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DETECTOR SYSTEM

 

Control room below the central telescope consists :

 

Telescope Control System (Orientation & Tracking)

High Voltage System ( Setting & Monitoring of HV to 49 PMTs)

DAq.System ( Recording of data on Trigger & Monitoring health of the system)

All the above systems are automated using PCs under LINUX O.S

 

Detector Array consists seven Telescopes placed in a hexagonal pattern of side 50m having one at its centre. Each of these telescopes has 7 parabolic mirrors with a fast PMT (UV TYPE 2268B) at their focus.

mmc mount1

 

These 7 mirrors of a telescope are mounted para-axially on a single platform. The telescopes have alt-azimuth mounts. Each axis of the telescope is driven by a stepper motor. The telescope movement control system consists of two 17 bit Rotary encoders, two stepper motors and Micro-controller-based Motion Control Interface Unit (MCIU).

Steady state pointing accuracy of the servo is +/- 10 arc-sec with maximum slew rate of 30 degree/minute. The resulting blind-spot size while tracking the stars near zenith is ~ 1.2 degree. The telescopes' movement is maneuvered by the control software developed under Linux. The telescope pointing is continuously monitored and corrected in real time during tracking.

An important issues in the pointing of 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.

 

 

 

 

 

 

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