Rotation, spectral variability, magnetic geometry and magnetosphere of the Of?p star CPD -28° 2561

• Autores: 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.; Maíz Apellaniz, J; Arias, Julia Ines; Gamen, Roberto Claudio; Morrell, Nidia Irene; Naze, Y.; Sota, A; ud-Doula, A.; MiMeS Collaboration
• Año de publicación: 2015
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: CPD -28° 2561 (estrella); Magnetic fields; Massive stars; Rotation
• Institución: Consejo Nacional de Investigaciones Científicas y Técnicas

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.