IMACS Multi-Object Echelle B. Sutin, T. Hare & A. McWilliam & many others N *Not yet released *

● IMACS Multi-Object Echelle (MOE) F/4 focus

● Grating + Prism cross-disperser in grating module ● Grating: 245 l/mm, 37-degree blaze?,160x214mm ( 20% overfill loss) ● Prism: fused silica, 13-degree apex angle,300x200mm, 63mm base

MOE Characteristics ● Wavelength range:  (10 orders) ● ~ objects ● Resolving power (0.6 arc sec): R=21,000 ● Slit length: 5 arc seconds ● 15x15 arc min. field ● ~900 counts/pixel in 1hr at H  for V~17.0 (~1400 counts/pix/hr at 7600A) ● Cost: Parts~$35K, Labor~$20K

MOE Engineering ● October/November 2004 ● Th-Ar lamp system installed & calibrated ● Problem #1: mechanical clash! (-3mm) IMACS model off by 9mm Solution: move prism

Slide the prism down. Minimum distance now 1-2 mm.

MOE Engineering ● Problem #2: very tight fit Solution: move cables & mill the prism mounting ● Problem #3: spectral clash! Design “feature” of grating roll Solution: unique software for mask cutting (empirical vs predicted) ● Problem #4: some spectra fell between CCD gaps Solution: software

MOE Engineering ● Problem #5: blaze not centered on CCD Design flaw or grating blaze 3 degrees off Solution: in progress

Off-center Blaze for central object HH O 2 B-band Carina star #1386 V=17.88 (1 hour exposure)

Object at edge of field HH O 2 B-band Carina Star # 1107 V=17.79

MOE Science ● 1 st Science/Engineering run Dec ● Collaborators: A.Koch (Basel) & V.Smith (Gemini) ● Carina dSph mask 20 objects 12 hrs ● Fornax dSph mask 20 (10) objects 8 hrs ● A blocking filter (4 orders) ● 1 st night seeing 1.1'' fwhm ● Problem?: Nod & Shuffle mode Solution: software

HH EuII NiI FeI VI CoI Chip #2

Procedural difficulties ● Re-alignment, after each exposure, results in a shift of the spectra on the array; requires quartz spectra to be taken each time MOE is moved. ● Number of spectra: 20 obj x 4 orders x 4 ccd x 12 exp = 3840 spectra => Pipeline reduction required

Summary ● MOE works, but the blaze problem needs to be resolved. ● Pipeline reduction is essential. ● MOE complements MIKE and MIKE+fibers. ● MOE can compete with VLT/UVES+GIRAFFE and enhances our ability to study the chemical evolution of nearby systems.