MARCS DataBase

Chemical composition

Standard : Representing chemically unevolved Pop I and II stars. −5.0 ≤ [Fe/H] ≤ +1.0. Solar relativeabundances except for metal-poor models ([Fe/H] < 0.0) which have enhanced oxygen and α element abundances.
Moderately CN-cycled : Chemically evolved spherical models (giants) with [Fe/H] between −2.0and +0.25, C/N=1.5, and 12C/13C=20.
Heavily CN-cycled : Chemically further evolved spherical models (giants) with [Fe/H] between−2.0 and +0.25, C/N=0.5, and 12C/13C=4.
Alpha poor : No α element enhancement and −2.5 ≤ [Fe/H] ≤ −0.25. (All abundance ratios Solar.
Alpha enhanced : [α/Fe],+0.40 and −0.75 ≤ [Fe/H] ≤ +1.0.
Alpha negative : [α/Fe]=−0.40 and −2.00 ≤ [Fe/H] ≤ +0.75.
Grevesse & Sauval : (1998) solar-composition. Fe, average α elements, C, N, and O up by+0.05, +0.16, +0.13, +0,14 and +0.17 dex relative to H, respectively.
S0/S1/…/S6 composition class : S-type star models with a range of C/O ratios. From S0 to S6: C/O = 0.500, 0.750, 0.899, 0.925, 0.951, 0.971, 0.991.Each subclass contains models with different metallicities, and s-element overabundances, for both giants and dwarfs.

Geometry

Plane parallel: Dwarfs and sub-giants with negligible photospheric depths, 3.0 ≤ log g ≤ 5.5. Mass independent, "Mass=0.0".
Spherical: Giants and supergiants with non-negligible photospheric depths, -0.5 ≤ log g ≤ 3.5. Mass=1.0 M_Sun with sparse sub-grids of 0.5, 2.0, and 5.0 M_Sun.

Lowest Values

Effective temperature

Log g

Overall Metallicity [Fe/H]

Mass

Microturbulence

α elements [α/Fe]

Carbon [C/Fe]

Nitrogen [N/Fe]

Oxygen [O/Fe]

Helium [He/H]

r process elements [r/Fe]

s process elements [s/Fe]

Highest Values

effectivetemperature

Stellar effective temperature in K; the temperature of an ideal black body with the same emitted power per surface area.

logg

The logarithm of the surface acceleration of gravity in units of cm/s2. For Spherical geometry −0.5 ≤ log g ≤ +3.5 and for plane-parallel models +3.0 ≤ log g ≤ +5.5. The "CN-cycled" models come only with Spherical geometry (giants).

overallmetallicity

The logarithmic overall metallicity [Fe/H] relative to the Sun. For most models, the carbon, nitrogen, oxygen, and α element abundances relative to iron are entirely determined by the choice of chemical composition class at the top.

mass

The Spherical-geometry models come with 4 different masses: 0.5, 1.0, 2.0, and 5.0 MSun. Only the 1.0 MSun subgrids have all the combinations of Teff and log g. The plane-parallel models are independent of mass, indicated by M=0.0 MSun.

microturbulenceparameter

Spherical-geometry models are generally avilable for a choice between 2.0 and 5.0 km/s. Plane-parallel models are usually made with 1.0 and 2.0 km/s, except for models with Teff < 4000 K for which also 0.0 km/s may be chosen.

alphaelements

The logarithmic abundance ratio of alpha elements to iron relative to the Sun. Alpha-elements are Ne, Mg, Si, S, A, Ca, and Ti.

carbon

The logarithmic abundance ratio of carbon to iron relative to the Sun.

nitrogen

The logarithmic abundance ratio of nitrogen to iron relative to the Sun.

oxygen

The logarithmic abundance ratio of oxygen to iron relative to the Sun.

helium

The logarithmic abundance of He relative to the Sun.

rprocesselements

The logarithmic abundance ratio of r-process element fractions to iron relative to the Sun. Only the fraction of the abundance pertaining to r-process in the solar system is scaled.

sprocesselements

The logarithmic abundance ratio of s-process element fractions to iron relative to the Sun. Only the fraction of the abundance pertaining to s-process in the solar system is scaled.

How do I use MARCS?

First chose "Chemical composition class" and model "Geometry". Click on the question marks to the right of the two menues for hints. The total number of available models to chose from is shown to the right, and a number of further menues to select detailed model parameters show up below. These give the total ranges available for the selected composition class and geometry.

Then continue downwards with the menues in the left-hand column to refine your selection. A menue will be grey when there is only one possible value. The question marks to the right of the menues give information of what is available, not all possible combinations of parameters will be there. "No models found" will indicate when a void combination has been chosen. Then you have to modify one or more of your previous choices.

Eventually a number of models will be listed in the right-hand column and you may chose to put all or just some of them into your star cluster (Download basket).

You will see the list of selected models on the left hand side.

Clicking the "Search form" button will let you make a new selection of models to add to your cluster.

Click the Download basket to see your stars.

When you are done, select hich types of model or flux files that you want, and then then click "Download" to get a tar ball of data.

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Search Results

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