars in Galactic GC stellar parameters
- Short Name:
- J/A+A/590/A9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Globular clusters trace the formation and evolution of the Milky Way and surrounding galaxies, and outline their chemical enrichment history. To accomplish these tasks it is important to have large samples of clusters with homogeneous data and analysis to derive kinematics, chemical abundances, ages and locations. We aim to obtain homogeneous metallicities and alpha-element enhancement for 51 Galactic bulge, disc, and halo globular clusters that are among the most distant and/or highly reddened in the Galaxy's globular cluster system. We also provide membership selection based on stellar radial velocities and atmospheric parameters. The implications of our results are discussed. We observed R~2000 spectra in the wavelength interval 456-586nm for over 800 red giant stars in 51 Galactic globular clusters. We applied full spectrum fitting with the code ETOILE together with libraries of observed and synthetic spectra. We compared the mean abundances of all clusters with previous work and with field stars. We used the relation between mean metallicity and horizontal branch morphology defined by all clusters to select outliers for discussion. [Fe/H], [Mg/Fe], and [alpha/Fe] were derived in a consistent way for almost one-third of all Galactic globular clusters. We find our metallicities are comparable to those derived from high-resolution data to within sigma=0.08dex over the interval -2.5<[Fe/H]<0.0. Further, a comparison of previous metallicity scales with ours yields sigma<0.16dex. We also find that the distribution of [Mg/Fe] and [alpha/Fe] with [Fe/H] for the 51 clusters follows the general trend exhibited by field stars. It is the first time that the following clusters are included in a large sample of homogeneous stellar spectroscopic observations and metallicity derivation: BH 176, Djorg 2, Pal 10, NGC 6426, Lynga 7, and Terzan 8. In particular, the first three clusters only had photometric metallicities previously and the available metallicity for NGC 6426 was based only on integrated spectroscopy and photometry. Two other clusters, HP 1 and NGC 6558, are confirmed as candidates for the oldest globular clusters in the Milky Way. Stellar spectroscopy in the visible at R~2000 for a large sample of globular clusters is a robust and efficient way to trace the chemical evolution of the host galaxy and to detect interesting objects for follow-up at higher-resolution and with forthcoming giant telescopes. The technique used here can also be applied to globular cluster systems in nearby galaxies with current instruments and to distant galaxies with the advent of ELTs.
- ID:
- ivo://CDS.VizieR/J/A+A/328/349
- Title:
- Role of Convection in A, F, and G stars
- Short Name:
- J/A+A/328/349
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We discuss the effects of convection on the theoretical uvby colours of A, F, and G stars. The standard mixing-length theory atlas9 models of Kurucz (1993, ATLAS9, SAO, Cambridge, USA), with and without approximate overshooting, are compared to models using the turbulent convection theory proposed by Canuto & Mazzitelli (1991ApJ...370..295C, 1992ApJ...389..724C) and implemented by Kupka (1996, ASPConf. Proc. 108, 73). Comparison with fundamental Teff and log g stars reveals that the Canuto & Mazzitelli models give results that are generally superior to standard mixing-length theory (MLT) without convective overshooting. MLT models with overshooting are found to be clearly discrepant. This is supported by comparisons of non-fundamental stars, with Teff obtained from the Infrared Flux Method and log g from stellar evolutionary models for open cluster stars. The Canuto & Mazzitelli theory gives values of (b-y)0 and c0 that are in best overall agreement with observations. Investigations of the m0 index reveal that all of the treatments of convection presented here give values that are significantly discrepant for models with Teff<6000K. It is unclear as to whether this is due to problems with the treatment of convection, missing opacity, or some other reason. None of the models give totally satisfactory m0 indices for hotter stars, but the Canuto & Mazzitelli models are in closest overall agreement above 7000K. Grids of uvby colours, based on the CM treatment of convection, are presented. These grids represent an improvement over the colours obtained from models using the mixing-length theory. The agreement with fundamental stars enables the colours to be used directly without the need for semi-empirical adjustments that were necessary with the earlier colour grids. For a description of the uvby photometric system, see e.g. <GCPD/04>
