IMACS Multi-Object Echelle

B. Sutin, T. Hare & A. McWilliam & many others

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*Not yet released

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● 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)● ~10-100 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

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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

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O2 B-band

Carina star #1386 V=17.88 (1 hour exposure)

Object at edge of field

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O2 B-band

Carina Star # 1107 V=17.79

MOE Science● 1st Science/Engineering run Dec. 2004● Collaborators: A.Koch (Basel) & V.Smith (Gemini)● Carina dSph mask 20 objects 12 hrs● Fornax dSph mask 20 (10) objects 8 hrs● 4800-7800A blocking filter (4 orders)● 1st night seeing 1.1'' fwhm● Problem?: Nod & Shuffle mode

Solution: software

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EuII

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FeI

FeIFeI

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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.