Slitmask Information

I've moved and have a new email address. How do I change the address listed in the database?

The preferred way to do this is simply to create a new identity and begin using that. Please note that doing so may result in warnings when you specify masks on your instrument configuration form due to a mismatch between your email address and that of the owner of the slitmasks. However, this is only a warning and should not prevent you from using your masks.

Slitmask Design

What is the minimum slit width I can create?

Slits are milled using an endmill with a diameter of 0.015 inches. We mill slits in two passes: a first rought cut, and a second cleanup cut that removes a section 10% the width of the tool. Hence, the minimum slit width is 0.018 inches on the mask; at the LRIS and DEIMOS telescope focal plane plate scales of 0.727 mm/arcsec, this corresponds to a projected slit width of 0.63 arcsec if the slit is not tilted (i.e., the position angle of the slit project onto the sky matches the postion angle of the mask).

What is the maximum tilt I can use with my slit?

The answer depends on your slit width, according to the formula
	pa_max = acos(0.63/w)*180./pi
where pa_max is the maximum PA of the slit (relative to the mask), and w is the slit width in arcsec. For a slit width of 1.0 arcsec, the slit may be tilted by up to 50° relative to the mask position angle. For a slit width of 0.7 arcsec, the maximum tilt is 26°.

Slitmask Submission

What is the deadline for slitmask submission?

The deadlines for submitting your slitmask designs are the same: four weeks for normal LRIS and DEIMOS slitmasks, and eight weeks for masks with more than 200 slits. Exceptions to the deadline may be granted for valid scientific reasons if a request is made by contacting the instrument support team (, before the deadline.

By what time must my masks be submitted to the slitmask database in order for files to be transferred to Keck that same day?

There are 3 steps in the process, all at different times: Thus, anything submitted after 05:00 PT will not get consistency checks, and anything submitted after 07:00 PT will be transferred.

How do I delete a record from the slitmask database?

The mask design files I submitted had an error and I want to replace them. How do I fix them?

Use the forget function to remove the old masks from the database, then submit revised mask files.

The mask system renamed my masks. Why did it do this?

Any newly submitted mask which has a “guiname” that matches any existing mask which is intended to be used in the future is assigned a new guiname. This is required in order to prevent confusion about the conflicting masknames. When a mask is renamed, the slitmask owner should receive an email about the change.

The slitmask database renamed my slitmasks; can you change them?

Unfortunately, no. Once the slitmask information has been ingested, it will be transferred to the milling site and the slitmask should be milled. Since the database computer in Santa Cruz has no way of knowing whether the mask data have been transferred to the slitmask mill on the Mauna Kea summit, it is not safe to change the slitmask name once the mask has been ingested. If we did change the name in the database, we could end up having the name recorded in the database disagree with the name milled into the physical mask. There is no way to change the metal, and the inscription on the mask is used as a cross-check by the technicians who are loading the masks. We wish to prevent such confusion.

What you can do is to forget the masks you submitted, change the mask names in your DSIMULATOR output files, and submit revised mask files.

The slitmask database renamed my LRIS masks to nonsensical names such as 1320643I. Why is this and how can I change them?

For security reasons, LRIS mask names are now being overridden with automatically generated names to prevent the possibility of a malicious filename causing trouble with the database. Your support astronomer can change the slitmask names back to their original values on the day of your run; however, when completing the LRIS configuration form you must use the nonsensical names assigned by the slitmask ingestion system.

I tried to submit a mask design file which someone else designed, and the database system rejected the file with an error "Attempt to look up '' via Observers:email FAILED". How can I submit the file?

Only registered users of the slitmask database system are permitted to submit slitmask design files. You can either have the other user register, or you can use the fv program as described above to edit the observer email. Then you should be able to submit the file successfully.

How can I know if my mask design is correct?

The final check to make sure that all your slits and alignment boxes will be correctly milled is to check the blueprints in the slitmask database, once the slitmask has been submitted (see sanity-check your slitmasks)

Slitmask Re-use

If I want to re-use old slitmask design files, can I simply resubmit them?

Generally, no. You'll need to update the Use Date field in the FITS header of the slitmask design files first, because if the mask design file has an invalid Use Date (i.e., a date which has already passed) then the slitmask database will reject the mask and it will not be milled. It's simple to edit the file if you install the fv program:

I want to reuse an old mask. How do I know whether the mask is still on the summit?

By default, slitmasks are retained for 6 months past their "Use Date". This is the date you specified in DSIMULATOR when you designed your DEIMOS mask, or the date you entered on the web page when you submitted your LRIS mask. If in doubt, check the LRIS/DEIMOS Slitmask Database and view the record for your mask. If it shows a valid barcode then we should still have the mask in our summit collection. If you plan to re-use a mask you probably want to extend the Use Date past the date of your upcoming run to ensure that it is not discarded; please see the next entry.

Even though my old mask still exists in the database, I want it to be remilled for use on my upcoming run. How do I achieve that?

Slitmask Configuration Requests

Why are my slitmasks not listed in the droplists on the LRIS/DEIMOS run configuration form?

By default, the slitmask droplists on the LRIS/DEIMOS run configuration form list all of the slitmasks which have "use dates" that occur during your run. If you wish to use a mask which has a use date outside of this range, simply do the following: Please note that this function only appears to work in the Firefox browser! Alternatively, you can update the use dates on your mask (as described below) to the date of the run. Doing so should cause them to become visible on your mask list within 5 minutes.

Slitmask Retention

How long are old slitmasks retained?

We delete a mask record from the database and discard the mask itself when it is over 6 months past its Use Date as recorded in the database.

How do I know whether my mask has been deleted?

An email is sent to the mask owner two weeks prior to the date of deletion notifying him or her of the pending mask removal.

I want you to retain my slitmask for future use. How can I make sure it does not get discarded?

To ensure that the mask is retained beyind the standard 6-month retention period, the mask owner must complete the following steps to extend the use date: