中川 貴雄

天文学の観測にとって、宇宙に浮かぶ人工衛星からの観測は、地上にある望遠鏡からの観測に比べて、大きなメリットが数多くある。これらのメリットを活かすべく、様々な宇宙天文台が打ち上げられてきた。ただし、そこに搭載される望遠鏡には、ロケットの限られた打ち上げ能力を活かすべく、徹底した軽量化が求めらる一方、ロケット打ち上げという過酷な機械環境に耐えるという、相反する機械的要求がある。本講演では、このような困難にうちかって各種の宇宙天文台を実現してきた活動のうち、特に日本での活動について紹介する。

A two-stage Stirling cooler has been developed and tested for the infrared astronomical satellite ASTRO-F that is planned to be launched by Japanese M-V rocket in 2005. ASTRO-F has a hybrid cryogenic system that is a combination of superfluid liquid helium and two-stage Stirling coolers. The cooler has a new linear-ball-bearing system for the piston-supporting structure in a compressor. The linear-ball-bearing supporting system achieves the piston clearance seal, the long piston-stroke operation and the low frequency operation. The typical cooling power is 0.2W at 20 K and the total input power to the compressor and the cold head is below 90 W. The engineering, the prototype and the flight models of the cooler have been fabricated and evaluated to verify the capability for ASTRO-F. This paper describes the design of the cooler and the results from verification tests including cooler performance test, thermal vacuum test, vibration test and lifetime test.

We review the next-generation Japanese infrared space mission, ASTRO-F. ASTRO-F will be the first survey of the entire sky at infrared wavelengths since the IRAS mission almost 20 years ago. ASTRO-F will survey the entire sky in four far-infrared bands from 50 to 200 μm and two mid-infrared bands at 9 and 20 μm to sensitivities 10-1000 times deeper than the IRAS satellite at angular resolutions of 25-45 arcsec (cf. 2-5 arcmin for IRAS). ASTRO-F can be considered as a super-IRAS. Using the galaxy evolution model of Pearson, we produce expected numbers of sources under three different cosmological world models. We predict that ASTROF will detect of the order of tens of millions of sources in the far-infrared wavelength bands, most of which will be dusty luminous infrared/ultraluminous infrared galaxies, of which as many as half will lie at redshifts greater than unity. We produce number-redshift distributions, flux-redshift and colour-colour diagrams for the survey and discuss various segregation and photometric redshift techniques. Furthermore, we investigate the large-scale structure scales that will be accessed by ASTRO-F, discovering that ASTRO-F and SIRTF-SWIRE probe both different scales and redshift domains and concluding that the two missions will supplement rather than supplant one another.

We have developed a new capacitive transimpedance amplifier (CTIA) that can be operated at 2 K, and have good array detectors. The circuit design of the present CTIA consists of silicon p-MOSFETs and other passive elements. The process is a standard Bi-CMOS process with 0.5 μm design rule. The open-loop gain of the CTIA is more than 300, resulting in good integration performance. The output voltage swing of the CTIA was 270 mV. The power consumption for each CTIA is less than 10 μW. The noise at the output showed a 1/f noise spectrum of 4 μV/√Hz at 1 Hz. The performance of this CTIA nearly fulfills the requirements for the far-infrared array detectors onboard ASTRO-F, Japanese infrared astronomical satellite to be launched in 2005.

日本初の赤外線天文衛星ASTRO-Fの打ち上げが近づいてきた.ASTRO-Fには極低温に冷却された口径67cmの望遠鏡が搭載され,高感度の赤外線天体観測を行う.具体的には,まず,波長50-200μmの遠赤外線領域において全天のサーベイ観測を行う.それに加えて,波長2-200μmの広い波長領域において個別天体の詳細観測を行う.これらの観測により,(1)銀河の誕生と進化,(2)星の一生と宇宙の化学進化との関わり,および(3)惑星系の形成機構の解明を目指す.

A two-stage Stirling cooler has been developed and tested for the infrared astronomical satellite ASTRO-F that is planned to be launched by Japanese M-V rocket in 2005. ASTRO-F has a hybrid cryogenic system that is a combination of superfluid liquid helium and two-stage Stirling coolers. The cooler has a new linear-ball-bearing system for the piston-supporting structure in a compressor. The linear-ball-bearing supporting system achieves the piston clearance seal, the long piston-stroke operation and the low frequency operation. The typical cooling power is 0.2W at 20 K and the total input power to the compressor and the cold head is below 90 W. The engineering, the prototype and the flight models of the cooler have been fabricated and evaluated to verify the capability for ASTRO-F. This paper describes the design of the cooler and the results from verification tests including cooler performance test, thermal vacuum test, vibration test and lifetime test.

We present X-ray observations of the ultraluminous infrared galaxy, UGC 5101, thought to contain a buried active galactic nucleus (AGN) based on observations in other wave bands. We detected an absorbed hard component at greater than 3 keV, as well as soft emission in the energy range 0.5-2 keV. The soft X-ray component, possibly due to a modestly dust-obscured extended starburst, has an absorption-corrected 0.5-2 keV X-ray luminosity of L (0.5-2 keV) = 1.2 × 10 ergs s . The 0.5-2 keV X-ray-to-infrared luminosity ratio is a factor of ∼5 lower than typical values for a normal starburst, suggesting that this extended starburst is unlikely to be energetically dominant in UGC 5101. The most plausible origin of the absorbed hard component is the putative buried AGN. The 6.4 keV Fe Ka emission line has a modest equivalent width (∼400 eV), suggesting that this hard component is direct emission from the AGN, rather than a scattered component. The absorption-corrected 2-10 keV X-ray luminosity of the buried AGN was estimated to be L (2-10 keV) ∼ 5 × 10 ergs s . The intrinsic 2-10 keV X-ray luminosity and the 2-10 keV X-ray-to-infrared luminosity ratio are both comparable to values measured for Mrk 463, a Seyfert 2 galaxy of similar infrared luminosity. x 41 -1 x 42 -1