24 research outputs found
Flight Performance of the AKARI Cryogenic System
We describe the flight performance of the cryogenic system of the infrared
astronomical satellite AKARI, which was successfully launched on 2006 February
21 (UT). AKARI carries a 68.5 cm telescope together with two focal plane
instruments, Infrared Cameras (IRC) and Far Infrared Surveyor (FIS), all of
which are cooled down to cryogenic temperature to achieve superior sensitivity.
The AKARI cryogenic system is a unique hybrid system, which consists of cryogen
(liquid helium) and mechanical coolers (2-stage Stirling coolers). With the
help of the mechanical coolers, 179 L (26.0 kg) of super-fluid liquid helium
can keep the instruments cryogenically cooled for more than 500 days. The
on-orbit performance of the AKARI cryogenics is consistent with the design and
pre-flight test, and the boil-off gas flow rate is as small as 0.32 mg/s. We
observed the increase of the major axis of the AKARI orbit, which can be
explained by the thrust due to thermal pressure of vented helium gas.Comment: 19 pages, 10 figures, and 6 tables. Accepted for publication in the
AKARI special issue of the Publications of the Astronomical Society of Japa
The Far-Infrared Surveyor (FIS) for AKARI
The Far-Infrared Surveyor (FIS) is one of two focal plane instruments on the
AKARI satellite. FIS has four photometric bands at 65, 90, 140, and 160 um, and
uses two kinds of array detectors. The FIS arrays and optics are designed to
sweep the sky with high spatial resolution and redundancy. The actual scan
width is more than eight arcmin, and the pixel pitch is matches the diffraction
limit of the telescope. Derived point spread functions (PSFs) from observations
of asteroids are similar to the optical model. Significant excesses, however,
are clearly seen around tails of the PSFs, whose contributions are about 30% of
the total power. All FIS functions are operating well in orbit, and its
performance meets the laboratory characterizations, except for the two longer
wavelength bands, which are not performing as well as characterized.
Furthermore, the FIS has a spectroscopic capability using a Fourier transform
spectrometer (FTS). Because the FTS takes advantage of the optics and detectors
of the photometer, it can simultaneously make a spectral map. This paper
summarizes the in-flight technical and operational performance of the FIS.Comment: 23 pages, 10 figures, and 2 tables. Accepted for publication in the
AKARI special issue of the Publications of the Astronomical Society of Japa
Proximate composition and carotenoids composition of <i>Halocynthia aurantium</i> in the Okhotsk Sea
Carotenoids of Sea Angels Clione limacina and Paedoclione doliiformis from the Perspective of the Food Chain
Sea angels, Clione limacina and Paedoclione doliiformis, are small, floating sea slugs belonging to Gastropoda, and their gonads are a bright orange-red color. Sea angels feed exclusively on a small herbivorous sea snail, Limacina helicina. Carotenoids in C. limacina, P. doliiformis, and L. helicina were investigated for comparative biochemical points of view. β-Carotene, zeaxanthin, and diatoxanthin were found to be major carotenoids in L. helicina. L. helicina accumulated dietary algal carotenoids without modification. On the other hand, keto-carotenoids, such as pectenolone, 7,8-didehydroastaxanthin, and adonixanthin were identified as major carotenoids in the sea angels C. limacina and P. doliiformis. Sea angels oxidatively metabolize dietary carotenoids and accumulate them in their gonads. Carotenoids in the gonads of sea angels might protect against oxidative stress and enhance reproduction