sciOps: La Silla Science Operations

EUROPEAN SOUTHERN OBSERVATORY

La Silla Science Operations: NTT

Current Procedure for Slit and Grism Alignment (April 2009)

This is an example for the current procedure for the slit and grism alignment for SofI. This procedure is based on the current hardware status (wheel switches and/or backup switches are operational as well as the wheel movement). The procedure might have to be adapted in case of component failures. For more information about emergency procedures for SofI please refer to the web page about recovery procedures.

To check the slit wheel alignment:

Run the AlignSlit template to measure the slit misalignment. Rule of the thumb: A misalignment by less than 1 pixel over the length of the slit is acceptable. Terminate the template without moving the encoder (i.e. select "no" when the template asks). Here the template is only used for the purpose of measuring the alignment.
If the slit alignment is better than 1 pixel you can stop here. If the slit is misaligned by more than 1 pixel please proceed with the following steps:
Open the motor control device by clicking on the top of the slit wheel in the instrument panel.
Make sure that the menue indeed indicates the "slit wheel".
Press the button for "hardware init". You will see that the wheel starts to move to the init position (this takes some time).
Once the wheel has reached the init position check the alignment by re-executing the AlignSlit template. If necessary iterate on the above procedure. However, the slit wheel is typically well-aligned after one hardware init.

To check the grism wheel alignment:

You will see whether or not the grism wheel is misaligned when taking a spectrum at night. If the grism wheel is misaligned the spectrum is inclined. Another way to visually check the alignment during day time is to take an arc lamp spectrum. If the border of the arc lines on the left and right-hand side of the array is not straight, the grism is misaligned.
If the grism is misaligned please proceed with the following steps:
Open the motor control device by clicking on the top of the grism wheel in the instrument panel.
Make sure that the menue indeed indicates the "grism wheel".
Press the button for "hardware init". You will see that the wheel starts to move to the init position (this takes some time).
Once the wheel has reached the init position check the alignment. If necessary iterate on the above procedure. It is currently a known feature that the grism wheel typically takes about 3 to 5 hardware inits until a good alignment is achieved.