松原 英雄

A diffuse far-infrared [C II] emission line has been detected in an extensive region (30° ≤ l ≤ 51°) along the Galactic plane. The [C II] line is bright and extended far from discrete luminous H II regions. Latitudinal and longitudinal profiles of the [C II] intensity distribution are quite similar to those of CO(J = 1-0) and the 100 μm continuum, but are completely different from those of H I 21 cm. The diffuse [C II] emission probably comes from the photodissociated C regions enveloping giant molecular clouds exposed to the general interstellar UV radiation field. The extended low-density ionized gas might also contribute to the diffuse [C II] emission. The mass of the C regions may be as much as 35%-50% of that of CO molecular gas. The total luminosity of the [C II] line emitted from the inner Galactic disk amounts to 2.8(±1.1) × 10 L , or about 0.36 % of the total far-infrared luminosity of the same region. 12 + + 7 +0.28 ⊙ -0.17

A wobbling mechanism for a secondary mirror has been developed for a balloon-borne infrared telescope. Friction of the wobbling mechanism is negligibly small, and hence the wobbling mechanism is very reliable for the use in a severe environment at balloon altitudes. Motion is controlled by servo electronics, whose transfer function includes the second-order differential term of the error signal in order to improve the waveform. Good performance of the drive mechanism has been confirmed in two balloon flights in 1988 at an altitude of 31 km.

Exceptionally high degrees (up to ∼100%) of polarization was observed in the L′ band (3.8 μm) toward the NGC 6334 V bipolar nebula. The observed symmetric polarization pattern indicates that the nebula is a reflection nebula consisting of two lobes illuminated by a central obscured star. The measured distribution of high degrees of polarization requires that one of the lobes consist of a lemon-shaped cavity which scatters light mainly at its surface, whereas a conical cavity model is appropriate for the other lobe. This asymmetry of the lobes is probably due to a density gradient in the ambient cloud material in this region.

A compact cluster of five luminous infrared sources has been found in the vicinity of the Galactic center radio arc. All of the sources have large polarizations in the near-infrared and deep silicate absorptions at 10 μm. Strong absorption lines of CO are seen at 4.6 μm toward each source. The observed polarization and spectral features are likely to be interstellar in origin. The temperatures of the sources, based on infrared photometry and corrected for extinction, are in the range 600-900 K. None of the sources show either infrared recombination line emission from atomic hydrogen, lines of molecular hydrogen, or overtone band of CO at 2.3 μm. Because the objects are tightly clustered, all are likely to be very young objects; however, accurate classifications cannot be made at the present time.

We have developed a Fabry-Perot spectrometer for far-infrared spectroscopic observations on the Balloon-borne Infrared Telescope (BIRT ). The spectrometer consists of two independent channels for simultaneous observations of two lines, and each channel is composed of two tandem Fabry-Perot interferometers. All the optical components, including the interferometers, are cooled down to 2K with super-fluid liquid helium. We have employed two modes of observations: (1) the frequency switching mode with spatial scanning, and (2) the conventional spatial chopping mode with fixed pointing. The former mode is especially suitable to observe spatially extended emission because the mode dose not require spatial chopping. We have made two successful flights in 1988 with our observing system. For the [CII] (158μm) line, the system NEP was measured to be 1 × 10 W Hz , and the spectral resolving power was 2100. We observed many kinds of objects during the flights, and the frequency switching method was proved to be very efficient to observe extended sources. 1 -14 - 1/2

A stressed Ge:Ga photoconductor array with 3 elements has been developed for the Infrared Telescope in Space (IRTS) satellite of Japan. The detectivity was very high at low temperature and under low infrared background. Nonlinear response dependent on photon influx was observed in the experiments and the phenomenon is discussed in the paper.

The Balloon-Borne Infrared Telescope (BIRT) has been developed for far-infrared astronomy by a joint project between the Institute of Space and Astronautical Science (ISAS) and Kyoto University in Japan. It has a 50 cm reflector telescope mounted on an alt-azimuthal pointing system actuated by a control-moment gyro (CMG) torquer in the azimuth. The pointing and tracking are accomplished by a unique offset guide system which utilizes a star tracker and a star field camera mounted on a two-axis offset gimbals. The motion of the gimbals is controlled by an on-board CPU which computes and corrects the rotation rate of the offset direction caused by the celestial diurnal motion as well as the horizontal motion of the balloon gondola. BIRT has been flown 6 times at Alice Springs, Australia in 1985 and 1986, and 2 times at Palestine, Texas in 1988. The pointing and tracking accuracies were less than 1 arcmin, and the peak-to-peak attitude stability was smaller than 30 arcsec in those flights. The last two flights, at which liquid helium cooled Fabry-Perot spectrometer was mounted on the Nasmyth focus, were quite successful for observing far-infrared spectral lines ([CII] 158 μm and [OI] 63 μm) over wide areas of several galactic nebula and Milky Way. These observations have demonstrated that balloon-borne observation is a quite useful method for far-infrared spectroscopy.

Sensitive far infrared stressed Ge:Ga photoconductors which have response up to 200μm wavelength have been fabricated and studied to apply them to astronomical and atmospherical observations using balloons and satellites. The stressed Ge:Ga photoconductors have shown very high detectivity, i.e. responsivity of 15 A/W and NEP = 2 × 10 W/√Hz when operated at 2 K and at photon fluxes 1.1 × 10 photons/s, and the stable stress operation has been achieved by using the compact stressing mechanism with cone disk springs. The good performance has been confirmed by balloon experiments to detect astronomical CII line at 157.7 μm. © 1989. -18 6

A far infrared monochromator of Czerny-Turner type has been devised which has an output optical system comprising two small spherical mirrors to obtain non-astigmatic image. The far infrared monochromator covers both 50-120 urn and 100-240 urn wavelengths ranges and can be used to measure spectral response of stressed Ge:Ga photoconductors having response up to 200 urn, which we have fabricated to apply them to far infrared astronomical observations by balloons and by sattelites. Experimental performance of the stressed Ge:Ga photoconductors under low photon fluxes conditions also will be given.