Evidence of an asymmetrical Keplerian disk in the Br-gamma and He I emission lines around the Be star HD 110432

Ph. Stee1, A. Meilland1,2, Ph. Bendjoya1, F. Millour1, M. Smith3, A. Spang1, G. Duvert4, K.-H. Hofmann5 and F. Massi6

1 Laboratoire Lagrange, UMR 7293, Université de Nice-Sophia Antipolis (UNS), Observatoire de la Côte d’Azur (OCA), Boulevard de l’Observatoire, BP 4229, 06304 Nice Cedex 4, France
2 Physics and Astronomy Department, The University of Western Ontario, London, N6A 3K7, Ontario, Canada
3 Catholic University of America, 3700 San Martin Dr., Baltimore, MD 21218, USA
4 UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), UMR 5274, 38041 Grenoble, France
5 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
6 INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy

Context. HD 110432 was classified as a “gamma Cas X-ray analog” since it has similar peculiar X-ray and optical characteristics, i.e. a hard-thermal X-ray variable emission and an optical spectrum affected by an extensive disk. It might be a Be star harboring an accreting white dwarf or that the X-rays may come from an interaction between the surface of the star and its disk.
Aims. To investigate the disk around this Be star we used the VLTI/AMBER instrument, which combines high spectral (R = 12000) and high spatial (theta_min = 4 mas) resolutions.
Methods. We constrain the geometry and kinematics of its circumstellar disk from the highest spatial resolution ever achieved on this star.
Results. We obtain a disk extension in the Br-gamma line of 10.2 D_star and 7.8 D_star in the He I line at 2.05 micrometer assuming a Gaussian disk model. The disk is clearly following a Keplerian rotation. We obtained an inclination angle of 55 degree, and the star is a nearly critical rotator with Vrot/Vc = 1.00 ± 0.2. This inclination is greater than the value found for gamma Cas (about 42 degree), and is consistent with the inference from optical Fe II emission profiles that the inclination should be more than the gamma Cas value. In the near-IR continuum, the disk of HD 110432 is 3 times larger than gamma Cas’s disk. We have no direct evidence of a companion around HD 110432, but it seems that we have a clear signature for disk inhomogeneities as detected for zeta Tau. This asymmetrical disk detection may be interpreted within the one-armed oscillation viscous disk framework. Another finding is that the disk size in the near-IR is similar to other Be stars with different spectral types and thus may be independent of the stellar parameters, as found for classical Be stars.

Published in Astronomy & Astrophysics 550, A65
Preprints on the web at: arXiv:1301.2877


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