Laboratory analyses on fine-grained diamond residues from primitive meteorites have shown that nano-diamonds represent the most abundant form of presolar dust preserved in meteoritic samples .
The presolar diamonds carry isotopic anomalies which indicate a very complex formation history .
Several groups of diamonds may exist with origin in different types of stars .
In order to identify the sites of formation observationally , we have extracted presolar diamonds from the Allende meteorite and measured the monochromatic absorption coefficient in a form which is useful for stellar atmosphere calculations .
The monochromatic absorption coefficient was measured in the wavelength ranges 400–4000 cm ^ { -1 } ( 2.5–25 \mu m ) and 12200–52600 cm ^ { -1 } ( 190–820 nm ) .
We have made identical laboratory measurements on CVD diamonds as on the meteoritic diamonds , in order to get a more solid basis for the interpretation of the diamond spectrum .
The monochromatic absorption coefficient for the presolar diamonds was incorporated in self-consistent carbon star photospheric models .
The main influence of the diamond dust in our photospheric models is a heating of the upper photospheric layers and a reduction of the C _ { 2 } H _ { 2 } abundance .
Due to the relatively small absorption coefficient of the diamonds compared to other stellar dust grains , their spectral appearance is weak .
However , the weak interaction of the diamonds with the radiation field may give them an important role in the dust nucleation process .
The gas pressure will stay high and the gas will be much closer to hydrostatic equilibrium during possible diamond nucleation than is normally the case in dust forming stellar regions , and therefore allow ample time for the nucleation process .