2004A&A...413.1087C

In this paper we report a new series of high-precision (median σ_B∼80 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 (1967, The Magnetic and Related Stars, ed. R. C. Cameron (Baltimore: Mono Book Corporation), 26) results, but inconsistent with apparent magnetic field detections by Babcock (1958ApJS....3..141B) and Romanov et al. (1987PAZh...13...69R, 1994BSAO...38..169R). 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.