THE CHROMOSPHERES OF CLASSICAL CEPHEIDS. 11. HIGH-RESOLUTION PROFILES OF THE Mg _II h AND k LINES

Authors

Edward G. Schmidt, University of Nebraska-LincolnFollow
Sidney B. Parsons, Laboratory for Astrophysics and Solar Physics, NASA/Goddard Space Fllght Center; and McDonald Observatory, The Un~verslty of Texas at Austin

Date of this Version

April 1984

Comments

Published in The Astrophysical Journal 279, 202 (1984). Published by the University of Chicago Press; copyright © 1984 American Astronomical Society; reproduced by permission of the AAS. http://www.journals.uchicago.edu/ApJ/front.html

Abstract

High-resolution spectra have been obtained with the long-wavelength camera of the International Ultraviolet Explorer for five Cepheids at a number of phases each. These data were used to study the profiles of the Mg _II h and k lines near 2900 Å. An emission feature often appears at the centers of the two lines. There are also central absorption features due to circumstellar or interstellar gas. They are often multiple and may or may not divide the emission into two peaks. The velocities of the circumstellar absorption components imply that they originate in a region which is at least several tenths of a stellar radius in extent. The strength of the emission rapidly increases to a maximum during rising light. It then tends to decline over most of the rest of the cycle, although there are instances of secondary maxima. The mean flux of the emission is lower than for nonvariable stars of similar temperature and luminosity, but at maximum strength the emission is appropriate to the instantaneous temperature.