GeminiFocus October 2015 | Page 17

year on the polishing and cabling methods that would make the fiber so efficient that one might forget it is even there. Today, with commissioning complete, we find that even the most optimistic estimates of throughput (i.e. the percentage of photons that hit the mirror and subsequently fall on the detector) with the fiber were below what we would ultimately achieve. The recent commissioning observations reveal that the total throughput of GRACES in the red part of the spectrum is the same (~12 percent) as it is for ESPaDOnS, which is fed by a much shorter fiber at the CFHT. In its Gemini state, GRACES’ sensitivity is ~ 22 magnitude at R band (i.e. a target with R = 22 magnitude gives a signal to noise of 1 after a 1 hour exposure). This sensitivity compares favorably (in some cases exceeds) what is possible with other similar instruments elsewhere in the world (see comparisons, Figure 3). Some early users have already benefited from GRACES’ high performance: For instance, Tim Davidge (Principal Research Officer at NRC-Herzberg) used GRACES to study aspects of galaxy evolution — to characterize the large-scale events that have influenced their present-day appearance. Figure 1. Different perspectives showing the conduit between CFHT and Gemini. “One thing I can say is that I am impressed by the signal-to-noise ratio of the M101 and NGC 6946 data”, Davidge says. Lison Malo, CFHT resident astronomer and scientific lead for the GRACES project, is equally enthusiastic about GRACES’ performance. She comments, “The exposure was 300 seconds long and the final signal-tonoise ratio is around 50 per pixel, which is higher than expected!!! And it was not possible to observe this object using just ESPaDOnS at CFHT”. Figure 2. Full GRACES spectrum of the Moon in the 1-fiber mode. Up to 36 orders are visible, i.e. from order #22 (centered on 1029nm) to #58 (centered on 408nm). Early Observations Gemini offered GRACES for the first time this year and the demand was huge! The Canadian and Brazilian communities requested GRACES for over 30 and 40 percent of their time, respectively. October 2015 GeminiFocus 15