LTE MODEL ATMOSPHERES FOR HOT, HELIUM-RICH DEGENERATE STARS

A new grid of hot, high-gravity LTE model atmospheres has been developed for the analysis of EXOSAT soft X-ray observations of He-rich degenerates. H, He, C, N and O opacity sources are included in the calculation and their distribution within the model stellar envelopes is homogeneous. Since He-rich degenerates have an extremely uncertain composition, these models span a uniquely large range of compositions in comparison with earlier publications - CNO: He varying from 0.01 to 80 times the solar value (by number) and H: He from 0 to 10 times solar abundance. The grid was calculated for temperatures of 50 000-200 000 K. A value of log g= 7 was used in most cases but it ranged from 5-8 for selected compositions. The emergent fluxes are presented for all the models calculated and the effect of surface gravity and composition on the emergent fluxes is discussed. A number of the models are compared with other published calculations to verify the code used and to assess the importance of non-LTE effects upon the emergent soft X-ray fluxes at high temperature and gravity. © Royal Astronomical Society.