An experimental 2.7 meter liquid mirror telescope

A 2.7-meter Liquid Mirror Telescope (LMT) is currently under construction at the University of British Columbia. The stationary, parabolic primary mirror is formed by uniformly rotating the highly reflective liquid, metallic mercury. Compensation for the lack of mechanical tracking will be accomplished by using the Time Delay and Integrate (TDI) readout technique with our Ford 2048 x 2048 CCD detector. The ability to produce large, diffraction-limited mirrors in the laboratory has been previously demonstrated; this project, the first of its kind, is an investigation into their potential for astronomical survey-work, in a working observatory environment. A set of 40 intermediate-band filters, one filter to be used per "photometric" night, will facilitate the collection of Spectral Energy Distributions (SEDs) of all objects, to a limiting stellar V[symbol omitted] ~21, in the 83.0 deg² strip (1/3 deg wide) available to this telescope. A catalog of >10⁵ galaxy and ~3,000 quasar SEDs is expected, providing the largest database of its type to date. A detailed stress-tensor analysis of the mercury-loaded mirror cell is given. The maximum flexure of the cell (at the mirror rim) was found to be ≲0.32 mm. The high resonant frequency of the cell was designed to minimise the excitement of both gravity and capillary waves, surface phenomena which can degrade image quality. An analysis of the support structure indicated that its maximum deflection under wind loading (≲0.3µm) would be significantly less than the Ford CCD's physical pixel size of 15 µm. Temperature-sensitive autofocussing was needed to ensure that thermal expansion/ contraction of the support structure did not lead to defocussing. Star-trail curvature at non-zero latitudes and the discrete nature of the TDI readout mode leads to elongation of north-south (NS) and east-west (EW) image structure, respectively. Convolving stellar Point Spread Functions (e.g. Gaussian) with the CCD's pixel width showed image broadening of ~5% (EW) and ~9% (NS). While these effects are expected to be negligible for our instrument, quantifying them under on-site testing will be imperative before proceeding with the development of larger LMTs.