The GMACS Spectrograph for GMT

Jennifer Marshall (Texas A&M)

I will describe the conceptual design of the GMACS spectrograph, a wide-field, multi-object, moderate-resolution optical spectrograph for the Giant Magellan Telescope (GMT). The primary optical design drivers are high throughput, simultaneous wide wavelength coverage, and a very wide field. The instrument provides two resolution modes, R ~ 2000 and R ~ 4000, over a wavelength range of 3700-10200 . In the low resolution mode the full bandpass is covered simultaneously. The field of view is 9 18 arcminutes and is divided into four, 4.5 x 9 arcminute fields by fold mirrors near the telescope focal plane. Each of these sub-fields is directed into an optical path comprising a double spectrograph with a red and blue channel. When GMACS is combined with the MANIFEST fiber feed, an increased field of view and higher resolution mode may be achieved.