Discovery of two new pulsating DA (ZZ Ceti) white dwarfs.
FONTAINE G., BERGERON P., BRASSARD P., BILLERES M. and CHARPINET S.
Abstract (from CDS):
We report the detection of multiperiodic luminosity variations in the light curves of the two DA white dwarfs GD 244 and KUV 02464+3239. We selected these objects as candidate ZZ Ceti stars on the basis of our analysis of their optical spectra, which revealed that their atmospheric parameters place them inside the empirical instability strip in the logg-Teff plane. We find that GD 244 is an intermediate-amplitude pulsator with at least four excited modes with periods in the range 203-307 s, which is consistent with its position in the middle of the ZZ Ceti instability strip at Teff=11,680 K and logg=8.08. We compare the properties of GD 244 with those of GD 66, a previously known ZZ Ceti star that appears to be a photometric clone of the former. We also find that KUV 02464+3239 is a large-amplitude, long-period variable, which is again consistent with its position at Teff=11,290 K and logg=8.08 in the logg-Teff diagram, near the red edge of the empirical instability strip. The light curve of KUV 02464+3239 is dominated by a quasi-period of ∼ 832 s and resembles that of its photometric twin GD 154. Our findings bring to 31 the number of known gravity-mode ZZ Ceti pulsators.