5. Summary and discussion
The sdB star PG 1618B, which is located well inside the region of the (, log g ) plane where the sdB pulsators are expected to be, has a quite simple temporal spectrum, with two close peaks at about 6.95 and 7.18 mHz, and possibly some further low amplitude signals. Its brightness permits time-series observations not only in white light, but also in different colour bands, allowing possible nonadiabatic studies and mode identification. The UBV amplitudes and phases we measured are a first step in this direction. Comparing the amplitude spectra taken in different nights and a few months apart, we note a variability of the pulsation amplitudes which could be real, but could also be related to a more complicated spectrum with unresolved structures. More detailed observations with higher frequency resolution are needed to solve this question. At this level, we can only make some conjecture on the nature of the two peaks, which may have different spherical harmonic degrees and perhaps different radial indices too. Another possibility is that their separation is due to the rotational splitting, with the other components of the multiplet hidden in the noise or not excited at all; this hypothesis would imply a fast rotation velocity 4.
© European Southern Observatory (ESO) 2000
Online publication: July 13, 2000