Detection of a centrifugal magnetosphere in one of the most massive stars in the rho Oph star-forming cloud

S. Hubrig (1), M. Schoeller (2), S.P. Jarvinen (1), M. Kueker (1), A.F. Kholtygin (3), P. Steinbrunner (4)

(1) AIP, (2) ESO, (3) Saint-Petersburg State University, (4) FU Berlin

Recent XMM-Newton observations of the B2 type star rho Oph A indicated a periodicity of 1.205d, which was ascribed to rotational modulation. Since variability of X-ray emission in massive stars is frequently the signature of a magnetic field, we investigated whether the presence of a magnetic field can indeed be invoked to explain the observed X-ray peculiarity. Two FORS2 spectropolarimetric observations in different rotation phases revealed the presence of a negative (B_z_all=-419+-101G) and positive (B_z_all=538+-69G) longitudinal magnetic field, respectively. We estimate a lower limit for the dipole strength as B_d = 1.9+-0.2kG. Our calculations of the Kepler and Alfven radii imply the presence of a centrifugally supported, magnetically confined plasma around rho Oph A. The study of the spectral variability indicates a behaviour similar to that observed in typical magnetic early-type Bp stars.

Reference: AN
Status: Manuscript has been accepted