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Astron. Astrophys. 330, 169-174 (1998)


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Detection of short-term variations in Mira-type variables
from Hipparcos  photometry*

P. de Laverny 1, M.O. Mennessier 2, F. Mignard 3 and J. A. Mattei 4

1 Astronomiska Observatoriet, Box 515, S-751 20 Uppsala, Sweden
2 GRAAL, Université Montpellier II, cc72, Place Bataillon, F-34095 Montpellier cedex 5, France
3 Observatoire de la Côte d'Azur, CERGA, UMR CNRS 6527, F-06130 Grasse, France
4 AAVSO, 25 Birch street, Cambridge, Massachusetts 02138-1205, USA

Received 23 May 1997 / Accepted 17 September 1997

Abstract

The Hipparcos  photometric observations carried out over 37 months have been investigated in detail for [FORMULA] 250 Miras. This leads to an unexpected by-product of the mission that we already suspected from ESOC real-time reductions: the first detection from space of photometric short-term brightness variations in Mira-type variables. Altogether, 51 events in 39 M-type Miras are detected and no similar variations are found for S and C-type Miras. Their amplitude ranges from 0.23 mag up to 1.11 mag and their duration extends from 2 hours up to almost 6 days. These events seem to occur preferentially in late spectral types. We suggest that they might be related to molecular opacity effects.

Key words: stars: variables – stars: late-type – stars: AGB and post-AGB

* Based on data from the Hipparcos  astrometry ESA satellite

Send offprint requests to: P. de Laverny (laverny@astro.uu.se)

© European Southern Observatory (ESO) 1998

Online publication: January 8, 1998
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