Masuo Tanaka

Three micron ice-band features in the Rho Ophiuchi sources

Low-resolution spectra in the 2.4-3.8 micron range are presented for 31 sources in the Rho Oph dark cloud. The characteristics of the 3-micron spectra for protostars, emission-line stars, associated early-type stars, and background M giant stars are examined. Consideration is given to the relationship between ice-band absorption and H-K magnitude. The results show the existence of ice-mantled grains in the circumstellar disks of emission-line stars. The processes controling the formation of H2O ice in dark clouds are discussed. 21 refs.

Infrared spectroscopy of interstellar molecular hydrogen - decomposition of thermal and fluorescent components

High-resolution spectroscopic observations of vibrationally excited H2 are reported for nine Galactic sources. Data were obtained using a cooled circular variable filter wheel in tandem with an ambient-temperature Fabry-Perot interferometer on the UKIRT in August 1987. It is found that collisional and fluorescent excitation processes are both evident in most of the sources, although one may be dominant. The ortho/para ratio is determined for sources with fluorescent excitation and found to range from 1.0 to 1.8, in contrast with the high-temperature equilibrium value of 3. 21 references.

Three micron spectroscopy of low-mass pre-main-sequence stars

Low-resolution spectra were obtained of 16 premain-sequence stars, and ice-band features are detected in young T Tauri stars (TTSs) and in low-mass protostars. The TTSs have an ice band optical depth tau(ice) of 0.1-0.4. The tau(ice) for objects in the Taurus dark cloud decreases progressively from protostars to TTSs. The apparent color temperatures of the continuum spectra are 800-1200 K for protostars and 1100-1500 K for TTSs. The color temperatures of the continuum increase to 1200-2000K after correcting the protostar spectra for foreground extinction. This common temperature range in both young TTSs and protostars suggests that the inner boundary of the circumstellar disk is determined by the sublimation of refractory grains. 39 refs.

H2 Line Ratios to Discriminate Dense Photodissociation Regions from Shocks: Application to NGC 2023 and NGC 7023

We measured the distribution of H2 line ratios, 2-1 S(1)/1-0 S(1) and 4-2 S(1)/3-1 S(1), in typical dense photodissociation regions (PDRs) associated with the reflection nebulae, NGC 2023 and NGC 7023. The line images were obtained with a recently developed wide-field (39 × 39) Fabry-Perot imager, MUSE. In both objects, the 2-1 S(1)/1-0 S(1) ratio varies spatially between 0.2 and 0.6 as a result of the variation of gas density (n ~ 105-106 cm-3) and UV intensity (G0 ~ 103-104) in PDRs. On the other hand, the 4-2 S(1)/3-1 S(1) ratio is nearly constant (~1) in both objects. This constancy of the 4-2 S(1)/3-1 S(1) ratio agrees with model predictions. Since the observed 4-2 S(1)/3-1 S(1) ratio is significantly larger than the expected ratio for shock excitation, the 4-2 S(1)/3-1 S(1) ratio is expected to discriminate both dense and diffuse PDRs from shocks.

The University of Tokyo Atacama 1.0-m telescope

The current status of the University of Tokyo Atacama 1.0m telescope project being constructed at the summit of Co. Chajnantor (5,640m) in Atacama, Chile, will be presented. This is an optical/infrared telescope at the worlds highest site. A precipitable water vapor (PWV) amount of 0.4 to 1.3 mm at the summit, much lower than that of 0.9 to 2.8 mm at Mauna Kea, Hawaii. provides excellent atmospheric transmission from the near- to the mid-infrared wavelength. Seeing and weather conditions are confirmed to be suitable for infrared observations at the summit. The telescope is an f/12 Ritchey-Chrétien type with a field of view of 10 arcmin. The telescope is installed in a 6-m dome and controlled from an operation room in a container separated from the dome. The operation room will be directly connected to a base support facility in San Pedro de Atacama by a wireless LAN and a satellite link. A power generator and solar panels are equipped for a main and a back-up power supply, respectively. The ANIR near-infrared camera and the MAX38 mid-infrared camera are equipped on the Cassegrain focus. This telescope will start operation at the beginning of 2009, and will be operated remotely from the base facility in the near future.

Seeing environment at a 5640m altitude of Co. Chajnantor in northern Chile

We have carried out a campaign to monitor seeing at a 5640m altitude on the summit of Co. Chajnantor at Atacama, for the 6.5m telescope TAO project planned by the University of Tokyo. The seeing conditions were measured at 0.5μm using a DIMM (Differential Image Motion Monitor) during 8 nights in November 2006 and April 2007. In April, the measurement was done on a 2m-tower to suppress effect of ground-layer turbulence. The best night showed median seeing of 0.38, while the total median seeing is 0.69. This is comparable or even better than most of the major observatories. Together with the high transparency in infrared wavelength owing to the extremely high altitude of 5640m and its accessibility, the summit of Co. Chajnantor is one of the best site for infrared astronomy on the Earth.

MiniTAO/MAX38 first light: 30-micron band observations from the ground-based telescope

We successfully carried out 30-micron observations from the ground-based telescope for the first time with our newly developed mid-infrared instrument, MAX38, which is mounted on the University of Tokyo Atacama 1.0-m telescope (miniTAO telescope). Thanks to the high altitude of the miniTAO (5,640m) and dry weather condition of the Atacama site, we can access the 30-micron wavelength region from ground-based telescopes. To achieve the observation at 30- micron wavelength, remarkable devices are employed in MAX38. First, a Si:Sb 128x128 array detector is installed which can detect long mid-infrared light up to 38-micron. Second, we developed metal mesh filters for 30-micron region band-pass filter, which are composed of several gold thin-films with cross-shaped holes. Third, a cold chopper, a 6-cm square plane mirror controlled by a piezoelectric actuator, is built into the MAX38 optics for canceling out the atmospheric turbulence noise. It enables square-wave chopping with a 50-arcsecound throw at a frequency more than 5- Hz. Finally, a low-dispersion grism spectrometer (R~50) will provide information on the transmission spectrum of the terrestrial atmosphere in 20 to 40 micron. In this observation, we clearly demonstrated that the atmospheric windows around 30-micron can be used for the astronomical observations at the miniTAO site.

Infrared fluorescence of H2 in NGC 6240 - A starburst origin for the H2 luminosity

It is shown here that the published emission line ratios for vibrationally excited molecular hydrogen in the near-IR for the highly luminous galaxy merger system NGC 6240 imply UV excitation followed by IR fluorescence. The line ratios for the central 2 kpc or so of the system are well-reproduced as a mixture of fluorescent and thermal components. Of the total H2 luminosity of 3 {times} 10 to the 9th solar, 70 percent is due to fluorescence. This emission is excited by UV photons probably radiated by many early B stars. The abundance of such stars and the deficit of O stars indicate a sharp upper mass cutoff at about 20 solar masses in the present-day mass spectrum in the central region. A starburst model is presented in which the observations can be reproduced if the central region experienced a cataclysmic starburst which stopped suddenly a few ten billion yr ago and if the initial mass function there had a lower mass cutoff at about 5 solar. 31 refs.

GROUND-BASED Paα NARROW-BAND IMAGING OF LOCAL LUMINOUS INFRARED GALAXIES. I. STAR FORMATION RATES AND SURFACE DENSITIES

Luminous infrared galaxies (LIRGs) are enshrouded by a large amount of dust, produced by their active star formation, and it is difficult to measure their activity in the optical wavelength. We have carried out Pa

First Paschen alpha imaging from the ground: the first light of Atacama Near-Infrared Camera on the miniTAO 1m telescope

\alpha