Discovery of pulsations, including possible pressure modes, in two new extremely low mass, He-core white dwarfs

@article{Hermes2012DiscoveryOP,
  title={Discovery of pulsations, including possible pressure modes, in two new extremely low mass, He-core white dwarfs},
  author={J. J. Hermes and Michael H. Montgomery and Don E. Winget and Warren R. Brown and Alexandros Gianninas and Mukremin Kilic and Scott J. Kenyon and Keaton J. Bell and Samuel Thomas Harrold},
  journal={arXiv: Solar and Stellar Astrophysics},
  year={2012}
}
We report the discovery of the second and third pulsating extremely low mass white dwarfs (WDs), SDSS J111215.82+111745.0 (hereafter J1112) and SDSS J151826.68+065813.2 (hereafter J1518). Both have masses < 0.25 Msun and effective temperatures below 10,000 K, establishing these putatively He-core WDs as a cooler class of pulsating hydrogen-atmosphere WDs (DAVs, or ZZ Ceti stars). The short-period pulsations evidenced in the light curve of J1112 may also represent the first observation of… 

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