The Correlation Between H\alpha\ Emission and Visual Magnitude During Long-Term Variations in Classical Be Stars

TL;DR

This study models the long-term variations in H-alpha emission and visual magnitude in Classical Be stars, showing how disk inclination, scale height, and stellar darkening influence observed correlations.

Contribution

It introduces simple disk models that explain positive and inverse correlations between H-alpha emission and brightness, highlighting the role of disk inclination and stellar rotation effects.

Findings

Correlation strength depends on disk scale height.

Inverse correlation linked to disk inclination.

Models align with observed Be star variability patterns.

Abstract

H\alpha\ equivalent widths and UBV magnitudes are calculated for Be star disk models that grow in size and/or density with time. We show that these simple models are consistent with the known Be star classes of positive and inverse correlations between long-term variations in H\alpha\ and V magnitude as identified by Harmanec. We support the conclusion of Harmanec that the distinction is controlled by the inclination of the disk to the line of sight. We demonstrate that the strength of these correlations, particularly those of an inverse correlation where the system becomes fainter as the H\alpha\ emission strength grows, is strongly influenced by the scale height of the inner Be star disk and the extent of the gravitational darkening of the central B star due to rapid rotation. This dependence may allow coordinated spectroscopic and photometric observations to better constrain these poorly known Be star parameters.