Castelli and Kurucz Atlas

Access the CASTELLI-KURUCZ ATLAS

The Castelli AND Kurucz 2004 Stellar Atmosphere Models

The atlas contains about 4300 stellar atmosphere models for a wide range of metal abundances, effective temperatures, and gravities. These LTE models with no convective overshooting computed by Fiorella Castelli, have improved opacities and abundances upon previously used by Kurucz (1990). The main improvements from previous opacity distribution functions listed in Castelli & Kurucz 2003 (IAU Symposium 210, Modelling of Stellar Atmospheres, Uppsala, Sweden, eds. N.E. Piskunov, W.W. Weiss. and D.F. Gray, 2003, ASP-S210) are:

1. The replacement of the solar abundances from Andres & Grevesse (1989, GCA,53,197; AG89) with those from Grevesse & Sauval (1998 Space. Sci. Rev.,85,161; GS98). See Table 2 of Castelli & Kurucz 2004.
2. The replacement of the TiO lines provided by Kurucz (1993) with the TiO lines from Schwenke (1998, Faraday Discuss., 109,321). Addition of the H₂ O lines (Partridge & Schwenke 1997, J. Chem. Phys., 106, 4618) and of the HI-HI and HI-H+ quasi-molecular absorptions near 1600 Å and 1400 Å (Allard et al. 1998, A&A, 335,1124), as distributed by Kurucz 1999a, 1999b. Extended molecular list and corrected previous bugs in Kurucz line lists.

These models are computed with the same wavelength resolution and a smaller temperature resolution than the Kurucz 1993 models. All of the models have the same number of plane-parallel layers from \(log(\tau_{Ross})=-6.875\) to +2.00, in steps of \(\Delta[log(\tau_{Ross})] = 0.125\) computed assuming pure mixing-length convection (no overshooting) with 1/Hp=1.25. As before the microturbulent velocity used is \(22\ km \ s^{-1}\).

The ATLAS9 installed in TRDS is from "The Grids of ATLAS9-ODFNEW models and fluxes" from Fiorella Castelli's web page created on January 2007. These grids are also available from Dr. R. Kurucz's website.

The ATLAS9 includes models for abundances [M/H]=0.0, -0.5, -1.0, -1.5, -2.0, -2.5, +0.5, +0.2 and gravity range from log g= 0.0 to +5.0 in steps of +0.5. The range in effective temperature from 3500 K to 50000 K is covered with an uneven grid (see Table 1a). The model spectra cover the ultraviolet (1000 Å) to infrared (10 μm) spectral range with non-uniform wavelength spacing (see Table 1b).

Table 1a: Grid of Temperatures for the Models

Table 1b: Wavelength Coverage for the Models

The TRDS version of the ATLAS9

The atlas is divided into 8 independent subdirectories, according to metal abundance. Within each subdirectory, the stellar atmosphere models are given in FITS table format. Each table consists of 12 different columns, the first contains the wavelength grid and the rest containing the spectrum of a star with the same effective temperature but different gravity, ranging from log g= 0.0 to +5.0. Columns filled with zeros indicate that the model spectrum for that particular metal abundance, effective temperature, and gravity combination is not covered by the atlas.

Within each individual table file, each column is named "gyy", where "yy" corresponds to 10*log g. For example, log g = +0.5 and log g = +4.0 models are located in columns named g05 and g40, respectively. See the appendix for an example of a standard header of a table file.

Physical fluxes of the spectra are given in FLAM surface flux units, i.e. \(ergs\ cm^{-2}\ s^{-1} A^{-1}\). These flux units differ from those in the Castelli & Kurucz tables by a factor of \(3.336 * 10^{-19} * \lambda^{2}/4\pi\), i.e. are converted from \(ergs\ cm^{-2} \ s^{-1}\ Hz^{-1} str^{-1}\) to \(ergs\ cm^{-2}\ s^{-1} {A} ^{-1}\)by multiplying the Castelli & Kurucz values by \(3.336 * 10^{-19} *\lambda^{2}/4\pi\), where \(\lambda\) is in Angstroms. To convert to the observed flux at Earth, multiply by a factor of \((R/D)^2\) where R is the stellar radius, and D is the distance to Earth.

The names of the files located in each metal abundance subdirectory are listed in the README file located in each subdirectory. The range in gravity covered by the models for the different temperatures is also indicated.

Use with Pysynphot or Astropy Synphot

Pysynphot or Astropy Synphot permits the selection of spectra within one of many columns in a single FITS table file using the "pysynphot. Icat ()" function. The syntax is "sp = pysynphot. Icat ('ck04models', t,m,g) where "t" is the effective temperature, "m" is the metal abundance [M/H], and "g" is the log gravity.

Please note that the model spectra in the atlas are in surface flux units. Thus, if the number of counts or the calculated absolute flux is needed, the model spectrum must be renormalized appropriately. One can do this in pysynphot with the "sp.renorm()" function or the "sp.normalize()" function in Astropy Synphot.

A list of solar abundance stars of different spectral types and luminosity classes together with their closest Castelli & Kurucz 2004 model spectrum is presented in Table 2. The physical parameters \(T_{eff}\), and log g, characterizing each of the O stars are taken from Martins, Schaerer, & Hiller's compilation of stellar parameters of Galactic O stars (Martins, Scharer & Hiller 2005, A&A,436,1049). The physical parameters for later stars are taken from Schmidt-Kaler's compilation of physical parameters of stars (Schmidt-Kaler 1982, Landolt-Bornstein VI/2b). For the later, the U-B and B-V colors of the closest model agree with the characteristic color of each star (see Schmidt-Kaler 1982) to better than 0.06 magnitude. For the cool end, K5I, M0I, and M2I stars, the physical parameters are taken from Leusque et al 2006, ApJ 645, 1102.

Table 2: Suggested Models for Specific Stellar Types

Appendix

Below is an example of a standard header for the table files in the CDBS version of Castelli & Kurucz 2004 atlas. In this example, the name of the file is ckp00_8000.fits and contains all the models for a star of metallicity log Z= 0.0 and effective temperature \(T_{eff}\)= 8000 K. Models cover a range of gravities from log g = +1.0 (g10 in the header) to log g = +5.0 (g50 in the header). Models for gravities log g = +0.0 and +0.5 are not available for this particular metallicity and effective temperature combination, and therefore do not appear listed in the header. Their corresponding columns (g00 and g05) are filled with zeros. The models are in FLAM surface flux units, i.e. \(ergs \ cm^{-2} \ s^{-1} \ A^{-1}\)

Header for table file ckp00_8000.fits

 1 TEFF        i 8000
 2 LOG_Z    d 0. This is actually metal abundance and not metallicity
 3 HISTORY  t  File created by F.R.Boffi
 4 HISTORY  t  ATLAS9 model atmospheres by Castelli and Kurucz (2004).
 5 HISTORY  t  Wavelength is in Angstrom.
 6 HISTORY  t  Fluxes tabulated in units of erg/s/cm^2/A
 7 HISTORY  t  (after converting original units into "flam",
 8 HISTORY  t  as described in README file and the SYNPHOT manual)
 9 HISTORY  t  and are surface fluxes. To transform to observed
10 HISTORY  t  fluxes multiply by (R/D)^2 where R is the
11 HISTORY  t  radius of the star and D the distance.
12 HISTORY  t  Each column in the table represents the
13 HISTORY  t  spectrum of a star for the same metallicity
14 HISTORY  t  and effective temperature but different gravity.
15 HISTORY  t  Gravities range from log_g = +0.0 (g00 in the column
16 HISTORY  t   header) to log_g = +5.0 (g50 in the column header).