New observations of GD 99 are analysed. The unusual pulsation behaviour,
showing both long and short periods, has been confirmed. All the available
periods show a grouping of short and long period modes with roughly regular
spacing. If we interpret the groups separately, a binary nature can be a
possible explanation as in the similar cases of WD 2350-0054 and G29-38.Comment: 2 pages, 1 eps figure; has been accepted for publication in
Communications in Asteroseismology (Vol. 150, 2007), Proceedings of the
Vienna Workshop on the Future of Asteroseismolog