We demonstrate that the angle between star ’ s rotation axis and the observer ’ s line-of-sight , usually called the inclination angle , can be reliably determined for Be stars via H \alpha emission-line profile fitting .
We test our method on a sample of 11 Be stars with available long-baseline interferometric data from the Navy Precision Optical Interferometer ( NPOI ) .
We fit the H \alpha emission line profile of each star to obtain a spectroscopic inclination angle i _ { H \alpha } .
We then obtain an independent inclination angle estimate , i _ { V ^ { 2 } } , by fitting the observed interferometric visibilities with model visibilities based on a purely geometric representation of the light distribution on the sky .
The sample differences , \Delta i \equiv i _ { H \alpha } - i _ { V ^ { 2 } } , are normally distributed with a mean of zero and a standard deviation of 6.7 degrees , and the linear correlation coefficient between i _ { H \alpha } and i _ { V ^ { 2 } } is r = 0.93 .
As Be stars comprise upwards of one fifth of all main-sequence B-type stars , this H \alpha line profile fitting technique has the potential to provide an efficient method for detecting correlated stellar spin axes in young open clusters .
Furthermore , if the orientation of the Be star circumstellar disk on the plane of the sky can be constrained by polarization measurements , it is possible to determine the full 3D stellar rotation vector of each Be star .