Observational Study of the Peculiar Carbon Stars with Silicate Emission Features

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Since the peculiar carbon stars with silicate emission were found in 1986, astronomers were puzzled about the origin of the circumstellar emission. We have surveyed the H_2O and SiO emission for the peculiar carbon stars in both the northern and southern skies. The H_2O maser is observed only in an oxygen-rich circumstellar shell. and the SiO around an oxygen-rich photosphere. Therefore, our survey was designed to answer the question about the unseen oxygen-rich star in the system.The H_2O observations were carried out using Nobeyama 45m and Parkes 64m telescopes. We have observed all the nine peculiar stars, of which two identifications were found to be wrong from our optical spectroscopic study. Of the remaining seven objects we have detected the maser emission from three stars. The existence of oxygen-rich circumstellar shell is now established by this survey. The high detection rate of 43% indicates that the rapid mass loss is underway in the system.Nobeyama 45m and ESO/SEST 15m telescopes were used in the SiO survey. None of the peculiar carbon stars showed the maser emission. The SiO maser is a good probe for the stellar photosphere with oxygen-rich abundances. The non-detection is against the binary model hypothesis with an oxygen-rich stellar component.In summary, our search for the maser emission confirmed the oxygen-rich chemistry in the circumstellar shell, but cast a question about the existence of the oxygen-rich star in the peculiar carbon star system.