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

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.