A representative sample of Be stars V: H{\alpha} variability

TL;DR

This study investigates Hα variability in Be stars over a decade, examining potential links to spectral subtype and vsini, and finds variability patterns related to spectral type and rotational velocity.

Contribution

It provides the first long-term analysis of Hα variability in a diverse sample of Be stars, exploring dependencies on spectral subtype and vsini.

Findings

Full phase transitions likely occur over centuries.

Earlier spectral types and higher vsini show greater variability.

Variability increases with longer observation baselines for later types and lower vsini.

Abstract

Aims. We attempt to determine if a dependency on spectral subtype or vsini exists for stars undergoing phase-changes between B and Be states, as well as for those stars exhibiting variability in H{\alpha} emission. Methods. We analyse the changes in H{\alpha} line strength for a sample of 55 Be stars of varying spectral types and luminosity classes using five epochs of observations taken over a ten year period between 1998 and 2010. Results. We find i) that the typical timescale between which full phase transitions occur is most likely of the order of centuries, although no dependency on spectral subtype or vsini could be determined due to the low frequency of phase-changing events observed in our sample, ii) that stars with earlier spectral types and larger values of vsini show a greater degree of variability in H{\alpha} emission over the timescales probed in this study, and iii) a trend of increasing variability between the shortest and longest baselines for stars of later spectral types and with smaller values of vsini.