Search for chromospheric MgII emission in Ap-type stars.

Abstract

Observations of the Mg II h and k line resonance doublet in the spectra of 10 of the latest Ap-type stars show no sign of emission cores in the broad absorption lines. Thus, the Mg II lines give no evidence for chromospheric activity in peculiar A-type stars; the present observations sharpen the boarder between active and non-active stars. This fact is discussed in connection with the problem of the onset of chromospheres and transition zones in A- and F-type main-sequence stars. Special attention is paid to the question of Alfvenic heating in the atmospheres of rapidly oscillating Ap-type stars.