STScI Logo

Calibration Database System

Castelli and Kurucz Atlas

NOTE: There is a known bug with trying to access the atlasas via ftp server with the Safari browser. The recommended browser for retrieving the files is Firefox.


List of models available in Synphot, by metallicity and log g


The atlas contains about 4300 stellar atmosphere models for a wide range of metallicities, 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 H_2 O lines (Partridge & Schwenke 1997, J. Chem. Phys., 106, 4618) and of the HI-HI and HI-H+ quasi-molecular absorptions near 1600 A and 1400 A (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 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 a pure mixing-length convection (no overshooting) with 1/Hp=1.25. As before the microturbulent velocity used is 2 km s^{-1}.

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

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 (1000A) to infrared (10 microns) spectral range with non-uniform wavelength spacing (see Table 1b).

TABLE 1a: Grid of temperatures for the models

Temperature Range (K) Grid Step (K)
3000 - 13000 250
13000 - 50000 1000

TABLE 1b: Wavelength coverage for the models

Wavelength Range (microns) Grid Step (A)
0.10 - 0.29 10
0.29 - 1.00 20
1.00 - 1.60 50
1.60 - 3.20 100
3.20 - 8.35 200
8.35 - 10.0 400


The new atlas is divided in 8 independent subdirectories, according to metallicity. Within each subdirectory the stellar atmosphere models are given in STSDAS multicolumn table format. Each table consist of 12 different columns, the first one containing the wavelength grid and each of 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 metallicity, effective temperature and gravity combination is not covered by the atlas.

The names of the table files are given as where "ck", for Castelli & Kurucz, are the first two letters of the atlas; "szz" is the metallicity of the model (zz) with its sign (s); and "ttttt" is the model's effective temperature, using four or five digits depending on the value. For instance, models for an effective temperature of 5000 K with [M/H]= -0.5 and [M/H]= +3.5 are indicated by ttttt= 5000, s= m, zz= 05 and ttttt= 5000, s= p, zz= 35, i.e. ckm05_5000.fits and ckp35_5000.fits.

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 x 10^{-19} x lambda^{2} x (4pi)^{-1}, i.e. are converted from ergs cm^{-2} s^{-1} Hz^{-1}steradian^{-1} to ergs cm^{-2} s^{-1} A^{-1} by mutiplying the Castelli & Kurucz values by 3.336 x 10^{-19} x lambda^{2} x (4pi)^{-1}, where lambda is in Angstroms. To convert to 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 metallicity 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.


Synphot tasks permit the use of spectra selected from one of many columns in a single STSDAS table file. One does this by specifying as the "spectrum" parameter the name of the disk file (as before), and appending the name of the column containing the flux in brackets. Thus, to select any model spectrum characterized by a given metallicity, effective temperature, and gravity, specify a "spectrum" of the form: crgridck04$m_directory/ckszz_ttttt.fits[gyy], where m_directory is the name of the subdirectory for a given metallicity. For example, to select the spectrum of a star with a metallicity of +0.1, a temperature of 10,000 K, and log gravity of 3.0, the specification would be: crgridck04$ckp01/ckp01_10000.fits[g30].

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 synphot with the "rn" function.

Synphot also allows the use of the cat() and icat() functions to select Castelli & Kurucz spectra. The syntax is "cat(ck04models,t,m,g) where "t" is the effective temperature, "m" is the log metallicity [M/H], and "g" is the log gravity. The idea is that, instead of having to remember a directory/file naming syntax, a synphot user could specify a spectrum from a specified catalog (the New ATLAS9 of Castelli & Kurucz, in this case) which most closely matches the specified attributes (in this case, T_{eff}, [M/H], and log_g) using an expression. The difference between the cat() and icat() functions is that cat() selects the nearest spectrum to the specified parameters and icat() interpolates between the spectra that bracket the specified parameters.

Since the entire atlas occupies close to 70MB of disk space, many applications could be satisfied by a copy of the solar metallicity spectra, only.

A list of solar metallicity 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 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.

TABLE 2: Suggested models for specific stellar types

Type T_{eff} log_g Kurucz model
O3V 44852 +3.92 ckp00_45000[g45]
O4V 42857 +3.92 ckp00_43000[g45]
O5V 40862 +3.92 ckp00_41000[g45]
O5.5V 39865 +3.92 ckp00_40000[g40]
O6V 38867 +3.92 ckp00_39000[g40]
O6.5V 37870 +3.92 ckp00_38000[g40]
O7V 36872 +3.92 ckp00_37000[g40]
O7.5V 35874 +3.92 ckp00_36000[g40]
O8V 34877 +3.92 ckp00_35000[g40]
O8.5 33879 +3.92 ckp00_34000[g40]
O9V 32882 +3.92 ckp00_33000[g40]
O9.5 31884 +3.92 ckp00_32000[g40]
B0V 30000 +3.90 ckp00_30000[g40]
B1V 25400 +3.90 ckp00_25000[g40]
B3V 18700 +3.94 ckp00_19000[g40]
B5V 15400 +4.04 ckp00_15000[g40]
B8V 11900 +4.04 ckp00_12000[g40]
A0V 9520 +4.14 ckp00_9500[g40]
A1V 9230 +4.10 ckp00_9250[g40]
A3V 8270 +4.20 ckp00_8250[g40]
A5V 8200 +4.29 ckp00_8250[g40]
F0V 7200 +4.34 ckp00_7250[g40]
F2V 6890 +4.34 ckp00_7000[g40]
F5V 6440 +4.34 ckp00_6500[g40]
F8V 6200 +4.40 ckp00_6250[g45]
G0V 6030 +4.39 ckp00_6000[g45]
G2V 5860 +4.40 ckp00_5750[g45]
G5V 5770 +4.49 ckp00_5750[g45]
G8V 5570 +4.50 ckp00_5500[g45]
K0V 5250 +4.49 ckp00_5250[g45]
K2V 4780 +4.5 ckp00_4750[g45]
K4V 4560 +4.5 ckp00_4500[g45]
K5V 4350 +4.54 ckp00_4250[g45]
K7V 4060 +4.5 ckp00_4000[g45]
M0V 3850 +4.59 ckp00_3750[g45]
M2V 3580 +4.64 ckp00_3500[g45]
M4V 3370 +4.80 ckp00_3500[g50]
M5V 3240 +4.94 ckp00_3500[g50]
M6V 3050 +5.00 ckp00_3500[g50]
B0III 29000 +3.34 ckp00_29000[g35]
B5III 15000 +3.49 ckp00_15000[g35]
G0III 5850 +2.94 ckp00_5750[g30]
G5III 5150 +2.54 ckp00_5250[g25]
K0III 4750 +2.14 ckp00_4750[g20]
K5III 3950 +1.74 ckp00_4000[g15]
M0III 3800 +1.34 ckp00_3750[g15]
O5I 40300 +3.34 ckp00_40000[g45]
O6I 39000 +3.24 ckp00_39000[g40]
O8I 34200 +3.24 ckp00_34000[g40]
BOI 26000 +2.84 ckp00_26000[g30]
B5I 13600 +2.44 ckp00_14000[g25]
AOI 9730 +2.14 ckp00_9750[g20]
A5I 8510 +2.04 ckp00_8500[g20]
F0I 7700 +1.74 ckp00_7750[g20]
F5I 6900 +1.44 ckp00_7000[g15]
G0I 5550 +1.34 ckp00_5500[g15]
G5I 4850 +1.14 ckp00_4750[g10]
K0I 4420 +0.94 ckp00_4500[g10]
K5I 3850 +0.34 ckp00_3750[g05]
M0I 3650 +0.14 ckp00_3750[g00]
M2I 3450 -0.06 ckp00_3500[g00]


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 particualr 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.
 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).