Inclination Bias in Techniques Used to Identify Be Star Candidates

TL;DR

This study evaluates the inclination bias of photometric and spectroscopic methods for identifying Be star candidates, revealing significant biases at high and low inclinations through analysis of synthetic star samples.

Contribution

It provides a comprehensive assessment of inclination biases in common Be star detection techniques and offers probability distributions for different observational methods.

Findings

Spectroscopic method biased against high inclinations (>80°).

Photometric methods biased against low inclinations, with one also biased above 80°.

Biases lead to overrepresentation of moderate inclinations (50°-80°) in detections.

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.