Fast Photometry Uisng CCD

Abstract

Observations of certain objects which exhibit fast changes in their light output seems to be of great interest in optical astronomy. Important informations can be obtained on their internal structures of the stars through the measurements of their pulsational frequencies. Long duration uninterrupted observations involving many observatories located at various longitudes on the globe have already been attempted in the case of white dwarfs and Ap stars, which have fundamental periods of 2 to 20 minutes, (Winget 1988). Pulsars have also evinced great interest which shows milliseconds to seconds periodicity in their radiation output. Such observations have been carried out using PMT as the detector (Santhanam et al. 1985). With the advent of solid state detectors like charge coupled devices (CCD) it is worth replacing the PMT with CCD for the following reasons. CCD has higher quantum efficiency (50%) as compared to PMT’s (20%). CCD also provides a large dynamic range 10/ sup 4/ than PMT and this factor is advantageous while measuring faint objects in the presence of bright ones. CCD’s operate at manageable voltages (±15V) and require no high voltages as demanded in the PMT operation. Though blue response of the CCD’s lack compared to the PMT , this limitation has been overcome by coating the CCD surface with a wavelength shifter (Coronene) which gives an efficiency of about 15% in the range of 2000 A0 < λ < 4000 A0 .