2007PASP..119..483G

The Gravity Probe B (GP-B) satellite photometric system and instrumentation are introduced. Observational results are presented for calibration stars demonstrating a single-orbit relative photometric precision capability of 500 µmag for bright stars. Broadband photometric observations of the bright star ζ Pegasi are then presented that display brightness variability of 488.2±6.6 µmag (parts per million), with a period of 22.952±0.804 hr (f ~ 1.04566 cycles/day). Over the short observational period, the variation is monosinusoidal, thus recommending the star for membership in the class of small-amplitude, slowly pulsating B (SPB) star variables oscillating in a nonradial g-mode.