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May 28, 2023



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Opinions: The visit from CIRCE


Steven Eikenberry is a Professor and Investigator at the University of Florida, but he is also responsible for the team building CIRCE (Canarias Infrared Camera Experiment), the Gran Telescopio CANARIAS' (GTC's) first visiting instrument.


Click to enlarge image
Click to enlarge image
Click to enlarge image

A visiting instrument is a science instrument that has neither been specifically recommended by the telescope's scientific committees nor directly financed by it, but which is considered to be of interest because of the capabilities that it will bring. CIRCE's visit to the telescope has had to receive prior approval from the GTC's governing bodies.

In this interview, Eikenberry talks to us about the capabilities that this instrument will have.


What is the current state of CIRCE?
CIRCE right now is in a fairly advanced state of development. For instance, our software system for the instrument is almost completely done. It's waiting really for some of the hardware to be tested. At this point, the critical components, the real drivers for CIRCE in terms of the hardware, the two toughest things are, of course, the optics (because it's a very cutting-edge optical approach that we're using for CIRCE with our reflective large-aperture aspherical mirrors) and the cryogenic mechanisms, always a challenge for any infrared instrument. Those have all been designed. At this point the mirror blanks have all been fabricated and we're now moving on to fabricating brackets and the bench itself, that will then go off to the diamond-turning company to finish them off. We're also getting ready to start fabricating the cryomechanical mechanisms. So we're in a situation now where we are well into the fabrication phase of CIRCE leading into integration and then test and delivery.

What’s the importance of CIRCE for the GTC?
I think it has a lot to offer even though it's a relatively small-scale inexpensive 'visitor' instrument. First of all, again there will almost certainly be some gap between the start of science operations at the GTC and the delivery and commissioning of the EMIR instrument. During that time, which could be in the order of a year or two, there won't be any other near-infrared capability on the GTC and the near-infrared is very important, because it combines fairly good sensitivity, like you get in the optical, with fairly good resolution that you would get in the mid-infrared.

Even though it's still seeing limited, the seeing is often much better in the near-infrared than in the optical, so getting some of the best, crispest images from the GTC will probably happen in the near-infrared band, certainly at the beginning.

Another thing about CIRCE is that it offers capabilities that EMIR, even though EMIR is a much larger and more powerful instrument in the end, won't be able to do. EMIR has wide-field imaging but CIRCE will offer a very fine pixel scale. So when the images are the best from the telescope you want to use CIRCE to take the pictures. It will also do narrow-band imaging, which is where some very exciting science can be done. Also CIRCE will do polarimetry and high time resolution imaging and photometry. So it's a very small but versatile instrument that in the early days will really provide an important capability for GTC that would otherwise be absent and it will also provide continued capabilities. Even after the delivery of EMIR, CIRCE will continue to complement the GTC.

Further information:

· Interview with Steven Eikenberry
· How will it work
· CIRCE’s web page

Natalia R. Zelman

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