Mass Loss in Red Giants

As we have already mentioned, red giant stars lose large amounts of mass from their outer envelopes. These losses are greatest in the RGB and in particular the AGB phases. An RGB star can eject mass at a rate corresponding to losing a solar mass every million years, while an AGB star can lose a solar mass every 10,000 years.

The adjacent image is a false-color radio emission map of the star TT Cygni, which is a cool red giant star about 1500 light years away in the constellation Cygnus. The observed radio emission is from carbon monoxide (CO) molecules that were presumably ejected from the envelope of the star (see the right panel). The large ring has a radius of about 1/4 light year; it is a shell of gas expanding outward from the star, which lies at the center. Based on its present motion, the ring appears to have been ejected from the star about 6000 years ago. The central radio emission (green and blue area in the center) is from material blown off from the star more recently (in the last few hundred years).