Heavenly Twins to Expand Britain's Astronomy|
by Rodney Steel
By the dawn of the 21st century British astronomy will span the world we live in and the universe around us. Two new giant telescopes, one in the northern hemisphere in Hawaii and the other in the southern hemisphere in Chile, will give British astronomers and their co-partners (American, Canadian, Chilean, Argentinean and Brazilian scientists) in the ambitious Gemini project access to the entire celestial sky.
United Kingdom industry and universities will be major contributors to the construction of these powerful instruments, and the overall director of the Gemini project, based at a headquarters in Tucson, Arizona, is Dr. Matt Mountain, a graduate of Imperial College London, who has been a member of the scientific staff at the Royal Observatory, Edinburgh, since 1987.
As a contribution to optical steadiness the primary mirror will be located 20 metres above ground level, substantially above the potentially turbulent boundary layer; dome ventilation will further reduce the adverse effect of the wind and provide optimum flushing, with careful thermal matching of the enclosing dome the telescope itself, and the optics to minimise the effect of thermal instability.
Especially important is the multi-object spectrograph being developed at Durham University in northern England, the Royal Observatory in Edinburgh, and the Dominion Astrophysical Observatory in Canada, which will offer as many as 600 spectrographic slits formed in custom-made masks that are deployed in the focal plane.
With resolving powers of up to 10,000 and a capability for measuring radial velocities to an accuracy of 1-2 km/s from one line with hourly wavelength calibration, the Gemini multi-object spectrograph could, for example, characterise velocity distributions in a dwarf spheroidal galaxy belonging to the local group in the equivalent of a single night's viewing.
On the 4200 metre summit of Mauna Kea, in Hawaii, the concrete foundations of the northern Gemini instrument have already been laid, and first light is expected in 1999. The southern site, 2700 metres up at Cerro Pachon in central Chile, is expected to commence operation about a year later.
Chosen for the clarity of their weather and excellent atmospheric stability, the two Gemini sites offer outstanding observation facilities for astronomers, well above the water vapour that hinders most ground-based observing.
Professor Ian Robson, the British director of the Joint Astronomy Center in Hawaii that will operate the Mauna Kea instrument, has no doubt of the important contribution that Gemini is going to make to international astronomy.
One of the unsolved questions that Gemini will address is the mystery of how stars are formed. How do stars condense from clouds of dust, and what do protostars look like? Newborn stars are only going to be observable in infra-red emissions that can penetrate the swirling dust cutting off visible light. Gemini's infra-red performance will make this area of investigation a priority objective.
Mature stars initially burn hydrogen and then progressively more complex elements, until eventually their nuclear furnaces generate heavy metals. These each have their own distinctive signatures in isotopic abundance patterns; spectroscopic studies with the Gemini telescopes will reveal the history of heavy element production not only in our own galaxy, the Milky Way, but also in its two neighbours, the Magellanic Clouds.
Detailed studies of this phenomenon require the Gemini combination of wave length coverage, angular resolution, and sensitivity to probe matter distributions and distinguish the signatures of microlensing and variable substructures within lensed sources.
And at the furthest extent of the universe that has so far been probed by telescopes, Gemini will be looking at the most remote - and therefore the youngest - galaxies of all. They can tell us how galaxies are born and how they evolve. The infra-red response of Gemini will enable astronomer s to explore their structures and stellar content and provide the key to understanding the relation between stellar populations, chemical enrichment history, and the life cycle of present galaxies.
Gemini, the aptly named heavenly twins, will usher in a new era of astronomy and ensure British scientists continue to play a leading role in the exploration of the heavens.
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