A representative sample of Be stars

V. Hα variability^⋆

Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead CH41 1LD, UK
e-mail: R.M.Barnsley@ljmu.ac.uk

Received: 20 September 2012
Accepted: 9 May 2013

Abstract

Aims. We attempt to determine if a dependency on spectral subtype or vsin i exists for stars undergoing phase-changes between B and Be states, as well as for those stars exhibiting variability in Hα emission.

Methods. We analysed the changes in Hα 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 vsin i 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 vsin i show a greater degree of variability in Hα 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 vsin i.