Content
Access to the STScI Kurucz 1993 ATLAS
The KURUCZ 1993 ATLAS contains about 7600 stellar atmosphere models covering a wide range of metallicities, effective temperatures and gravities. The original Atlas was created on August 22, 1993 by Dr. Kurucz (CD-ROM No. 13). In here we provide with an overview of the original Atlas and then more details about the TRDS version offered here. Our Atlas also contains model spectra for Alpha_Lyrae and the Sun.
Original Kurucz 1993 Models
The Atlas contains about 7600 stellar atmosphere models for a wide range of metallicities, effective temperatures and gravities and with a microturbulent velocity of \(2\ km\ s^{-1}\). These new LTE models have improved opacities and are computed with a finer wavelength and temperature resolution than the previous Buser-Kurucz Atlas installed also in TRDS.
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 ranges 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: Temperature Grid for the Models
| Temperature Range (K] |
Grid Step (K) |
|---|---|
| 3500 - 10000 | 250 |
| 10000 - 13000 | 500 |
| 13000 - 35000 | 1000 |
| 35000 - 50000 | 2500 |
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 TRDS Version of the 1993 Kurucz Atlas
The new atlas installed in the TRDS is from the Kurucz database at Goddard Space Flight Center and mentioned above. Within TRDS the atlas is divided into 19 independent subdirectories, according to metallicity. Within each subdirectory the stellar atmosphere models are given in multicolumn FITS 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 kszz_ttttt.fits 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 example, models with effective temperature of 5000 K, log_Z= -0.5 and log_Z= +3.5 have parameters ttttt= 5000, s= m, zz= 05 and ttttt= 5000, s= p, zz= 35; which result in tables with file names km05_5000.fits and kp35_5000.fits.
Within a 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 for 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 \(3.336 x 10^{-19} * \lambda^{2} /4\pi\); 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 indicated.
Access to the STScI Kurucz 1993 ATLAS
Use with Pysynphot
Pysynphot permits the use of spectra selected from one of many columns within a single FITS table file. One does this by specifying the name of the disk file (as before), and appending the name of the column containing the flux in brackets as the "spectrum" parameter. Thus, to select any model spectrum characterized by a given metallicity, effective temperature, and gravity, specify a "spectrum" of the form: crgridk93$m_directory/kszz_ttttt.tab[gyy], where m_directory is the name of the subdirectory for a given metallicity. For example, to select the spectrum of a star with a metallicity of +0.1, a temperature of 10,000 K, and log gravity of 3.0, the specification would be: crgridk93$kp01/kp01_10000.tab[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 pysynphot with the "renom" function.
An enhancement to pysynphot 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 "pysynphot.Icat(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 pysynphot 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.
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 ofm 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] |
Appendix
Below is an example of a standard header for the table files in the TRDS version of Kurucz atlas. In this example the name of the file is kp00_8000.fits and contains all of the models for a star of metallicity log_Z= 0.0 and effective temperature T_{eff}= 8000 K. The 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 kp00_8000.fits
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.