THE 1993 KURUCZ STELLAR ATMOSPHERES ATLAS The atlas contains about 7600 stellar atmosphere models for a wide range of metal abundances, 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}. The new atlas installed in the CDBS is from the Kurucz d.fitsase 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 metal abundances (M/H) 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 HST/CDBS VERSION OF THE 1993 KURUCZ ATLAS The atlas is divided into 19 independent subdirectories, according to metal abundance. Within each subdirectory the stellar atmosphere models are given in fits table format. Each table consist of 12 different columns, the first one containing 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. The names of the table files are given as ksmh_ttttt.fits; where "k", for Kurucz, is the first letter of the atlas; "smh" is the metal abundance of the model (mh) 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, mh = 05 and ttttt = 5000, s = p, mh = 35, i.e. km05_5000.fits and kp35_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 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. the fluxes are converted from ergs cm^{-2} s^{-1} Hz^{-1} steradian^{-1} to ergs cm^{-2} s^{-1} A^{-1} by dividing the flux in ergs cm^{-2} s^{-1} Hz^{-1} steradian^{-1} 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 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 OF KURUCZ ATLAS WITH SYNPHOT Synphot tasks permit the use of spectra selected from one of many columns in a single 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 metal abundance, effective temperature, and gravity, specify a "spectrum" of the form: crgridk93$m_directory/ksmh_ttttt.fits[gyy], where m_directory is the name of the subdirectory for a given metal abundance. For example, to select the spectrum of a star with [M/H]= +0.1, a temperature of 10,000 K, and log gravity of 3.0, the specification would be: crgridk93$kp01/kp01_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 Kurucz spectra. The syntax is "cat(k93models,t,m,g) where "t" is the effective temperature, "m" is the metal abundance [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 Kurucz atlas, 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 abundance spectra, only. A list of solar abundance 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. 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 Type T_{eff} log_g Kurucz model O3V 52500 +4.14 kp00_50000[g40] O5V 44500 +4.04 kp00_45000[g40] O6V 41000 +3.99 kp00_40000[g40] 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[g40] F0V 7200 +4.34 kp00_7250[g40] F5V 6440 +4.34 kp00_6500[g40] G0V 6030 +4.39 kp00_6000[g45] G2V 5860 +4.40 kp00_5860[g44] 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[g30] O6I 39000 +3.24 kp00_40000[g30] O8I 34200 +3.24 kp00_34000[g30] 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[g10] G5I 4850 +1.14 kp00_4750[g10] K0I 4420 +0.94 kp00_4500[g10] K5I 3850 +0.00 kp00_3750[g00] M0I 3650 -0.10 kp00_3750[g00] M2I 3600 -0.10 kp00_3600[g00] APPENDIX 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 kp00_8000.fits and contains all the models for a star of [M/H]=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 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.fitsulated 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.