Twin Telescope observations of the Sun at Kodaikanal Observatory

Abstract

We report the design, fabrication and installation of a ‘Twin Telescope’ at Kodaikanal Observatory intended to augment the ongoing synoptic observations of the Sun that have been carried out since 1904. The telescope uses a 15 cm objective capable of taking Ca-K line filtergrams and photoheliograms in continuum of the full disk of the Sun simultaneously, at a frequency of 0.1 Hz using 2kX2k format CCD cameras. The telescope has been in operation since February 2008 and images are being obtained at a cadence of 5 min during normal observing periods. In case of solar activity, images of the active regions can be taken at a frequency of 1 Hz by restricting the field of view and spatial resolution. In this paper, we describe the telescope, instruments, image acquisition, data calibration and image processing. We also discussed a method of determining the network element and plage area index. The preliminary results show that while the network element covers about 30% of the disk, the percentage of the network element area index varies marginally with the seeing conditions during the day.