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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 umag for bright stars. Broadband photometric observations of the bright star z Pegasi are then presented that display brightness variability of 488.2 +- 6.6 umag (parts per million), with a period of 22.952 +- 0.804 hr (f [?] 1.04566 cycles day-1). 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.

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 ?mag for bright stars. Broadband photometric observations of the bright star ? Pegasi are then presented that display brightness variability of 488.2 ± 6.6 ?mag (parts per million), with a period of 22.952 ± 0.804 hr (f? 1.04566 cycles day?1). 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.

Three 2 × 64 element Si:Bi accumulation-mode charge-injection-device (CID) arrays were tested at low and moderate background to evaluate their usefulness for space-based astronomical observations. Testing was conducted both in the laboratory and in ground-based telescope IR observations. The devices showed an average readout noise level below 200 equivalent electrons, a peak responsivity of 4 A/W, and a noise equivalent power of 3 × 10^−17 W/Hz^1/2. This sensitivity compares well with that of nonintegrating discrete extrinsic silicon photoconductors. The array well capacity was significantly smaller than predicted. The measured sensitivity makes extrinsic silicon CID arrays useful for certain astronomical applications. However, their readout efficiency and frequency response represent serious limitations in low-background applications.