A High Speed CCD Photometer for McDonald Observatory

Abstract

A two-dimensional detector offers several potential advantages over a conventional two-star photoelectric photometer for high-speed photometry. These include the ability to monitor several objects and the sky simultaneously, thereby allowing for some compensation for the effects of atmospheric transparency variations, and the use of smaller effective apertures, thereby increasing the signal-to-noise ratio. We describe a system using imaging detectors based on either RCA 320x512 or TI 800x800 Charge Coupled Devices (CCDs) operated in frame transfer mode to minimize the dead time due to readout. A Micro VAX II computer was added to an existing McDonald Observatory system to provide realtime data reduction and an operator interface based on modern window and mouse-pointer software. The Micro VAX sends commands to the NOVA 4X controlling the existing CCD systems and receives data back over an Ethernet. The system has been operated successfully several times on the McDonald 0.8m and 2.1m telescopes. The ability of the system to compensate for transparency variations is illustrated by results obtained for the pulsating white dwarf GD358 and the eclipsing cataclysmic variable RW Tri.