39 research outputs found
OCTAD-S: Digital Fast Fourier Transform Spectrometers by FPGA
We have developed a digital fast Fourier transform (FFT) spectrometer made of
an analog-to-digital converter (ADC) and a field-programmable gate array
(FPGA). The base instrument has independent ADC and FPGA modules, which allow
us to implement different spectrometers in a relatively easy manner. Two types
of spectrometers have been instrumented, one with 4.096 GS/s sampling speed and
2048 frequency channels and the other with 2.048 GS/s sampling speed and 32768
frequency channels. The signal processing in these spectrometers has no dead
time and the accumulated spectra are recorded in external media every 8 ms. A
direct sampling spectroscopy up to 8 GHz is achieved by a microwave
track-and-hold circuit, which can reduce the analog receiver in front of the
spectrometer. Highly stable spectroscopy with a wide dynamic range was
demonstrated in a series of laboratory experiments and test observations of
solar radio bursts.Comment: 20 pages, 7 figures, accepted for publication in Earth, Planets and
Spac
Near-Infrared Extinction in The Coalsack Globule 2
We have conducted J, H, and Ks imaging observations for the Coalsack Globule
2 with the SIRIUS infrared camera on the IRSF 1.4 m telescope at SAAO, and
determined the color excess ratio, E(J-H)/E(H-Ks). The ratio is determined in
the same photometric system as our previous study for the rho Oph and Cha
clouds without any color transformation; this enables us to directly compare
the near-infrared extinction laws among these regions. The current ratio
E(J-H)/E(H-Ks) = 1.91 +- 0.01 for the extinction range 0.5 < E(J-H) <1.8 is
significantly larger than the ratios for the rho Oph and Cha clouds
(E(J-H)/E(H-Ks) = 1.60-1.69). This ratio corresponds to a large negative index
alpha = 2.34 +- 0.01 when the wavelength dependence of extinction is
approximated by a power law which might indicate little growth of dust grains,
or larger abundance of dielectric non-absorbing components such as silicates,
or both in this cloud. We also confirm that the color excess ratio for the
Coalsack Globule 2 has a trend of increasing with decreasing optical depth,
which is the same trend as the rho Oph and Cha clouds have.Comment: 13 pages, 5 figures, and 2 tables, Ap
Aurora and Airglow Observations with an All-Sky Imager on Shirase to Fill the Observation Gap over the Southern Ocean
The Tenth Symposium on Polar Science/Special session: [S] Future plan of Antarctic research: Towards phase X of the Japanese Antarctic Research Project (2022-2028) and beyond, Tue. 3 Dec. / Entrance Hall (1st floor) at National Institute of Polar Research (NIPR
Interstellar Extinction Law in the J, H, and Ks Bands toward the Galactic Center
We have determined the ratios of total to selective extinction in the
near-infrared bands (J, H, Ks) toward the Galactic center from the observations
of the region |l| < 2.0deg and 0.5deg < |b| < 1.0deg with the IRSF telescope
and the SIRIUS camera. Using the positions of red clump stars in
color-magnitude diagrams as a tracer of the extinction and reddening, we
determine the average of the ratios of total to selective extinction to be
A(Ks)/E(H-Ks) = 1.44+-0.01, A(Ks)/E(J-Ks) = 0.494+-0.006, and A(H)/E(J-H) =
1.42+-0.02, which are significantly smaller than those obtained in previous
studies. From these ratios, we estimate that A(J) : A(H) : A(Ks) = 1 :
0.573+-0.009 : 0.331+-0.004 and E(J-H)/E(H-Ks) = 1.72+-0.04, and we find that
the power law A(lambda) \propto lambda^{-1.99+-0.02} is a good approximation
over these wavelengths. Moreover, we find a small variation in A(Ks)/E(H-Ks)
across our survey. This suggests that the infrared extinction law changes from
one line of sight to another, and the so-called ``universality'' does not
necessarily hold in the infrared wavelengths.Comment: 18 pages, 9 figures, Accepted for publication in the Ap
Atacama Compact Array Antennas
We report major performance test results of the Atacama Compact Array (ACA)
7-m and 12-m antennas of ALMA (Atacama Large Millimeter/submillimeter Array).
The four major performances of the ACA antennas are all-sky pointing (to be not
more than 2.0 arcsec), offset pointing (to be < 0.6 arcsec) surface accuracy (<
25(20) micrometer for 12(7)m-antenna), stability of path-length (15 micrometer
over 3 min), and high servo capability (6 degrees/s for Azimuth and 3 degrees/s
for Elevation). The high performance of the ACA antenna has been extensively
evaluated at the Site Erection Facility area at an altitude of about 2900
meters. Test results of pointing performance, surface performance, and fast
motion capability are demonstrated.Comment: 3 pages, 2010 Asia-Pacific Radio Science Conference: J2 Millimeter-
and Sub-millimeter-wave Telescope and Arra
Subaru near infrared coronagraphic images of T Tauri
High angular resolution near-infrared (JHK) adaptive optics images of T Tau were obtained with the infrared camera Coronagraphic Imager with Adaptive Optics (CIAO) mounted on the 8.2m Subaru Telescope in 2002 and 2004. The images resolve a complex circumstellar structure around a multiple system. We resolved T Tau Sa and Sb as well as T Tau N and S. The estimated orbit of T Tau Sb indicates that it is probably bound to T Tau Sa. The K band flux of T Tau S decreased by ˜ 1.7 Jy in 2002 November compared with that in 2001 mainly because T Tau Sa became fainter. The arc-like ridge detected in our near-infrared images is consistent with what is seen at visible wavelengths, supporting the interpretation in previous studies that the arc is part of the cavity wall seen relatively pole-on. Halo emission is detected out to ˜2\u27\u27from T Tau N. This may be light scattered off the common envelope surrounding the T Tauri multiple system
A Young Brown Dwarf Companion to DH Tauri
We present the detection of a young brown dwarf companion DH Tau B associated
with the classical T Tauri star DH Tau. Near-infrared coronagraphic
observations with CIAO on the Subaru Telescope have revealed DH Tau B with H =
\~15 mag located at 2.3" (330 AU) away from the primary DH Tau A. Comparing its
position with a Hubble Space Telescope archive image, we confirmed that DH Tau
A and B share the common proper motion, suggesting that they are physically
associated with each other. The near-infrared color of DH Tau B is consistent
with those of young stellar objects. The near-infrared spectra of DH Tau B show
deep water absorption bands, a strong K I absorption line, and a moderate Na I
absorption line. We derived its effective temperature and surface gravity of
Teff = 2700 -- 2800 K and log g = 4.0--4.5, respectively, by comparing the
observed spectra with synthesized spectra of low-mass objects. The location of
DH Tau B on the HR diagram gives its mass of 30 -- 50 M_Jupiter.Comment: 10 pages, 14 figures, 1 table, accepted for publication in Ap