Timothy G. Hawarden

JHK standard stars for large telescopes: the UKIRT Fundamental and Extended lists

We present high-precision JHK photometry with the 3.8-m UK Infrared Telescope (UKIRT) of 82 standard stars, 28 from the widely used preliminary list known as the ‘UKIRT Faint Standards’, referred to here as the Fundamental List, and 54 additional stars referred to as the Extended List. The stars have 9:4 , K , 15:0 and all or most should be readily observable with imaging array detectors in normal operating modes on telescopes of up to 10-m aperture. Many are accessible from the southern hemisphere. Arcsec-accuracy positions (J2000, epoch ,1998) are given, together with optical photometry and spectral types from the literature, where available, or inferred from the J 2 K colour. K-band finding charts are provided for stars with proper motions exceeding 0.3arcsecyr 21 . We discuss some pitfalls in the construction of flat-fields for array imagers and a method to avoid them. On 30 nights between late 1994 and early 1998 the stars from the Fundamental List, which were used as standards for thewhole programme, were observed on an average of 10 nights each, and those from the Extended List on an average of six nights. The average internal standard error of the mean results for the K magnitudes is 0.005mag; for the J 2 H colours it is 0.003mag for the Fundamental List stars and 0.005mag for those of the Extended List; for H 2 K the average is 0.004mag. The results are on the natural system of the IRCAM3 imager, which used a 256 � 256 InSb detector array with ‘standard’ JHK filters, behind gold-coated fore-optics and a gold- or silver-dielectric coated dichroic. We give colour transformations on to the CIT, Arcetri and LCO/Palomar NICMOS systems, and preliminary transformations on to the system defined by the new Mauna Kea Observatory near-infrared filter set.

Critical science with the largest telescopes: science drivers for a 100m ground-based optical-IR telescope

Extremely large filled-aperture ground-based optical-IR telescopes, or ELTs, ranging from 20 to 100m in diameter, are now being proposed. The all-important choice of the aperture must clearly be driven by the potential science offered. We here highlight science goals from the Leiden Workshop in May 2001 suggesting that for certain critical observations the largest possible aperture - assumed to be 100m (the proposed European OverWhelmingly Large telescope (OWL) - is strongly to be desired. Examples from a long list include: COSMOLOGY: * Identifying the first sources of ionisation in the universe, out to z ≥14 * Identifying and stufdying the first generation of dusty galaxies * More speculatively, observing the formation of the laws of physics, via the evolution of the fundamental physical contants in the very early Universe, by high-resolution spectroscopy of very distant quasars. NEARER GALAXIES: *Determining detailed star-formation histories of galaxies out to the Virtgo Cluster, and hence for all major galaxy types (not just those available close to the Local Group of galaxies). THE SOLAR SYSTEM: A 100-m telescope would do the work of a flotilla of fly-by space probes for investigations ranging from the evolution of planetary sutfaces and atmospheres to detailed surface spectroscopy of Kuiper Belt Objects. (Such studies could easily occupy it full-time.) EARTHLIKE PLANETS OF NEARBY STARS: A propsect so exciting as perhaps to justify the 100-m telescope on its own, is that of the direct detection of earthlike planets of solar-type stars by imaging, out to at least 25 parsecs (80 light years) from the sun, followed by spectroscopic and photometric searches for the signature of life on the surfaces of nearer examples.

Wide-field camera for the United Kingdom Infrared Telescope

This paper describes an ambitious new wide field IR camera for the 3.8m UK IR Telescope (UKIRT), located on Mauna Kea, Hawaii. The camera, currently under design at the UK Astronomy Technology Center, will include 4 2048 by 2048 pixel focal plane array IR detectors operating over a wavelength range of 1-2.5 micrometers . The optics provide a 1 degree diameter corrected field of view and a pixel scale of 0.4 arcsec per pixel. A novel Schmnidt type optical design allows the large field to be imaged with excellent image quality. The optical design includes a cold stop to maximize rejection of background radiation and stray light. Precise microstepping will be used to improve sampling. Four parallel data acquisition and processing channels will be used to cope with the large data rates expected. It is envisaged that a substantial fraction of UKIRT time will be devoted to large area sky surveys once WFCAM is operational, resulting in a unique IR catalogue containing hundreds of millions of objects.

Lightweighted secondary mirror for the United Kingdom Infrared Telescope

The paper describes the manufacture and testing of a lightweighted Zerodur secondary mirror for the United Kingdom Infrared Telescope on Mauna Kea, Hawaii. The 313 mm diameter mirror is mounted on a Piezo platform for fast tip/tilt corrections. Therefore, the mirror mass has to be minimized to achieve high dynamic properties of the adaptive tip/tilt platform. The goal was to test the convex secondary without large auxiliary optics (Hindle sphere). We measured the mirror through the back surface using a small null lens system. A special transparent and highly homogeneous Zerodur was used for this purpose. We demonstrate that grinding a honeycomb structure and acid-etching of the back side of the mirror does not affect the figure of the polished convex surface.

Postupgrade performance of the 3.8-m United Kingdom Infrared Telescope (UKIRT)

The upgraded 3.8 m UK Infrared Telescope is now provided with: (1) tip-tilt image stabilization by a light-weighted secondary mirror on piezo-electric actuators, controlled by a fast guider sampling at >= 40 Hz on guide stars V m6; (2) active primary mirror figure and secondary mirror alignment control, via a regularly-maintained look-up table; (3) active focus measurements and correction by the fast guider, supplementing a focus maintenance model which corrects for elastic and thermal changes; (4) ventilation of the 2600 m3 dome by 16 apertures totalling 50 m2; (5) insulation of the underside of the concrete dome floor; and (6) internal air circulation during the day, to reduce heating of the upper telescope steelwork.

UKIRT Upgrades Program: control of the telescope thermal environment

The control of the telescope thermal environment at the 3.8-m United Kingdom Infrared Telescope (UKIRT) is based on the requirements that dome seeing should not degrade the image quality by more than 0.05 arcsec (FWHM) and that mirror seeing should be reduced to negligible proportions. After quantifying steady state and transient heat flow around and through the building, we set out on a program to meet these requirements. Major telescope enclosure upgrades to address dome seeing include natural dome ventilation with 16 apertures in the base of the dome and for near still-air nights, forced-air ventilation via the plant room exhaust system. To address mirror seeing, we are in the process of installing a day-time mirror cooling system that can drive and/or keep the primary mirror between 0 degrees Celsius and 2.5 degrees Celsius colder than the predicted night-time local dome air temperature. Nevertheless, during the night, if the primary mirror is warmer than the local dome air, a flushing system is available to blow away warm convective air cells as they form. This paper describes design considerations of the natural dome ventilation system (DVS), the hardware of the primary mirror cooling and flushing system and the performance of the mirror flushing system on a dummy mirror segment.

Optical design of a visible and infrared survey telescope for astronomy

A number of preliminary optical designs for a new generation of 4 meter astronomical survey telescopes have been investigated. These have large fields of view and operate in both the visible and near IR astronomical wavebands. Typical requirements for dual band systems of this type are presented. Two designs for prime focus refractive field corrector systems are presented, with and without aspheric surfaces. The use of aspheric surfaces on the field corrector lenses is shown to allow a large field of view to be achieved. A design for a three mirror reflective system is presented which also allows a 2 degree field to be achieved. An IR imager, based on a modified Schmidt camera, is presented which allows a 1 degree field of view to be achieved. Additionally, a modified Ritchey-Chretien telescope, incorporating refracting field corrector lenses is presented. This design provides a large field of view over both the visible and IR wavebands. The mechanical constraints of combining these systems into dual channel systems are also discussed.