|
The heart of the 6.5 Magellan AO system (MagAO) is a 585 actuator adaptive secondary
mirror (ASM) with <1 msec response times (0.7 ms typically). This adaptive secondary will
allow low emissivity and high-contrast AO science. We fabricated a high order (561 mode)
pyramid wavefront sensor (similar to that now successfully used at the Large Binocular
Telescope). The relatively high actuator count (and small projected ~23 cm pitch) allows
moderate Strehls to be obtained by MagAO in the “visible” (0.63-1.05 μm). To take advantage
of this we have fabricated an AO CCD science camera called "VisAO". Complete “end-to-end”
closed-loop lab tests of MagAO achieve a solid, broad-band, 37% Strehl (122 nm rms) at 0.76
μm (i’) with the VisAO camera in 0.8” simulated seeing (13 cm ro at V) with fast 33 mph
winds and a 40 m Lo locked on R=8 mag artificial star. These relatively high visible
wavelength Strehls are enabled by our powerful combination of a next generation ASM and a
Pyramid WFS with 400 controlled modes and 1000 Hz sample speeds (similar to that used
successfully on-sky at the LBT). Currently only the VisAO science camera is used for lab
testing of MagAO, but this high level of measured performance (122 nm rms) promises even
higher Strehls with our IR science cameras. On bright (R=8 mag) stars we should achieve very
high Strehls (>70% at H) in the IR with the existing MagAO Clio2 (λ=1-5.3 μm) science
camera/coronagraph or even higher (~98% Strehl) the Mid-IR (8-26 microns) with the existing
BLINC/MIRAC4 science camera in the future. To eliminate non-common path vibrations,
dispersions, and optical errors the VisAO science camera is fed by a common path advanced
triplet ADC and is piggy-backed on the Pyramid WFS optical board itself. Also a high-speed
shutter can be used to block periods of poor correction. The entire system passed CDR in June
2009, and we finished the closed-loop system level testing phase in December 2011. Final
system acceptance (“pre-ship” review) was passed in February 2012. In May 2012 the entire
AO system is was successfully shipped to Chile and fully tested/aligned. It is now in storage in
the Magellan telescope clean room in anticipation of “First Light” scheduled for December
2012. An overview of the design, attributes, performance, and schedule for the Magellan AO
system and its two science cameras are briefly presented here.
|
