Towards a pure ZZ Ceti instability strip

Abstract

We have observed again two stars inside the ZZ Ceti instability strip that were previously classified as not-observed-to-vary (NOV) by Mukadam et al. (2004) and found them to be low-amplitude variables. Some evidence points to a pure ZZ Ceti instability strip; other evidence contests it. The two stars previously classified as NOV have Sloan Digital Sky Survey (SDSS) spectroscopic effective temperatures that place them inside the ZZ Ceti instability strip, and they were "contaminating" the strip as constant stars, which could indicate that the instability strip was no longer a simple evolutionary stage. A pure instability strip indicates that pulsation is a normal phase which all DAs must go through. We used effective temperatures derived from SDSS optical spectra by comparing them with model atmospheres to look for pulsators through time-resolved photometry and stars previously classified as NOV. Our new results indicate, but do not prove, a pure instability strip, because there are still other NOV stars that need to be observed again. Additionally, we have discovered five other ZZ Ceti stars based on their effective temperatures.

12 pages, 3 figurs

References in corpus (12)

• A Catalog of Spectroscopically Confirmed White Dwarfs from the Sloan Digital Sky Survey Data Release 4
• A Catalog of Spectroscopically Identified White Dwarf Stars in the First Data Release of the Sloan Digital Sky Survey
• On the Purity of the ZZ Ceti Instability Strip: Discovery of More Pulsating DA White Dwarfs on the Basis of Optical Spectroscopy
• Understanding the Cool DA White Dwarf, G29-38
• Towards an Empirical Determination of the ZZ Ceti Instability Strip
• Ensemble Characteristics of the ZZ Ceti stars
• Mass-radius relations for massive white dwarf stars
• Whole Earth Telescope observations of BPM 37093: a seismological test of crystallization theory in white dwarfs
• A CCD Time-Series Photometer
• Pulsational Instabilities in Accreting White Dwarfs
• Discovery of fourteen new ZZ Cetis with SOAR
• Gemini spectra of 12000K white dwarf stars

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