2.2 The Liverpool Telescope

The Liverpool Telescope project grew from a need long recognized by astronomers for a telescope which could monitor astronomical objects which vary in brightness or in their spectral properties (Steele, 2000). When completed in mid 2002 the Liverpool Telescope (LT) will be a 2.0 metre aperture (and hence the world’s largest) Ritchey-Chretien fully robotic telescope, to be sited at the Observatorio del Roque de Los Muchachos, La Palma, Spain. At an altitude of 2400 metres in the trade wind zone, it lies in a constant and undisturbed airflow, resulting in some of the best astronomical seeing in the world. The median image quality (FWHM) of the site is 0.7 arc-seconds. The skies are also some of the clearest in the world, giving an average of 2400 hours of clear astronomical night time per year.

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The normal mode of operation of the LT will be fully robotic (Steele, 2001). This means that the telescope will not be supervised either locally or remotely during its routine operation. Instead it will carry out a programme of observations selected from those held in a database (Steele, 1998) according to a flexible scheduling algorithm (Steele and Carter, 1997), and return the data to the observer in the form they require (Steele, 2000) through automated reduction procedures.

This unique mode of operation will allow science programs to be carried out which otherwise would have little chance of success, such as fast response to target of opportunity observations and long term monitoring, that are virtually impossible with a conventionally scheduled telescope (Bode, 1995). In addition proper matching of programmes to observing conditions can be carried out so that, for example, programmes requiring the “best” seeing can be scheduled with a genuine chance of being done. Finally as both Bode (1997) and Bohannan (2001) point out there are considerable cost and convenience benefits in going to a fully robotic mode of operation.

Initially the LT will have an optical camera fitted containing a back illuminated EEV CCD42-40 CCD. This has 2048×2048 active pixels, with a pixel scale of 13.5 microns. With the LT this corresponds to a pixel scale of 0.135 arc-seconds/pixel, giving a field of view of 4.6×4.6 arc-minutes.

The LT’s design comprises a altitude-azimuth mounting, with hydrostatic mountings for each axis, permitting a pointing accuracy of ~ 2'' and unguided tracking precision of 0.4'' over a 10-min interval, with guided pointing better than 0.2''. The optical and tracking specification of the LT are given in Table 2.1. There will be two, seven position filter wheels mounted in-line above the camera, giving a total of twelve filter selections. The core filter set for the CCD has been defined and it is intended that these filters will be available continuously and long term on the camera. There are a total of eight core filters, which have been chosen to maximize scientific utility to both stellar and extragalactic astronomers combined with high throughput. In future semesters up to an additional four single semester filters may be offered for more specialised scientific programmes (e.g., Strömgren photometry). The core filter set is shown in Table 2.2.

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Conservatively, an analysis shows that over 70% of the applications to the LT Time Allocation Groups (TAGS) (i.e., including internal, PPARC and Spanish TAGS) requested either photometry or relative photometry of point sources. These requests included; Gamma Ray Bursters (GRBs), Quasars, Brown Dwarfs, symbiotic and cataclysmic variables and Be  stars. With such a large proportion of time centered on one scientific theme the justification for automating the procedure is clear. The high level of automation in the LT operation, together with a high observing efficiency leads to a requirement for a commensurate level of automation in the reduction of the subsequent data.