Pulsations of the Low Mass ZZ Ceti Star HS 1824+6000

TL;DR

This study confirms known pulsation frequencies and discovers a new one in the white dwarf HS 1824+6000, providing insights into its interior structure and motivating future research on lower mass ZZ Ceti stars.

Contribution

The paper precisely measures pulsation frequencies of HS 1824+6000 and reports a new pulsation, enhancing understanding of white dwarf interiors near the core transition.

Findings

Confirmed three known pulsation frequencies with higher precision.

Detected an additional pulsation at 4.443120 mHz.

Frequencies are similar to other ZZ Ceti stars of comparable mass.

Abstract

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.