Mass loss in red giants

Extract

On high-dispersion spectrograms of some luminous M giants, the zero-volt lines of all abundant atoms and ions are double. (Fig. 1 (a), Pl. I, p. 112). This spectroscopic peculiarity was discovered by W. S. Adams and Miss MacCormack (1935), who wrote that “a possible explanation of the origin of the abnormal lines…… may be an envelope of gas surrounding the stars and expanding with a moderate velocity”. Recently it was found that some of the abnormal lines which occur in the M 5 II star α Herculis can also be seen in the spectrum of its visual companion, a giant G-type star. In this system, it is clear that the Adams-MacCormack model is correct: both stars are enveloped in gas that has been ejected from the M star (Fig. 2). Moreover, the circumstellar envelope of α Herculis must measure at least 2000 astronomical units in diameter, and in it the gas velocity exceeds the velocity of escape. The M star is clearly losing mass to the interstellar medium at a rate that has been estimated to be a about 10⁻⁷ solar masses per year.