The Canada-France-Hawaii Telescope (CFHT) is a non-profit
organization which operates a world class 3.6 meter telescope
atop Mauna Kea, a dormant Hawaiian volcano rising
4,200 meters (14,000 feet) above the Pacific ocean.
It is funded according to a tripartite agreement between
Canada, France and the University of Hawaii signed in June
1974. CFHT's staff includes experts in a wide variety of
fields including mechanics, electronics, computer science,
optics and astrophysics. The technical groups are complemented
by a library and administrative service.
The role of CFHT is to operate, maintain and upgrade all the observatory
systems, to make sure that the telescope remains
competitive, and to provide first rate instrumentation
to astronomers in Canada, France and the University of
Hawaii.
|
Left: CFHT dome atop Mauna Kea
Right: CFHT 3.6 meter telescope (notice the human scale)
|
The Mauna Kea volcano, located on the Big Island of Hawaii,
is the best ground based
astronomical observing site known in the Northern Hemisphere,
and CFHT was built on one of the best locations near the
summit. The observatories on Mauna Kea benefit from
the high altitude of the site
which results in a clearer and dryer atmosphere, a darker
sky, more clear nights per year and, most importantly, sharper
images thanks to the low turbulence of the atmosphere
at the top of the mountain.
Astronomers from the funding agencies, Canada, France, and the University of
Hawaii, use the CFHT. They submit proposals
describing their observing program twice a year, and
a committee of peers allocates telescope time to
the best programs. Astronomers used to typically spend
2 to 4 nights observing at the telescope. However, nowadays,
for all instruments, in order to optimize the scientific
return of the telescope, CFHT is running the observations
in service mode under the New Observing Process (NOP) where
various components concur to acquire the data under the best
conditions fitted for a given scientific program and provide
optimally reduced and calibrated data to the astronomers. The
NOP ensures that the best ranked scientific programs will be
completed (versus the traditional way where the success was
randomly associated to the weather conditions). Sensitive
electronic detectors and computer-controlled instruments provide
the astronomers with enough data to analyze for many months
at their home institutions and publish results in astronomical journals.
CFHT was built in the late 1970s and saw first light
in 1979. At the time of the first observations,
the 3.6 meter telescope was the sixth largest
in the world. Today's largest telescopes have mirror
sizes in the range of 8 to 10 meters! Without innovative
instruments, CFHT would soon become obsolete. Therefore,
CFHT has undertaken an aggressive development
program to equip the telescope with state-of-the-art
instruments to remain competitive with
the larger telescopes. The latest evolution on this front, started
in the late 90s, is the wide-field imaging program.
Most very large telescopes (8-10 m) were designed to collect
vast amounts of light but they have a reduced field of view.
CFHT was originally designed for use with
large photographic plates covering four times the
size of the full moon on the sky. Taking advantage of the rapid
evolution of optical electronic detectors (CCDs) over the
past two decades, CFHT is now able to
cover most of its useful field of view with a
detector 40 times more sensitive than the photographic
plates! The MegaPrime imager which includes the MegaCam (CEA)
camera, a mosaic of forty individual
CCD detectors, is the largest close-packed array
in use in the world today (~18,400 x 18,400 pixels, 340 Mpixels).
It saw first light on the telescope in January 2003 and has
since collected an enormous amount of data on hot scientific
topics, keeping the CFHT community at the very forefront of
the scientific competition. The scientific operations started in February
2003 with a special observing program that covered very large
areas of the sky to an unprecedented depth. The CFHT Legacy Survey
used more than 500 telescope nights over 6 years, providing the
scientific community with a unique opportunity to conduct a wide range of
studies. The most prominent scientific programs in the CFHTLS are:
1) the determination of the large scale structure in the Universe
by using the phenomenon of weak gravitational lensing; and 2) to use
distant supernovae (exploding stars), to achieve both a more complete
understanding of the stars that formed in the early Universe and a
better characterization of the mysterious dark energy that appears to
control the geometry of the Universe.
Significant CFHT Instruments
Direct imaging and spectroscopy are the two fundamental types of
astronomical observations (CFHT's ESPADONS is a high resolution spectrograph).
The CFHT is a highly versatile telescope and is very efficient in both of
these domains thanks to its four foci and various instruments. Its infrared
capability (WIRCAM a wide-field imager) allows astronomers to optimize their
use of sky time: optical instruments when the phases of the Moon are low, infrared
instruments otherwise (the sky in the infrared remains dark even when the moon is up).
|
Left: CFH12K CCD mosaic camera
Right:The Helix planetary nebula by CFH12K
|
Wide-field imaging:
Wide-field imaging has been the major scientific strength of CFHT
since the arrival of CFH12K early 1999 but other instruments
played this important role over the past decade:
Adaptive Optics System:
This instrument, made available to the CFHT community in 1996, improves
the image sharpness obtained with the telescope: it corrects the blur
caused by turbulence in the Earth's atmosphere (the effect that causes
stars to twinkle) and yields an image quality nearly equivalent to that
of a telescope outside the atmosphere, i.e. in orbit around Earth like
the Hubble Space Telescope. The instrument is very well suited to the
study of processes associated with the formation of stars.
|
Left:Saturn by CFHT with the Adaptive Optics System
Right:CFHT Multiple Object Spectrograph image
|
Multiple Object Spectrograph:
A spectrograph separates an object's light into a spectrum and records
the relative intensity at different wavelengths. From this information,
astronomers can study the physical properties of the object: distance,
velocity, temperature, composition and luminosity. The Multiple Object
Spectrograph, made available to the CFHT community in the early 90's,
allows the observer to collect up to one hundred different spectra on
a single exposure, significantly improving the efficiency of the telescope
for the observation of large samples of objects. One use of this instrument
at the CFHT has contributed many important results that have advanced our
understanding of large scale structures in the Universe.
|