Carbon and Hydrocarbon Molecules in Very Cool White Dwarfs

Abstract

We report on our investigations in progress on the importance of polyatomic molecules – especially of carbon and hydrocarbon – in the atmospheres of very cool helium-rich white dwarfs. For two sets of abundance ratios, model atmospheres with Teff = 5000 K, log g = 8.0 have been computed and the dependence of C3, C2H and C2H2 on abundance variations of H/He, C/He, O/He and N/He has been calculated in detail, with the absorption of carbon molecules included quantitatively. We discuss the possibility that C2H features can explain the observed IR flux deficiency for LHS 1126 at 1.6 μm and 2.0–2.3 μm.