Testing the Purity of the ZZ Ceti Instability Strip

Details Testing the Purity of the ZZ Ceti Instability Strip Testing the Purity of the ZZ Ceti Instability Strip

Sep 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aspc..372..571c&link_type=abstract

15th European Workshop on White Dwarfs ASP Conference Series, Vol. 372, proceedings of the conference held 7-11 August, 2006 in

Astronomy and Astrophysics

Astronomy

Scientific paper

We have re-observed for variability two stars with SDSS spectroscopic effective temperatures (Teff) that place them inside the ZZ Ceti instability strip, but were previously classified as Not-Observed to Vary (NOV) by Mukadam et al. (2004), finding them to be low amplitude pulsators. The potential contamination of the ZZ Ceti instability strip with constant stars could indicate that pulsations were no longer an unavoidable evolutionary stage in the white dwarf cooling sequence. To examine the reliability of the published SDSS spectral fits when the spectra's signal-to-noise rate (SNR) is particularly low, we decided to obtained spectra of four stars with Teff˜ 12 000 K with the GMOS spectrograph of the 8m Gemini north telescope. Comparing our results of line-profile fits (LPT) of spectra with SNR ≃ 100 with the published values, the average differences are Δ Teff≃ 320 K, systematically higher than SDSS values, and Δ log g≃ 0.24 dex, systematically lower than SDSS values. Kleinman et al. (2004) and Eisenstein et al. (2006) uncertainties in Teff are underestimated by 60% and by a factor of 4 in log g. We also used the results of Eisenstein et al. (2006) to look for new pulsators and found five new ZZ Cetis. Our results indicate, but do not yet prove, that the ZZ Ceti instability strip is pure.

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