Welcome to MARCS

This is a grid of one-dimensional, plane-parallel and spherical LTE model atmospheres. These are often used together with atomic and molecular spectral line data and software for radiative transfer to generate synthetic stellar spectra.

The MARCS site contains some 37,000 stellar atmospheric models of spectral types F, G and K in 3 different formats and also flux sample files indicating rough surface fluxes. The data files are downloadable in limited amounts in the form of tar archives after registration. We ask users to cite the basic reference containing a description of the models:
Gustafsson B., Edvardsson B., Eriksson K., Jørgensen U.G., Nordlund Å., Plez B. 2008, Astronomy & Astrophysics 486, 951

News

July 10, 2010: A new metallicity class "alpha enhanced" has been produced containing models with [α/Fe]=+0.40 for -0.75≤[Fe/H]≤+0.50.

July 10, 2010: The file name field delimiters ":" have been replaced by "_" to avoid problems for Windows users.

File types

The ASCII data files are individually gzipped and the file types are identified by their file name endings:

• ".mod" contain the most detailed lists of the model structures, thermodynamical quantities, and many partial gas pressures. Their sizes gzipped/unzipped are typically 10/25 kB. Here is a FORTRAN program to read these models.
• ".opa" contain the basic model structures and continuous opacities as a function of wavelength and optical depth useful for synthetic spectrum calculations. Their sizes gzipped/unzipped are typically 0.4/1.4 MB.
• ".krz" contain model files in a format explained HERE . Their sizes gzipped/unzipped are typically 2/6 kB.
• ".flx" contain statistical samples of the model surface fluxes derived in the model calculations. They give rough estimates of the surface fluxes and are NOT synthetic spectra why they should not be used for synthetic photometry. The units are erg/cm²/s/Å. The wavelengths range from 1300 to 200,000 Å in vacuum and come in a separate file "flx_wavelengths.vac.gz". The wavelength scale is NOT equidistant but has rather a constant resolving power R=λ/Δλ=20,000. The file sizes are typically 0.4/1.4 MB.

Model parameters

The stellar atmospheric model parameters range in effective temperature from 2500 to 8000 K in steps of 100 K from 2500 to 4000 K and 250 K between 4000 and 8000 K. The logarithmic surface gravities (cgs units) between -1.0 and 5.5 in steps of 0.5. Overall logarithmic metallicities relative to the Sun are between -5.0 and +1.0 in variable steps. The reference solar abundance mixture is that of Grevesse, Asplund & Sauval (2007). The atmospheres of more luminous stars with low surface gravities (-1.0 to +3.5) are calculated in spherical geometry and with different stellar masses: the standard mass is 1.0 solar mass with sparse grids at 0.5, 2.0, and 5.0 Msun. Plane parallel models are computed for gravities between 3.0 and 5.0 or 5.5 for the cooler models. Models with different choices of "microturbulence parameters" are also available.

Since the mixture of metals vary among stars there are presently six different "metallicity classes": "Standard composition", "Moderately CN cycled", "Heavily CN cycled", "Alpha poor", "Alpha enhanced", and for solar [Fe/H] there is also a subgrid with abundances according to Grevesse & Sauval (1998).

The model grids lack many models due to convergence problems, particularly for low-gravity models, and specifically the warm low-gravity corners of the sperical-geometry subgrids are all empty.

The tables below show the abundance mixtures for the different metallicity classes. The complete elemental composition of a model is given in the ".mod" files and in a different format in the ".krz" files.

The pp and sph columns display the available microturbulence parameters (km/s).

Standard composition, 41% of all models

[Fe/H]	[α/Fe]	[C/Fe]	[N/Fe]	[O/Fe]	pp				sph
+1.00	0.00	0.00	0.00	0.00	0	1	2			2	5
+0.75	0.00	0.00	0.00	0.00	0	1	2			2	5
+0.50	0.00	0.00	0.00	0.00	0	1	2			2	5
+0.25	0.00	0.00	0.00	0.00	0	1	2			2	5
0.00	0.00	0.00	0.00	0.00	0	1	2	5	1	2	5
-0.25	+0.10	0.00	0.00	+0.10	0	1	2			2	5
-0.50	+0.20	0.00	0.00	+0.20	0	1	2			2	5
-0.75	+0.30	0.00	0.00	+0.30	0	1	2			2	5
-1.00	+0.40	0.00	0.00	+0.40	0	1	2			2	5
-1.50	+0.40	0.00	0.00	+0.40	0	1	2			2	5
-2.00	+0.40	0.00	0.00	+0.40	0	1	2			2	5
-2.50	+0.40	0.00	0.00	+0.40	0	1	2			2	5
-3.00	+0.40	0.00	0.00	+0.40	0	1	2			2	5
-4.00	+0.40	0.00	0.00	+0.40	0	1	2			2	5
-5.00	+0.40	0.00	0.00	+0.40	0	1	2			2	5

Moderately CN cycled, ¹²C/¹³C=20, 12% of all models

[Fe/H]	[α/Fe]	[C/Fe]	[N/Fe]	[O/Fe]	pp				sph
+0.25	0.00	-0.13	+0.31	0.00						2	5
0.00	0.00	-0.13	+0.31	0.00						2	5
-0.50	+0.20	-0.13	+0.31	+0.20						2	5
-1.00	+0.40	-0.13	+0.31	+0.40						2	5
-1.50	+0.40	-0.13	+0.31	+0.40						2	5
-2.00	+0.40	-0.13	+0.31	+0.40						2	5

Heavily CN cycled, ¹²C/¹³C=4, 11% of all models

[Fe/H]	[α/Fe]	[C/Fe]	[N/Fe]	[O/Fe]	pp				sph
+0.25	0.00	-0.38	+0.53	0.00						2	5
0.00	0.00	-0.38	+0.53	0.00						2	5
-0.50	+0.20	-0.38	+0.53	+0.20						2	5
-1.00	+0.40	-0.38	+0.53	+0.40						2	5
-1.50	+0.40	-0.38	+0.53	+0.40						2	5
-2.00	+0.40	-0.38	+0.53	+0.40						2	5

Alpha enhanced, 16% of all models

[Fe/H]	[α/Fe]	[C/Fe]	[N/Fe]	[O/Fe]	pp				sph
+0.50	+0.40	0.00	0.00	+0.40	0	1	2			2	5
+0.25	+0.40	0.00	0.00	+0.40	0	1	2			2	5
0.00	+0.40	0.00	0.00	+0.40	0	1	2			2	5
-0.25	+0.40	0.00	0.00	+0.40	0	1	2			2	5
-0.50	+0.40	0.00	0.00	+0.40	0	1	2			2	5
-0.75	+0.40	0.00	0.00	+0.40	0	1	2			2	5

Alpha poor, 17% of all models

[Fe/H]	[α/Fe]	[C/Fe]	[N/Fe]	[O/Fe]	pp				sph
-0.25	0.00	0.00	0.00	0.00	0	1	2			2	5
-0.50	0.00	0.00	0.00	0.00	0	1	2			2	5
-0.75	0.00	0.00	0.00	0.00	0	1	2			2	5
-1.00	0.00	0.00	0.00	0.00	0	1	2			2	5
-1.50	0.00	0.00	0.00	0.00	0	1	2			2	5
-2.00	0.00	0.00	0.00	0.00	0	1	2			2	5

Grevesse & Sauval (1998), 3% of all models

[Fe/H]	[α/Fe]	[C/Fe]	[N/Fe]	[O/Fe]	pp				sph
+0.05	+0.11	+0.08	+0.09	+0.12	0	1	2			2	5

References

• Grevesse N., Asplund M., Sauval A.J. 2007, Space Science Review 130, 205
• Grevesse N., Sauval A.J. 1998, Space Science Review 85, 161
• Gustafsson B., Edvardsson B., Eriksson K., Jørgensen U.G., Nordlund Å., Plez B. 2008, Astronomy & Astrophysics 486, 951