Be Star Inclination Angles Derived from Hα Line Profile Fitting

T. A. A. Sigut, A. K. Mahjour, C. Tycner

We show that reliable estimates of the angle between a star's rotation axis and the line-of-sight (the stellar inclination angle) can be efficiently determined for Be stars via Hα emission-line profile modelling. Using a sample of eleven Be stars with available optical interferometry from the Naval Precision Optical Interferometer (NPOI), we compare stellar inclinations angles derived from fitting Hα line profiles to inclinations derived from the major and minor axes of the Be star disk light distributions on the sky. The differences between these two methods are consistent with a normal distribution of a mean of zero and a standard deviation of 7^◦. As Be stars comprise approximately one-fifth of all upper-main sequence B stars, the Hα profile fitting method is an efficient method for detecting correlated rotation axis in young, open clusters. In addition, the combination of a measured inclination angle and a polarization position angle (that constrains the orientation of the disk's major axis on the sky) can be used to reconstruct the 3D direction of a Be star's rotation axis.

Proceedings of the Polish Astronomical Society, vol. 11, 81-88 (2020)

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