A photometric comparison of B and Be stars using Gaia DR3

Previous studies have observed significant photometric differences between non-emission B-type and classical Be stars, however the precise mechanism responsible for these differences is unclear. This study combines the Bright Star Catalogue with Tycho and Gaia photometry to create a homogeneous sample of 1015 of the closest and brightest B and Be-type field stars with 90 per cent of objects at distances <500 pc. Due to their proximity, the extinction towards these objects is very low, ensuring we minimize any obfuscation in the reddening correction and final photometry. We present our findings in both Tycho and Gaia photometry through colour magnitude diagrams and present intrinsic colours and absolute magnitudes for each spectral type. We find Be stars are on average ∼0.5 mag brighter in both Gaia G and Tycho VT compared to non-emission B stars of the same spectral type. Additionally, we find tentative evidence that Be stars are redder in Gaia Bp−Rp, particularly for the earlier types, but have similar Tycho BT−VT colours. We test the effects of gravitational darkening due to rapid rotation and binarity on the photometry of our sample and find both to be insufficient to explain the observed photometric differences between B and Be stars. We conclude that the most likely mechanism responsible for the observed photometric differences is the combined effect of the circumstellar disc and stellar evolution up the main sequence, with the disc dominating early-types and evolution dominating late type stars.