Masato Nakamura

One of the methods to research the escaping atmosphere is to observe the resonance-scattered light from the escaping particles. Especially, the escaping H, He and O particles resonantly scatter extreme ultraviolet (EUV) lights (H I: 121.6 nm, He I: 58.4 nm, He II: 30.4 nm, O II: 83.4 nm). Therefore, it is important to develope the optics for EUV. In addition, imaging observation is necessary to observe the temporal variation of the escaping atmosphere. In this method, the optics consist of the bandpass filters and the multilayer-coated mirror for EUV. And the optics were loaded onto the satellites and rockets, and observed EUV. With these optics the demerit is non spectrum observation, in other words, single optics can detect single wavelength of EUV. Therefore plural optics using filters and mirror or the spectroscope are necessary to observe the plural particles simultaneously. But the demerit of spectroscope is much more loss of light than that with filters and mirror.This time we produce the the Mo/Si multilayer-coated gratings for EUV light : 30.4nm, and evaluate their performance. We evaporate on the gratings with top layer of Si: 5.0 nm and 20 pairs of Mo: 4.4nm and Si: 13.3 nm. By Atomic Force Microscope, we verify that the grooves of the multilayer gratings are not buried. In addition, maximum reflective efficiency of multilayer blazed grating is 2.2 %, that of multilayer laminar grating is 2.9 %. By multilayer technology, reflective efficiency of multilayer grating exceeded approximately 5 times higher than that of Pt monolayer grating.

An extreme ultraviolet imaging spectrometer (EUIS) for the Mercury mission is under development. The instrument is designed to measure extreme ultraviolet radiations from the atmosphere of Mercury, which could not be identified by the Mariner 10 mission. In this paper, the performance of a Mo/Si multilayer grating, which is newly developed optics to improve the diffraction efficiency in the EUV, is presented. Two types of grating are fabricated, i.e. mechanical ruling and holographic gratings. The results show;a) Stray light of the holographic grating is less than that of the mechanical ruling grating.b) The efficiency of a Mo/Si multilayer grating is one order higher than that of a gold coated grating.

A Venus orbiter to start observation in 2009 is planned by ISAS. Already at a previous meeting. Inamura (ISAS) discussed the scientific purposes. In the present talk, main optical instruments and their role for the scientific purposes are shown. The ma in purpose of this mission is to determine meteorological parameters by imaging whole night- and day-side Venus disk at various wavelengths.

According to PVO observations, a significant amount of plasmas in the dayside flows to the nightside. This fact suggests that there should be an effective loss process in the Venus ionosphere. "Clouds" is considered to be one of the candidates which are related to plasma loss process. However, the global shape, formation and the dependence on the IMF of the clouds are still unknown, because the PVO obtained only local information on plasmas. Global imaging by using EUV technique is a promising means to investigate such a study. We propose the EUV telescope onboard Venus orbitor. This instrument has a imaging capability for He I, He II, O II, and H I emissions simultaneously. In this paper, we present our motivations for conducting EUV imaging. And also, the design of the telescope is shown.

Ultra-Violet Imaging Camera (UVI) on Venus mission measures dayside airglow of Venus by using SiCCD as a detection element. UVI is specialized and used for an imaging of Venus dayside clouds to investigate the dynamics of Venus atmosphere at 〜70 km altitude. The measurement wavelengths are 275 nm and 305 nm in the absorption bands of SO_2. The spatial and temporal resolutions are 〜10 km at a distance of 3.7 Rv from Venus and 〜100 ms, which are much better than that of Orbiter Cloud Photopolarimeter on Pioneer Venus. From the observations by UVI and other Imaging Cameras with different wavelengths, we investigate the structure and dynamics of Venus clouds and atmosphere.

The purpose of the Longwave IR camera onboard Planet-C is to observe the horizontal distribution of cloud top temperature. In this paper, the science objectives, the selection criteria of observation wavelengths and the required specifications are summarized.

We report on the optical observation of resonantly scattered plasmaspheric He II(304A) emission by a newly developed helium emission monitor (HEM) on board sounding rocket S-520-19. HEM is a normal incidence telescope consisting of a spherical Mo/Si multi-coated mirror, an Al/C thin-filter, and microchannel plates and exhibits high sensitivity at 304A(∿100cps/Rayleigh), high spatial resolution (2.5°), and contamination free from other major emission lines. The sounding rocket S-520-19 was launched from Kagoshima, Japan (131°05´E, 31°15´N) at 0100 LT on January 29,1995. From an altitude of 220km on upleg HEM was directed to the White dwarf, Hz43,which is located near the galactic north pole. This operation was mainly for observation of Hz43 by the other onboard telescopes. During a scanning period (altitude 210-170km on downleg), the instrument's line of sight was changed to the dawnside of the Earth's limb. We compare the optical observation data by HEM with the intensity of He II emission calculated from models. Here we use a diffusive equilibrium model for predicting global He^+ distribution in the plasmasphere and the empirical model based on mass spectrometer and incoherent scatter data for quantifying thermospheric absorption rate. Best-fitted results indicate He^+ number density of 3700/cm^3 at the topside ionosphere and equatorial temperature of 8000K near the dawnside of the plasmapause. There values are consistent with recent satellite observation under low Kp and low solar activity. At completion of the scanning operation, a distinct difference was apparent between calculated and observed intensity, probably due to contamination of multiply scattered He I (584A) emission from the dayside ionosphere.