SOFI Calibration Plan: Rotator Alignment

European Southern Observatory
New Technology Telescope

General :
Observations :
Operations :

Procedure :	Rotator Alignment
Author :	Sofi team
Release :	12/09/99 : update 06/01/99 : creation

For spectroscopic observations, the telescope is moved so that objects are observed along different parts of the slit. For this to work well, the rotator offset angle must be defined so that North-South offsets occur along detector rows. This test should be done once month and after the instrument has been temperature cycled.

Measuring the angle.

Preset the telescope to a 12th magnitude star with the position angle on the sky set to zero. The NICMOS standards are suitable. The test can be done during twilight. Set DIT to 2 and NDIT to 5.

Move the star to the left hand side of the array and measure the position of the star with the RTD. Take an image. Move the object to the right hand side of the array and measure the position of the star with the RTD. Take another image.

If the misalignment is less than 1 pixel in 1000 pixels, do nothing. If the misalignment is greater, remeasure the position of the star on the saved images (Use either MIDAS or IRAF), and compute the offset angle. Compute the offset in the standard astronomical convention, i.e. from North to East.

The new rotator offset value will be the old value plus the offset computed above.

Updating the Rotator Offset Angle in the TCS Database

From an x-terminal on the TCS workstation, type RtapXColorMngr &.

From the same terminal, type RtapPtDisplay & .

From the same terminal, type RtapDbConfig & .

In the RtapDbConfig window, double click on the attribute Appl_data:TCS:Msw:insdata .

In the RtapPtDisplay window, double click on TABLE.

Edit the rotator offset angle. The next time the TCS is started, the new offset angle will be used.

Exit RtapPtDisplay and RtapDbConfig.

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