Massive stars are expected to play an important role in predominately supplying metal elements an... more Massive stars are expected to play an important role in predominately supplying metal elements and dust particles into the interstellar space in the early universe due to their short lifetime in the main sequence. The amount of newly formed dust in the ejecta of a supernova obtained from the observational results, however, remains only in a range of 10-3-10-5Msun, which is much smaller than the amount of dust needed for a SN to form to account for the dust content in the early universe. Recent observations of dust-forming type-Ib supernova 2006jc made with AKARI and Spitzer have shown that the newly-formed dust in the SN ejecta is also only in the range of 10-4-10-5Msun (Sakon et al. 2009; Mattila et al. 2008), but they recognize the presence of pre-existing circumstellar dust possibly formed in the mass loss wind associated with the events prior to the SN explosion. Recent studies reveal that many of the Wolf-Rayet stars form in binary system and that around 10% of WR stars may for...
Space Telescopes and Instrumentation 2008: Optical, Infrared, and Millimeter, 2008
The Infrared Camera (IRC) is one of two focal-plane instruments on the AKARI satellite. It is des... more The Infrared Camera (IRC) is one of two focal-plane instruments on the AKARI satellite. It is designed for wide-field deep imaging and low-resolution spectroscopy in the near- to mid-infrared (1.8-26.5 micron) in the pointed observation mode of AKARI. The IRC is also operated in the survey mode to make an All-Sky Survey at 9 and 18 microns. The IRC is
We observed an area of 10 deg2 of the Large Magellanic Cloud using the Infrared Camera (IRC) on b... more We observed an area of 10 deg2 of the Large Magellanic Cloud using the Infrared Camera (IRC) on board AKARI. The observations were carried out using five imaging filters (3.2, 7, 11, 15, and 24 mum) and a dispersion prism (2-5 mum, lambda/Deltalambda˜20) equipped in the IRC. Here we describe an outline of our survey project, and present some initial results using imaging data that detected over 5.9×105 near-infrared and 6.4×104 mid-infrared point sources. The 10 sigma detection limits of our survey are about 16.5, 14.0, 12.3, 10.8, and 9.2 in Vega-magnitude at 3.2, 7, 11, 15, and 24 mum, respectively. The first point source catalog is planned to be released to the public in 2009. We found a new sequence in the color-magnitude diagram, suggesting that this may be attributed to red giants with aluminum oxide dust but without silicate features.
Far-ultraviolet radiation over a wide sky region of −110° 60° was observed by a rocket-borne two-... more Far-ultraviolet radiation over a wide sky region of −110° 60° was observed by a rocket-borne two-dimensional imager in the wavelength around 150 nm. The background far-ultraviolet radiation from the Virgo cluster region was also observed in the pointing phase of the same rocket experiment. Contributions from several components, such as airglows, faint stars, or molecular hydrogen emission, to the observed radiation were examined, and the diffuse far-ultraviolet background radiation at high Galactic latitudes was derived.
We report the design and testing of a compact system of baffles for cooled infrared telescopes. T... more We report the design and testing of a compact system of baffles for cooled infrared telescopes. The baffle system consists of a reflecting forebaffle and a black aftbaffle and provides a high level of rejection of emission from off-axis sources. The forebaffle reflects radiation incident at angles greater than 40° off axis out of the telescope, thereby reducing the aperture heat load. The black aftbaffle absorbs radiation scattered or diffracted by the forebaffle, as well as radiation from sources within 40° off axis. We describe ground-based measurements at λ = 0.9 µm of the baffle system at ambient temperature and rocketborne measurements at far-infrared wavelengths of the baffle system at ~3 K. The effective emissivity of the cooled forebaffle was measured to be 7 × 10(-3). The system has been successfully used in rocketborne measurements of the diffuse infrared background and will be used in the Infrared Telescope in Space.
A mechanically ruled aberration-corrected concave grating was developed for use in the low-resolu... more A mechanically ruled aberration-corrected concave grating was developed for use in the low-resolution mid-infrared spectrometer aboard the cryogenically cooled Infrared Telescope in Space. The design and the performance testing of the grating are reported. The spectrometer requires a wide spectral range (4.5-11.7 µm) and a wide field of view (8 × 8 arcmin) with a low wavelength resolution (Δλ ≤ 0.3 µm). The aberration-corrected concave grating provides a flat focal plane with a small aberration in the spatial direction compared with those caused by the finite size of the entrance slit. It also permits a simple design for the spectrometer, which is advantageous for applications in space cryogenic instruments. The measurements of the wavelength resolution and the spatial resolution are shown to be in good agreement with the predicted performance. The diffraction efficiency of the grating is more than 80% at the blaze wavelength (6 µm) and fairly high (>30%) over the entire wavelength range in question. The grating produces polarization of less than 10% for λ < 6.4 µm and of 10-20% for 6.7 µm <λ 9.7 µm. These results indicate the potential applicability of this type of grating to the wide-field IR spectroscopic observations.
The observational fact that the interstellar and circumstellar dust grains are not crystalline bu... more The observational fact that the interstellar and circumstellar dust grains are not crystalline but amorphous has been accumulated and it leads to the idea that the grain formation in space is a non-equilibrium phenomenon. In order to investigate the non-equilibrium condensation, we have developed a plasma jet apparatus. The high power of the apparatus enables to dissociate molecular sample gas completely and to obtain condensates from atomized gas. The purpose of our experiments is to examine the condensates from rapidly cooled atomized gas with various abundance ratios. In the experiments, we first focused on the condensation from mixtures of H, C, O, and Si atoms. Three kinds of gas mixtures, a mixture af H and C atoms, that of H, C, and Si atoms, and that of H, C, O, and Si atoms, were chosen as reactant condensable gases. Our experiments were executed with entirely new features: (1) condensation from atomized gas and (2) condensation from mixtures of silicon, oxygen, carbon and hydrogen atoms.
Two H II regions, the Carina nebula and Sharpless 171, and the ρ Oph cloud region, have been mapp... more Two H II regions, the Carina nebula and Sharpless 171, and the ρ Oph cloud region, have been mapped with PHT-S and LWS full grating scan (45-170 μm). The unidentified infrared (UIR) emission bands at 6.2, 7.7, 8.6, and 11.2 μm were detected at most observed positions. Their spatial variations are examined in relation to the far-infrared emission from the submicron dust grains. The temperature and optical depth of submicron grains are derived from the fit of the LWS spectra with modified blackbody. The strength of the incident radiation field in units of the solar vicinity value (G0) is estimated from the dust temperature. The ratio of the UIR 7.7 μm band to the total far-infrared intensity (FIR) shows a similar trend in the two H II regions. It decreases as G0 increases for G0 > 1000. The ratio, however, stays constant in the ρ Oph region, even for G0 > 1000. A more general relation is found if the ratio is plotted against [O III] 88 μm line intensity divided by FIR. The plot ...
Abstract The Carina Nebula region ( l ∼ 287° and b ∼ −0.6°) of about 20′ × 40′ has been observed ... more Abstract The Carina Nebula region ( l ∼ 287° and b ∼ −0.6°) of about 20′ × 40′ has been observed by ISO/LWS with the spatial separation of 3′. Several emission lines, such as [OI] 63, 145 μ m, [OIII] 52, 88 μ m, [NIII] 57 μ m, [NII] 122 μ m and [CII] 157 μ m have been detected in the spectra of most observed positions. The LWS observations of the ionic lines indicate the presence of very low electron density gas ( n e −3 ) extended over the Galactic plane in a scale of kpc unambiguously for the first time.
Symposium - International Astronomical Union, 1999
We performed systematic infrared observations of the intermediate-age Magellanic Clouds clusters ... more We performed systematic infrared observations of the intermediate-age Magellanic Clouds clusters NGC 419, NGC 1783 and NGC 1978. Mid-infrared stars discovered in NGC 419 and NGC 1978 are very red and must be undergoing intense mass loss (comparable to superwinds). They are probably carbon stars but do not seem to show any FIR excesses. Three optically visible carbon stars as well as (at least) 2 near-infrared carbon stars observed with ISOPHOT show 60 μm excesses which may indicate mass loss in the past. It seems that the MIR stars are fainter than the AGB tip luminosity and that their Mbols are close to those of the transition luminosity from M type to C stars. Therefore, these MIR stars may not be in the final stage of the AGB phase. This may suggest that AGB stars lose mass heavily at some other time, possibly during the transition from M type to C stars.
Proceedings of the International Astronomical Union, 2006
The InfraRed Camera (IRC) (Onaka et al. 2004), a wide-field (~10 × 10 arcmin2) NIR-MIR 2–26(μm) c... more The InfraRed Camera (IRC) (Onaka et al. 2004), a wide-field (~10 × 10 arcmin2) NIR-MIR 2–26(μm) camera and spectrograph onboard the AKARI (formerly ASTRO-F) space telescope (Murakami et al. 2004), can perform slit-less spectroscopic survey. Many faint galaxies have been serendipitously detected during its in-orbit performance verification period thanks to the power of the slit-less spectroscopy. They are as faint as a few – several mJy in flux, but they can be easily recognized by their prominent spectroscopic features (e.g., PAH). Their redshift (≲0.3) can be measured through spectral template fitting over the features. We can thus obtain their basic information (redshift, activity type, and luminosity) to investigate nature of galaxies out to much greater distance at MIR than before. With the new IRC/AKARI data, we might be able to address some of the most interesting questions on galaxy evolution at z≃0.3–2 (e.g., Genzel & Cesarsky 2000; Peeters et al. 2004; Pearson 2005): What c...
Massive stars are expected to play an important role in predominately supplying metal elements an... more Massive stars are expected to play an important role in predominately supplying metal elements and dust particles into the interstellar space in the early universe due to their short lifetime in the main sequence. The amount of newly formed dust in the ejecta of a supernova obtained from the observational results, however, remains only in a range of 10-3-10-5Msun, which is much smaller than the amount of dust needed for a SN to form to account for the dust content in the early universe. Recent observations of dust-forming type-Ib supernova 2006jc made with AKARI and Spitzer have shown that the newly-formed dust in the SN ejecta is also only in the range of 10-4-10-5Msun (Sakon et al. 2009; Mattila et al. 2008), but they recognize the presence of pre-existing circumstellar dust possibly formed in the mass loss wind associated with the events prior to the SN explosion. Recent studies reveal that many of the Wolf-Rayet stars form in binary system and that around 10% of WR stars may for...
Space Telescopes and Instrumentation 2008: Optical, Infrared, and Millimeter, 2008
The Infrared Camera (IRC) is one of two focal-plane instruments on the AKARI satellite. It is des... more The Infrared Camera (IRC) is one of two focal-plane instruments on the AKARI satellite. It is designed for wide-field deep imaging and low-resolution spectroscopy in the near- to mid-infrared (1.8-26.5 micron) in the pointed observation mode of AKARI. The IRC is also operated in the survey mode to make an All-Sky Survey at 9 and 18 microns. The IRC is
We observed an area of 10 deg2 of the Large Magellanic Cloud using the Infrared Camera (IRC) on b... more We observed an area of 10 deg2 of the Large Magellanic Cloud using the Infrared Camera (IRC) on board AKARI. The observations were carried out using five imaging filters (3.2, 7, 11, 15, and 24 mum) and a dispersion prism (2-5 mum, lambda/Deltalambda˜20) equipped in the IRC. Here we describe an outline of our survey project, and present some initial results using imaging data that detected over 5.9×105 near-infrared and 6.4×104 mid-infrared point sources. The 10 sigma detection limits of our survey are about 16.5, 14.0, 12.3, 10.8, and 9.2 in Vega-magnitude at 3.2, 7, 11, 15, and 24 mum, respectively. The first point source catalog is planned to be released to the public in 2009. We found a new sequence in the color-magnitude diagram, suggesting that this may be attributed to red giants with aluminum oxide dust but without silicate features.
Far-ultraviolet radiation over a wide sky region of −110° 60° was observed by a rocket-borne two-... more Far-ultraviolet radiation over a wide sky region of −110° 60° was observed by a rocket-borne two-dimensional imager in the wavelength around 150 nm. The background far-ultraviolet radiation from the Virgo cluster region was also observed in the pointing phase of the same rocket experiment. Contributions from several components, such as airglows, faint stars, or molecular hydrogen emission, to the observed radiation were examined, and the diffuse far-ultraviolet background radiation at high Galactic latitudes was derived.
We report the design and testing of a compact system of baffles for cooled infrared telescopes. T... more We report the design and testing of a compact system of baffles for cooled infrared telescopes. The baffle system consists of a reflecting forebaffle and a black aftbaffle and provides a high level of rejection of emission from off-axis sources. The forebaffle reflects radiation incident at angles greater than 40° off axis out of the telescope, thereby reducing the aperture heat load. The black aftbaffle absorbs radiation scattered or diffracted by the forebaffle, as well as radiation from sources within 40° off axis. We describe ground-based measurements at λ = 0.9 µm of the baffle system at ambient temperature and rocketborne measurements at far-infrared wavelengths of the baffle system at ~3 K. The effective emissivity of the cooled forebaffle was measured to be 7 × 10(-3). The system has been successfully used in rocketborne measurements of the diffuse infrared background and will be used in the Infrared Telescope in Space.
A mechanically ruled aberration-corrected concave grating was developed for use in the low-resolu... more A mechanically ruled aberration-corrected concave grating was developed for use in the low-resolution mid-infrared spectrometer aboard the cryogenically cooled Infrared Telescope in Space. The design and the performance testing of the grating are reported. The spectrometer requires a wide spectral range (4.5-11.7 µm) and a wide field of view (8 × 8 arcmin) with a low wavelength resolution (Δλ ≤ 0.3 µm). The aberration-corrected concave grating provides a flat focal plane with a small aberration in the spatial direction compared with those caused by the finite size of the entrance slit. It also permits a simple design for the spectrometer, which is advantageous for applications in space cryogenic instruments. The measurements of the wavelength resolution and the spatial resolution are shown to be in good agreement with the predicted performance. The diffraction efficiency of the grating is more than 80% at the blaze wavelength (6 µm) and fairly high (>30%) over the entire wavelength range in question. The grating produces polarization of less than 10% for λ < 6.4 µm and of 10-20% for 6.7 µm <λ 9.7 µm. These results indicate the potential applicability of this type of grating to the wide-field IR spectroscopic observations.
The observational fact that the interstellar and circumstellar dust grains are not crystalline bu... more The observational fact that the interstellar and circumstellar dust grains are not crystalline but amorphous has been accumulated and it leads to the idea that the grain formation in space is a non-equilibrium phenomenon. In order to investigate the non-equilibrium condensation, we have developed a plasma jet apparatus. The high power of the apparatus enables to dissociate molecular sample gas completely and to obtain condensates from atomized gas. The purpose of our experiments is to examine the condensates from rapidly cooled atomized gas with various abundance ratios. In the experiments, we first focused on the condensation from mixtures of H, C, O, and Si atoms. Three kinds of gas mixtures, a mixture af H and C atoms, that of H, C, and Si atoms, and that of H, C, O, and Si atoms, were chosen as reactant condensable gases. Our experiments were executed with entirely new features: (1) condensation from atomized gas and (2) condensation from mixtures of silicon, oxygen, carbon and hydrogen atoms.
Two H II regions, the Carina nebula and Sharpless 171, and the ρ Oph cloud region, have been mapp... more Two H II regions, the Carina nebula and Sharpless 171, and the ρ Oph cloud region, have been mapped with PHT-S and LWS full grating scan (45-170 μm). The unidentified infrared (UIR) emission bands at 6.2, 7.7, 8.6, and 11.2 μm were detected at most observed positions. Their spatial variations are examined in relation to the far-infrared emission from the submicron dust grains. The temperature and optical depth of submicron grains are derived from the fit of the LWS spectra with modified blackbody. The strength of the incident radiation field in units of the solar vicinity value (G0) is estimated from the dust temperature. The ratio of the UIR 7.7 μm band to the total far-infrared intensity (FIR) shows a similar trend in the two H II regions. It decreases as G0 increases for G0 > 1000. The ratio, however, stays constant in the ρ Oph region, even for G0 > 1000. A more general relation is found if the ratio is plotted against [O III] 88 μm line intensity divided by FIR. The plot ...
Abstract The Carina Nebula region ( l ∼ 287° and b ∼ −0.6°) of about 20′ × 40′ has been observed ... more Abstract The Carina Nebula region ( l ∼ 287° and b ∼ −0.6°) of about 20′ × 40′ has been observed by ISO/LWS with the spatial separation of 3′. Several emission lines, such as [OI] 63, 145 μ m, [OIII] 52, 88 μ m, [NIII] 57 μ m, [NII] 122 μ m and [CII] 157 μ m have been detected in the spectra of most observed positions. The LWS observations of the ionic lines indicate the presence of very low electron density gas ( n e −3 ) extended over the Galactic plane in a scale of kpc unambiguously for the first time.
Symposium - International Astronomical Union, 1999
We performed systematic infrared observations of the intermediate-age Magellanic Clouds clusters ... more We performed systematic infrared observations of the intermediate-age Magellanic Clouds clusters NGC 419, NGC 1783 and NGC 1978. Mid-infrared stars discovered in NGC 419 and NGC 1978 are very red and must be undergoing intense mass loss (comparable to superwinds). They are probably carbon stars but do not seem to show any FIR excesses. Three optically visible carbon stars as well as (at least) 2 near-infrared carbon stars observed with ISOPHOT show 60 μm excesses which may indicate mass loss in the past. It seems that the MIR stars are fainter than the AGB tip luminosity and that their Mbols are close to those of the transition luminosity from M type to C stars. Therefore, these MIR stars may not be in the final stage of the AGB phase. This may suggest that AGB stars lose mass heavily at some other time, possibly during the transition from M type to C stars.
Proceedings of the International Astronomical Union, 2006
The InfraRed Camera (IRC) (Onaka et al. 2004), a wide-field (~10 × 10 arcmin2) NIR-MIR 2–26(μm) c... more The InfraRed Camera (IRC) (Onaka et al. 2004), a wide-field (~10 × 10 arcmin2) NIR-MIR 2–26(μm) camera and spectrograph onboard the AKARI (formerly ASTRO-F) space telescope (Murakami et al. 2004), can perform slit-less spectroscopic survey. Many faint galaxies have been serendipitously detected during its in-orbit performance verification period thanks to the power of the slit-less spectroscopy. They are as faint as a few – several mJy in flux, but they can be easily recognized by their prominent spectroscopic features (e.g., PAH). Their redshift (≲0.3) can be measured through spectral template fitting over the features. We can thus obtain their basic information (redshift, activity type, and luminosity) to investigate nature of galaxies out to much greater distance at MIR than before. With the new IRC/AKARI data, we might be able to address some of the most interesting questions on galaxy evolution at z≃0.3–2 (e.g., Genzel & Cesarsky 2000; Peeters et al. 2004; Pearson 2005): What c...
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Papers by T. Onaka