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Researchers have discovered a quasar
with a redshift of z=4.7 as part of the high redshift quasar survey in
which UK Schmidt Telescope plates are scanned in the Automatic Plate Measuring
Machine (APM) to select objects of particular B-R, R-I colour. Spectroscopic
confirmation was obtained with the Faint Object Spectrograph on the INT.
Over half of the highest redshift
quasars have been discovered as a result of the UKST-APM-INT combination,
including no less than four of the top six. Although it just fails to take
the record for the highest known redshift (recently established at 4.89),
the I magnitude of this object is 17.5, making it the brightest known object
in the Universe at optical wavelengths. The particular importance of this
discovery is that it is sufficiently bright for relatively high dispersion
spectroscopy. Apart from the intrinsic interest in the object itself, detailed
study of the intervening gas clouds and galaxies is therefore posssible.
Ironically, one by product of the
APM high-redshift quasar search has been one of the nearest and faintest
stars yet discovered. The star, called BRI0021-0214, was selected on the
basis of its BJ-R, R-I colours, then confirmed as a low temperature
M dwarf by a spectrum obtained with the Faint Object Spectrograph on the
INT. Infrared obsservations indicate a bolometric luminosity of about 14mag
or 10-4 solar luminosities, and an effective temperature of
around 2250K. The star, which is about 10pc distant, is very near the hydrogen
burning limit of 0.075 solar masses. The discovery of such stars is important
for the determination of the stellar luminosity function at its faint end
and the contribution of low mass stars to the galactic mass density.
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information
ING facilities involved:
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Isaac Newton Telescope,
using FOS-1
Some references:
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McMahon, R. and Irwin,
M., 1992, "APM surveys for high-redshift quasars", Digitised Optical Sky
Surveys. Proceedings of the Conference on "Digitised Optical Sky Surveys",
held in Edinburgh, Scotland, June 18-21, 417
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