These files described the energy transfer and the radiation flux exchange in the star itself, at different layers. They take into account accurate values of atom parameters, as well as latest equation on stellar and atoms physic. This a complex science, and there is no real need to master it. But at least, it is interesting to see different face of the astronomy, there is not only observations...

The models which are very often referenced in the litterature are the Richard L. Kurucz models - Harvard-Smithsonian Center for Astrophysics. This section will give some indications on where to find some and how to use them in SPECTRUM software.

 

On Spectrum web site, there is a section which describe the format required.

The models are ASCII files - SPECTRUM needs only a first line with the temperature Teff, the log(g), the metallicity ratio [M/H], the number of layers (=lines) and then the data in 7 columns. Here is an example of a model format used in SPECTRUM.

3800.0 4.50 0.00 64
8.47207656E-03 2371.7 2.679E+02 1.759E+09 1.384E-04 1.467E-02 1.000E+05
1.10719330E-02 2819.3 3.501E+02 4.619E+09 1.869E-04 1.056E-02 1.000E+05
1.39465087E-02 2839.3 4.410E+02 5.758E+09 2.269E-04 1.012E-02 1.000E+05
1.71015816E-02 2861.2 5.408E+02 7.041E+09 2.726E-04 9.826E-03 1.000E+05
2.06161847E-02 2881.8 6.519E+02 8.471E+09 3.234E-04 9.679E-03 1.000E+05
2.45891756E-02 2899.1 7.776E+02 1.005E+10 3.785E-04 9.498E-03 1.000E+05
...

If you find models on the web, make sure you format them as above. The meaning of each column is quite opaque for me yet...

 

Up to now, I found two sources of stellar models, but not in the exact format as described.

The first source is the ftp site of R.L.Kurucz himself

The models are in the [GRIDS] directory. If you ftp the site, as indicated on Kurucz's web pages, user name is guest and password is cfaguest. To get into the logical directory of grids, you can make a chgdir from the KUE5:[GUEST] into KUE5:[GRIDS]. You can access to it also from the web pages.

Once you are in the grids directory, select one of the sub-directories. They are referenced by metallicity. Enter the M01 for example. There are plenty of files. The one I found equivalent to the Spectrum models was having a "a" prefixe and a datcd extension. The dat extension files seems to have more columns. Files are big, around 3Mb each... Each file is a collection of stellar atmosphere models for different gravity and temperature. To use it, you will have to break it into each individual file for each temperature and log(g). You will also have to remove the header and the footer. Be patient...

Here is an extract from the am01k02.datcd file in the M01 directory.

TEFF 3500. GRAVITY 0.00000 LTE
TITLE SDSC GRID [-0.1] VTURB 2.0 KM/S L/H 1.25
OPACITY IFOP 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 0 0 0 0 0
CONVECTION ON 1.25 TURBULENCE OFF 0.00 0.00 0.00 0.00
ABUNDANCE SCALE 0.79430 ABUNDANCE CHANGE 1 0.91100 2 0.08900
ABUNDANCE CHANGE 3 -10.88 4 -10.89 5 -9.44 6 -3.48 7 -3.99 8 -3.11
ABUNDANCE CHANGE 9 -7.48 10 -3.95 11 -5.71 12 -4.46 13 -5.57 14 -4.49
ABUNDANCE CHANGE 15 -6.59 16 -4.83 17 -6.54 18 -5.48 19 -6.82 20 -5.68
ABUNDANCE CHANGE 21 -8.94 22 -7.05 23 -8.04 24 -6.37 25 -6.65 26 -4.37
ABUNDANCE CHANGE 27 -7.12 28 -5.79 29 -7.83 30 -7.44 31 -9.16 32 -8.63
ABUNDANCE CHANGE 33 -9.67 34 -8.69 35 -9.41 36 -8.81 37 -9.44 38 -9.14
ABUNDANCE CHANGE 39 -9.80 40 -9.54 41 -10.62 42 -10.12 43 -20.00 44 -10.20
ABUNDANCE CHANGE 45 -10.92 46 -10.35 47 -11.10 48 -10.18 49 -10.58 50 -10.04
ABUNDANCE CHANGE 51 -11.04 52 -9.80 53 -10.53 54 -9.81 55 -10.92 56 -9.91
ABUNDANCE CHANGE 57 -10.82 58 -10.49 59 -11.33 60 -10.54 61 -20.00 62 -11.04
ABUNDANCE CHANGE 63 -11.53 64 -10.92 65 -11.94 66 -10.94 67 -11.78 68 -11.11
ABUNDANCE CHANGE 69 -12.04 70 -10.96 71 -11.28 72 -11.16 73 -11.91 74 -10.93
ABUNDANCE CHANGE 75 -11.77 76 -10.59 77 -10.69 78 -10.24 79 -11.03 80 -10.95
ABUNDANCE CHANGE 81 -11.14 82 -10.19 83 -11.33 84 -20.00 85 -20.00 86 -20.00
ABUNDANCE CHANGE 87 -20.00 88 -20.00 89 -20.00 90 -11.92 91 -20.00 92 -12.51
ABUNDANCE CHANGE 93 -20.00 94 -20.00 95 -20.00 96 -20.00 97 -20.00 98 -20.00
ABUNDANCE CHANGE 99 -20.00
READ DECK6 64 RHOX,T,P,XNE,ABROSS,ACCRAD,VTURB
3.80866308E-01 1060.9 3.803E-01 3.435E+02 3.447E-06 1.465E-03 2.000E+05
4.47733038E-01 2363.1 4.471E-01 6.924E+06 8.517E-06 8.530E-04 2.000E+05
5.16626250E-01 2377.6 5.159E-01 8.022E+06 8.744E-06 7.229E-04 2.000E+05
6.05444443E-01 2396.7 6.047E-01 9.491E+06 9.057E-06 6.447E-04 2.000E+05

next file to extract is for

TEFF 3500. GRAVITY 0.50000 LTE
TITLE SDSC GRID [-0.1] VTURB 2.0 KM/S L/H 1.25

And so on up to 50 000°K by 0.5 step for log(g)

I did extract a file at Teff=4250°K, log(g)=2.0 , Micro-turbulence = 2.0 and [M/H]=-0.5 - those parameters are the ones of the Arcturus star. I did create a model file meeting the Spectrum format and I compared it to the one I used for the Arcturus line identification. (43045k1p00 : teff 4300°K, Log(g)=4.5, Turbulence 1.0 and [M/H]=0). The process seems to work well.

In blue the original model used, in purple the new one from the Kurucz web site. In green, the observed spectrum.

Download 42520k2m05.mod , 43045k1p00.mod models

It seems that we can also get CDs from R.L.Kurucz, but I did not try, ftp site worked well.

Other sources ?

I found another one, from the CDBS (Calibration Data Base System) from the Space Telescope Science Institute. It has links to several atlas of stellar atmosphere and spectra.

The problem faced here is that all files are in fits format, not in ASCII. And until I wrote a fits reader for this specific fits file which are not images, I have no access to them...

Anyway, be careful. It is so easy to do dumb things when we do not understand what's behind.

And, I will be more than happy to be informed of any other web site you have found.

 

In the introduction to his 1993 atlas of stellar atmosphere, Kurucz provided the following table. I guess this can help.