| We are continuing the adjustment of Subaru Telescope and observational
instruments in preparation for the Open Use which will begin at
the end of the year. We will continue to release new results obtained
during test observations.
We feature HDS
(High Dispersion Spectrograph) this month. HDS observes objects
in visible light (300 - 1,000 nanometers) and splits their light
into 100,000 separate colors using an "echelle spectrograph."
HDS is a huge instrument, measuring about 6 x 6 x 3 meters and
weighing 6 tons. Therefore, it is mounted at a Nasmyth
focus, which can provide the necessary room and stability.
There are two Nasmyth foci, one on each side of the Subaru Telescope.
OHS (CISCO)
is mounted at the other Nasmyth focus.
After adjustment in Japan, HDS was dismantled and transported
to the Nasmyth focus of the Subaru Telescope in March. We usually
perform additional tests of new instruments in the simulator lab
at the base facility
before taking them to the summit of Mauna Kea but the size of
HDS made this impossible. It took about three weeks to reassemble
HDS, and then the final adjustments were made for first light.
With the instrument group looking on, HDS achieved its first
light on July 1. The following image shows what the observers
at the summit saw on the computer screen at the moment of first
light. Test observations continued for a week, with the instrument's
operation and performance being monitored.
On July 5, HDS made observations of topical Comet
LINEAR. This image was taken with the slit viewer camera,
which allows the observer to see which region of the object will
have its light dispersed.
The first dispersed spectrum of Comet LINEAR taken with HDS is
shown here. Because HDS observes such a wide wavelength region
and disperses it into so many individual colors, it is necessary
to fold the spectrum into many rows otherwise a very large number
of detectors would be required. This is done by means of a "cross-disperser"
(one is also installed in IRCS).
The horizontal stripes mean that the comet emits light at all
visible wavelengths; this is because it reflects light from the
Sun. The vertical lines show emission from particular atoms and
molecules in the comet; the chemical composition of the cometary
material can be determined from the wavelengths of these lines.
A small region of the spectrum (indicated by the black box in
the above figure) is shown below. The emission features indicate
that NH2 and C2 are abundant molecules in Comet LINEAR.
HDS will be used to study the chemical compositions of old stars
in the Galaxy and distant clouds of gas to understand the chemical
evolution history of the Universe. In addition, HDS' high precision
will allow the detection of planets around other stars from the
"wobble" they produce in the star.
|
