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Astron. Astrophys. 337, 393-402 (1998)

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Light variations of massive stars ([FORMULA] Cyg variables) *

XVI. The LMC supergiants R 85 (LBV) and R 110 (LBV) and the SMC supergiants R 42 and R 45

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

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

Received 19 February 1998 / Accepted 20 May 1998

Abstract

Multi-colour photometry of four variable supergiants in the LMC and SMC, viz. R 85, R 110, R 42 and R 45, is searched for periods, studied and discussed. The suspected LBV R 85 is undoubtedly an active LBV, though not as spectacular as R 110. Their microvariations superimposed on the S Dor-activity are analyzed as well as those exhibited by R 42 and R 45. Often, a period search is difficult because of the very complicated micro-variability. We suggest that this is caused by an intricate multi-cyclic behaviour combined with stochastic processes. The length of the strongest cyclicity in the power spectrum of R 42 (128 d) is of the order of the rotation periods of BA-type supergiants.

In connection with our findings described in the present paper and the previous ones, we discuss various competing theoretical models on the instability of [FORMULA] Cyg variables, including the LBVs.

Key words: stars: variables – stars: supergiants – stars: individual R 42 = HD 7099, R 45 = HD 7583, R 85 = HDE 269321, R 110 = HDE 269662

* Based on observations obtained at the European Southern Observatory at La Silla, Chile (observing proposals 55D-0317, 56D-0249, 57D-0133 and 58D-0118)
** Belgian Fund for Scientific Research (FWO)

Send offprint requests to: A.M. van Genderen

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© European Southern Observatory (ESO) 1998

Online publication: August 17, 1998
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