奥村 真一郎

We have developed a near-infrared (1-2.5 mum) camera and spectrograph, called OASIS (Okayama Astrophysical System for Infrared imaging and Spectroscopy). OASIS was designed for the 188 cm telescope at Okayama Astrophysical Observatory, and developed as a common-use facility instrument. It has two observing capabilities: imaging with a field of view of 4' x 4' and long-slit spectroscopy with a resolving power of similar to 1000. This paper describes the design of OASIS and reports on the total system performance of the camera+telescope+atmosphere at the Okayama Observatory, together with the performance of an array detector, NICMOS 3, which OASIS utilizes.

We performed near-infrared imaging photometry of five evolved planetary nebulae (PNe). The sizes of the J-band images are nearly the same as those of the optical and radio images for the four PNe, while K4-47 has a bipolar image greater than the radio size. The near-infrared colors are presented for the four PNe.

Young stellar objects (YSOs) usually appear in molecular clouds as infrared objects associated with a molecular envelope. Wouterloot and Brand (1989, AAA 50.133.012) searched 1302 IRAS point sources with reliable fluxes at 25, 60, and 100 mu m near to the galactic plane for (CO)-C-12 (J = 1-0) emission; 1077 sources were detected. Among their far-infrared sources without detectable CO emission, we found that at least 18 objects are invisible at optical and near-infrared wavelengths. The infrared spectral indices between 2.2 mu m and 25 mu m correspond to those of class I YSOs, and the IRAS colors are similar to those of the usual YSOs. These peculiar far-infrared objects are highly concentrated around the galactic plane and the distances are estimated to be similar to 1 kpc. Although their distribution is away from molecular clouds, some of them seem to be associated with large dark clouds or weak radio sources. These objects are possible YSOs with low CO abundance in the envelopes.

We carried out a near-infrared imaging search for optically obscured galaxies behind the Milky Way. The imagings were made for a 4' x 4' field on each of 58 IRAS point sources, located within a region of 90 degrees < l < 240 degrees, \b\ < 10 degrees and having reliable flux densities at 25, 60, and 100 mu m but no Galactic CO emission. The results revealed that 16 of these IRAS point sources can be associated with galaxies or possible galaxies, and another 16 can be associated with stars or H II regions; however, the remaining 26 are 'empty' objects without any optical and near-infrared counterpart. The empty objects are colder than galaxies and seem to be Galactic objects.

We present large-scale (5.8degx5.8deg) near-infrared emission line images of the Orion nebula. Using the Near-Infrared Ultra Wide Field Camera, Br gamma and H-2 v=1-0 S(1) narrow band images were obtained. We have detected extended diffuse H-2 v=1-0 S(1) line emission. The shell shape H-2 v=1-0 S(1) line emission traces the edges of the Br gamma line emission in M42 and NGC1977. The Br gamma line emission which comes from the ionized regions of M42 extends more than 20 arcmin. The H-2 v=1-0 S(1) line emission would represent the existence of the photo-dissociation regions(PDRs) around the HII regions. The H-2 emission from the PDRs which is formed by UV-photons from nearby O-stars (Trapezium) is due to UV fluorescence. The ratio of H-2 v=1-0 S(1) to Br gamma of NGC1977 is much higher than that of M42. This is consistent with the spectral types of the central UV source stars.

We carried out observations of Jupiter during the impact of comet Shoemaker-Levy 9 with Jupiter at the Okayama Astrophysical Observatory with a near-infrared camera, OASIS. In this paper we report on result of absolute photometry of radiation from the impacts of fragment C,D and K at 2.35 mu m and discues on the impact phenomena. Lightcurve of the K impact event had four stages. We interpret the first as flash from the comet entry and the second as radiation from shock wave and/or high temperature plume itself, seen directly by Earth. The third, in which rapid increment of the infrared radiation was observed, may be caused by the increase of optical depth due to dust grain formation in the expanding and cooling plume. The fourth shows slowly decrease of the flux, which may be re-entry phenomena of the plume.

We carried out imaging observations of Jupiter using the Near-Infrared Camera at the Okayama Astrophysical Observatory during the impacts of Periodic Comet Shoemaker-Levy 9. We obtained sequential data of the the plume due to the impact of fragment K at 2.35 mu m. The first indication of the impact was detected at 10h24m02s UT on 1994 July 19. A secondary peak was recognized at 10h25m26s UT, the flux of which was 1.9 x 10(-12) W m(-2) mu m(-1). The maximum flux of the plume was 2.5 x 10(-10) W m(-2) mu m(-1) recorded at 10h38m37s UT. Possible interpretations for the complicated brightness variation of this plume are also discussed in this paper.