THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT
2001-2002

2. Scientific Highlights

UKIRT was used in several studies of galaxy evolution, often as part of a multi-wavelength campaign. Extremely Red Objects (EROs) and Active Galactic Nuclei (AGN) were observed, as well as objects at extremely high redshifts.

Smith (Durham) reported a possible detection of Hα in a spectacular multiply-imaged ERO in the massive cluster Abell 68 at z=1.6 (Smith et al. 2002, MNRAS 333, L16). They show that the ERO is an early-type disk galaxy; if gas continues to cool on to this galaxy in the manner predicted by hierarchical galaxy formation models, then the ERO could evolve into a very luminous spiral galaxy. Willott (Oxford) studied very red Chandra sources in the K-band detecting all but one, which showed the targets to be EROs. Most were resolved as compact galaxies, probably host to the buried AGN. Lumsden (Leeds) studied the relation between mid-infrared emision in Seyferts and the luminosity of the AGN; early results suggest that the core mid-infrared luminosity is a good indicator of AGN luminosity. Ward (Leicester) obtained N-band spectroscopy of AGN using the high spatial resolution of MICHELLE to separate the dust emission from the nuclear component. UIST was used by Willott (Oxford) to observe emission lines in the most distant QSO known, confirming its redshift at z=6.4 and measuring the mass of the black hole. Imaging of dwarf galaxies by Mobasher (STSCI) established the infrared surface brightness of these objects and enabled their study at unprecedented redshifts.

2.2. Interstellar Medium

Various forms of interstellar hydrogen were observed during 2001 and 2002. The extremely widespread presence of H₃⁺ in the interstellar medium (ISM) was confirmed by McCall (Chicago). This programme has now produced detections of H₃⁺ virtually everywhere it has been sought, and some challenging column densities in the diffuse ISM (McCall et al. 2002, ApJ 567, 391). Hoare (Leeds) obtained Fabry-Perot observations of HII regions probing the luminosity function to new, low, limits.

2.3. Circumstellar Disks and Envelopes

Gledhill (Herts) detected extended structures in polarized light in protoplanetary nebulae, consistent with 10µm imaging obtained at Gemini. The results will enable powerful tests of grain properties in these young planetary nebulae (Bains et al. 2003, MNRAS 338, 287). Polarimetry was also used by Kuhn (UH) to study the properties of dusty disks, using a novel focal-plane coronagraphic mask with IRCAM. His limits on scattered light in sources such as Vega are extremely precise.

High spectral resolution was used in studies of stellar envelopes. Dhillon (Sheffield) observed CO ratios in cataclysmic variables and obtained an interesting result in previously common-envelope systems: ¹³CO is virtually absent despite prior co-existence with the envelope of a giant star. Magnier's (UH) observations of brown dwarfs with the CGS4 echelle reflects the increasing ambition with which observers are following up these objects with UKIRT. The programme was aimed at measuring accretion rates in the sample (in the Taurus dark cloud), as a way to filter out field-star contaminants. Harries (Exeter) carried out time-series echelle spectroscopy of T Tauris, detecting clumps accelerating in their accretion flow.

2.4. Stellar/Substellar

Probing the low-mass end of the main sequence continued to be a productive use of UKIRT time. Longmore & Casali (UKATC) followed up their programme of photometry near the hydrogen-burning limit in Ophiuchus with CGS4 spectroscopy, finding that half of their objects had surprisingly featureless spectra; an enigmatic result. Leggett (JAC) carried out further followup spectroscopy of brown dwarf candidates from the Sloan and 2MASS sky surveys, confirming a dozen new T dwarfs, including the latest-type Sloan T dwarf to date, a T7. Photometric observations in the L- and M-bands were also obtained by the group, and have provided a good test of the models for the atmospheres of these objects, constraining both the CH₄ and CO opacities. It appears that significant turbulent mixing is needed to produce the required abundances of CO, CH₄, H₂O and NH₃ (Saumon et al. 2003, Proc. IAU Symp. 211).

Multiple low-mass systems were also studied. Howell (LPI) continued his work on white dwarf / brown dwarf binaries (e.g. Harrison et al. 2003, AJ 125, 2609). One target shows no CO in a spectrum which otherwise closely resembles that of an M7 star. This was proposed as a good candidate for a brown-dwarf secondary, however the suggestion is controversial. Neuhaeuser (MPI) started a long term program searching for companions to stars with known planetary systems; they have found promising candidates for which orbital parameters will be determined in semester 03A.

2.5. Transient Objects

Figure 1: MICHELLE spectrum of Sakurai's object from Evans et al. (2002), showing silicate absorption.

Sakurai's object (Eyres, Preston) was observed for the penultimate time with CGS4 (Geballe et al. 2002, Ap&SS 279, 39). A MICHELLE spectrum of Sakurai's object (Figure 1, Evans et al. 2002, A&A 394, 971) shows clear evidence for the presence of an interstellar silicate absorption feature allowing the only direct determination of the extinction to this source, which is important for distance determinations.

Figure 2: Doppler image of WZ Sge from Howell et al. (2003) produced from spectra obtained on day four of the 2001 superoutburst. The two symmetric arc-shaped regions in the He II map are consistent with the presence of spiral arms in the accretion disk.

Time-resolved J- and K-band spectra were obtained for WZ Sge four days into its 2001 superoutburst (Howell et al., 2003 A&A 399, 219). These data represent the first time-resolved infrared spectra obtained of any dwarf nova during a superoutburst. The spectra indicate the presence of asymmetric emission within the accretion flow, in agreement with the optical detection of prominent spiral arms present within the accretion disk (Figure 2).

Meikle's programme on supernovae (SN), in conjunction with the European SN consortium, produced excellent data for two SN, and the UKIRT service programme produced data for the type Ia SN 2002cv. These observations led to the identification of the most highly extinguished type Ia event ever seen. The spectra provide detailed early-time coverage of a type Ia, revealing the development and subsequent fading of the not yet understood J-band deficit.

2.6. Solar System

June 2001 saw the first detection of rotational modulation of the auroral emissions on Uranus (Miller, UCL). MICHELLE was used by Green (Open University) to detect faint asteroids in the N-band, producing good data for thermal modelling of the surfaces. Tholen (IfA Hawaii) observed Pluto occulting a background star in IRCAM's last ever run. The data were obtained as part of a multi-telescope campaign, and provide evidence for extinction in, and expansion of, Pluto's atmosphere (Elliot et al. 2003, Nature 424, 165).