49 research outputs found
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
Scattering polarization of 3-m water-ice feature by large icy grains
Water ice has a strong spectral feature at a wavelength of approximately
m, which plays a vital role in our understanding of the icy universe. In
this study, we investigate the scattering polarization of this water-ice
feature. The linear polarization degree of light scattered by m-sized icy
grains is known to be enhanced at the ice band; however, the dependence of this
polarization enhancement on various grain properties is unclear. We find that
the enhanced polarization at the ice band is sensitive to the presence of
m-sized grains as well as their ice abundance. We demonstrate that this
enhancement is caused by the high absorbency of the water-ice feature, which
attenuates internal scattering and renders the surface reflection dominant over
internal scattering. Additionally, we compare our models with polarimetric
observations of the low-mass protostar L1551 IRS 5. Our results show that
scattering by a maximum grain radius of a few microns with a low water-ice
abundance is consistent with observations. Thus, scattering polarization of the
water-ice feature is a useful tool for characterizing ice properties in various
astronomical environments.Comment: 19 pages, 17 figures, 1 table; Accepted for publication in Ap
Current Performance and On-Going Improvements of the 8.2 m Subaru Telescope
An overview of the current status of the 8.2 m Subaru Telescope constructed
and operated at Mauna Kea, Hawaii, by the National Astronomical Observatory of
Japan is presented. The basic design concept and the verified performance of
the telescope system are described. Also given are the status of the instrument
package offered to the astronomical community, the status of operation, and
some of the future plans. The status of the telescope reported in a number of
SPIE papers as of the summer of 2002 are incorporated with some updates
included as of 2004 February. However, readers are encouraged to check the most
updated status of the telescope through the home page,
http://subarutelescope.org/index.html, and/or the direct contact with the
observatory staff.Comment: 18 pages (17 pages in published version), 29 figures (GIF format),
This is the version before the galley proo