The CFHT Story  

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 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) Photographs by J.-C. Cuillandre (CFHT), © 1995, 2001

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 (4,200 meters), 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 Canada, France, and the University of Hawaii use the CFHT. They submit proposals describing their observing program and twice a year a committee of peers allocates telescope time to the best programs. Astronomers typically spend 2 to 4 nights observing at the telescope. For a few given instruments, in order to optimize the scientific return of the telescope, CFHT is now running the observations 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 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 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 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). It saw first light on the telescope in January 2003 and has since collected an enormous amount of data, placing the CFHT community at the very forefront of the scientific competition. The scientific operations started in February 2003 with a special observing program that will cover very large areas of the sky to an unprecedented depth. The CFHT Legacy Survey will use more than 450 telescope nights over 5 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 observation of a large sample of the small, primitive bodies that orbit the sun beyond Neptune. 2) the determination of the large scale structure in the Universe by using the phenomenon of weak gravitational lensing; and 3) 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. A wide field of view infrared camera (WIRCAM) is also in preparation to complement this optical facility by 2005.
  

Direct imaging and spectroscopy are the two fundamental types of astronomical observations. 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 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 Photograph and image by J.-C. Cuillandre, © 1999 CFHT

Wide-field imaging:
Wide-field imaging has been the major strength of CFHT ever 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. An upgrade of this system, called PUEO NUI, is planned and should see first light on the sky in 2005. Our present system operates at infrared wavelengths only and this upgrade will improve the image sharpness at visible wavelengths, where the information gain over uncorrected images is far greater.

Left:Saturn by CFHT with the Adaptive Optics System Right:CFHT Multiple Object Spectrograph image Image by R. Arsenault (left) and J.-C. Cuillandre (right), © 1996,2000 CFHT

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.