This document summarizes what DEIMOS observers should do to
prepare for their observing run.
The DEIMOS slitmask cassette has 11 slots available, but since one
slot is dedicated to the focusing mask there are 10 slots
available for observer masks. Please plan accordingly.
Slitmask Due Dates
If you plan to use custom slitmasks during your DEIMOS run, plan
to begin the process early. Due dates depend on the complexity
of your mask designs:
- Standard masks (<200 slits):
design files are due at least 4
weeks prior to your run.
- Complex masks (>200 slits): files are due
at least 8 weeks prior to your run.
Mask Design Software
To begin designing masks, you'll need a working version of IRAF
with the official DEIMOS slitmask design package
DSIMULATOR; both the software and the documentation are
available from Drew
Phillips's DEIMOS slitmask design page at UCSC.
Selecting “Coarse Alignment” Stars
DEIMOS observers typically use the DSIMULATOR package to provide
predicted coordinates for a star on the guider; by placing the
star at these coordinates, coarse alignment is achieved in
DEIMOS observers must consider two characteristics when
selecting guide stars:
Once your slitmask designs are completed, you can submit them
for milling by using the DEIMOS
Slitmask Database Access page at UCSC via these steps:
- Placement. The DEIMOS guider field of view
consists of two parts, one viewing the pickoff mirror and one
the reflected sky off the slitmask. The pickoff mirror, which
covers about 1/3 of the field of view, is the preferred place
to position your coarse alignment star. Stars can also be
placed on the slitmask region, but it is only about 30%
reflective and so stars seen there will be somewhat dimmed.
If possible, avoid choosing a star near the break between
the mirror and slitmask. If multiple coarse alignment
stars are available, it's definitely wise to select several in
case one presents problems.
- Brightness. Your coarse alignment stars should be
in the 15<R<17 magnitude range. Fainter stars become
increasingly more difficult to identify, but can be used if
Masks are now milled at the Keck summit, but in order to keep
the backlog of masks manageable we do require observers to
submit most masks 4 weeks in advance of the observing run;
please see the Slitmask Incentives
Protocol for details.
Important: verify your slitmask designs by checking the
online plot for each mask!
- Access to this page is restricted to known sites, so if
you find you can't access it, please contact the web page
() to add your site.
- Once you reach the site, please register to create your
account for submitting masks if you haven't already got one.
The system will email you a password which you should retain
for future reference.
- Enter your name, email address, and password to log in.
- Click on the Submit a Mask Design
File button to access the page for sending in your masks.
We now have a web
form for submitting your choice of DEIMOS gratings, filters,
and slitmasks. Please submit this information as soon as your
masks are milled. When specifying your list of slitmasks, please
note that the GOH_X mask is needed to complete the
afternoon focus procedure; it is selected by default on the web
form and you should include it in your mask list.
If you plan to observe in Hawaii and stay at either the Visiting
Scientists Quarters in Waimea or at Hale Pohaku on Mauna Kea,
please use the WMKO Lodging Reservation
Request form to make your arrangements. The VSQ in Waimea
sometimes fills up, so to avoid being sent off to Waimea Country
Lodge purgatory, make your reservation several weeks before your
If some or all of your observing team want to use one of our
sites to observe, please use our web form to submit a
request. All you need to do is log in to your WMKO
observer home page.
Your home page shows a list of any upcoming runs for which you
are the PI. For each run, there's a link which will take you to
the mainland observing request page. If you're not the PI, then
you can still submit a request by logging into your observer
home page and clicking the link that reads:
- Log in to the DEIMOS
Slitmask Database Access page at UCSC.
- Click on the Show Me My Mask
Inventory button to list your masks.
- For each mask, click the Plot
button to generate a plot of your mask. (Ignore any message
about the site's security certificate being invalid.)
- Inspect the plot and verify that all of your slits are
blue. Slits which cannot be cut (e.g., because they are too
small or lie are outside the legal milling area) are shown in
red. Slits which will not be cut because they are marked as
type "G" are shown in yellow-orange. This example
plot shows some sample yellow-orange slits, which can be
hard to see if you're not careful.
- If "bad" slits exist, consider redesigning and
resubmitting your slitmasks. If you do so, please use the
"Forget" button to remove your "bad" mask files so we do not
Click here to submit a mainland observing request
Certain things will make your life much easier during your
DEIMOS observing run. Please remember to generate and bring the
Within 24 hours after you submit your DEIMOS configuration
request, Keck's Summit
Instrument Activity Schedule will be updated to show the
slitmasks, filters, and gratings that are to be used on your
night. Please check this to verify that the configuration for
your night is correct!
- Slitmask plot. It is imperative that
observers bring a plot of their slitmask to the telescope in
order to verify that the proper mask is being observed. The
optional plotfile from DSIMULATOR is fine for
this purpose as it contains the coordinates and a sketch of
the TV field.
- Slitmask finder charts. In addition to an image of
the guider field, it can be useful to have an image showing
the slitmask targets. An image of your field which identifies
the alignment stars to be used on the slitmask has proven
crucial in recovering from catastrophic slitmask alignment
- Guider finder charts. When you design your masks,
we highly recommend that you identify at least one star -- or
better yet, several -- to use to achieve the coarse alignment
of the slitmask. As described above, these stars should
ideally be in the 15<R<18 magnitude range and be placed
on the guider's pickoff mirror (rather than reflected off of
the slitmask). If you do this, it's critically important that
you bring along a finding chart showing the guider field of
view and the desired guider pixel location for the star. See
this plot for an
example of the ideal guider finding chart, which identifies
several stars, lists their predicted locations, and
prominently shows the field name. A finder
chart generated from the Digital Sky Survey
would be just fine in most cases. If you bring your
DSIMULATOR output files to Keck, you can use Dan Magee's
handy DEIMOS Guider
Finderchart Generator to generate your own DEIMOS guider
- Starlist file. You must prepare a (starlist file) listing the RA/Dec
coordinates of your slitmask centers. The same tool that you
use to generate the guider finder charts in the previous step
will also create a starlist file that lists your masks. Edit
this file as needed to insert additional targets such as
standard stars. When your file is complete, copy this file to your Keck
account. Doing this all electronically instead of
manually precludes transcription errors in making the
starlist, which is a common source of lost time in slitmask