A new rotator for HiPERCAM on the GTC: design study

HiPERCAM is a revolutionary new astronomical instrument that saw first light on the GTC, the world's largest optical/IR telescope, in February 2018. The instrument was funded by a 3.5Meuro ERC Advanced Grant awarded to me in January 2014, and was built by a consortium from the Universities of Sheffield, Warwick, Durham, the UKATC and IAC.

HiPERCAM is arguably the most powerful ground-based optical imager in the world. This is because of three unique characteristics: 1. HiPERCAM images in 5 wavebands simultaneously on its 5 CCD detectors, covering the entire optical spectrum from 300-1000 nm. It is therefore up to 5 times more efficient than other cameras. 2. HiPERCAM uses custom-built (for 1.0Meuro) low-noise, frame-transfer e2v CCDs that are cooled thermo-electrically to 183 K, thereby allowing both long-exposure, deep imaging of faint targets, as well as high-speed (over 1000 frames per second) imaging of rapidly varying targets. It is therefore much more versatile than other cameras. 3. HiPERCAM is mounted on the world's largest telescope, located at one of the world's best observing sites. It is therefore much more sensitive than other cameras.

The next few years will be witness to a revolution in our knowledge of the Universe with the advent of large survey facilities such as LSST, Gaia, TESS, PLATO, SKA, Euclid and LIGO/VIRGO. Many new variable and transient sources will be discovered by these facilities. Time-domain astrophysics is set to become a core activity, and detailed follow-up studies of the most interesting objects will be essential. HiPERCAM on the GTC has been designed to fulfill this role. Targets will include: LIGO/VIRGO gravitational-wave transients with localisations from smaller telescopes; supernovae; gamma-ray bursts; fast-radio bursts; broadband transmission "spectroscopy" of rocky exoplanets; occultations by dwarf planets in the Kuiper belt; accreting black-holes in binaries; testing quantum mechanics and general relativity by observing millisecond pulsar binaries; pre-imaging and simultaneous imaging of the proposed ultra-deep JWST Time-Domain Field (TDF), which is only visible to ground-based telescopes in the northern-hemisphere. These are just a few examples of the many science areas that HiPERCAM could have a major impact on in the years to come.

HiPERCAM is currently mounted on one of the two available Folded Cassegrain focii of the GTC. Unfortunately, from 2019, HiPERCAM will have to share this focus with two common-user GTC instruments: CanariCam (from Q1 2019) and MIRADAS (from Q4 2019/Q1 2020). There are two other Folded Cass focii available at the GTC, but neither have been commissioned, i.e. they do not currently have rotators, cable wraps and services, and both were originally assigned for use by (as yet unbuilt) engineering instruments to assist in calibration of the telescope. I recently proposed to the GTC Director, Dr. Romano Corradi, that there will be exciting new scientific opportunities available in time-domain astrophysics if we are able to mount
HiPERCAM permanently at one of these spare focii, thereby allowing us to respond immediately to transients discovered by survey facilities. Romano presented my proposal at the most recent GTC Steering Committee meeting, who responded very positively: "The Committee acknowledge the unique capabilities that HiPERCAM provides in combination with the GTC, and is therefore happy to explore the possibility to mount the instrument
permanently in one of the free Folded Cass focii."

This grant will allow us to design a new rotator for HiPERCAM, hold a Preliminary Design review, submit a detailed technical feasibility report to the GTC board on the new rotator, and obtain reliable quotes for the new rotator. With all of the above complete, we will then be in a position to apply to STFC for additional funding to build and commission the rotator on the GTC.

This grant is aimed at designing a new rotator for HiPERCAM on the 10.4-m Gran Telescopio Canarias on La Palma in order to give HiPERCAM a permanent home on the GTC, thereby significantly improving its scientific productivity.

HiPERCAM is a unique instrument, capable of far higher frame rates than normal CCD cameras used on astronomical telescopes. It achieves
these high frame rates by using custom frame-transfer CCDs made by e2v in conjunction with a high-speed data acquisition system. The latter was
sub-contracted to the UKATC in Edinburgh. We provided scientific direction and defined the functional and performance requirements. Much of the detailed technical work on the detectors and data acquisition system was performed by engineers at the UKATC. This contract provided the UKATC
with an opportunity to develop a new data acquisition system based on the ESO New General Controller (NGC), thereby giving their staff experience of cutting-edge controller technology. The experience will undoubtedly be of benefit to future UKATC projects.

The new rotator for HiPERCAM on the GTC will be a one-off, custom-designed unit, based on one of the existing GTC designs that they have given us access to, so we do not envisage any significant new knowledge as a result of this specific piece of work.