Monday, 25 March 2013
HAGAR telescope system
HAGAR telescope system is co alignment of 7 mirrors mounted para-axially with the guiding telescope and the telescope axes. The following procedure was developed to attain good accuracy in the pointing of telescopes as well as all mirrors in each telescope.
Alignment of guiding telescope with the telescope axes was done by sighting large number of bright stars. A CCD camera (ST-4) was used to obtain the pointing data and pointing models for the guide telescopes were worked out.
All mirrors in a telescope were initially co-aligned with the guide telescope by sighting a distant stationary light source. There after, several scans in RA/DEC space were performed by pointing the telescopes to isolated bright stars. In these scans, the direction of telescopes are offset from the direction of star in RA and DEC in steps of 0.5 deg and the photo-tube count rates are recorded.
Profles of count rate as a function of offset was generated for each mirror. The centroid of these profiles give the pointing direction of mirror, or rather offsets in the pointing of each mirror with respect to the telescope direction.
Based on these offsets the mirror alignments were fine tuned and checked by repeated RA-DEC scans. These scans also provide data on the pointing of mirrors as a function of altitude and azimuth. They are used for fine tuning pointing models of all telescopes as well.
The High Altitude Gamma Ray Telescope (HAGAR) is an atmospheric Cerenkov experiment with 7
telescopes setup in 2008.IT is the part of the Indian Astronomical Observatory (IAO), located near Leh in Ladakh, India, has one of the world's highest sites for optical, infrared and gamma-ray telescopes.
It is operated by the Indian Institute of Astrophysics, Bangalore.It is currently the second highest optical telescope in the world.The Indian Astronomical Observatory stands on Mt. Saraswati, Digpa-ratsa Ri, Hanle in south-eastern Ladakh in the eastern Jammu and Kashmir state of India