21 research outputs found
Spin Temperatures of Ammonia and Water Molecules in Comets
The nuclear spin temperature, which is derived from the ortho-to-para abundance ratio of molecules measured in cometary comae, is a clue to the formation conditions of cometary materials, especially the physical temperature at which the molecules were formed. In this paper we present new results for the nuclear spin temperatures of ammonia in comets Hale-Bopp (C/1995 O1) and 153P/Ikeya-Zhang based on observations of NH2 at 26 and 32 K, respectively. These results are similar to previous measurements in two other comets, and the nuclear spin temperatures of ammonia in the four comets are concentrated at about 30 K. We emphasize that the nuclear spin temperatures of water measured thus far have also been about 30 K. In particular, the spin temperatures of ammonia and water are equal to each other within ±1 Ï error bars in the case of comet Hale-Bopp. These nuclear spin temperatures of ammonia and water were measured under quite different conditions (heliocentric distances and gas production rates). There is no clear trend between the nuclear spin temperatures and the heliocentric distances, the gas production rates, or the orbital periods of the comets. The possibilities of the ortho-to-para conversion in the coma and in the nucleus are discussed. The present data set implies that the ortho-to-para ratios were not altered after the molecules were incorporated into the cometary nuclei. It appears that cometary ammonia and water molecules formed on cold grains at about 30 K
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
Down-Sizing in Galaxy Formation at z~1 in the Subaru/XMM-Newton Deep Survey (SXDS)
We use the deep wide-field optical imaging data of the Subaru/XMM-Newton Deep
Survey (SXDS) to discuss the luminosity (mass) dependent galaxy colours down to
z'=25.0 (5 x 10^9 h_{70}^{-2} Msun) for z~1 galaxies in colour-selected high
density regions. We find an apparent absence of galaxies on the red
colour-magnitude sequence below z'~24.2, corresponding to ~M*+2 (~10^{10} Msun)
with respect to passively evolving galaxies at z~1. Galaxies brighter than
M*-0.5 (8 x 10^{10} Msun), however, are predominantly red passively evolving
systems, with few blue star forming galaxies at these magnitudes.
This apparent age gradient, where massive galaxies are dominated by old
stellar populations while less massive galaxies have more extended star
formation histories, supports the `down-sizing' idea where the mass of galaxies
hosting star formation decreases as the Universe ages. Combined with the lack
of evolution in the shape of the stellar mass function for massive galaxies
since at least z~1, it appears that galaxy formation processes (both star
formation and mass assembly) should have occurred in an accelerated way in
massive systems in high density regions, while these processes should have been
slower in smaller systems. This result provides an interesting challenge for
modern CDM-based galaxy formation theories which predict later formation epochs
of massive systems, commonly referred to as ``bottom-up''.Comment: proof corrected version (MNRAS in press), 10 pages, 12 figures (of
which 3 are in jpg format
LCROSS (Lunar Crater Observation and Sensing Satellite) Observation Campaign: Strategies, Implementation, and Lessons Learned
Dynamical Structure of Edgeworth-Kuiper Belt Objectsin/around Mean Motion Resonances with Neptune
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Development and Space-Qualification of a Miniaturized CubeSatâs 2-W EDFA for Space Laser Communications
The Japanese National Institute of Information and Communications Technology (NICT) is currently developing a high-performance laser-communication terminal for CubeSats aimed at providing a high-datarate communication solution for LEO satellites requiring transmission of large volumes of data from orbit. A key aspect of the communication system is a high-power optical amplifier capable of providing enough gain to the transmitted signals to be able to close the link on its counterpartâs receiver with the smallest impact in terms of energy and power on the CubeSatâs platform. This manuscript describes the development of a miniaturized 2-W space-grade 2-stage erbium-doped fiber amplifier (EDFA) compatible with the CubeSat form factor, showing the best power-to-size ratio for a space-qualified EDFA to the best of the authorsâ knowledge. Performance results under realistic conditions as well as full space qualification and test are presented, proving that this module can support short-duration LEO-ground downlinks as well as long-duration intersatellite links