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About this site in general
Welcome to the revised (2008) MARCS stellar model-atmosphere and flux library.
On this site you find information about the models as well as a search and
download utility which you may use freely after registering as a user.
They should, however, be properly acknowledged in publications based on their results,
see below.
The models are organised in a database with an easy-to-use interface for searching.
A tar archive containing the (gzipped) data files that you chose will be created
for you to download and save locally.
About the MARCS models
This is a grid of over 30000 one-dimensional, plane-parallel and spherical LTE model
atmospheres and sampled fluxes.
The library supplies model-atmosphere tables (<10/25 kbyte each, gzipped/unzipped),
continuous-opacity data
files (<450/2000 kbytes each), and sampled energy fluxes
(<400/1300 kbytes each) for 29870 stellar atmospheric models with
effective temperatures between 2500 and 8000K (step 100K below Teff=4000 and 250K
for warmer models), logarithmic surface gravities between (cgs) -1.0 to 5.0 or 5.5
(step 0.5), and overall metallicities between -5.0 and 1.0
(with a variable step from 1.0 to 0.25 dex).
Plane-parallel models are calculated for log g from +3.0 to +5.0 and have
microturbulent-velocity parameters 1.0 and 2.0 km/s.
For the cooler models (Teff<4000K) surface gravity log g 5.5 and
microturbulenceparameter 0.0 km/s are also included.
Models with spherical geometry are supplied for models with log g < +4.0,
masses of 0.5, 1.0, 2.0 and 5.0 MSun, and microturbulence
parameters 2.0 and 5.0 km/s. Only the 1.0 MSun subgrids contain all
combinations of Teff and log g.
Models are missing in the regular grids due to lack of convergence.
The model data format and units are given in the fortran programme "readmarcs.f" which
is supplied under "Software" above, where also a fortran routine for interpolation
of model structures can be found.
An alternative model format
with extension ".krz" (<2.5/6 kbytes each) is also available.
Chemical abundances
The reference solar abundances of chemical elements is adopted from
Grevesse, Asplund & Sauval 2007, Space Sciences Review 130, 105.
The table below shows the five chemical-composition groups.
The last two columns show for which microturbulence parameters (km/s) that
plane-parallel, Pp., and spherical, Sph., models are available.
Elements treated as α elements are Ne, Mg, Si, S, Ar, Ca and Ti.
Oxygen also follows the α elements in this "solar-type" model grid.
The CN-cycled models preserve the "Standard" abundance sum of C+N for the same [Fe/H].
The logarithmic chemical number abundances are given in each model file on a scale
where log10 N(hydrogen) = 12.00.
| Standard composition. About 15500 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 |
| α-poor composition. About 6300 models |
| [Fe/H] |
[α/Fe] |
[C/Fe] |
[N/Fe] |
[O/Fe] |
Pp. |
Sph. |
| -0.50 | 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 |
| Moderately CN-cycled composition, C/N=1.5, 12C/13C=20.
About 4000 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 composition, C/N=0.5, 12C/13C=4.0.
About 4000 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 |
| Grevesse & Sauval (1998, SSR 85, 161) solar composition. About 1000 models |
| [Fe/H] |
[α/Fe] |
[C/Fe] |
[N/Fe] |
[O/Fe] |
Pp. |
Sph. |
| +0.05 | +0.11 | +0.08 | +0.09 | +0.12 | 1, 2 | 2, 5 |
The solar model
The solar model has parameters Teff=5777 K, log g=4.44, [Fe/H]=0.0, [α/Fe]=0.0,
[C/Fe]=0.0, [N/Fe]=0.0, [O/Fe]=0.0, and microturbulence parameter 1.0 km/s.
It can be obtained via the final model request page.
About the MARCS model fluxes
The flux data files are not proper spectra, merely one-dimensional
files of sampled photospheric surface fluxes (in ergs/cm2/s/Å)
from 1300Å to 20μm sampled with λ/Δλ = 20,000.
This means that spectral lines are not resolved and that the flux in a limited
wavelength region may give a poor representation of the integrated flux in that region.
It also follows that the wavelength spacing is not equidistant
which has to be taken into account when the flux is integrated over wavelength.
The wavelength scale of the flux sample data is in vacuum, and the
wavelengths (about 100,000 points) are supplied in a separate
one-dimensional file, which is the same one for all models.
Using the MARCS models and fluxes
The new (2008) MARCS models are presently being documented in a series of publications,
the first of which is
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Gustafsson B., Edvardsson B., Eriksson K., Jørgensen U.G., Nordlund Å,
Plez B. 2008, A&A 486, 951-970.
(ps) or
(pdf) .
Fluxes of models for the Sun and solar-type stars are compared to those of
low-resolution spectrophotometric data in
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Edvardsson B. 2008, in "A stellar journey. A symposium in celebration of
Bengt Gustafssons' 65th birthday", submitted to Physica Scripta
(ps) or
(pdf) .
Some MARCS history, comparisons with observed M star fluxes, and some effects of
spectral sampling and line scattering are discussed in
-
Plez B. 2008, in "A stellar journey. A symposium in celebration of
Bengt Gustafssons' 65th birthday", submitted to Physica Scripta
(pdf) .
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