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Session 80 - Central Stars of Planetary Nebulae.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center
We present the results of a CCD survey for variability in a sample of 29 hot, hydrogen-deficient planetary-nebula nuclei (PNNs). We identify six central stars (those of NGC 246, 1501, 2371-2, 2867, 5189, and 6905) as new low-amplitude, non-radially pulsating variables, similar to PG 1159-035 (GW Vir). This brings to 14 the number of objects now known in this class: nine are PNNs (the other three being K 1-16, Lo 4, and RX J2117+341), four are isolated PG 1159-type white dwarfs, and one is the peculiar WO field star Sand 3. The spectra of these stars range from Wolf-Rayet class WC 4 to white-dwarf type O(C), but all are hot, extremely hydrogen deficient, and rich in carbon and oxygen.
All our pulsating PNNs are characterized by power spectra that are highly variable on a timescale of weeks to months. One consequence of this instability is that the percentage of stars detected as pulsating is almost certainly an underestimate, and it is likely that most hot, hydrogen-deficient PNNs pulsate. In general, the principal pulsation periods of the PNN pulsators are longer than those of their GW Vir white-dwarf counterparts, suggesting that there is an evolutionary connection with the older, more compact white dwarfs whose nebulae have had time to dissipate. However, within the PNN subclass, there is no obvious correlation of period with PNN spectral type.
