Open AccessSimultaneous photometry and spectroscopy of the Be star 28 (ω) CMa – I. Observational evidence of the periodic components of rapid variability
Author(s) -
Štefl S.,
Aerts C.,
Balona L. A.
Publication year - 1999
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1999.02324.x
Subject(s) - physics , photometry (optics) , astrophysics , amplitude , stars , be star , light curve , astronomy , principal component analysis , rotation period , line (geometry) , starspot , geometry , optics , statistics , mathematics
We analyse the periodic variability of the Be star 28 (ω) CMa. The data consist of 275 new He I 6678 line profiles of high spectral and temporal resolution, and new Strömgren and Geneva photometry. The photometric analysis has been extended by including previously published data to cover an interval of 16 yr. The principal spectroscopic period of 1.37 d is confirmed by analysis of He I 6678 modes and moments. There is evidence to show that a single period is insufficient to explain the variation in the line wings. In particular, the variation of the second moment, which samples the line wings, is best described when a second period is included. The photometric data have been divided into 10 sets in which the time is sufficiently contiguous for period analysis. These sets have been smoothed to remove as well as possible the long‐term irregular variations which are always present in Be stars. The residuals have then been analysed for coherent periodicities using several techniques. Evidence for one or the other of the two known spectroscopic periods can be found in individual data sets. By an analysis in which two periods are assumed, it is possible to recover both the principal spectroscopic period and the satellite period of 1.46 d. Unlike in the He I 6678 line profiles, the latter period seems to be most often present in the light variations. The amplitude of the periodic components of the light variation is only a few millimagnitudes, in contrast to the very large radial velocity amplitude. We find that the photometric amplitudes of the two periodic components, and their ratio, vary smoothly on a time‐scale of years. The amplitudes are larger in seasons when the mean brightness is higher.