From observations made with the ESPaDOnS spectropolarimeter, recently installed on the 3.6‐m Canada–France–Hawaii Telescope, we report the discovery of a strong magnetic field in the Of?p spectrum variable HD 191612 – only the second known magnetic O star (following θ1 Ori C). The stability of the observed Zeeman signature over four nights of observation, together with the non‐rotational shape of line profiles, argues that the rotation period of HD 191612 is significantly longer than the 9‐d value previously proposed. We suggest that the recently identified 538‐d spectral variability period is the rotation period, in which case the observed line‐of‐sight magnetic field of −220 ± 38 G implies a large‐scale field (assumed dipolar) with a polar strength of about −1.5 kG. If confirmed, this scenario suggests that HD 191612 is, essentially, an evolved version of the near‐zero‐age main‐sequence magnetic O star θ1 Ori C, but with an even stronger field (about 15 kG at an age similar to that of θ1 Ori C). We suggest that the rotation rate of HD 191612, which is exceptionally slow by accepted O‐star standards, could be due to angular momentum dissipation through a magnetically confined wind.

We present a catalogue of new spectral types for hot, luminous stars in the Small Magellanic Cloud. The catalogue contains 4161 objects, giving an order of magnitude increase in the number of SMC stars with published spectroscopic classifications. The targets are primarily B- and A-type stars (2862 and 853 objects respectively), with 1 Wolf-Rayet, 139 O-type, and 306 FG stars, sampling the main sequence to ~mid-B. The selection and classification criteria are described, and objects of particular interest are discussed, including UV-selected targets from the Ultraviolet Imaging Telescope (UIT) experiment, Be and B[e] stars, `anomalous A supergiants', and composite-spectrum systems. We examine the incidence of Balmer-line emission, and the relationship between H-gamma equivalent width and absolute magnitude for BA stars.Comment: 27 pages, 17 figures (reduced size). Accepted for publication in MNRAS. Both a postscript version with normal res. figs and the full catalogue is available from http://www.ing.iac.es/~cje/2dF.htm

This paper reports high‐precision Stokes V spectra of HD 191612 acquired using the ESPaDOnS spectropolarimeter at the Canada–France–Hawaii Telescope, in the context of the Magnetism in Massive Stars (MiMeS) Project. Using measurements of the equivalent width of the Hα line and radial velocities of various metallic lines, we have updated both the spectroscopic and orbital ephemerides of this star. We confirm the presence of a strong magnetic field in the photosphere of HD 191612, and detect its variability. We establish that the longitudinal field varies in a manner consistent with the spectroscopic period of 537.6 d, in an approximately sinusoidal fashion. The phases of minimum and maximum longitudinal field are, respectively, coincident with the phases of maximum and minimum Hα equivalent width and Hp magnitude. This demonstrates a firm connection between the magnetic field and the processes responsible for the line and continuum variability. Interpreting the variation of the longitudinal magnetic field within the context of the dipole oblique rotator model, and adopting an inclination i= 30° obtained assuming alignment of the orbital and rotational angular momenta, we obtain a best‐fitting surface magnetic field model with obliquity β= 67°± 5° and polar strength Bd= 2450 ± 400 G. The inferred magnetic field strength implies an equatorial wind magnetic confinement parameter η*≃ 50, supporting a picture in which the Hα emission and photometric variability have their origin in an oblique, rigidly rotating magnetospheric structure resulting from a magnetically channelled wind. This interpretation is supported by our successful Monte Carlo radiative transfer modelling of the photometric variation, which assumes the enhanced plasma densities in the magnetic equatorial plane above the star implied by such a picture, according to a geometry that is consistent with that derived from the magnetic field. Predictions of the continuum linear polarization resulting from Thompson scattering from the magnetospheric material indicate that the Stokes Q and U variations are highly sensitive to the magnetospheric geometry, and that expected amplitudes are in the range of current instrumentation.

We report magnetic and spectroscopic observations and modelling of the Of?p star HD 148937 within the context of the Magnetism in Massive Stars (MiMeS) Large Program at the Canada–France–Hawaii Telescope. 32 high signal‐to‐noise ratio circularly polarized (Stokes V) spectra and 13 unpolarized (Stokes I) spectra of HD 148937 were acquired in 2009 and 2010. A definite detection of a Stokes V Zeeman signature is obtained in the grand mean of all observations [in both least‐squares deconvolved (LSD) mean profiles and individual spectral lines]. The longitudinal magnetic field inferred from the Stokes V LSD profiles is consistently negative, in contrast to the essentially zero field strength measured from the diagnostic null profiles. A period search of new and archival equivalent width measurements confirms the previously reported 7.03 d variability period. The variation of equivalent widths is not strictly periodic: we present evidence for evolution of the amount or distribution of circumstellar plasma. Interpreting the 7.03 d period as the stellar rotational period within the context of the oblique rotator paradigm, we have phased the equivalent widths and longitudinal field measurements. The longitudinal field measurements show a weak sinusoidal variation of constant sign, with extrema out of phase with the Hα variation by about 0.25 cycles. From our constraint on v sin i≤ 45 km s−1, we infer that the rotational axis inclination i≤ 30°. Modelling the longitudinal field phase variation directly, we obtain the magnetic obliquity β= 38+17−28° and dipole polar intensity Bd= 1020−380+310 G. Simple modelling of the Hα equivalent width variation supports the derived geometry. The inferred magnetic configuration confirms the suggestion of Nazé et al., who proposed that the weaker variability of HD 148937 as compared to other members of this class is a consequence of the stellar geometry. Based on the derived magnetic properties and published wind characteristics, we find a wind magnetic confinement parameter η*≃ 20 and rotation parameter W= 0.12, supporting a picture in which the Hα emission and other line variability have their origin in an oblique, rigidly rotating magnetospheric structure resulting from a magnetically channelled wind.

We present for the first time phase-resolved UV spectroscopy of an Of?p star, namely, HD 191612. The observations were acquired with the Space Telescope Imaging Spectrograph (STIS) on-board the Hubble Space Telescope (HST). We report the variability observed in the main photospheric and wind features and compare the results with previous findings for the Of?p star HD 108. We show that UV line strengths, Hα, and longitudinal magnetic field, vary coherently according to the rotational period (P rot = 537.6d), providing additional support for the magnetic oblique rotator scenario. The stellar and wind parameters of HD 191612 are obtained based on NLTE expanding atmosphere models. The peculiar wind line profile variations revealed by the new STIS data -not reproduced by 1D atmosphere models -are addressed through non-spherical MHD simulations coupled with radiative transfer. The basic aspects of the UV variability observed are explained and the structure of the dynamical magnetosphere of HD 191612 is discussed.

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We report ultra‐high‐resolution observations of Na i, Ca ii, K i, CH and CH+ for interstellar sightlines towards 12 bright stars in Orion. These data enable the detection of many more absorption components than previously recognized, providing a more accurate perspective on the absorbing medium. This is especially so for the line of sight to the Orion nebula, a region not previously studied at very high resolution. Model fits have been constructed for the absorption‐line profiles, providing estimates for the column density, velocity dispersion and central velocity for each constituent velocity component. A comparison between the absorption occurring in sightlines with small angular separations has been used, along with comparisons with other studies, to estimate the line‐of‐sight velocity structures. Comparisons with earlier studies have also revealed temporal variability in the absorption‐line profile of ζ Ori, highlighting the presence of small‐scale spatial structure in the interstellar medium on scales of ≈10 au. Where absorption from both Na0 and K0 is observed for a particular cloud, a comparison of the velocity dispersions measured for each of these species provides rigorous limits on both the kinetic temperature and turbulent velocity prevailing in each cloud. Our results indicate the turbulent motions to be subsonic in each case. abundance ratios are derived for individual clouds, providing an indication of their physical state.

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