All Rights Reserved. Please see the source code for details. These are evolved, intermediate mass stars which are ejecting large amounts of circumstellar gas and dust, and can readily be observed in CO lines.
Carbon stars are the single most important source of carbon returned to the interstellar medium.
The aim of the survey was to measure the relative amounts of the isotopes 12C and 13C in the stellar envelopes, and see how these ejecta will affect the isotopic ratio in surrounding gas clouds. Examples of the spectra are shown in the figure. This source had very weak 13CO emission, of only 13 mK, and the spectrum took 35 minutes of integration to detect. The line intensities were modelled using a radiative transfer code, based on large velocity gradients within the expanding envelope. 13, much more 13C-rich than the solar value of 89.