The MiMeS survey of Magnetism in Massive Stars: magnetic analysis of the O-type stars

Abstract

We present the analysis performed on spectropolarimetric data of 97 O-type targets included in the framework of the MiMeS (Magnetism in Massive Stars) Survey. Mean Least-Squares Deconvolved Stokes I and V line profiles were extracted for each observation, from which we measured the radial velocity, rotational and nonrotational broadening velocities, and longitudinal magnetic field B ℓ . The investigation of the Stokes I profiles led to the discovery of 2 new multi-line spectroscopic systems (HD 46106, HD 204827) and confirmed the presence of a suspected companion in HD 37041. We present a modified strategy of the Least-Squares Deconvolution technique aimed at optimising the detection of magnetic signatures while minimising the detection of spurious signatures in Stokes V . Using this analysis, we confirm the detection of a magnetic field in 6 targets previously reported as magnetic by the MiMeS collaboration (HD 108, HD 47129A2, HD 57682, HD 148937, CPD-28 2561, and NGC 1624-2), as well as report the presence of signal in Stokes V in 3 new magnetic candidates (HD 36486, HD 162978, HD 199579). Overall, we find a magnetic incidence rate of 7 ± 3%, for 108 individual O stars (including all O-type components part of multi-line systems), with a median uncertainty of the B ℓ measurements of about 50 G. An inspection of the data reveals no obvious biases affecting the incidence rate or the preference for detecting magnetic signatures in the magnetic stars. Similar to A-and B-type stars, we find no link between the stars' physical properties (e.g. T eff , mass, age) and the presence of a magnetic field. However, the Of?p stars represent a distinct class of magnetic O-type stars.

Accretion, Outflows, and Winds of Magnetized Stars

“…The horizontal solid line marks the transition between the CM domain above and the DM domain below, while the vertical dashed line marks the divide between O-and B-type main sequence stars. Note that all O-stars show emission, with all but one (Plaskett's star, which has likely been spun-up by mass exchange from its close binary companion; Grunhut et al 2013.) located among the slow rotators Fig.…”

“…The two most extreme examples (ID 45 and 47) may be very close to critical rotation, and so provide a potential link to Be stars, which have not been found to have strong ordered fields, but for which rapid rotation is linked to decretion into an orbiting Keplerian disk. • The only rapidly rotating O-star is Plaskett's star (ID 6), which has likely been spun up by mass exchange with its close binary companion (Grunhut et al 2013). Many O-stars have very long rotation period, e.g.…”

The effects of surface fossil magnetic fields on massive star evolution – II. Implementation of magnetic braking in mesa and implications for the evolution of surface rotation in OB stars

“…Magnetic fields are routinely detected in stars across the entire Hertzsprung-Russell diagram (HRD), from early to late evolutionary phases (Donati & Landstreet 2009). Surface magnetic fields are detected in 7% of hot, massive, OB stars (Wade et al 2014(Wade et al , 2016Martins et al 2015;Neiner et al 2015;Morel et al 2015;Fossati et al 2015;Grunhut et al 2017;Shultz et al 2018;Petit et al 2019). Unlike those E-mail: z.keszthelyi@uva.nl detected in cool stars, these surface fields are likely not being actively generated by a dynamo mechanism, especially because there is no evidence that extended convection zones 1 1 Hot stars do have thin sub-surface layers where inefficient convection (accounting for usually ≈ 3% of the energy transport) occurs due to the iron opacity bump (Cantiello et al 2009), and while there might perhaps be dynamo activity in those layers (Cantiello & Braithwaite 2011), that would not give rise to the strong, globally organized fields which are observed in magnetic OB stars.…”

A search for strong magnetic fields in massive and very massive stars in the Magellanic Clouds

“…Knowledge of the magnetic properties of Galactic O and B stars has advanced remarkably over the last decade, largely due to the Magnetism in Massive Stars (MiMeS; Wade et al 2016) and B-Fields in OB stars (BOB; Fossati et al 2015) projects. These large-scale surveys have established their statistical incidence in the Galaxy (∼ 7 % of B-and O-type stars are magnetic; Grunhut et al 2017), the basic characteristics of these fields (i.e. strong, stable, and organised; e.g.…”