Development and Performance of the PHOT (Portable High-Speed Occultation Telescope) Systems

Abstract

The PHOT (Portable High-Speed Occultation Telescope) systems were developed for the specific purpose of observing stellar occultations by solar system objects. Stellar occultations have unique observing constraints: they may only be observable from certain parts of the globe; they often require a rapid observing cadence; and they require accurate time-stamp information for each exposure. The PHOT systems consist of 14 inch telescopes, CCD cameras, camera mounting plates, GPS-based time standards, and data acquisition computers. The PHOT systems are similar in principle to the POETS systems (Portable Occultation, Eclipse, and Transit Systems), with the main differences being (1) different CCD cameras with slightly different specifications and (2) a standalone custom-built time standard used by PHOT, whereas POETS uses a commercial time standard that is controlled from a computer. Since 2005, PHOT systems have been deployed on over two-dozen occasions to sites in the US, Mexico, Chile, Namibia, South Africa, France, Austria, Switzerland, Australia, and New Zealand, mounted on portable 14 inch telescopes or on larger stationary telescopes. Occultation light curves acquired from the 3.9 m AAT (Anglo-Australian Telescope) have produced photometric signal-to-noise ratios (S/N) of 333 per scale height for a stellar occultation by Pluto. In this article we describe the seven PHOT subsystems in detail (telescopes, cameras, timers, and data stations) and present S/N estimates for actual and predicted occultations as functions of star brightness, telescope aperture, and frame rate. © 2011. The Astronomical Society of the Pacific.