Abstract
Remedial measures for ‘dome seeing’ effects are discussed with special reference to the removal of the Isaac Newton Telescope to an excellent site at the Observatory of Roque de los Muchachos, La Palma. From knife-edge and related tests, the chief contributions to bad seeing at the present site are found to be: (a) air near the surface of the primary mirror, (b) air surrounding the prime focus cage; there is evidence from telescopes at better sites that there may also be a contribution, (c) from warm ambient air inside the dome. The cure for (c) lies in adequate insulation accompanied by measures permitting rapid ventilation. A novel feature of the dome proposed for the Isaac Newton Telescope on La Palma is the provision of a large ventilating aperture opposite the dome slit. The cure for (b) lies mainly in the avoidance of heat sources on the telescope. To eliminate (a) the mirror will be refrigerated up to 2 K below ambient night air temperature almost all of the time; simple calculations show that this can be achieved with a flow of cooled air at about 0.2 m/s during the day-time only.
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