Discovery of Two New Pulsating DA (ZZ Ceti) White Dwarfs

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 log g-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 log g = 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 log g = 8.08 in the log g-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.

[1]  James Liebert,et al.  Discovery of p-Mode Instabilities in the Hot Subdwarf B Star PG 1047+003 , 1997 .

[2]  G. Fontaine,et al.  Optical and Ultraviolet Analyses of ZZ Ceti Stars and Study of the Atmospheric Convective Efficiency in DA White Dwarfs , 1995 .

[3]  Didier Saumon,et al.  New model atmospheres for very cool white dwarfs with mixed H/He and pure He compositions , 1995 .

[4]  R. Ashley,et al.  Asteroseismology of new pulsating white dwarfs , 1995 .

[5]  R. Stobie,et al.  A new large-amplitude variable white dwarf , 1993 .

[6]  Pierre Brassard,et al.  Adiabatic properties of pulsating DA white dwarfs. IV - an extensive survey of the period structure of evolutionary models , 1992 .

[7]  S. O. Kepler,et al.  The discovery of a new DAV star using IUE temperature determination , 1992 .

[8]  James Liebert,et al.  A spectroscopic determination of the mass distribution of DA white dwarfs , 1992 .

[9]  P. Bergeron,et al.  A spectroscopically predicted new ZZ Ceti variable: GD 165 , 1990 .

[10]  J. Liebert,et al.  Discovery of Helium in the Atmospheres of Cool DA Stars and Evidence for Convective Mixing , 1990 .

[11]  G. Fontaine,et al.  G238-53 - A new pulsating DA white dwarf , 1984 .

[12]  G. Fontaine,et al.  On the statistics of ZZ Ceti stars , 1982 .

[13]  S. Starrfield,et al.  Two new variable white dwarfs - G185-32 and G191-16 , 1981 .

[14]  G. Fontaine,et al.  GD 385 - A new ZZ Ceti variable , 1980 .

[15]  J. McGraw.  The physical properties of the ZZ Ceti stars and their pulsations. , 1979 .

[16]  H. Horn.  The physics of white dwarfs , 1979 .

[17]  E. L. Robinson,et al.  A new pulsating white dwarf - GD 154 , 1978 .

[18]  J. McGraw.  Southern hemisphere ZZ Ceti stars: the new variable L19-2 and BPM 30551. , 1977 .

[19]  J. McGraw.  BPM 31594: A new Southern-Hemisphere variable white dwarf , 1976 .

[20]  B. Lasker,et al.  High-frequency stellar oscillations. XI. The ZZ Ceti star BPM 30551. , 1976 .

[21]  E. L. Robinson,et al.  Observations of variable white dwarfs: one new variable and 35 nonvariables. , 1976 .

[22]  J. Greenstein.  Multichannel spectrophotometry and the luminosities of white dwarfs. , 1976 .

[23]  E. L. Robinson,et al.  High-speed photometry of luminosity-variable DA dwarfs : R 808, GD 99,and G 117-B15A. , 1976 .

[24]  E. L. Robinson,et al.  G 29-38 and G 38-39. Two new large-amplitude variable white dwarfs , 1975 .

[25]  T. Ulrych,et al.  High-frequency optical variables. II. Luminosity-variable white dwarfs and maximum entropy spectral analysis , 1974 .

[26]  B. Lasker,et al.  HIGH-FREQUENCY STELLAR OSCILLATIONS. VI. R548, A PERIODICALLY VARIABLE WHITE DWARF. , 1971 .

[27]  J. Ostriker,et al.  Ultrashort-period stellar oscillations. III. Power-spectrum analysis of photometric observations of white dwarfs. , 1969 .

[28]  A. Landolt.  A New Short-Period Blue Variable , 1968 .