Opening Up Med-infrared Astronomy with COMICS
October 1, 2003
(Cooled Mid-Infrared Camera and Spectrometer) is the
instrument which observes the mid-infrared, the longest
wavelengths among the Subaru instruments. In addition to
the imaging camera, COMICS also has the spectrograph to
carry out spectroscopic observations.
The mid-infrared wavelengths that COMICS observes spans from 10 to 20 μm (1 micrometer = 0.001 millimeters) and are radiated even from objects at room temperature. In order to detect faint mid-infrared radiation from stars, we install COMICS's optical systems and detectors into a vacuum vessel of 1-meter in diameter, and cooled them down to -240 degrees Celsius (-269 degrees Celsius especially for detectors), suppressing the radiation from the instrument itself.
|Outside of COMICS (Blue part is the Subaru Telescope)|
The earth's atmosphere also radiates the mid-infrared strongly,
and we devise subtraction of the influence of the background
radiation. The most characteristic method is called "chopping."
We quickly change the direction of the telescope's secondary
mirror, observe a nearby sky, and then process the subtraction
of the influence of the atmospheric radiation from the data.
|Motion of secondary mirror and stellar images taken with COMICS's detector using the chopping method.|
Furthermore, the detector will saturate
very quickly because the night sky itself is very bright
in the mid-infrared. We developed a technique to obtain
about 10 images of 80 thousand pixels in a second.
Warm dust in space strongly radiates in the mid-infrared. For example, when a star similar to our Sun is born, it will heat up the dust in its plotoplanetary disk and the disk radiates in the mid-infrared. Thus we will be able to study the structure and evolution of the planetary forming disk with COMICS. Young stars more massive than our Sun are also a source of mid-infrared radiation because they heat up the ionized gas and make the dust around them very effectively. COMICS is a powerful tool for probing the birth of massive stars. On the other hand, dying stars are believed to be ejecting a large amount of dust into space. COMICS is suitable to investigating how dust in the space is formed in the final epoch of stellar evolution.
Observational example with COMICS:
Young star in high-mass star formation region K3-50A
(Okamoto et al. 2003, ApJ 584, 368-384)
The COMICS's observing wavelengths contain
spectral features emitted from various dust particles as
well. It is one of the most important subjects for COMICS
to detect and to observe spectra from organic matter in
space and from silicates which are contained also in earth's
rocks and meteorites.
Spectrum of Hen3-600A taken with
the COMICS spectroscopic mode.
(Honda et al. 2003, ApJ, 585, L59-63)
We expect that COMICS plays an active part
in various scenes of the mid-infrared astronomy such as
the study of the production and evolution of dust in various
environments as well as the study of planetary forming disks.
Dr. Yoshiko Okamoto at Kitasato University, a member of
COMICS development team, says that "So far there were
not so many opportunities for astronomical observations
in mid-infrared wavelengths because of the difficulties
in observation method and development of instruments. Now
we have COMICS and it will be a powerful tool for observations
in these developing wavelengths."
Size and Weight Approximately 2m x 2m x 2m and 2 tons Detectors Six 320pix x 240 pix Si:As IBC detectors
(one for imaging and five for spectral observations)
Pixel size 50 microns Pixel scale 0.13 arcsec (imaging), 0.165 arcsec (spectrograph) Field-of-view 42 arcsec x 32 arcsec