National Research Council’s engineers help build the biggest astronomical camera in the world

MegaPrime, the world’s largest digital camera has now been released for
scientific use on the Canada-France-Hawaii Telescope (CFHT), a 3.6m
telescope located on the summit of Mauna Kea, Hawaii. Early observations
conducted during the installation phase have already demonstrated the
power of this new instrument: many previously unknown moons of Jupiter
have been discovered, potentially hazardous asteroids that pass near to
the Earth have been studied, and wide areas of the sky have been
surveyed to prepare targets for a future space mission.

MegaPrime is a collaboration between several research institutes in
France, and NRC’s Herzberg Institute of Astrophysics (HIA) in Victoria,
B.C. Several major industrial contractors participated in building the
large optical and mechanical components of this device, which is mounted
at the prime focus of the CFHT. At the heart of MegaPrime is MegaCam, a
unique camera built by the French Commissariat à l’Energie Atomique
(CEA). This camera is an array of 40 charge-coupled detectors (CCDs),
each of which has nine million individual pixels. In routine use,
MegaCam produces an image containing 324 million pixels.

MegaPrime on the CFHT provides Canadian astronomers with a capability
that newer and larger optical telescopes do not offer: the ability to
observe large areas of sky, in this case, an area larger than that
covered by four full moons. The huge number of pixels means that the
images are obtained at very high resolution, allowing astronomers to
zoom in and separate individual stars in crowded star fields, and to see
the detailed structure of faint, distant galaxies.

Taking advantage of the capabilities of MegaPrime, a large team of
astronomers in Canada and France has initiated the CFHT Legacy Survey
(LS). Under this five-year program, an equal partnership between Canada
and France, some 500 nights of telescope time will be dedicated to three
major projects: (1) the study of the Kuiper Belt — a mysterious
reservoir of ancient, dim asteroids that encircle the sun beyond the
orbit of Neptune), (2) a survey that will reveal the large-scale
structure of the dark matter in the universe by observing its weak
gravitational lens effect on distant galaxies, and (3) a program to
detect and study distant supernovae, titanic stellar explosions that can
reveal the effect of dark energy on the evolution of the universe.

The availability of MegaPrime opens a new era in astronomical wide-field
imaging that will benefit the worldwide astronomical community. All
images taken with MegaPrime will be archived at the Canadian Astronomy
Data Centre (CADC), part of NRC’s HIA. Astronomers from around the world
will be able to access and retrieve MegaPrime images using the internet
services offered through the CADC.

HIA’s Director General, Dr. Gregory G. Fahlman, notes that “MegaPrime is
a groundbreaking instrument that finally realizes a long-standing goal
of optical astronomers: to acquire digital images of large areas of sky
that were previously obtainable only with inefficient photographic
plates. The speed and accuracy of MegaPrime opens entirely new
opportunities for astronomical research and offers the promise of
exciting new discoveries. The CFHT LS is a scientific program of
remarkable ambition, made possible by MegaPrime and the development of
new observing procedures at the CFHT. Canadian astronomers have a
world-leading tool to further their original research and an opportunity
to have a major impact in resolving fundamental questions about the
nature of the universe. Moreover, the carefully archived images will
provide a lasting legacy for the entire world to exploit in the future.”

Canada has contributed three components to MegaPrime.

1) Before being captured by the MegaCam CCD sensors, the stellar light
must pass through the Wide Field Corrector (WFC). This device is needed
to ensure that a good image of the whole field of view is projected onto
the camera’s sensors. With four lenses, 50 to 80 cm in diameter, mounted
in a structure that is two metres long and has a mass of 660 kg, the WFC
is an amazing feat of optical construction. The WFC was designed at the
NRC’s Herzberg Institute for Astrophysics (HIA) in Victoria, BC, Canada,
and manufactured at the Sagem works in Saclay, France.

2) The camera must be able to move along the optical axis of the
telescope, to ensure that the images remain in sharp focus throughout
the course of the night. An automated system, the focus stage assembly
(FSA), was designed to sense continually the sharpness of the images
formed by the WFC and to make small adjustments in the camera position
as needed. The FSA was designed and built at HIA in Victoria.

3) As the Earth rotates on its axis, the telescope is tracked to
compensate precisely for the apparent motion of the sky with time.
However, this tracking is rarely precise enough to keep stellar images
exactly fixed on the camera for the long exposures needed to see the
faintest objects in the sky. The Earth’s atmosphere also causes the
stellar images to dance about and this would blur the images if
uncorrected. In MegaPrime, these problems are addressed by two small
‘guiding cameras’ or ‘guiders’. These devices form images of stars just
outside of the field of view on the main camera. Several images are
produced every second. These are analyzed and the data used to guide the
main telescope automatically, making small adjustments that keep the
field of view absolutely steady. These guiders were designed and built
at HIA.

Recognized globally for research and innovation, Canada’s National
Research Council (NRC) is a leader in the development of an innovative,
knowledge-based economy for Canada through science and technology. NRC
operates world-class research facilities as well as information,
technology and innovation support networks from coast to coast.

For more information, please visit the NRC’s Website at http://www.nrc-cnrc.gc.ca
or contact:

Dr. David Bohlender
Herzberg Institute of Astrophysics
National Research Council Canada,
Telephone: (250) 363-0025
Fax: (250) 363-0045
Email: david.bohlender@nrc.gc.ca

Mr. Joeleff Fitzsimmons
Herzberg Institute of Astrophysics
National Research Council Canada
Telephone: (250) 363-0034
Fax: (250) 363-0045
Email: Joeleff.Fitzsimmons@nrc.gc.ca

P.S.: More images of the telescope, of MegaPrime, and of science so far,
can be seen at this web site:
http://www.cfht.hawaii.edu/News/MegaPrime/

==== TECHNICAL INFORMATION ====

CFHT:

With a telescope mirror of 3.6m, the Canada-France-Hawaii Telescope
(CFHT) is one of the oldest facilities on the summit of Mauna-Kea. The
new instrument, MegaPrime, comes into operation this month after six
years of development, and a few months of engineering on the sky,
placing CFHT once more at the forefront of optical astronomy. Canada has
a 42.5% interest in the CFHT that is funded and managed by the NRC.

Wide Field Corrector:

The wide field corrector (WFC) was designed at HIA (Victoria, BC,
Canada) to provide an excellent image quality across the whole field of
view. It is made of four lenses polished from a material known as BSL7Y,
a UV-enhanced glass provided by Ohara (Japan). The lenses have been
fabricated by SAGEM (Saclay, France), which also built the mechanical
structure of the WFC and coated the lenses.

Focus Stage Assembly:

The Focus Stage Assembly (FSA) supports the camera and allows its motion
along the optical axis in order to accommodate the focus variation due
mainly to filter changes and temperature-induced telescope dilatation.
The FSA hardware was designed and built at HIA, while the software
control was designed and written at CFHT.

GUIDER and Focus Sensor Unit:

Two guiders (GFSU) located under the top plate of the FSA give position
and focus information from two guide stars on the North and South edges
of the MegaCam field of view. The GFSU hardware was designed and built
at HIA, while the software control was designed and written at CFHT.