Evidence for Instability Among Sub-Luminous Stars

Extract

A programme of spectroscopic study of sub-luminous stars has been in progress at Palomar, using the coudé spectrograph. Various types of objects have been studied and some preliminary results are available. Certain other programmes will, when completed, be relevant to the subject-matter of this Symposium. A survey of possible velocity variations in sub-dwarfs of spectral types A to G is in progress. So far I can report that no emission lines have been found, and that there are very few spectroscopic binaries in this group. In another programme, the depth of the late-type absorption lines in the composite spectra of SS Cygni stars will be used to estimate the luminosities of the hot components near their minima. Spectra of old novae are also being obtained with a dispersion of 38 å/mm. Plates obtained thus far show that complex structure still exists in the emission bands.