Suchergebnisse

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. ; Fil: Wade, G. A. Royal Military College of Canada. Department of Physics; Canadá ; Fil: Barba, R. H. . Universidad de la Serena; Chile ; Fil: Grunhut, J. European Southern Observatories; Alemania ; Fil: Martins, F. Universite Montpellier Ii; Francia ; Fil: Petit, V. University of Delaware. Department of Physics and Astronomy. Bartol Research Institute; Estados Unidos ; Fil: Sundqvist, J. O. . Institut fur Astronomie und Astrophysik der Universität München; Alemania ; Fil: Townsend, R. H. D. . University of Wisconsin-Madison. Department of Astronomy; Estados Unidos ; Fil: Walborn, N. R. . Space Telescope Science Institute; Estados Unidos ; Fil: Alecian, E. UJF-Grenoble 1/CNRS-INSU. Institut de Planetologie et d'Astrophysique ´ de Grenoble (IPAG); Francia ; Fil: Alfaro, E. J. Consejo Superior de Investigaciones Cientificas. Instituto de Astrofísica de Andalucía; España ; Fil: Maíz Apellaniz, J. Consejo Superior de Investigaciones Cientificas. Instituto de Astrofísica de Andalucía; España ; Fil: Arias, Julia Ines. Universidad de la Serena; Chile ; Fil: Gamen, Roberto Claudio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Astrofísica de La Plata; Argentina ; Fil: Morrell, Nidia Irene. Observatories of the Carnegie Institution of Washington. Las Campanas Observatory; Estados Unidos ; Fil: Naze, Y. Universitée de Liéege; Bélgica ; Fil: Sota, A. Consejo Superior de Investigaciones Cientificas. Instituto de Astrofísica de Andalucía; España ; Fil: ud-Doula, A. Penn State Worthington Scranton; Estados Unidos ; Fil: MiMeS Collaboration.