Discovery of a magnetic field in the B pulsating system HD 1976

The presence of a magnetic field can have a strong impact on the evolution of a binary star. However, only a dozen of magnetic OB binaries are known as of today and available to study this effect, including very few magnetic pulsating spectroscopic OB binaries. We aim at checking for the presence of a magnetic field in the B5IV hierarchical triple system HD 1976 with spectropolarimetric data obtained with Narval at the Bernard Lyot Telescope (TBL). We use orbital parameters of HD 1976 available in the literature to disentangle the Narval intensity spectra. We compute Stokes V profiles with the Least Square Deconvolution (LSD) technique to search for magnetic signatures. We then derive an estimate of the longitudinal magnetic field strength for each observation and for various line lists. Our disentangling of the intensity spectra shows that HD 1976 is a double-lined spectroscopic (SB2) binary, with the lines of the secondary component about twice broader than the ones of the primary component. We do not identify the third component. Moreover, we find that clear magnetic signatures are present in the spectropolarimetric measurements of HD 1976 and seem to be associated with the primary component. We conclude that HD 1976 is a magnetic slowly-pulsating double-lined spectroscopic binary star, with an undetected third component. It is the second such example known (with HD 25558).Comment: Accepted in A&A Letter to the Editor, 4 pages, 2 figures, 2 table

The Incidence of Magnetic Fields in Massive Stars: An Overview of the MiMeS Survey Component

With only a handful of known magnetic massive stars, there is a troubling deficit in the scope of our knowledge of the influence of magnetic fields on stellar evolution, and almost no empirical basis for understanding how fields modify mass loss and rotation in massive stars. Most remarkably, there is still no solid consensus regarding the origin physics of these fields - whether they are fossil remnants, or produced by contemporaneous dynamos, or some combination of these mechanisms. This article will present an overview of the Survey Component of the MiMeS Large Programs, the primary goal of which is to search for Zeeman signatures in the circular polarimetry of massive stars (stars with spectral types B3 and hotter) that were previously unknown to host any magnetic field. To date, the MiMeS collaboration has collected more than 550 high-resolution spectropolarimetric observations with ESPaDOnS and Narval of nearly 170 different stars, from which we have discovered 14 new magnetic stars.Comment: 7 pages (+1 for questions), 3 figures, to appear in proceedings of Stellar polarimetry: From birth to deat

Magnetic field topology of the unique chemically peculiar star CU Virginis

The late-B magnetic chemically peculiar star CU Vir is one of the fastest rotators among the intermediate-mass stars with strong fossil magnetic fields. It shows a prominent rotational modulation of the spectral energy distribution and absorption line profiles due to chemical spots and exhibits a unique strongly beamed variable radio emission. Little is known about the magnetic field topology of CU Vir. In this study we aim to derive, for the first time, detailed maps of the magnetic field distribution over the surface of this star. We use high-resolution spectropolarimetric observations covering the entire rotational period. These data are interpreted using a multi-line technique of least-squares deconvolution (LSD) and a new Zeeman Doppler imaging code based on detailed polarised radiative transfer modelling of the Stokes I and V LSD profiles. This new magnetic inversion approach relies on the spectrum synthesis calculations over the full wavelength range covered by observations and does not assume that the LSD profiles behave as a single spectral line with mean parameters. We present magnetic and chemical abundance maps derived from the Si and Fe lines. Mean polarisation profiles of both elements reveal a significant departure of the magnetic field topology of CU Vir from the commonly assumed axisymmetric dipolar configuration. The field of CU Vir is dipolar-like, but clearly non-axisymmetric, showing a large difference of the field strength between the regions of opposite polarity. The main relative abundance depletion features in both Si and Fe maps coincide with the weak-field region in the magnetic map. Detailed information on the distorted dipolar magnetic field topology of CU Vir provided by our study is essential for understanding chemical spot formation, radio emission, and rotational period variation of this star.Comment: 14 pages, 14 figures; accepted for publication in A&