2015MNRAS.447.2551W -
Mon. Not. R. Astron. Soc., 447, 2551-2567 (2015/March-1)
Rotation, spectral variability, magnetic geometry and magnetosphere of the Of?p star CPD -28° 2561.
WADE G.A., BARBA R.H., GRUNHUT J., MARTINS F., PETIT V., SUNDQVIST J.O., TOWNSEND R.H.D., WALBORN N.R., ALECIAN E., ALFARO E.J., MAIZ-APELLANIZ J., ARIAS J.I., GAMEN R., MORRELL N., NAZE Y., SOTA A., UD-DOULA A. (The MiMeS Collaboration)
Abstract (from CDS):
We report magnetic and spectroscopic observations and modelling of the Of?p star CPD -28° 2561. Using more than 75 new spectra, we have measured the equivalent width variations and examined the dynamic spectra of photospheric and wind-sensitive spectral lines. A period search results in an unambiguous 73.41 d variability period. High-resolution spectropolarimetric data analysed using least-squares deconvolution yield a Zeeman signature detected in the mean Stokes V profile corresponding to phase 0.5 of the spectral ephemeris. Interpreting the 73.41 d period as the stellar rotational period, we have phased the equivalent widths and inferred longitudinal field measurements. The phased magnetic data exhibit a weak sinusoidal variation, with maximum of about 565 G at phase 0.5, and a minimum of about -335 G at phase 0.0, with extrema approximately in phase with the (double-wave) Hα equivalent width variation. Modelling of the Hα equivalent width variation assuming a quasi-3D magnetospheric model produces a unique solution for the ambiguous couplet of inclination and magnetic obliquity angles: (i, β) or (β, i) = (35°, 90°). Adopting either geometry, the longitudinal field variation yields a dipole polar intensity Bd = 2.6±0.9 kG, consistent with that obtained from direct modelling of the Stokes V profiles. We derive a wind magnetic confinement parameter η* ≃ 100, leading to an Alfvén radius RA ≃ 3-5R*, and a Kepler radius RK ≃ 20R*. This supports a physical scenario in which the Hα emission and other line variability have their origin in an oblique, corotating `dynamical magnetosphere' structure resulting from a magnetically channelled wind. Nevertheless, the details of the formation of spectral lines and their variability within this framework remain generally poorly understood.
Abstract Copyright:
© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society (2015)
Journal keyword(s):
stars: individual: CPD -28° 2561 - stars: magnetic field - stars: massive - stars: rotation
Errata:
erratum vol. 450, p. 2822 (2015)
Simbad objects:
7
Full paper
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