A Statistical Evaluation of the Limitations of Single-channel Intermediate-band Photoelectric Stellar Photometry

Error distribution in differential photometry for a moving solar system object is investigated. The results of differential photometry of several dozen pairs of planetary comparison stars observed since 1972 are reviewed. Each pair of stars was observed along with the corresponding planet or satellite, typically about ten times during the course of a single apparation lasting about four months. The comparison stars are chosen to bracket the opposition position of the planet, the expected opposition magnitude, and solar color. In practice, this means that the range of spectral type was mid-F to early K, the range of B-Y color was about 0.25 to 0.95 mag, the range of differential magnitude was less than 2 mag but most often less than 1.0 mag, and the difference in declination was typically less than 3 deg. The difference in air mass at meridian transit was usually less than 0.03, and rarely exceeded 0.01. Hence, differential extinction effects are negligible, except under extraordinary conditions.