On the incidence of magnetic fields in slowly-pulsating B, β Cephei and B-type emission line stars

We have obtained 40 high-resolution circular spectropolarimetric measurements of 12 slowly-pulsating B (SPB) stars, 8 β Cephei stars and two Be stars with the ESPaDOnS and NARVAL spectropolarimeters. The aim of these observations is to evaluate recent claims of a high incidence of magnetic field detections in stars of these types obtained using low-resolution spectropolarimetry by Hubrig et al. (2006, 2007, 2009). The precision achieved is generally comparable to or superior to that obtained by Hubrig et al., although our new observations are distinguished by their resolution of metallic and He line profiles, and their consequent sensitivity to magnetic fields of zero net longitudinal component. In the SPB stars we confirm the detection of magnetic field in one star (16 Peg), but find no evidence of the presence of fields in the remaining 11. In the β Cep stars, we detect a field in ξ CMa, but not in any of the remaining 7 stars. Finally, neither of the two B-type emission line stars shows any evidence of magnetic field. Based on our results, we conclude that fields are not common in SPB, β Cep andB-type emission line stars, consistent with the general rarity of fields in the broader population of main sequence B-type stars. A relatively small, systematic underestimation of the error bars associated with the FORS1 longitudinal field measurements of Hubrig et al. (2006, 2007, 2009) could in large part explain the discrepancy between their results and those presented here.