MARCS is a set of theoretical stellar model atmospheres and flux sample files based on the Uppsala software by the same name (Gustafsson et al. 1975, 2008). The atmosphere of a star consists of the stellar outer layers from where the light that we can observe comes. A MARCS model atmosphere is basically a large table describing how temperature, pressure and many other quantities vary with depth in the atmosphere. It is calculated from physical principles and knowledge of how light and different kinds of gases interact with each other.

The MARCS models are hydrostatic and computed under the assumption of local thermodynamic equilibrium (LTE) and local mixing-length convection.  The models are one-dimensional and calculated for plane-parallel or spherical geometry.  They cover dwarf stars to supergiants in the effective temperature range 8000 to 2500 K.  Models with overall metallicities [Fe/H] ranging from -5.0 to +1.0, with different [alpha/Fe] ratios, and some giant models with the atmospheric effects of CN-cycling are included. MARCS models in different formats and corresponding flux sample files are available at


  • Gustafsson et al. 1975, A&A 42, 407
  • Gustafsson et al. 2008, A&A 486, 951


Bengt GustafssonBengt Edvardsson