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Twin Telescope observations of the Sun at Kodaikanal Observatory
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 has 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.Comment: 17 pages, 10 Figures, to appear in the 2012 March issue of the
Bulletin of the Astronomical Society of Indi
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