Astronomy & Astrophysics

Free access article

A&A 412, L25-L28 (2003)
DOI: 10.1051/0004-6361:20031675

Letter

$\mathsf{\eta}$ Car: the optical features at the 2003.5 low-excitation event

A. M. van Genderen¹, C. Sterken², W. H. Allen³ and W. Liller⁴

¹ Leiden Observatory, Postbus 9513, 2300RA Leiden, The Netherlands
² Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
³ Alvine Estate, Vintage Lane, RD 3, Blenheim, New Zealand
⁴ Casilla 5022, Reñaca, Viña del Mar, Chile

(Received 2 October 2003 / Accepted 31 October 2003)

Abstract
UBV and BVR photometry of $\eta$ Car during the 2003.5 low-excitation event - the considered periastron passage of a binary - is presented. The light and colour curves show a number of features, which were also seen at previous periastron passages: a light maximum of long duration with a superimposed flare-like event which is temporarily interrupted by an eclipse-like dip, and a steep decline in the U-B color index. The R brightness reached a minimum at the time of mid X-ray totality, probably implying that the H $\alpha$ emission line reached a minimum. The source of the optical flare-like event is probably not the same as the one causing the the X-ray radiation. It is tempting to consider the epoch of the R minimum and the mid- X ray totality - which roughly coincides with the UBV minimum - as the central moment of the 2003.5 low-excitation event.

Key words: technique: photometric -- stars: individual: $\eta$ Carinae -- variables -- supergiants

Offprint request: A. M. van Genderen, genderen@strw.leidenuniv.nl

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