The Carlsberg Meridian Telescope
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The Carlsberg Meridian Telescope |
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Description
Current Aims
Results
Astrometric links
Pictures of the telescope
Contacting us
The Carlsberg Meridian Telescope (formerly the
Carlsberg Automatic Meridian Circle) is dedicated to carrying out
high-precision optical astrometry. It was until recently
operated jointly by the Copenhagen
University Observatory (CUO), the
Institute of Astronomy, Cambridge (IoA) and the Real Instituto y
Observatorio de la Armada en San Fernando (ROA), however it is now
run solely by the ROA.
Although not one of the
Isaac Newton Group of telescopes, it is nevertheless part of the
Observatorio del Roque de los Muchachos on La
Palma. It began operation in May 1984.
When the telescope was first moved to La Palma in 1984 it was one of the
first fully automatic telescopes in the world. When the skies were clear a
selection of stars (about 500 a night) would be made and at about sunset the
dome would open automatically and start observing. An observer would be
present on the site (usually in the flat underneath the telescope), but
would only be needed if there was a failure of a piece of equipment. Click
here for more information on the old
system.
In the spring of 1997 a further stage of automation was made when we
converted the telescope to remote operation. Since then, the telescope has been
operated over the Internet from Britain, Denmark or Spain and no observer has
been present at the telescope. Most of the problems can be solved over the
network, but sometimes local help is needed. By operating in this way a
considerable saving is made on travel costs.
The main task that is currently being done by the telescope is to map the
Northern sky using the upgraded CCD detector. This will give accurate positions of
stars, allowing a reliable link to be made between the bright stars measured
by Hipparcos and the fainter stars seen on photographic plates (as measured
by the APM and similar measuring machines).
The current area of the survey is between
-30° and +50° in declination and has been recently completed.
At the IAU General Assembly in Manchester (August 2000) a meeting was held
on astrometric surveys. The viewgraphs from the
meeting are here.
The results of observations with the old micrometer were published annually
in catalogues. As well as the positions and magnitudes,
the catalogues contain the improved proper motions of many stars derived by
combining the Carlsberg position with previous epoch observations retrieved
from a data-bank. The average accuracy of the proper motions so derived is
0.003 arcsec/year.
Catalogues 10 and 11 were finished in June 1999 and
were the last to be published using data from the old
micrometer.
Carlsberg Meridian Catalogues numbers 1 to 11 can now be
interrogated online via the interface at the UK Astronomy Data Centre.
Alternatively, the complete data files from the CD-ROM for CMC1-11 can be found
here.
Carlsberg Meridian Catalogue 14 has
been released (31 December 2005). This is an
astrometric and photometric catalogue of 95.9 million stars in the red
(SDSS r') magnitude range 9 to 17.
This catalogue covers the declination
range -30° to +50° and supercedes CMC12
which covered -3° to +3° and CMC13
which covered -3° to +30°.
From observations of about 50 photometric standards, the Carlsberg Meridian
Telescope provided nightly values of
atmospheric extinction in V for La Palma. The data is split up into
yearly files going back as far as 1984. The most recent file is that for 2012.
From the end of 1999 March this differs from the previous years as it is
derived from the new CCD camera which works in the
Sloan r' band. For more information look
here.
Measurements of temperature, pressure, windspeed, wind direction and humidity
at the site are taken every 5 minutes day and night. This large database of
meteorological records
is available to interested persons directly over the web.
Details of past projects of the CMT using the old micrometer can be found
here.
A bibliography
featuring Carlsberg observations is available.
Some more views of the Carlsberg Meridian Telescope.
Description
The telescope is a
refractor with an objective of 17.8 cm diameter and focal length of 266 cm.
The observing procedure is entirely automatic, with the acquisition
controlled by a Pentium PC. The data reduction is carried out in the
morning on another Pentium running Linux.
In June 1998 we changed the detector from
a photoelectric scanning-slit micrometer to a Charge Coupled Device (CCD)
mainly operating in drift-scan mode. This has not only helped us observe
fainter stars, but it also has enabled us to observe many stars at once.
This one improvement has increased the number of stars we observe a night by
a factor of more than 20.
The most recent development (April 1999) has been to upgrade the
CCD system
to a 2k by 2k chip and to fit a SDSS r' filter. These and other improvements
with the CCD have allowed us to observe about 4 times as many stars with
the new CCD. Our current magnitude limit is r'=17 and we observe between
100,000 and 200,000 stars a night.
There is also an RGO leaflet on
Meridian Astronomy.Current Aims
Results
Astrometric links
Pictures of the telescope etc.
