IRAS 03201+5459: a C-rich AGB star with silicate absorption

Abstract

IRAS 03201+5459 is a late-type star with a circumstellar envelope according to its IRAS color. It has no identification at optical or near-infrared wavelengths. A full ISO-SWS spectrum between 2.3 and 43 mu m was taken at a resolution of about ~ 300 to investigate its nature. The spectrum shows the 9.7 mu m feature in absorption, usually seen in O-rich envelopes, and the 3 mu m feature in absorption which is related to C-rich late-type stars. Furthermore, modeling of the spectral energy distribution indicates the necessity of C-based dust. To understand these conflicting spectral features, we have estimated interstellar extinction in the direction of IRAS 03201+5459 by different methods. In no case can we get a sufficiently large A_V to explain the observed strength of the 9.7 mu m absorption feature as due to interstellar extinction. Therefore, we investigated the hypothesis that a central C-rich star is surrounded by an inner C-rich shell and an outer O-rich shell (the object may be in the transition stage of evolution from an O-rich to a C-rich star). However, this require a very short lifetime of the object as a C-rich star, and then the similarity between IRAS and ISO spectra makes this hypothesis difficult to sustain. Alternatively O-rich material around the C-star IRAS 03201+5459 might be confined into more stationary disk-like configuration which is seen (almost) edge-on. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with participation of ISAS and NASA