Pulsations of the Low Mass ZZ Ceti Star HS 1824+6000
  Measuring g-mode pulsations of isolated white dwarfs can reveal their interior properties to high precision. With a spectroscopic mass of ~0.51 M_{\odot} (log g = 7.82), the DAV white dwarf HS 1824+6000 is near the transition between carbon/oxygen core and helium core white dwarfs, motivating our photometric search for additional pulsations from the Palomar 60-inch telescope. We confirmed (with much greater precision) the three frequencies: 2.751190 +/- 0.000010 mHz (363.479 sec), 3.116709 +/- 0.000006 mHz (320.851 sec), 3.495113 +/- 0.000009 mHz (286.114 sec), previously found by B. Voss and collaborators, and found an additional pulsation at 4.443120 +/- 0.000012 mHz (225.067 sec). These observed frequencies are similar to those found in other ZZ Ceti white dwarfs of comparable mass (e.g. log g < 8). We hope that future observations of much lower mass ZZ Ceti stars (< 0.4 M_{\odot}) will reveal pulsational differences attributable to a hydrogen covered helium core. 
Justin D. R. Steinfadt, Lars Bildsten, Eran O. Ofek, and Shri R.   Kulkarni