The asteroseismological potential of the pulsating DB white dwarf stars CBS 114 and PG 1456 + 103

We have acquired 65 h of single-site time-resolved CCD photometry of the pulsating DB white dwarf star CBS 114 and 62 h of two-site high-speed CCD photometry of another DBV, PG1456+103. The pulsation spectrum of PG1456+103 is complicated and variable on time scales of about one week and could only partly be deciphered with our measurements. The modes of CBS 114 are more stable in time and we were able to arrive at a frequency solution somewhat affected by aliasing, but still satisfactory, involving seven independent modes and two combination frequencies. These frequencies also explain the discovery data of the star, taken 13 years earlier. We find a mean period spacing of 37.1 ± 0.7 s significant at the 98% level between the independent modes of CBS 114 and argue they are due to nonradial g-mode pulsations of spherical degree l = 1. We performed a global search for asteroseismological models of CBS 114 using a genetic algorithm, and we examined the susceptibility of the results to the uncertainties of the observational frequency determinations and mode identifications (we could not provide m values). The families of possible solutions are identified correctly even without knowledge ofm. Our optimal model suggests Teff = 21 000K andM∗ = 0.730M⊙ as well as log(MHe/M∗) = −6.66, XO = 0.61. This measurement of the central oxygen mass fraction implies a rate for the C(α, γ)O nuclear reaction near S300 = 180keVb, consistent with laboratory measurements.