Carbon stars with 10 μm silicate features

Abstract

23 carbon stars with IRAS LRS 2n, 3n and 6n are presented in this paper. Among them 7 samples have been identified to have 10 μm silicate features. It is found that on the IRAS color-color diagram most samples presented here are located in M star region or in the overlapping region of S-type stars and carbon stars. This means that the circumstellar shells of the stars are oxygen rich or are undergoing the stage of transition from the oxygen rich to the carbon rich. Observations of near infrared photometry and spectrophotometry indicate that the color distribution of stars presented here in the near infrared are the same as that of normal carbon stars. Furthermore, the stars observed all show deep absorption at 3.1μm caused by C 2H 2 and HCN. This means that central stars are really carbon rich. It is possible that the stars discussed in this paper are undergoing the evolutionary stage between oxygen rich M stars and normal carbon stars.