Shock-wave interpretation of emission lines in long-period variable stars. I. The velocity of the shock.

The emission lines seen in long-period variables are classified according to the mechanism by which they are formed. This leads to information on the physical conditions in several. regions, and especially to an estimate of the velocity differences between regions. The results are interpreted in terms of a spherical shock wave expanding outward at V 50 km 5- `and gradually decelerating. This high shock velocity in turn implies substantial mass loss and mechanical energy output. This also implies that (a) mechanical energy dominates in determining the atmospheric structure and (b) the atmosphere is extended and spherical geometry must be used. Subject headings: shock waves stars: emission-line - stars: long-period variables