5 Constancy of comparison and check stars from Hipparcos photometry

Adelman (1998) advocated that astronomers who perform differential photometry check the observations of their comparison and check stars in the Hipparcos photometry database (ESA 1997). In this section, we do this for groups of B, A, and F stars that are on his observing program, or were observed, but their data has not yet been analyzed, with the Four College Automated Photoelectric Telescope. Table 5 contains this type of data as well as that for the variable stars when observed by Hipparcos: the mean magnitude, the standard error, and the amplitude taken to be the difference between the 95 th and 5 th percentile observations. Periods from the Hipparcos database are given.

In selecting comparison (c) and check (ch) stars, one tries to find non-variable stars close on the sky to the variable (v) which are similar in magnitude and in color and also will be the only star in the photometer's aperture. Sometimes it is impossible to satisfy all of these requirements and either one must compromise or does not perform differential photometry of a given star. Most of the comparison and check stars were found by consulting the Bright Star Catalogue and its supplement (Hoffleit 1982; Hoffleit et al. 1983) and the rest from finding which stars other photometrists had used. In deciding which comparison and check stars were questionable, we considered how the Hipparcos standard errors grow as the stars get fainter. We have also included any original comparison and check stars indicated as oc and oh, respectively, which we have replaced as part of this exercise.

Acknowledgements

This work was supported in part by NSF grants AST-9115114 and 9528506 and in part by grants from The Citadel Development Foundation. We appreciate the continuing efforts of Louis J. Boyd, Robert J. Dukes, Jr., and George P. McCook to keep the FCAPT operating properly.