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Progress report to SAC for
the GISMO -- Gladders
Image-Slicing Mutlislit Option
for IMACS -- A. Dressler
Basic mechanical/optical
assembly -- Feb ‘07
GISMO reimages these slices
at the same scale and on the
same focal surface -- to
IMACS optics, it appears that
these slices are actually being
imaged by the telescope.
Objects are selected by a slit
mask at the reimaged focal
surface. The slit mask must
be changed manually (GISMO
must be removed from
IMACS), but each slitmask
contains 5 setups, and these
are selected remotely.
Typical slit density in a
4’ x 4’ field
Great multiplex advantage for
fields with high target density:
Galaxy deep fields, clusters of
galaxies (grav. lenses), globular
cluster systems of nearby
galaxies, Galactic bulge stars…
GISMO can also be used in
combination with MOE (Multi-Object
Echelle) to obtain, for example one
or two orders at R=20,000 for ~50
stars in a globular cluster
The GISMO Pre-Ship Review -- March 15, 2007 at OCIW.
Alan Uomoto organized the review. Attending were Matt Johns,
Frank Perez, Mark Phillips, Steve Shectman, Ian Thompson, Andy
Szentgyorgyi (phone), Dave Osip (phone), and Wendy Freedman
Presentations were made by Dressler, Hare, and Gladders (phone).
Tyson Hare also answered technical questions from the Committee
and Dressler and Gladders answered operational and scientific
By early March, GISMO was 95% assembled -- optics, structure, and
electromechanics and some testing had been done. The GISMO
team requested the Review because it wanted to ship GISMO to
Magellan in order to make (1) a mechanical “fit-up” of GISMO in the
IMACS mask-server and (2) an imaged starfield and focus run before
5 proceeding with the final assembly.
GISMO (Gladders Image-Slicing Multislit Option for IMACS)
Pre-Ship Review ΠMarch 15, 2007, Carnegie Observatories
-- pre pared by Alan Dressler, Mi ke Gladders, & Tyson Hare
1) A functional Description of GISMO
Software and Science Operations with GISMO
2) Mechanical Description of GISMO
Operating Requirements
3) Commisioning GISMO
Instrument Characterization
slicing mirrors
Pre-Ship Review report to Director:
linear motor
slit mask
Approved of shipping GISMO to Chile for mechanical fit up
and verification sky images.
Recommended returning GISMO to Pasadena before final
shipping back to Chile, to address the final placement of
electronics and cabling. (The electronics is for positioning
the five-position multislit mask -- the only moving part.) Also,
team would address problem of slipping in the brake of the
slit mask motion (~50 microns), possibly with a detent
system. Also investigate a baffle to protect the optics, and
logistical issues -- Installation/handling cart?
Director suggested a brief review before sending back
GISMO in May for further tests.
GISMO shipped to Chile for March 29-31st
Baade engineering run.
GISMO mechanical fitup successful -- installed in
box and inserted into IMACS on first try.
Two issues: (1)
GISMO is too heavy (35 lbs) to be installed against
gravity -- will be inserted in horizontal position of
mask server. Since GISMO will only be used with
direct f/4 imaging (no other masks), it will be
inserted for periods of several hours at a time, if not
all night, so this is not a serious operational penalty.
GISMO shipped to Chile for March 29-31st
Baade engineering run.
GISMO mechanical fitup successful -- installed in
box and inserted into IMACS on first try.
Two issues: (2)
Because of GISMO’s weight, the air-cylinder that
inserts it (and the slitmasks) is unable to hold
GISMO against the two stops -- there is a slight
“rotation” as IMACS is turned around. This is
unacceptable because of the motion of about 1
arcsec of the objects on the slit (worse case, full
hard stops
Great weight of GISMO and IFU cause
a “rotation” (falling off of top hardstop) when vertical wrt gravity. Both
units will be secured by a cam-latch in
line with the guide wheels on top.
Will this also fix the IFU drift?
Air cylinder
First light GISMO images,
March 31, 2007.
IMACS f/4 image of Cen
Focus run on March 31 made by moving Baade secondary
mirror. Significant variation in best focus, but all slices
reach 0.7” at some focus, which was the seeing at the time.
Time was allocated in subsequent engineering run, May 4-6, but
attempt to return GISMO to Pasadena in first week of April failed -GISMO sat in Santiago customs for almost 3 weeks. Return cancelled.
Work continued in the SBS shops to finish final dressing of
electronics and fabricate a detent system for the moving slit mask.
These modifications were taken to Chile on May 1. Christoph Birk,
Alan Bagish, and Tyson Hare finished the electronic and mechanical
work. GISMO had not been returned to Chile as the PSR had
requested, but it was acknowledged that the Commissioning would not
begin until a progress review by the PSR Committee.
During May 4-6, Mike Gladders and Jennifer Marshall continued
tests. Dressler consulted. Principally, they worked to tune up the
optics and make a focus-run Hartmann mask images (on sky) for more
accurate offsets of slices foci.
Data from May 4-6, 2007
-- globular cluster in IMACS f/4 (15’ x 15’)
After “steering”
with the fold
mirrors to direct
output to proper
positions in field,
also align with
decker mask
Most important result of the May tests
was that the focus variations (especially
of the outer 4 segments) are in the
direction of “two short a path length”
compared to most of the slices. It is
likely that this is due to ~10% radius of
curvature errors in the most difficult
slicing mirrors. Z-MAX was used to
investigate the best way to fix the
problem, and no simple translation of
optics preserved the optical paths.
Excellent results were obtained,
however, but simply extending focal
lengths of folding mirrors.
These mirrors are easy and rapid to
obtain, and relatively inexpensive (Sunny
Precision). They will be ordered next
week and will show up in July.
Remaining Issues
Detents in the brake have solved the slitmask slip
problem, but mysterious jumps in the zero point needs to
be fixed. Ran out of time.
Cabling issues almost complete, but final dressing
(tensioner) needs to be done in situ.
Protective shroud still needs to be fabricated.
Cam-latch is being designed.
These issues will be addressed and finished by August.
June 14-16 has been given to Mike Gladders to make
observational tests using the many modes of GISMO.
Tyson Hare and Christoph Birk will accompany him. They
will also attend to other IMACS issues.
The GISMO team expects to submit a further report in
July or August to the the Director and the PSR
Commnittee with a request to proceed with
Commissioning during a Baade engineering run in the last
quarter of 2007. GISMO might be offered in 2008A.
The following complete list of tasks has been developed,
some of which have been investigated to some extent,
but not throughly and documented.
add wiring to all ow GISMO to communicate with the IMACS control computer
Åú verify reli able remote operation of the single axis motion in GISMO (the mask sli de)
Åú verify reli able insertion and removal of GISMO from the IMACS mask cassette
Åú verify lock-up of GISMO and reli able comm unications at all rotator angles
Åú check for possible operator/instrument/telescope safety issues
Åú verify and document instrument storage when not in telescope
Instrument Characterization:
Åú measure focus of each of the 16 GISMO optical trains, and adjust to common focus
using physical shim s on second mirror
Åú measure as trometry of GISMO in imaging mode and adjust curre nt astrometric model
in maskgen to reflect 'as-buil t' values
Åú re-make and re-install decker p late (using mask laser cutter) to reflect 'as-buil t'
astrometry, if necessary
prelim Åú check flexure stabili ty of GISMO with rotator angle
prelim Åú check GISMO susceptibili ty to scattered li ght at a range of locations within GISMO
Åú characterize new f/4 grating
Åú characterize all 4 new fil ters, designed for GISMO operations
Åú check GISMO operations using relevant existing fil ters and gratings (principally ,
check for spectral isolation using appropriate fil ter/gra ting/til t combinations)
Åú measure GISMO throughput as functions of wavelength for entire possible range
Åú verify GISMO central longsli t mode
Softwa re/Operations:
Åú verify reverse mapping o f GISMO im ages using updated astrometry
Åú verify reli able motion of GISMO mask at a range of rotator angles
prelim Åú document repeatabili ty and absolute accuracy of GISMO mask motion
Åú verify correct operation of mask ali gnment software on reverse-mapped im ages, at
several sky positions and rotator angles
Åú perform test observations using both new and existing gratings and fil ters on bright
Åú execute test GISMO observations in standard micro nod-shuffl e mode
Åú execute test GISMO observations GISMO 1/7 macro nod-shuffl e mode
Åú construct a GISMO engineering cookbook
Åú construct a GISMO operations cookbook for various observing modes
Åú construct a comprehensive GISMO homepage
prelim Åú facili tate flow of GISMO engineering and operations knowledge from build team to
observatory staff
Åú ensure proper communication li nes between observatory and buil d team in case of
future issues
Åú document and respond to observatory concerns which arise as part of commi ssioning
and the lead-up to commi ssioning