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