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Astron. Astrophys. 339, 846-857 (1998)


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Limb-darkening and radii of M-type Mira models

K.-H. Hofmann 1, M. Scholz * 2 and P.R. Wood 3

1 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
2 Institut für Theoretische Astrophysik der Universität Heidelberg, Tiergartenstrasse 15, D-69121 Heidelberg, Germany
3 Mount Stromlo and Siding Spring Observatories, Institute of Advanced Studies, The Australian National University,
Weston Creek P.O. ACT 2611, Australia

Received 1 July 1998 / Accepted 2 September 1998

Abstract

Monochromatic limb-darkening and monochromatic radii predicted by the M-type Mira models of Bessell et al. (1996) and by new models described in Sect. 2 were computed for selected typical bandpasses used in interferometric and lunar occultation work. The new self-excited pulsation model series have periods and luminosities similar to o Ceti and R Leonis and comprise both fundamental (1 [FORMULA], 1.2 [FORMULA]) and first overtone (2 [FORMULA]) pulsators. Fundamental problems of defining and measuring radii of Mira variables caused by the large extension of their atmospheres are discussed. Effective temperatures defined in terms of Rosseland and continuum radii are generally well determinable with an inherent inaccuracy of a few percent, but special problems occur for very cool models or at phases when models are very cool, below about 2500 K.

Fits of simple uniform disk (UD), fully darkened disk (FDD) and Gauss-shaped limb-darkening curves to the model-predicted visibilities were performed and tabulated for a set of 26 [FORMULA] 12 model-filter-combinations covering a large variety of typical brightness distributions. These fits show that either the FDD or the Gauss curve is often a good or even excellent approximation. Limb-darkening curves for specific bandpasses of observational programs can be provided upon request.

Key words: techniques: interferometric – stars: AGB – stars: atmospheres – stars: late-type

* Visitor (March 1996) at Astrophysical Theory Centre (ATC), School of Mathematics and Mount Stromlo and Siding Spring Observatories, Australian National University

Send offprint requests to: K.-H. Hofmann, (khh@speckle.mpifr-bonn.mpg.de)

© European Southern Observatory (ESO) 1998

Online publication: October 22, 1998

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