The pulsating pre-white dwarf star PG 0122+200

We present an analysis of single-site time-series photometry of the pulsating pre-white dwarf PG 0122+200. We show the pulsations are consistent with a pattern of modes equally spaced in period; both the observed period range and spacing confirm that PG 0122 is a g-mode pulsator. PG 0122 shows a pattern similar to that seen in multisite observations of PG 2131+066 and PG 1159-035. The measured period spacing, combined with the spectroscopic temperature, constrain the stellar mass much more precisely than the published measurement of its surface gravity. Based on stellar models, the mass of PC 0122 falls in the range 0.66-0.72 M(.). Fine structure in the power spectrum indicates that PC 0122 rotates once every 1.6 days. Future multisite observation (e.g., using the Whole Earth Telescope) should increase the precision of these results and reveal detailed information on the internal structure of this variable pre-white dwarf star.