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Astron. Astrophys. 326, 640-646 (1997)

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Cyclicities in the light variations of LBVs *

I. The multi-periodic behaviour of the LBV candidate [FORMULA]  Sco

small.htm C. Sterken1; **, 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, 2300RA Leiden, The Netherlands

Received 2 June 1996 / Accepted 14 May 1997

Abstract

Differential Strömgren uvby photometry of [FORMULA]  Sco collected during the time interval 1982-1995 is analysed together with new VBLUW photometry with a complementary discussion of unpublished JHKLM data. We report the discovery of a [FORMULA] 1750-2200 d regular oscillation of amplitude [FORMULA] in all bands, and pulsation-like oscillations with at least one frequency [FORMULA] ([FORMULA] days) and a possible second frequency [FORMULA] days). Most likely, all such stars exhibit multi-periodic light variability. A strong noise component remaining in the prewhitened signal leads us to postulate that the driver for LBV-like eruptions is stochastic resonance. This hypothesis is supported by the historic light curve of [FORMULA]  Sco which shows that two centuries ago the star was about 2 magnitudes brighter, while a millenium ago it was only 1 magnitude brighter than today, an indication that [FORMULA]  Sco should be regarded as a candidate Luminous Blue Variable.

Key words: stars: variables stars: oscillations stars: LBVs stars: individual:  Sco techniques: photometric

* Based on observations obtained at the European Southern Observatory at La Silla, Chile
** Belgian Fund for Scientific Research (FWO)

Send offprint requests to: C. Sterken

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© European Southern Observatory (ESO) 1997

Online publication: October 15, 1997
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