The structure of HO shells in Mira atmospheres

Correlation with disk brightness distributions and a spectrophotometric signature

¹ Observatoire Astronomique de Strasbourg, Université L. Pasteur & CNRS (UMR 7550), 67 000 Strasbourg, France
² Institut f. Theoretische Astrophysik der Universität Heidelberg, Tiergartenstr. 15, 69121 Heidelberg, Germany and School of Physics, University of Sydney, NSW 2006, Australia e-mail: scholz@ita.uni-heidelberg.de

Corresponding author: A. Tej, tej@astro.u-strasbg.fr

Received: 19 November 2002
Accepted: 6 January 2003

Abstract

Dynamic models of M-type Mira variables predict the occurrence of water “shells", i.e. of zones of high H₂O density and high H₂O absorption inside the stellar atmosphere. The density, position and width of these shells is closely correlated with different types of two-component shapes of the intensity distribution on the disk in the H, K and L near-continuum bandpasses. We investigate these correlations and highlight the role of a spectrophotometric H₂O index that warns against serious complications in diameter measurements in the case of substantial water contamination of the bandpass of observation. Simultaneous spectrophotometric and interferometric measurements may allow observers to estimate real continuum diameters more precisely.