Progress report to SAC for the GISMO -- Gladders Image-Slicing Mutlislit Option for IMACS -- A. Dressler Basic mechanical/optical assembly -- Feb ‘07 1

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. 2

Typical slit density in a 4’ x 4’ field 3

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 4

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 (briefly) 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 questions. 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 proceeding with the final assembly. 5

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Pre-Ship Review report to Director: 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. Ian slicing mirrors slit mask ? linear motor brake 7

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. 8

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 amplitude). 9

Air cylinder actuator hard stops Great weight of GISMO and IFU cause a “rotation” (falling off of top hard- stop) 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? 10

First light GISMO images, March 31, IMACS f/4 image of  Cen 11

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. 12

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. 13

Data from May 4-6, 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 14

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. 15

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 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. 16

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 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. 17

prelim 18

prelim 19