Re-evaluation of the Effect of Brown Dwarfs’ Viewing Geometry using a Bayesian Framework

A brown dwarf’s viewing geometry can affect measurements of variability amplitudes and emergent spectra. Historically, this angle was derived by combining rotation periods and vsini assuming that they are statistically independent. Recently, Masuda & Winn showed that this assumption could lead to biased results. The same study presented a solution that properly incorporates the correlation between the equatorial and projected rotational velocities. We use this Bayesian framework to re-calculate the viewing angles of 18 variable brown dwarfs with known vsini values and photometric rotation periods. We find that the viewing angle distributions change most significantly in equator-on cases. We re-derive the correlation coefficients between the viewing angle, variability amplitude, and color anomaly. These results confirm and refine these correlations and highlight the importance of proper posterior sampling to determine the inclination angle of the spin axis.