349 research outputs found
Monolithic Ge:Ga Detector Development for SAFARI
We describe the current status and the prospect for the development of
monolithic Ge:Ga array detector for SAFARI. Our goal is to develop a 64x64
array for the 45 -- 110 um band, on the basis of existing technologies to make
3x20 monolithic arrays for the AKARI satellite. For the AKARI detector we have
achieved a responsivity of 10 A/W and a read-out noise limited NEP (noise
equivalent power) of 10^-17 W/rHz. We plan to develop the detector for SAFARI
with technical improvements; significantly reduced read-out noise with newly
developed cold read-out electronics, mitigated spectral fringes as well as
optical cross-talks with a multi-layer antireflection coat. Since most of the
elemental technologies to fabricate the detector are flight-proven, high
technical readiness levels (TRLs) should be achieved for fabricating the
detector with the above mentioned technical demonstrations. We demonstrate some
of these elemental technologies showing results of measurements for test
coatings and prototype arrays.Comment: To appear in Proc. Workshop "The Space Infrared Telescope for
Cosmology & Astrophysics: Revealing the Origins of Planets and Galaxies".
Eds. A.M. Heras, B. Swinyard, K. Isaak, and J.R. Goicoeche
CSIP - a Novel Photon-Counting Detector Applicable for the SPICA Far-Infrared Instrument
We describe a novel GaAs/AlGaAs double-quantum-well device for the infrared
photon detection, called Charge-Sensitive Infrared Phototransistor (CSIP). The
principle of CSIP detector is the photo-excitation of an intersubband
transition in a QW as an charge integrating gate and the signal amplification
by another QW as a channel with very high gain, which provides us with
extremely high responsivity (10^4 -- 10^6 A/W). It has been demonstrated that
the CSIP designed for the mid-infrared wavelength (14.7 um) has an excellent
sensitivity; the noise equivalent power (NEP) of 7x10^-19 W/rHz with the
quantum efficiency of ~2%. Advantages of the CSIP against the other highly
sensitive detectors are, huge dynamic range of >10^6, low output impedance of
10^3 -- 10^4 Ohms, and relatively high operation temperature (>2K). We discuss
possible applications of the CSIP to FIR photon detection covering 35 -- 60 um
waveband, which is a gap uncovered with presently available photoconductors.Comment: To appear in Proc. Workshop "The Space Infrared Telescope for
Cosmology & Astrophysics: Revealing the Origins of Planets and Galaxies".
Eds. A.M. Heras, B. Swinyard, K. Isaak, and J.R. Goicoeche
AKARI Detections of Hot Dust in Luminous Infrared Galaxies
We present a new sample of active galactic nuclei (AGNs) identified using the
catalog of the AKARI Mid-infrared(MIR) All-Sky Survey. Our MIR search has an
advantage in detecting AGNs that are obscured at optical wavelengths due to
extinction. We first selected AKARI 9micron excess sources with
F(9micron)/F(K_S)>2 where K_S magnitudes were taken from the Two Micron All Sky
Survey. We then obtained follow-up near-infrared spectroscopy with the
AKARI/IRC, to confirm that the excess is caused by hot dust. We also obtained
optical spectroscopy with the Kast Double Spectrograph on the Shane 3-m
telescope at Lick Observatory. On the basis of on these observations, we
detected hot dust with a characteristic temperature of ~500K in two luminous
infrared galaxies. The hot dust is suspected to be associated with AGNs that
exhibit their nonstellar activity not in the optical, but in the near- and
mid-infrared bands, i.e., they harbor buried AGNs. The host galaxy stellar
masses of 4-6 x 10^9 M_sun are small compared with the hosts in
optically-selected AGN populations. These objects were missed by previous
surveys, demonstrating the power of the AKARI MIR All-Sky Survey to widen AGN
searches to include more heavily obscured objects. The existence of multiple
dusty star clusters with massive stars cannot be completely ruled out with our
current data.Comment: 15 pages, 4 figures, to be published in Astronomy & Astrophysic
Near-infrared Brightness of the Galilean Satellites Eclipsed in Jovian Shadow: A New Technique to Investigate Jovian Upper Atmosphere
We have discovered that Europa, Ganymede and Callisto are bright around 1.5
{\mu}m even when not directly lit by sunlight, based on observations from the
Hubble Space Telescope and the Subaru Telescope. The observations were
conducted with non-sidereal tracking on Jupiter outside of the field of view to
reduce the stray light subtraction uncertainty due to the close proximity of
Jupiter. Their eclipsed luminosity was - of their uneclipsed
brightness, which is low enough that this phenomenon has been undiscovered
until now. In addition, Europa in eclipse was <1/10 of the others at 1.5
{\mu}m, a potential clue to the origin of the source of luminosity. Likewise,
Ganymede observations were attempted at 3.6 {\mu}m by the Spitzer Space
Telescope but it was not detected, suggesting a significant wavelength
dependence. The reason why they are luminous even when in the Jovian shadow is
still unknown, but forward-scattered sunlight by haze in the Jovian upper
atmosphere is proposed as the most plausible candidate. If this is the case,
observations of these Galilean satellites while eclipsed by the Jovian shadow
provide us a new technique to investigate Jovian atmospheric composition, and
investigating the transmission spectrum of Jupiter by this method is important
for investigating the atmosphere of extrasolar giant planets by transit
spectroscopy.Comment: 7 pages, 3 figures, accepted to Ap
Phase Diagram of Lattice-Spin System RbCoBr
We study the lattice-spin model of RbCoBr which is proposed by Shirahata
and Nakamura, by mean field approximation. This model is an Ising spin system
on a distorted triangular lattice. There are two kinds of frustrated variables,
that is, the lattice and spin. We obtain a phase diagram of which phase
boundary is drawn continuously in a whole region. Intermediate phases that
include a partial disordered state appear. The model has the first-order phase
transitions in addition to the second-order phase transitions. We find a
three-sublattice ferrimagnetic state in the phase diagram. The three-sublattice
ferrimagnetic state does not appear when the lattice is not distorted.Comment: 5 pages, 4 figures, jpsj2.cls, to be published in J. Phys. Soc. Jpn.
Vol.75 (2006) No.
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