THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT
1999

2. Scientific Highlights from 1999

UKIRT is used to provide data for a remarkably wide range of science programmes; highlights are identified below from the two semesters in 1999. The year was characterized by the widespread use of UFTI for programmes ranging from photometric studies at the bottom of the main sequence and beyond, to studies of morphological properties of galaxies at high redshift, and the followup of deep surveys with SCUBA on the JCMT and space-based X-ray surveys. UKIRT's image quality has been likened to HST/NICMOS by observers and its powerful infrared imaging capability complements the optical imaging possible on the 10-metre-class telescopes on Mauna Kea. A good example of this is the composite R,I,K image of Abell 851 produced by Smail and collaborators, shown in Figure 1, which used the Keck for the short wavelengths and UKIRT for the K-band.

Figure 1: The Abell 851 galaxy cluster: composite image using Keck I-band data and UKIRT K-band data. The insert shows a region near the centre created from HST, Keck and UKIRT R-, I- and K-band images. Data courtesy of I. Smail and collaborators.

Brown dwarf studies have been increasingly important for UKIRT over the last two years, both in terms of the production of candidate lists, their verification and their spectroscopic followup. 1999 saw good examples of all three of these areas. Lucas (then Oxford) carried out CGS4 spectroscopy to detect water vapour absorption in, and thus verify the nature of, the Orion brown dwarf candidates located with UFTI in the previous year; Leggett (JAC) and coworkers used CGS4 to detect water vapour and methane absorptions in objects detected in the Sloan survey; Jameson (Leicester) and collaborators used infrared colours from UFTI to confirm brown dwarf members of the Pleiades cluster; and Longmore and Casali (UKATC) used UFTI to push YSO surveys in the Ophiuchus dark cloud down to the brown dwarf regime.

Work on the early stages of star formation is a constant backdrop to UKIRT science. This year saw the combination of UKIRT's high spatial resolution with spectroscopy, producing the identification of spinning ``microjet'' structures near to a sample of these objects, which might be the key to the long-standing problem of carrying angular momentum away from the rapidly-spinning central object (Smith (Armagh) et al.).

Transient objects and targets of opportunity remain a UKIRT speciality, this year seeing the continuation of the long-term programme monitoring Sakurai's object. The development of the spectrum is now steadying, with little spectral structure and only a single helium line (probably formed outside the main ejecta shells) superposed on a strong, featureless dust continuum. We present in Figure 2 the time-development of the object's spectrum as determined from UKIRT spectroscopy over the last five years; the dramatic changes in the spectrum have been used to diagnose physical conditions in the ejecta (Evans (Keele) and collaborators). Secondly, the fast-moving asteroid 1999RQ36 was observed when at a distance of only 2.2 million km from the Earth, allowing its surface properties to be determined (Geballe (Gemini) observing the asteroid as a target of opportunity for Davies, JAC).

Solar-system highlights also include the determination of thermospheric temperatures on Titan, the detection of cloud formation on Uranus (UKIRT forecasting weather on an outer-solar-system object! - Geballe (Gemini) and collaborators) and the first detection of hydrated minerals on the surface of a stony asteroid (Davies (JAC) et al.).

Figure 2: Development of the energy distribution of Sakurai's object, note the strong He 1.08 µm line in emission in the later plots. Data courtesy of A. Evans.