| Acceptance of proposals for Subaru Telescope's very first
semester of Open Use ("S00") came to an end on July
3rd with over 100 submissions received. Given that only 36 nights
will actually be available for observing this first time around,
the Telescope Allocation Committee now has the difficult task
of choosing who will be granted time and who will be disappointed.
This situation is not at all unusual, with most of the world's
telescopes receiving far more requests than they have time available.
In fact, this is one of the very reasons why Japanese astronomers
have worked so hard to build a large telescope of their own. The
world's astronomy community is, of course, grateful that Subaru
is offering some of its time for use by non-Japanese astronomers.
Semester S00 begins in December of this year.
Two instruments are being offered for use during the first semester:
IRCS;
and Suprime-Cam, Subaru Telescope's wide-field camera for imaging
at visible wavelengths.
At the heart of Suprime-Cam is a cooled vacuum chamber ("dewar")
currently filled with eight of the planned ten light detectors
called Charge-Coupled Devices ("CCDs"). Each CCD contains
a grid of 2048 x 4096 light-sensing areas, giving the finished
camera a total of over 80 million resolution elements or "pixels".
This is about ten times the number of pixels found in a photograph
created using a very good 35mm camera or 40 times the number found
in a high-end digital camera.
Following Subaru Telescope's First Light in December of 1998,
Suprime-Cam was used at the Cassegrain
focus of Subaru Telescope to allow an initial detailed testing
of both the telescope and instrument. Subaru Telescope can bring
light to a focus at any one of four
locations. Because each of these foci uses a different combination
of mirrors, it was necessary to conduct extensive testing to ensure
optimum performance was achieved at each focus. The first to be
commissioned was the Cassegrain focus, followed in turn by the
Prime, IR
Nasmyth and Optical
Nasmyth focus. Although not optimized for use at the Cassegrain
focus, Suprime-Cam produced some very exciting results during
this period.
In July of 1999, Suprime-Cam was finally united with its seven-element,
20-inch diameter corrector lens, essential for use of the camera
at Subaru's prime focus. This custom-made lens makes the final
subtle adjustments to the converging light beam to ensure images
are absolutely sharp all the way to the corners of the camera's
large field of view. Instruments placed at the natural ("Prime")
focus of Subaru Telescope's 8.3-meter diameter mirror see the
sky at much lower magnification and therefore with a much wider
field of view than if placed at any of the other foci on Subaru
Telescope. From this position 50 feet above the primary mirror,
Suprime-Cam can image an area 24 x 30 arcmin in a single exposure
(about the size of the full moon), over 30 times the area covered
when located at the Cassegrain focus. In prime-focus mode, the
telescope is operating at an incredibly fast f/1.9!
The tremendous increase in performance is nicely illustrated
by the following figure. The top panel shows a portion of the
nearby galaxy M31 (The Andromeda Galaxy) as viewed by Suprime-Cam
mounted at the prime focus in August 1999. The blue rectangle
indicates the field of view available when the camera was mounted
at the cassegrain focus earlier. The lower panels show a region
(marked in yellow) common to both the cassegrain-focus (left)
and prime-focus (right) images greatly enlarged to show the finest
details visible in both images. Note that the prime-focus view
shows just as much detail as the cassegrain view, even though
the total area imaged has increased by a factor of 30.
Although the CCDs in Suprime-Cam are sensitive to all colors
of visible light, individual exposures made with the instrument
are generally taken looking through glass filters to select specific
colors (wavelengths) of light. For research purposes, often there
is no need for exposures taken with more than just one or two
filters. That is why many of the images you'll see showing astronomical
discoveries are only available in "black and white".
Images gathered for research are generally analyzed using computer
software that can precisely measure and catalog details such as
location, size, shape and total brightness for each of the multitude
of objects found in each image. Studying these cataloged values,
astronomers generally can "see" much more subtle and
complex relationships that exist between the objects than could
ever be found simply by looking at the images. For example, color
information can be used to estimate the distance to remote galaxies
(determining "photometric redshifts"), and very subtle
distortions in the appearance of a large sample of galaxies can
be used to map out the distribution of dark matter in the universe
(evaluating the "cosmic shear"). We can also use the
cataloged values to quickly sift through a multitude of objects
to find just those which are unusual and warrant further study.
Subaru Telescope is unique among the 6-10 meter class telescopes
(operating in the northern hemisphere) in providing such a large
field of view at such high angular resolution. This makes it an
ideal tool for surveying large swaths of the distant universe,
or looking for elusive primordial planetesmals orbiting at the
very edge of our solar system.
Suprime-Cam was developed collectively by the University of Tokyo
(Graduate School of Science, Institute for Cosmic Ray Research)
and NAOJ.
|
