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Astron. Astrophys. 333, 565-570 (1998)


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Cyclicities in the light variations of Luminous Blue Variables *

II. R 40 developing an S Doradus phase

C. Sterken ** 1, M. de Groot 2 and A.M. van Genderen 3

1 University of Brussels (VUB), Pleinlaan 2, B-1050 Brussels, Belgium
2 Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland
3 Leiden Observatory, Postbus 9513, 2300 RA Leiden, The Netherlands

Received 2 June 1997 / Accepted 13 January 1998

Abstract

Strömgren differential photometry of R 40 collected during the time interval 1986-1996 is analysed together with Walraven photometry. The gradual brightening of the star over the last 10 years can be described by a linear trend with superimposed oscillations (in [FORMULA] and y) with frequency 0.0008 cd-1
([FORMULA]  d cycle). We interpret these oscillations as "normal S Dor" phases, and suggest that the quasi-linear brightening of the star is the ascending branch of a growing very-long-term S Dor phase (VLT-SD), as found by van Genderen et al. (1997a) in AG Car and S Dor itself. As R 40 is now becoming fainter and bluer, the length of the VLT-SD cycle is about 20 years.

Key words: stars: individual: HD 68884= R 40(SMC) – stars: variables: other – supergiants – stars: oscillations – Magellanic Clouds

* Based on observations obtained at the European Southern Observatory at La Silla, Chile (applications ESO 56D-0249 and 58D-0118)
** Belgian Fund for Scientific Research (FWO)

Send offprint requests to: C. Sterken

© European Southern Observatory (ESO) 1998

Online publication: April 20, 1998
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