Variations of the high-level Balmer line spectrum of the helium-strong star Sigma Orionis E

Abstract

Using the high-level Balmer lines and continuum, we trace the density structure of two magnetospheric disk segments of the prototypical Bp star sigma Ori E (B2p) as these segments occult portions of the star during the rotational cycle. High-resolution spectra of the Balmer lines >H9 and Balmer edge were obtained on seven nights in January-February 2007 at an average sampling of 0.01 cycles. We measured equivalent width variations due to the star occultations by two disk segments 0.4 cycles apart and constructed differential spectra of the migrations of the corresponding absorptions across the Balmer line profiles. We first estimated the rotational and magnetic obliquity angles. We then simulated the observed Balmer jump variation using the model atmosphere codes synspec/circus and evaluated the disk geometry and gas thermodynamics. We find that the two occultations are caused by two disk segments. The first of these transits quickly, indicating that the segment resides in a range of distances, perhaps 2.5-6R_star, from the star. The second consists of a more slowly moving segment situated closer to the surface and causing two semi-resolved absorbing maxima. During its transit this segment brushes across the star's "lower" limb. Judging from the line visibility up to H23-H24 during the occultations, both disk segments have mean densities near 10^{12} cm^{-3} and are opaque in the lines and continuum. They have semiheights less than 1/2 of a stellar radius, and their temperatures are near 10500K and 12000K, respectively. In all, the disks of Bp stars have a much more complicated geometry than has been anticipated, as evidenced by their (sometimes) non-coplanarity, de-centerness, and from star to star, differences in disk height.

arXiv commentAccepted by Astron. Astrophys, 13 pages, 4 embedded figures

References in corpus (11)

• A Grid of NLTE Line-Blanketed Model Atmospheres of Early B-type Stars
• Physical Parameters and Wind Properties of Galactic Early B Supergiants
• The Rigidly Rotating Magnetosphere of Sigma Ori E
• Centrifugal Breakout of Magnetically Confined Line-Driven Stellar Winds
• The light variability of the helium strong star HD 37776 as a result of its inhomogeneous elemental surface distribution
• XMM-Newton observations of the sigma Ori cluster. I. The complex RGS spectrum of the hot star sigma Ori AB
• Discovery of X-ray flaring on the magnetic Bp-star sigma Ori E
• Wind Circulation in Selected Rotating Magnetic Early-B Stars
• Multicomponent radiatively driven stellar winds IV. On the helium decoupling in the wind of sigma Ori E
• Distribution of magnetically confined circumstellar matter in oblique rotators
• The magnetic Bp star 36 Lyncis, II. A spectroscopic analysis of its co-rotating disk

Cited by in corpus (5)

• HR 5907: Discovery of the most rapidly rotating magnetic B-type star by the MiMeS Collaboration
• The Discovery of a Strong Magnetic Field and Co-rotating Magnetosphere in the Helium-weak Star HD 176582
• Metal abundances in hot white dwarfs with signatures of a superionized wind
• Polarimetric observations of $\sigma$ Orionis E
• Spots structure and stratification of helium and silicon in the atmosphere of He-weak star HD 21699