119 research outputs found
The Infrared Cloud Monitor for the MAGNUM Robotic Telescope at Haleakala
We present the most successful infrared cloud monitor for a robotic
telescope. This system was originally developed for the MAGNUM 2-m telescope,
which has been achieving unmanned and automated monitoring observation of
active galactic nuclei at Haleakala on the Hawaiian island of Maui since 2001.
Using a thermal imager and two aspherical mirrors, it at once sees almost the
whole sky at a wavelength of . Its outdoor part is
weather-proof and is totally maintenance-free. The images obtained every one or
two minutes are analysed immediately into several ranks of weather condition,
from which our automated observing system not only decides to open or close the
dome, but also selects what types of observations should be done. The whole-sky
data accumulated over four years show that 5060 % of all nights are
photometric, and about 75 % are observable with respect to cloud condition at
Haleakala. Many copies of this system are now used all over the world such as
Mauna Kea in Hawaii, Atacama in Chile, and Okayama and Kiso in Japan.Comment: 18 pages, 15 figures, 7 tables, accepted for publication in PAS
High Precision CTE-Measurement of SiC-100 for Cryogenic Space-Telescopes
We present the results of high precision measurements of the thermal
expansion of the sintered SiC, SiC-100, intended for use in cryogenic
space-telescopes, in which minimization of thermal deformation of the mirror is
critical and precise information of the thermal expansion is needed for the
telescope design. The temperature range of the measurements extends from room
temperature down to 10 K. Three samples, #1, #2, and #3 were
manufactured from blocks of SiC produced in different lots. The thermal
expansion of the samples was measured with a cryogenic dilatometer, consisting
of a laser interferometer, a cryostat, and a mechanical cooler. The typical
thermal expansion curve is presented using the 8th order polynomial of the
temperature. For the three samples, the coefficients of thermal expansion
(CTE), \bar{\alpha}_{#1}, \bar{\alpha}_{#2}, and \bar{\alpha}_{#3} were
derived for temperatures between 293 K and 10 K. The average and the dispersion
(1 rms) of these three CTEs are 0.816 and 0.002 (/K),
respectively. No significant difference was detected in the CTE of the three
samples from the different lots. Neither inhomogeneity nor anisotropy of the
CTE was observed. Based on the obtained CTE dispersion, we performed an
finite-element-method (FEM) analysis of the thermal deformation of a 3.5 m
diameter cryogenic mirror made of six SiC-100 segments. It was shown that the
present CTE measurement has a sufficient accuracy well enough for the design of
the 3.5 m cryogenic infrared telescope mission, the Space Infrared telescope
for Cosmology and Astrophysics (SPICA).Comment: in press, PASP. 21 pages, 4 figure
High-precision CTE measurement of hybrid C/SiC composite for cryogenic space telescopes
This paper presents highly precise measurements of thermal expansion of a
"hybrid" carbon-fiber reinforced silicon carbide composite,
HB-Cesic\textregistered - a trademark of ECM, in the temperature region of
\sim310-10K. Whilst C/SiC composites have been considered to be promising for
the mirrors and other structures of space-borne cryogenic telescopes, the
anisotropic thermal expansion has been a potential disadvantage of this
material. HB-Cesic\textregistered is a newly developed composite using a
mixture of different types of chopped, short carbon-fiber, in which one of the
important aims of the development was to reduce the anisotropy. The
measurements indicate that the anisotropy was much reduced down to 4% as a
result of hybridization. The thermal expansion data obtained are presented as
functions of temperature using eighth-order polynomials separately for the
horizontal (XY-) and vertical (Z-) directions of the fabrication process. The
average CTEs and their dispersion (1{\sigma}) in the range 293-10K derived from
the data for the XY- and Z-directions were 0.8050.003\times10
K and 0.837\pm0.001\times10 K, respectively. The absolute
accuracy and the reproducibility of the present measurements are suggested to
be better than 0.01\times10 K and 0.001\times(10)^{-6} K^{-1},
respectively. The residual anisotropy of the thermal expansion was consistent
with our previous speculation regarding carbon-fiber, in which the residual
anisotropy tended to lie mainly in the horizontal plane.Comment: Accepted by Cryogeincs. 12 pages, 3 figures, 1 tabll
The Transit Light Curve Project. V. System Parameters and Stellar Rotation Period of HD 189733
We present photometry of HD 189733 during eight transits of its close-in
giant planet, and out-of-transit photometry spanning two years. Using the
transit photometry, we determine the stellar and planetary radii and the
photometric ephemeris. Outside of transits, there are quasiperiodic flux
variations with a 13.4 day period that we attribute to stellar rotation. In
combination with previous results, we derive upper limits on the orbital
eccentricity, and on the true angle between the stellar rotation axis and
planetary orbit (as opposed to the angle between the projections of those axes
on the sky).Comment: Accepted for publication in AJ [21 pages]; minor change
The Infrared Camera (IRC) for AKARI - Design and Imaging Performance
The Infrared Camera (IRC) is one of two focal-plane instruments on the AKARI
satellite. It is designed for wide-field deep imaging and low-resolution
spectroscopy in the near- to mid-infrared (1.8--26.5um) in the pointed
observation mode of AKARI. IRC is also operated in the survey mode to make an
all-sky survey at 9 and 18um. It comprises three channels. The NIR channel
(1.8--5.5um) employs a 512 x 412 InSb array, whereas both the MIR-S
(4.6--13.4um) and MIR-L (12.6--26.5um) channels use 256 x 256 Si:As impurity
band conduction arrays. Each of the three channels has a field-of-view of about
10' x 10' and are operated simultaneously. The NIR and MIR-S share the same
field-of-view by virtue of a beam splitter. The MIR-L observes the sky about
$25' away from the NIR/MIR-S field-of-view. IRC gives us deep insights into the
formation and evolution of galaxies, the evolution of planetary disks, the
process of star-formation, the properties of interstellar matter under various
physical conditions, and the nature and evolution of solar system objects. The
in-flight performance of IRC has been confirmed to be in agreement with the
pre-flight expectation. This paper summarizes the design and the in-flight
operation and imaging performance of IRC.Comment: Publications of the Astronomical Society of Japan, in pres
Inner Size of a Dust Torus in the Seyfert 1 Galaxy NGC 4151
The most intense monitoring observations yet made were carried out on the
Seyfert 1 galaxy NGC 4151 in the optical and near-infrared wave-bands. A lag
from the optical light curve to the near-infrared light curve was measured. The
lag-time between the V and K light curves at the flux minimum in 2001 was
precisely 48+2-3 days, as determined by a cross-correlation analysis. The
correlation between the optical luminosity of an active galactic nucleus (AGN)
and the lag-time between the UV/optical and the near-infrared light curves is
presented for NGC 4151 in combination with previous lag-time measurements of
NGC 4151 and other AGNs in the literature. This correlation is interpreted as
thermal dust reverberation in an AGN, where the near-infrared emission from an
AGN is expected to be the thermal re-radiation from hot dust surrounding the
central engine at a radius where the temperature equals to that of the dust
sublimation temperature. We find that the inner radius of the dust torus in NGC
4151 is 0.04 pc corresponding to the measured lag-time, well outside
the broad line region (BLR) determined by other reverberation studies of the
emission lines.Comment: Accepted for publication in ApJ Letters, 13 pages, 3 figures;
Corrected typo
The Optical/Near-Infrared Light Curves of SN 2002ap for the First 140 Days after Discovery
Supernova (SN) 2002ap in M74 was observed in the bands for the
first 40 days following its discovery (2002 January 29) until it disappeared
because of solar conjunction, and then in June after it reappeared. The
magnitudes and dates of peak brightness in each band were determined. While the
rate of increase of the brightness before the peak is almost independent of
wavelength, the subsequent rate of decrease becomes smaller with wavelength
from the to the band, and is constant at wavelengths beyond . The
photometric evolution is faster than in the well-known ``hypernovae''
SNe~1998bw and 1997ef, indicating that SN 2002ap ejected less mass. The
bolometric light curve of SN 2002ap for the full period of observations was
constructed. The absolute magnitude is found to be much fainter than that of SN
1998bw, but is similar to that of SN 1997ef, which lies at the faint end of the
hypernova population. The bolometric light curve at the early epochs was best
reproduced with the explosion of a C+O star that ejects 2.5~M_\sun with
kinetic energy . A comparison of the
predicted brightness of SN 2002ap with that observed after solar conjunction
may imply that -ray deposition at the later epochs was more efficient
than in the model. This may be due to an asymmetric explosion.Comment: 15 pages, 6 figures, quality of figure1 is reduced for smaller
filesize, accepted for publication in Ap
The SPICA coronagraphic instrument (SCI) for the study of exoplanets
We present the SPICA Coronagraphic Instrument (SCI), which has been designed
for a concentrated study of extra-solar planets (exoplanets). SPICA mission
provides us with a unique opportunity to make high contrast observations
because of its large telescope aperture, the simple pupil shape, and the
capability for making infrared observations from space. The primary objectives
for the SCI are the direct coronagraphic detection and spectroscopy of Jovian
exoplanets in infrared, while the monitoring of transiting planets is another
important target. The specification and an overview of the design of the
instrument are shown. In the SCI, coronagraphic and non-coronagraphic modes are
applicable for both an imaging and a spectroscopy. The core wavelength range
and the goal contrast of the coronagraphic mode are 3.5--27m, and
10, respectively. Two complemental designs of binary shaped pupil mask
coronagraph are presented. The SCI has capability of simultaneous observations
of one target using two channels, a short channel with an InSb detector and a
long wavelength channel with a Si:As detector. We also give a report on the
current progress in the development of key technologies for the SCI.Comment: 22 pages, 10 figure
The Type Ic Hypernova SN 2002ap
Photometric and spectroscopic data of the energetic Type Ic supernova (SN)
2002ap are presented, and the properties of the SN are investigated through
models of its spectral evolution and its light curve. The SN is
spectroscopically similar to the "hypernova" SN 1997ef. However, its kinetic
energy [ erg] and the mass ejected (2.5-5
) are smaller, resulting in a faster-evolving light curve. The SN
synthesized of Ni, and its peak luminosity was
similar to that of normal SNe. Brightness alone should not be used to define a
hypernova, whose defining character, namely very broad spectral features, is
the result of a high kinetic energy. The likely main-sequence mass of the
progenitor star was 20-25 , which is also lower than that of both
hypernovae SNe 1997ef and 1998bw. SN 2002ap appears to lie at the low-energy
and low-mass end of the hypernova sequence as it is known so far. Observations
of the nebular spectrum, which is expected to dominate by summer 2002, are
necessary to confirm these values.Comment: 10 pages, 4 figures, accepted for publication in ApJL, 30 April 2002
(minor changes to match the accepted version, with figures being colored
Multiple Regression Analysis of the Variable Component in the Near-Infrared Region for Type 1 AGN MCG+08-11-011
We propose a new method of analysing a variable component for type 1 active
galactic nuclei (AGNs) in the near-infrared wavelength region. This analysis
uses a multiple regression technique and divides the variable component into
two components originating in the accretion disk at the center of AGNs and from
the dust torus that far surrounds the disk. Applying this analysis to the
long-term monitoring data of MCG+08-11-011 that were obtained by the
MAGNUM project, we found that the -color temperature of the dust
component is K K, which agrees with the sublimation
temperature of dust grains, and that the time delay of to variations is
days, which indicates the existence of a radial temperature
gradient in the dust torus. As for the disk component, we found that the
power-law spectrum of in the to near-infrared
bands varies with a fixed index of -- +0.4, which is
broadly consistent with the irradiated standard disk model. The outer part of
the disk therefore extends out to a radial distance where the temperature
decreases to radiate the light in the near-infrared.Comment: 10pages + 5figures, accepted by ApJ
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