Background

The LRIS blue shutter is prone to getting stuck, preventing observers from acquiring images in the normal way. Fixing the stuck shutter is a major repair requiring removal of the entire LRIS blue dewar; hence, this repair will probably not be made until the conclusion of the run. Fortunately, if the blue shutter fails during a run it is possible to operate the blue side in shutterless mode and still obtain useable data as long as certain procedures are followed. This document describes the required hardware modifications and observing procedures to carry out observing in shutterless mode.

Hardware Changes

In the event that the blue side shutter is stuck, the following hardware changes must be made to operate the LRIS trapdoor as a shutter for the blue side.

Force the shutter open. This will have to be done by a summit instrument technician if the shutter is stuck closed.
Have the summit instrument technician put the shutter into "manual" mode via the toggle switch on the blue-side shutter controller on the instrument.
- put the rotator at 0 deg
- Open the Blue side electronics enclosure, on the back of the instrument. The enclosure is on the left when looking at the back of the instrument.
- There is a blue box two two buttons: one red for closing and a black one for open. There is also a swith to change from manual and automatic motion. Put the switch to manual and press the open button to open the shutter.
- A green LED should indicate that the shutter is open. A red LED indicates that the shutter is closed.
If necessary, increase the speed of the trapdoor to open and close the trapdoor in under 0.5 seconds by adjusting the air pressure supplied to the solenoids on the trapdoor. (Q: what pressure [in PSI] is the "normal" value and what is used for high-speed mode?)

Observing strategy notes

Observer notes

[This section needs info on how to acquire data in shutterless mode. Especially mention procedure for on-sky acquisition (long image followed by 1-sec B image, then subtract).]

To align a slitmask using the blue side detector, it is quicker to use take an exposure without using the trapdoor as a shutter. To initiate an exposure you should be able to start an exposure using the blue XPOSE GUI. From the command line in a punaluu xterm: mb expose=1.
The exposure times must be set using the XPOSE GUI or the keywords.
To follow science observations with arclamp data. Close the trapdoor, acquire all the red side data first. then use the scripts (see below) to acquire the Blue side cals.
Guiding: Let the OAs know that you will be closing the trapdoor in order to use it as a shutter for the blue side. They will coordinate guiding with the trapdoor movements.

OA notes

[Also include information for the OA]

Useful Scripts

The following scripts may be used to acquire the arc lamp data, flats and science data using the trapdoor as a shutter.

cal_trap_hg_blue

Acquires a single Hg arc lamp exposure using only the blue side. The exposure length is hardcoded, and could be a variable to acomodate different slit widths. The script does the following:

Turns on the Hg lamp for 15 seconds to allow it to warm up.
Turns off all of the lamps.
Sets the exposure time to 60 sec.
Erases the CCD.
Turns on the Hg lamp for 7 seconds.
Resets the exposure time to 7 sec to initiate readout.
Turns off the lamp.
Reads out the array.

cal_trap_cd_zn_blue

Acquires a single Cd+Zn arc lamp exposure using only the blue side. The exposure length is hardcoded (but the script could be modified to make this variable to accommodate different slit widths and grisms). Prior to running the script the observers must allow the lamps to warm up for 5 min. The script does the following:

Turns off all of the lamps.
Sets the exposure time to 60 sec.
Erases the CCD.
Turns on the Cd and Zn lamps for 5 seconds.
Resets the exposure time to 5 sec to initiate readout.
Turns off the lamp.
Reads out the array.
Turns on the Cd and Zn lamp for 5 seconds. [??]

cal_trap_flat_blue exptime

Acquires a single Halogen lamp flat using only the blue side. The variable exptime is a required variable defining the exposure time [in seconds] for the internal Halogen flat field lamp. The script does the following:

Turns off all of the lamps.
Sets the exposure time to exptime+13 sec.
Erases the CCD.
Turns on the flat lamp for exptime seconds.
Resets the exposure time to exptime sec to initiate readout.
Turns off the lamp.
Reads out the array.

goitrapb [-both]

Acquires images on the blue side, operating the trapdoor as a shutter for the blue side detector. The optional keyword "-both" will acquire a single image on the red and blue sides simultaneously. The script will check to ensure that the red side exposure time is 3 seconds less than the exposure time on the blue side. The script will do the following:

If -both is specified, starts an exposure on the red side and pauses the exposure after the erase.
Closes the trapdoor.
Erases the blue side CCD.
Opens the trapdoor to start the blue side exposure.
If -both is set, resumes the red side exposure. The red side exposure will complete before the blue side finishes.
When the blue exposure finishes, closes the trapdoor.
Reads out both arrays.
Opens the trapdoor when the blue side finishes readout.

To focus the LRIS BLUE side CCD

The procedure is similar to the standard focusing procedure, except that the acquisition of the blue-side images required running a special script. Follow these steps to acquire the images:

Set the blue side exposure time to 3 seconds.
Set the blue filter to G
Set the grism to clear.
Turn on the spec dome flatfield lamps.
Insert the focus_holes mask.
In a punaluu xterm enter:
```
	xfocuslooptrapb 7 -2800 70 
```

Once the images have been acquired, you can analyze them as usual using the XFOCUS blue IDL widget accessible from the desktop menu.