Kenji Mochizuki

PHOTON-DOMINATED REGION MODELS FOR GLOBAL PROPERTIES OF THE GALAXY

New photon-dominated region (PDR) models were constructed for investigation of the [C II] 158 μm fine-structure line emission, particularly of the Galactic [C II] emission observed with the Balloon-borne Infrared Carbon Explorer (BICE). The new models have two noteworthy features: (1) a spherical model cloud is immersed in isotropic stellar radiation, and (2) the incident stellar radiation has a wavelength range from the ultraviolet (UV) to the near-infrared. These features are in contrast to those of previous plane-parallel models in which the incident stellar radiation has been restricted to the UV. This makes the new model more suitable for general Galactic PDRs. Equations for chemical equilibrium and thermal balance are solved simultaneously with radiative transfer in the model cloud. Then the luminosities of the cloud are derived for the [C II] line, the 12CO (J = 1-0) line, and the continuum at a wavelength of λ = 100 μm. In order to explain the intensity ratios of [C II]/CO (I/ICO = 1.3 × 103) and [C II]/100 μm [I/λIλ(100 μm) = 5 × 10-3] observed toward the inner Galactic plane, the new models require a moderate (only several times as large as the solar neighborhood value) UV flux of the incident radiation. This flux is an order of magnitude smaller than those required by the previous models. Since the previous models required large incident UV fluxes, PDRs were sometimes considered not to be the primary origin of the diffuse [C II] emission in the Galactic plane. However, the new models show that the observed [C II] emission can originate in molecular clouds immersed in the general Galactic radiation field. This indicates that general Galactic PDRs are a promising candidate for the primary origin of the Galactic [C II] emission.

Deficit of Far-Infrared [C II] Line Emission toward the Galactic Center

We have observed the [C II] 158 μm line emission from the Galactic plane (-10° < l < 25°, |b| ≤ 3°) with the Balloon-borne Infrared Carbon Explorer (BICE). The observed longitudinal distribution of the [C II] line emission is clearly different from that of the far-infrared continuum emission; the Galactic center is not the dominant peak in the [C II] emission. Indeed, the ratio of the [C II] line emission to that of the far-infrared continuum (I[C II]/IFIR) is systematically low within the central several hundred parsecs of the Galaxy. The observational results indicate that the abundance of the C+ ions themselves is low in the Galactic center. We attribute this low abundance mainly to soft UV radiation with fewer C-ionizing photons. This soft radiation field, together with the pervasively high molecular gas density, makes the molecular self-shielding more effective in the Galactic center. The self-shielding further reduces the abundance of C+ ions, and raises the temperature of molecular gas at the C+/C/CO transition zone.

Trigonognathus kabeyai, a New Genus and Species of the Squalid Sharks from Japan

Two specimens of the peculiar squalid shark,Trigonognathus kabeyai gen. et sp. nov., were collected from the coastal waters of Wakayama and Tokushima, Japan, by bottom trawl at depths of 330 and 360 meters. Shape of teeth similar in both jaws; slender, unicuspid, canine-like, without any cusplets or serrations, with weak thin fold on both lingual and labial sides in anterior teeth on both jaws; tooth at symphysis of each jaw longest. Interspace between teeth very wide. Both jaws triangular in shape. Most of dermal denticles on body and head roughly rhombic, swollen very much near central part, with about 10–40 facets on the dorsal surface of its crown. Preoral snout length very short. Many small organs considered to be photophores present mainly on ventral surfaces of head and body.

Flight performance of the Mid-Infrared Spectrometer on the Infrared Telescope in Space mission

The mid-infrared spectrometer (MIRS) was one of four focal- plane science instruments that flew aboard the orbiting infrared telescope in space (IRTS). This telescope was a joint NASA/Japanese Scientific Space Agency (ISAS) project that was launched on March 18, 1995 aboard a Japanese HII expendable launch vehicle and was subsequently retrieved by the space shuttle. The telescope itself was liquid helium- cooled with a 15 cm aperture and surveyed approximately 7% of the sky over the course of its 26 day mission life before its cryogen expired and it began to warm up. The MIRS was developed jointly by NASA, the University of Tokyo, and ISAS and operated over a wavelength range of 4.5 to 11.7 microns with a spectral resolution of 0.23 to 0.36 microns. The MIRS has a conventional entrance aperture, so that spectral studies could be made of extended as well as point-sources. A cold shutter and an internal calibrator allowed accurate absolute flux determinations. The realized in-flight performance of the MIRS followed the pre-launch calibration performance as measured on the ground, with the exception of some degradation in the spectrometer throughput, some unanticipated detector behavior due to the passages through the South Atlantic anomaly, and to unavoidable observations of the moon.

A new lophiid anglerfish, Lophiodes fimbriatus from the coastal waters of Japan

A new species of lophiid anglerfish,Lophiodes fimbriatus, Is described. The holotype was captured from Wakayama and the paratype from Kuba-jima, Okinawa Prefecture, The present species is distinguished from its congeners by the combinations of the following characters: slender and branched tendrils present on both dorsal and ventral surfaces of the body, lightly pigmented illicium, simple vestigial esca, and paired tendrils on the third dorsal spine.