Dust grains and gas in the circumstellar envelopes around luminous red giant stars

Abstract

With 12, 25, 60, and 100 μm fluxes given in the IRAS Point Source Catalog, the authors have constructed color-color plots that include more than 100 infrared bright red-giant stars. Carbon-rich and oxygen-rich red giants can be distinguished from each other based on the ratio of their 25 to 60 μm fluxes. Previously, the authors reported CO rotational emission from 64 cool red giants with large fluxes in the IRAS Point Source Catalog. Here they report CO emission from an additional 15 stars as well as HCN emission toward 11 stars. The HCN data and the color-color plots are used to classify and reclassify various stars as oxygen- or carbon-rich. In 1985 June the carbon star V Hya displayed a narrow CO emission feature superposed on a standard broad stellar CO profile. The narrow emission is probably the first example of a CO maser ever seen in either a circumstellar or interstellar environment.