title: Rapid alternate detection system of the Rothney Astrophysical Observatory.
abstract: A new differential variable-star photometry system has been designed, constructed, and tested at the Rothney Astrophysical Observatory of the University of Calgary. The system uses a single telescope, photometer, and detector and consists of gated pulse-counting electronics synchronized to a chopped secondary mirror. The mirror is driven to four positions, permitting rapid alternate detection of a variable star, comparison star, and two sky-background regions. Within certain constraints the system is insensitive to the effects of transparency, sky-brightness, and detector-sensitivity variations occurring on time scales longer than the system's duty cycles. The system has proved effective under as much as three magnitudes of cloud and attendant sky-brightness variation.
authors.forename: E F
authors.initials: EF
authors.lastname: Milone
authors.forename: R M
authors.initials: RM
authors.lastname: Robb
authors.forename: F M
authors.initials: FM
authors.lastname: Babott
authors.forename: C H
authors.initials: CH
authors.lastname: Hansen