Ca II K emission-line asymmetries among red giants.
SMITH G.H. and SHETRONE M.D.
Abstract (from CDS):
Measurements of the asymmetry of the K2emission line of Ca II have been made for a sample of bright field giants with B-V>1.15 observed with the Cassegrain echelle spectrometer on the McDonald Observatory 2.1 m telescope. The asymmetry of the Ca II K2line is quantified through measurement of a parameter V/R, which is defined as the ratio between the maximum counts recorded in the violet and red components of the double-peaked emission profile. Red-maximum asymmetry (V/R<1.0) is found in our sample of 35 giants only among stars with B-V>1.35, a trend that is still maintained (with one exception) with the inclusion of an additional sample of giants previously observed by us with the same spectrograph. Although exceptional stars can be found in the literature, the data support an earlier finding by R. Stencel that among luminosity class III field giants the occurrence of V/R<1.0 is generally restricted to effective temperatures cooler than 4320 K. This limit may coincide with the onset of pulsation.