Take one of the world's most complicated instruments, a 400 ton behemoth telescope, and marry it to a high tech sophisticated and sensitive mid-infrared (MIR) camera, and you know you have quite a challenge in front of you. That's what happened over the past two weeks on top of the Roque de los Muchachos observatory site in La Palma, Canary Islands. The University of Florida's MIR CanariCam was powered up and placed on the Nasmyth focus of the 10.4 GTC segmented mirror telescope.
But before commissioning of the new CanariCam instrument could begin, the weather had to cooperate - and it didn't. Three days of clouds, wind and torrential rains assaulted the peak, making any useful testing impossible. After that, the lingering humidity continued to pose a problem for the telescopic optics and seeing.
Finally Monday night, September 27, with just three nights left on the observing run set aside for CanariCam, the weather and humidity cooperated with clear skies. Star images through the GTC were somewhat degraded, but with some manipulation, pinpoint imaging was obtained and CanariCam began taking images on the sky. Much to the satisfaction of the GTC observing staff and Florida team members, CanariCam began performing very close to the diffraction limit of the telescope. For a 10.4 meter telescope operating in the mid-infrared (0.2 arc second angular resolution at 10 micron MIR range), that's saying a lot!
Because light acts as a wave, any attempt to resolve very small images will be limited by the size of the instrument being used. The larger the aperture of the telescope, the better the resolution. That's the common sense reason why bigger telescopes see more than backyard scopes. CanariCam can take this size advantage of the GTC and operate very near its diffraction limit because the longer specific wavelengths of the mid-infrared reduce distortions caused by the atmosphere. As the accompanying photo shows, stellar images are indeed resolved near the diffraction limits of the GTC.
But operating in the mid-infrared range also produces extra demands on the telescope. "Chopping and nodding" is the process previously described of introducing small offsets in multiple images to reduce extraneous radiation and allow a better view of the astronomical target. This requires, however, that the GTC subsystems must perform these minor adjustments flawlessly, especially the GTC secondary mirror which must move tiny fractions of space in very small increments of time.
Large structure holding secondary mirror of GTC, required to oscillate up to 10 arc seconds several times a second
When the commissioning testing attempted to introduce chopping and nodding to the mix, problems were encountered, especially when combined with the tracking and guiding needs of the observations. Throughout the first full night of observations, various faults kept cropping up, making useful commissioning tests impossible. Still, learning that CanariCam can operate at or near the diffraction limit was an important milestone.
The two remaining nights available for commissioning were likewise frustrating. High humidity, combined with various fault warnings with the telescope's operation, resulted in the inability to test CanariCam on any more "interesting" objects.
Throughout the operation, the GTC engineering and science staff worked closely at all times with the Florida team, demonstrating obviously intense commitment to the overall scientific project. Principal Investigator Charlie Telesco believes that, given the logistics of getting to and from the Canary Island site, the real possibility exists of finding more ways to use remote access between the teams (video link and internet link) so that effective coordination might allow the GTC staff to carry out many of the commissioning activities with "real time" help from the Florida team. For example, most of the GTC problems encountered so far appear to be software issues, which Senior Software Engineer Frank Varosi may be able to assist with long distance.
GTC staff astronomers and University of Florida team members in control room
Meanwhile, what about that pesky coldhead that caused such anxiety during the initial stages? Even though the detector had to be powered off a few times to accommodate telescope adjustments, it basically maintained temperatures in the 8.74K to 8.76K range, good enough for getting useful data. Putting a newer one on will improve on this, but the old coldhead has been a true workhorse during the frustrating final days. Meanwhile, CanariCam is still cold and remains on the telescope, making continued commissioning over the next several weeks a real possibility.
So final commissioning of CanariCam will have to wait, but its performance to date is extremely promising. Once the "prenuptial agreements" between it and the GTC have been worked out, a successful marriage appears to be in the works. Congratulations are due to the entire Florida team and the hardworking staff at GTC. CanariCam and the GTC will soon be combining their resources to discover new secrets lurking behind obscuring clouds of interstellar dust.
CanariCam at GTC Nasmyth focus, waiting for clear skies
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