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Astron. Astrophys. 362, 1065-1071 (2000)


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The derivation of pulsation velocities from Doppler line profiles in M-type Mira variables

M. Scholz 1,3 and P.R. Wood 2

1 Institut für Theoretische Astrophysik der Universität Heidelberg, Tiergartenstrasse 15, 69121 Heidelberg, Germany (scholz@ita.uni-heidelberg.de)
2 Australian National University, Research School of Astronomy and Astrophysics, Private Bag, Weston Creek PO, ACT 2611, Australia (wood@mso.anu.edu.au)
3 University of Sydney, Chatterton Department of Astronomy, School of Physics, NSW 2006, Australia

Received 12 April 2000 / Accepted 8 September 2000

Abstract

Model atmospheres for pulsating Mira variables have been used to examine the correction factor that should be used to convert radial velocities derived from the Doppler profiles of observed infrared lines into the velocities immediately above and below the strong shock in the atmosphere. The correction factor varies by a moderate amount depending on the lines selected. Correction factors of [FORMULA]1.25 and 1.4 are appropriate for the conversion of the observed velocities of the outflowing, post-shock and infalling pre-shock material, respectively, when the lines are strong. This is the case for the low excitation CO 1st vibrational overtone lines in the K band. A correction factor of 1.6 or more is appropriate for the weaker lines of OH and the 2nd vibrational overtone of CO in the H band. These results mean that the true pulsation velocity amplitude of a typical Mira variable is [FORMULA]34 km s-1. Such large pulsation velocity amplitudes are inconsistent with current models for Mira variables pulsating in the first overtone mode but are consistent with pulsation in the fundamental mode.

Key words: line: profiles – stars: atmospheres – stars: late-type – stars: oscillations – stars: variables: general

Send offprint requests to: M. Scholz

© European Southern Observatory (ESO) 2000

Online publication: October 30, 2000

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