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Calibration Database System

Kurucz 1993 Models


The atlas contains about 7600 stellar atmosphere models for a wide
range of metallicities, effective temperatures and gravities. These new
LTE models have improved opacities and are computed with a finer
wavelength and temperature resolution than the previous Buser-Kurucz
atlas installed in the CDBS (crgridbk). The microturbulent velocity is
2 km s^{-1}.

For a complete list of all the available models refer to our 

The new atlas installed in the CDBS is from the Kurucz database at
Goddard Space Flight Center. The original atlas (CD-ROM  No. 13) was
created on August 22, 1993 and can be obtained from Dr. R. Kurucz.

The atlas includes models of abundances (log_Z) relative to solar of
+1.0, +0.5, +0.3, +0.2, +0.1, +0.0, -0.1, -0.2, -0.3, -0.5, -1.0, -1.5,
-2.0, -2.5,-3.0, -3.5, -4.0, -4.5, and -5.0. The grid of models cover
the 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      Grid Step
		       K                   K

		  3000 - 10000            250 
                 10000 - 13000            500
                 13000 - 35000           1000
                 35000 - 50000           2500

	  TABLE 1b: Wavelength coverage for the models

		Wavelength Range       Grid Step
		    microns                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 atlas is divided in 19 independent subdirectories, according to
metallicity.  Within each subdirectory the stellar atmosphere models
are given in STDAS 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 "k", for
Kurucz, is the first letter 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 log_Z=
-0.5 and log_Z= +3.5 are indicated by ttttt= 5000, s= m, zz= 05 and
ttttt= 5000, s= p, zz= 35, i.e. and

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 Kurucz CD-ROM 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}.  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


Synphot tasks now 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:
crgridk93$m_directory/[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:

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.

An enhancement to synphot is planned for the near term that will allow
a model spectrum to be selected within a synphot expression, using a
special operator.  The syntax will be something like
"cat(kurucz,t,g,m)" where "t" is the effective temperature, "g" is the
log gravity, and "m" is the log metallicity in solar units.  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
Kurucz atlas, in this case) which most closely matches the specified
attributes (in this case, T_{eff}, log_g, and log_Z) using an
expression.  The on-line help and the Synphot User's Guide will be
updated when this feature is available.

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 Kurucz model spectrum is
presented in Table 2. The physical parameters, T_{eff} and log_g,
characterizing each star are taken from Schmidt-Kaler's compilation of
physical parameters of stars (Schmidt-Kaler 1982, Landolt-Bornstein
VI/2b). 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      52500     +4.14      kp00_50000[g50]
             O5V      44500     +4.04      kp00_45000[g50] 
             O6V      41000     +3.99      kp00_40000[g45] 
             O8V      35800     +3.94      kp00_35000[g40] 
             B0V      30000     +3.9       kp00_30000[g40] 
             B3V      18700     +3.94      kp00_19000[g40] 
             B5V      15400     +4.04      kp00_15000[g40] 
             B8V      11900     +4.04      kp00_12000[g40] 
             A0V       9520     +4.14       kp00_9500[g40] 
             A5V       8200     +4.29       kp00_8250[g45] 
             F0V       7200     +4.34       kp00_7250[g45] 
             F5V       6440     +4.34       kp00_6500[g45] 
             G0V       6030     +4.39       kp00_6000[g45] 
             G5V       5770     +4.49       kp00_5750[g45] 
             K0V       5250     +4.49       kp00_5250[g45] 
             K5V       4350     +4.54       kp00_4250[g45] 
             M0V       3850     +4.59       kp00_3750[g45]   
             M2V       3580     +4.64       kp00_3500[g45]   
             M5V       3240     +4.94       kp00_3500[g50]   
             B0III    29000     +3.34      kp00_29000[g35]   
             B5III    15000     +3.49      kp00_15000[g35]   
             G0III     5850     +2.94       kp00_5750[g30]   
             G5III     5150     +2.54       kp00_5250[g25]   
             K0III     4750     +2.14       kp00_4750[g20]   
             K5III     3950     +1.74       kp00_4000[g15]   
             M0III     3800     +1.34       kp00_3750[g15]   
             O5I      40300     +3.34      kp00_40000[g45]   
             O6I      39000     +3.24      kp00_40000[g45]   
             O8I      34200     +3.24      kp00_34000[g40]   
             BOI      26000     +2.84      kp00_26000[g30]   
             B5I      13600     +2.44      kp00_14000[g25]   
             AOI       9730     +2.14       kp00_9750[g20]   
             A5I       8510     +2.04       kp00_8500[g20]   
             F0I       7700     +1.74       kp00_7750[g20]   
             F5I       6900     +1.44       kp00_7000[g15]   
             G0I       5550     +1.34       kp00_5500[g15]   
             G5I       4850     +1.14       kp00_4750[g10]   
             K0I       4420     +0.94       kp00_4500[g10]   
             K5I       3850     +0.34       kp00_3750[g05]   
             M0I       3650     +0.14       kp00_3750[g00]   
             M2I       3450     -0.06       kp00_3500[g00]   


Below is an example of a standard header for the table files in the
CDBS version of Kurucz atlas. In this example the name of the file is 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

 1 TEFF     i 8000
 2 LOG_Z    d 0.0000000000000000
 3 HISTORY  t g10
 4 HISTORY  t g15
 5 HISTORY  t g20
 6 HISTORY  t g25
 7 HISTORY  t g30
 8 HISTORY  t g35
 9 HISTORY  t g40
10 HISTORY  t g45
11 HISTORY  t g50
12 HISTORY  t   
13 HISTORY  t Kurucz model atmospheres (1993)
14 HISTORY  t   
15 HISTORY  t Fluxes tabulated in units of erg s^{-1} cm^{-2} A^{-1}
16 HISTORY  t are surface fluxes. To transform to observed
17 HISTORY  t fluxes multiply by (R/D)^{2} where R is the
18 HISTORY  t radius of the star and D the distance.
19 HISTORY  t Each column in the table represents the
20 HISTORY  t spectrum of a star for the same metallicity
21 HISTORY  t and effective temperature but different gravity.