- ID:
- ivo://CDS.VizieR/J/MNRAS/399/699
- Title:
- Parameters of atmospheres of white dwarfs
- Short Name:
- J/MNRAS/399/699
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is possible to reliably identify white dwarfs (WDs) without recourse to spectra, instead using photometric and astrometric measurements to distinguish them from main-sequence stars and quasars. WDs' colours can also be used to infer their intrinsic properties (effective temperature, surface gravity, etc.), but the results obtained must be interpreted with care. The difficulties stem from the existence of a solid angle degeneracy, as revealed by a full exploration of the likelihood, although this can be masked if a simple best-fitting approach is used. Conversely, this degeneracy can be broken if a Bayesian approach is adopted, as it is then possible to utilize the prior information on the surface gravities of WDs implied by spectroscopic fitting. The benefits of such an approach are particularly strong when applied to outliers, such as the candidate halo and ultracool WDs identified by Vidrih et al. A reanalysis of these samples confirms their results for the latter sample, but suggests that most of the halo candidates are thick-disc WDs in the tails of the photometric noise distribution.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/430/223
- Title:
- Parameters of cool companions of sdB stars
- Short Name:
- J/A+A/430/223
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the analysis of a high-resolution, high-quality sample of optical spectra for 76 subdwarf B (sdB) stars from the ESO Supernova Ia Progenitor Survey (SPY, Napiwotzki et al., 2001A&A...367..973N). Effective temperature, surface gravity, and photospheric helium abundance are determined simultaneously by fitting the profiles of hydrogen and helium lines using synthetic spectra calculated from LTE and NLTE model atmospheres. We perform a detailed comparison of our measurements with theoretical calculations, both for single star evolution and for binary population synthesis models of close binary evolution.
- ID:
- ivo://CDS.VizieR/J/A+A/439/1137
- Title:
- PHOENIX model chromospheres of M dwarfs
- Short Name:
- J/A+A/439/1137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an extensive identification catalog of chromospheric emission lines in the optical range. The data were obtained with ESO's Kueyen telescope equipped with the UVES spectrograph from March, 13th to 16th in 2002. The instrument was operated in dichroic mode (spectral coverage from 3030 to 3880 and from 4580 to 6680{AA}). The data for the stars Prox Cen, UV Ceti and LHS 292 were obtained with the same instrument in winter 2000/2001 with a monochroic setup providing only the blue part of the spectrum. We tabulated measured wavelength, equivalent width (EW) and FWHM for every line and star and also provide the rest wavelength from the Moore catalog which was used for identification (Moore 1972). Few lines were identified with the NIST database. The spectra were all corrected for radial velocity besides Kelu-1, DENIS-P J1058.7-1548 and 2MASSI J1315309-264951. DENIS-P J1058.7-1548 has no detected lines, and therefore no data in the table.
- ID:
- ivo://CDS.VizieR/J/A+A/654/A172
- Title:
- Photoionization of the CH radical
- Short Name:
- J/A+A/654/A172
- Date:
- 07 Mar 2022 07:12:57
- Publisher:
- CDS
- Description:
- The primary motivation of this paper is to provide accurate data for the photoionization of the CH radical, including absolute total photoionization cross section, partial cross sections and photo electron angular distribution. In addition,the near threshold features in the photoionization curve (which are absent in previous studies) are produced with high precision. A multichannel wavefunction based on R-matrix approach, which uses the configuration interaction (CI) method to describe electronic correlation, is carried out in the present calculations. A set of B-spline orbitals is employed to represent the accurate continuum. The distinctive feature of the present calculations allows us to generate a more accurate description of the bound and continuum states than those employed before. Total photoionization cross sections from the ground state of CH radicals and partial cross sections corresponding to 1{pi}, 3{sigma}, and 2{sigma} states of CH+ ions are presented for photon energies ranging from threshold to 80eV. Extensive resonance structures, which are absent in previous studies, near the ionization threshold, are observed for the first time. The cross-section dataset obtained from the present calculations is expected to be sufficiently accurate and comprehensive for most current modeling applications involving the photon and CH radicals scattering system.
- ID:
- ivo://CDS.VizieR/J/A+A/497/497
- Title:
- Physical parameters from JHK flux
- Short Name:
- J/A+A/497/497
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The effective temperature scale of FGK stars, especially at the lowest metallicities remains a major problem in the chemical abundance analysis of metal-poor stars. We present a new implementation of the infrared flux method (IRFM) using the 2MASS catalogue.
- ID:
- ivo://CDS.VizieR/J/A+A/504/259
- Title:
- Polarization models for planets
- Short Name:
- J/A+A/504/259
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Reflected light from giant planets is polarized by scattering, offering the possibility of investigating atmospheric properties with polarimetry. Polarimetric measurements are available for the atmospheres of solar system planets, and instruments are being developed to detect and study the polarimetric properties of extrasolar planets. We investigate the intensity and polarization of reflected light from planets in a systematic way with a grid of model calculations. Comparison of the results with existing and future observations can be used to constrain parameters of planetary atmospheres.
- ID:
- ivo://CDS.VizieR/VI/109
- Title:
- Population Synthesis Models at very low metallicities
- Short Name:
- VI/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using new sets of stellar evolution models at very low metallicities (Z=10^-7^; 10^-5^) and previously published grids we examine spectral properties of the ionising continua, the Lyman-break, and the Ly{alpha} and He1640 recombination lines in starbursts. The metallicity dependence of these properties, especially the transition from primordial galaxies (Population III) to currently observed metallicities, is examined for various IMFs and star formation histories.
- ID:
- ivo://CDS.VizieR/J/A+A/616/A39
- Title:
- Power-2 limb-darkening law from STAGGER-grid
- Short Name:
- J/A+A/616/A39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Inaccurate limb-darkening models can be a significant source of error in the analysis of the light curves for transiting exoplanet and eclipsing binary star systems, particularly for high-precision light curves at optical wavelengths. The power-2 limb-darkening law, I_{lambda}_({mu})=1-c(1-{mu}^{alpha}^), has recently been proposed as a good compromise between complexity and precision in the treatment of limb-darkening. My aim is to develop a practical implementation of the power-2 limb-darkening law and to quantify the accuracy of this implementation. I have used synthetic spectra based on the 3D stellar atmosphere models from the Stagger-grid to compute the limb- darkening for several passbands (UBVRI, CHEOPS, TESS, Kepler, etc.). The parameters of the power-2 limb-darkening laws are optimized using a least-squares fit to a simulated light curve computed directly from the tabulated I_{lambda}_({mu}) values. I use the transformed parameters h_1_=1-c(1-2^(-{alpha})^) and h_2_=c2^(-{alpha}^) to directly compare these optimized limb-darkening parameters to the limb darkening measured from Kepler light curves of 16 transiting exoplanet systems. The posterior probability distributions (PPDs) of the transformed parameters h_1_ and h_2_ resulting from the light curve analysis are found to be much less strongly correlated than the PPDs for c and {alpha}. The agreement between the computed and observed values of (h_1_, h_2_) is generally very good but there are significant differences between the observed and computed values for Kepler-17, the only star in the sample that shows significant variability between the eclipses due to magnetic activity (star spots). The tabulation of h_1_ and h_2_ provided here can be used to accurately model the light curves of transiting exoplanets. I also provide estimates of the priors that should be applied to transformed parameters h_1_ and h_2_ based on my analysis of the Kepler light curves of 16 stars transiting exoplanets.
- ID:
- ivo://CDS.VizieR/J/A+A/588/A32
- Title:
- Precipitable water vapour at Cerro Armazones
- Short Name:
- J/A+A/588/A32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We studied the precipitable water vapour (PWV) content near Cerro Armazones and discuss the potential use of our technique of modelling the telluric absorption lines for the investigation of other molecular layers. The site is designated for the European Extremely Large Telescope (E-ELT) and the nearby planned site for the Cherenkov Telescope Array (CTA). Spectroscopic data from the Bochum Echelle Spectroscopic Observer (BESO) instrument were investigated by using line-by-line radiative transfer model (LBLRTM) radiative transfer models for the Earths atmosphere with the telluric absorption correction tool molecfit. All observations from the archive in the period from December 2008 to the end of 2014 were investigated. The dataset completely covers the El Nino event registered in the period 2009-2010. Models of the 3D Global Data Assimilation System (GDAS) were used for further comparison. Moreover, for those days with coincidence of data from a similar study with VLT/X-shooter and microwave radiometer LHATPRO data at Cerro Paranal, a direct comparison is presented. This analysis shows that the site has systematically lower PWV values, even after accounting for the decrease in PWV expected from the higher altitude of the site with respect to Cerro Paranal, using the average atmosphere found with radiosondes. We found that GDAS data are not a suitable method for predicting of local atmospheric conditions - they usually systematically overestimate the PWV values. Due to the large sample, we were furthermore able to characterize the site with respect to symmetry across the sky and variation with the years and within the seasons. This kind of technique of studying the atmospheric conditions is shown to be a promising step into a possible monitoring equipment for CTA.
- ID:
- ivo://CDS.VizieR/J/A+A/363/1051
- Title:
- Properties of He-rich stars. III.
- Short Name:
- J/A+A/363/1051
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of helium rich atmospheres in the interval He/H 0.1-1.0 as derived from fully consistent model computations for effective temperature (from 15000K up to 32000K) and surface gravity (log(g)=3.5 and 4.0).
