The two new variables are probably multiperiodic. Additional rapid photometry observations are needed to get more informations on the richness of their non radial modes spectrum. The global amplitude-period correlation observed in ZZ Ceti stars, i.e. the amplitude increases with the periods, seems to be verified by the two new variables: KUV08368+4026 has a longer period and a larger amplitude than KUV11370+4222. There is another correlation between the periods (and amplitude) and the effective temperature: cooler ZZ Cetis have longer periods. To check whether the two new variables verify this correlation would require a determination of their effective temperature. The (B-V) color index, usually considered as an effective temperature indicator, is the same for the two stars. They should not have largely different effective temperature even if the (B-V) color index is a rather uncertain temperature indicator. More detailed atmospheric analysis are needed for these two DA white dwarfs.
With the discovery of these two new ZZ Ceti variables, the number of known pulsating white dwarfs of this type increases to 26. When comparing the power spectrum of KUV 08368 with the power spectrum of other ZZ Ceti stars, one finds a striking similarity with G29-38, HL Tau 76 and G255-2. The four of them show large amplitude variations and have common frequencies around 1.6 mHz and 2.0 mHz. That similarity is probably the signature of some fondamental mechanism we still have to decipher.
© European Southern Observatory (ESO) 1997
Online publication: June 30, 1998