THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT
1998

5. Longer-Term Plans

5.1. The UKIRT Wide Field Camera (WFCAM)

In 1997 the potential of UKIRT as a future wide-field facility, first endorsed by the Williams Panel, was explored in more detail. Early in 1998 plans emerged for a practical facility able to image 0.25 degree² in one exposure in the near-IR (J, H and K bands). In May 1998 a meeting was held in London to address the future roles of UKIRT and the INT as widefield facilities, and a consensus emerged that such facilities were urgently required and that UKIRT should become the UK's IR facility and the INT supply the visible band capability. After the presentation of a science case for a widefield IR imaging facility, in part for use in large-scale surveys, in September 1998 the Ground-Based Facilities Committee endorsed the proposal at a high priority and authorised the UKATC to commence a design study leading to a Conceptual Design review in mid-1999.

The outline design of the instrument is for an f/9 Cassegrain focus located at a field lens well ahead of the primary mirror. This keeps the size of the secondary compatible with the present top-end with a tip-tilt system similar to the present one. The design avoids acquiring a new topend for a much larger secondary, the larger optic itself, and a much larger actuation system. The focus is re-imaged by a Schmidt-type optical system onto four 2048 x 2048 HgCdTe arrays spaced by 90% of their widths, giving a pixel scale of 0.4". Such a layout (pioneered by the Cambridge CIRSI imager using 1024 x 1024 arrays) would allow a field of view of almost a square degree to be fully covered in four exposures. Since the longest exposure through broad-band filters would be only about 10 seconds, multiple exposures would be required for deep images. The coarse spatial resolution due to the large pixels would be refined using microstepping and pixel interlacing on data reduction. The imager, with the largest cryostat yet proposed for UKIRT, would be mounted on the central plug of the primary mirror.

The proposed system is an immensely powerful facility for IR surveys, able to image to K=20 at 3 in 1 hour over a degree². By the end of 1998 the instrument (WFCAM), had attracted interest from several outside groups including the Max Planck Institute fur Extraterrestrial Physik Garching, and Subaru, on behalf of the Japanese community. The latter proposed to contribute to the data reduction and possibly in hardware procurement, and at year's end mechanisms for collaboration were being explored.

5.2. Adaptive Secondary Mirror (ASM)

The most attractive prospect for very high-resolution imaging on UKIRT remains the option of an adaptive secondary mirror, which offers simplicity, low emissivity and lack of polarimetric complication in a single system, and would be available to all instruments with minimum complications. The JAC accordingly communicated with the UCL group which is developing a laboratory demonstrator mirror with a view to proving the ASM concept. The low-keyed UCL approach appears more suited to the likely needs of UKIRT than the considerably higher-tech system being developed at the University of Arizona and at Arcetri for the 6.5 m MMT.