Inclination Bias in Techniques Used to Identify Be Star Candidates

Abstract

Several methods for identifying Be star candidates are reviewed for observational bias with respect to system inclination, that is the angle between the stellar/disk rotation axis and the observer's line of sight, with focus on two photometric methods that leverage narrow-band filters centred on H$\alpha$ and a spectroscopic method using a H$\alpha$ peak-finding algorithm. Tests for bias were performed using a sample of 20,000 synthetic Be stars drawn from a Salpeter initial mass function and computed libraries of spectral energy distributions and H$\alpha$ profiles. The spectroscopic method showed substantial bias against high inclinations ($i > 80^\circ$). Both photometric methods were biased against low inclinations, with one also biased against inclinations above $80^\circ$, resulting in a surplus in the Be star candidate detection rate for moderate inclinations ($ 50^\circ < i < 80^\circ$). Inclination probability distributions, including the random $\sin i$ factor, are given for the three methods that can be applied to observational samples.