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Astron. Astrophys. 330, 1109-1119 (1998)

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Near-infrared narrow-band photometry of M-giant and Mira stars: models meet observations

R. Alvarez 1 and B. Plez 2, 3

1 GRAAL, Université Montpellier II, UPRESA 5024/CNRS, F-34095 Montpellier Cedex 05, France
2 Astronomiska Observatoriet, box 515, S-751 20 Uppsala, Sweden
3 Atomspektroskopi, Fysiska Institution, box 118, S-221 00 Lund, Sweden (plez@fysik.lu.se)

Received 20 June 1997 / Accepted 19 September 1997

Abstract

From near-infrared, narrow-band photometry of 256 oxygen-rich Mira variables we obtain evidence about the loops that these stars follow in colour-colour diagrams. We also find a phase lag between indices related to molecular band-strength of titanium oxide and vanadium oxide. We compute colours for normal M-giants and Miras using hydrostatic and hydrodynamic model atmospheres and very extensive up-to-date line lists. Normal M-giants colours are well reproduced, reaching a high quantitative agreement with observations for spectral types earlier than M7. The out-of-phase variations of the various spectral features of Miras are also acceptably reproduced, despite limitations in the modelling. This enables us to confirm that the phase lag phenomenon results from the propagation of perturbations in the extended atmosphere. It opens new perspectives in the spectral modelling of Miras.

Key words: physical data and processes: molecular data – stars: atmospheres – stars: AGB and post-AGB – stars: variables: Miras

Send offprint requests to: alvarez@graal.univ-montp2.fr

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© European Southern Observatory (ESO) 1998

Online publication: January 27, 1998
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