No evidence of a strong magnetic field in the Blazhko star RR Lyrae^*

¹ Observatoire de la côte d'Azur, UMR 6528, BP 4229, 06304 Nice Cedex 04, France
² Department of Physics, Royal Military College of Canada, PO Box 17000, Station “Forces”, Kingston, Ontario, Canada K7K 4B4
³ Department of Physics & Astronomy, the University of Western Ontario, London, Ontario, Canada N6A 3K7

Corresponding author: M. Chadid, chadid@obs-nice.fr

Received: 9 April 2003
Accepted: 9 October 2003

Abstract

In this paper we report a new series of high-precision (median  G) longitudinal magnetic field measurements of RR Lyrae, the brightest Blazhko star, obtained with the MuSiCoS spectropolarimeter over a period of almost 4 years from 1999-2002. These data provide no evidence whatsoever for a strong magnetic field in the photosphere of RR Lyrae, a result consistent with Preston's ([CITE]) results, but inconsistent with apparent magnetic field detections by Babcock ([CITE]) and Romanov et al. ([CITE], [CITE]). Following discussion of these disparate results, we conclude that RR Lyrae is a bona fide non-magnetic star, a conclusion which leads to the general falsification of models of the Blazkho effect requiring strong photospheric magnetic fields. Furthermore, due to the 4 year baseline of our observations, we can also dismiss the hypothesis that RR Lyrae undergoes a 4-year “magnetic cycle”. Therefore the origin of the observed 4–year modulation of RR Lyrae remains unexplained, and we stress the need for additional theoretical efforts to come to a better understanding of this phenomenon.