We present the SPICA Coronagraphic Instrument (SCI), which has been designed for a concentrated study of extra-solar planets (exoplanets). SPICA mission provides us with a unique opportunity to make ...high contrast observations because of its large telescope aperture, the simple pupil shape, and the capability for making infrared observations from space. The primary objectives for the SCI are the direct coronagraphic detection and spectroscopy of Jovian exoplanets in infrared, while the monitoring of transiting planets is another important target. The specification and an overview of the design of the instrument are shown. In the SCI, coronagraphic and non-coronagraphic modes are aplicable for both an imaging and a spectroscopy. The core wavelength range and the goal contrast of the coronagraphic mode are 3.5–27
μm, and 10
−6, respectively. Two complemental designs of binary shaped pupil mask coronagraph are presented. The SCI has capability of simultaneous observations of one target using two channels, a short channel with an InSb detector and a long wavelength channel with a Si:As detector. We also give a report on the current progress in the development of key technologies for the SCI.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We have collected one-dimensional raster-scan observations of the active star-forming region Sharpless 171 (S171), a typical HII region-molecular cloud complex, with the three spectrometers (LWS, ...SWS, and PHT-S) on board ISO. We have detected 8 far-infrared fine-structure lines, $\ion{O}{iii}$ 52 μm, $\ion{N}{iii}$ 57 μm, $\ion{O}{i}$ 63 μm, $\ion{O}{iii}$ 88 μm, $\ion{N}{ii}$ 122 μm, $\ion{O}{i}$ 146 μm, $\ion{C}{ii}$ 158 μm, and $\ion{Si}{ii}$ 35 μm together with the far-infrared continuum and the H2 pure rotation transition ($J=5$–3) line at 9.66 μm. The physical properties of each of the three phases detected, highly-ionized, lowly-ionized and neutral, are investigated through the far-infrared line and continuum emission. Toward the molecular region, strong $\ion{O}{i}$ 146 μm emission was observed and the $\ion{O}{i}$ 63 μm to 146 μm line ratio was found to be too small (∼5) compared to the values predicted by current photodissociation region (PDR) models. We examine possible mechanisms to account for the small line ratio and conclude that the absorption of the $\ion{O}{i}$ 63 μm and the $\ion{C}{ii}$ 158 μm emission by overlapping PDRs along the line of sight can account for the observations and that the $\ion{O}{i}$ 146 μm emission is the best diagnostic line for PDRs. We propose a method to estimate the effect of overlapping clouds using the far-infrared continuum intensity and derive the physical properties of the PDR. The $\ion{Si}{ii}$ 35 μm emission is quite strong at almost all the observed positions. The correlation with $\ion{N}{ii}$ 122 μm suggests that the $\ion{Si}{ii}$ emission originates mostly from the ionized gas. The $\ion{Si}{ii}$ 35 μm to $\ion{N}{ii}$ 122 μm ratio indicates that silicon of 30% of the solar abundance must be in the diffuse ionized gas, suggesting that efficient dust destruction is undergoing in the ionized region.
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Context. AKARI is the first Japanese astronomical satellite dedicated to infrared astronomy. One of the main purposes of AKARI is the all-sky survey performed with six infrared bands between 9 μm and ...200 μm during the period from 2006 May 6 to 2007 August 28. In this paper, we present the mid-infrared part (9 μm and 18 μm bands) of the survey carried out with one of the on-board instruments, the infrared camera (IRC). Aims. We present unprecedented observational results of the 9 μm and 18 μm AKARI all-sky survey and detail the operation and data processing leading to the point source detection and measurements. Methods. The raw data are processed to produce small images for every scan, and the point sources candidates are derived above the 5σ noise level per single scan. The celestial coordinates and fluxes of the events are determined statistically and the reliability of their detections is secured through multiple detections of the same source within milli-seconds, hours, and months from each other. Results. The sky coverage is more than 90% for both bands. A total of 877 091 sources (851 189 for 9 μm, 195 893 for 18 μm) are confirmed and included in the current release of the point source catalog. The detection limit for point sources is 50 mJy and 90 mJy for the 9 μm and 18 μm bands, respectively. The position accuracy is estimated to be better than 2''. Uncertainties in the in-flight absolute flux calibration are estimated to be 3% for the 9 μm band and 4% for the 18 μm band. The coordinates and fluxes of detected sources in this survey are also compared with those of the IRAS survey and are found to be statistically consistent.
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We obtained maps of the central $40\arcmin \times 20\arcmin$ region of the Carina nebula, an active star forming region in the southern Milky Way, in various emission lines in the spectral range ...43–197 μm with the LWS on board the ISO. This paper reports on the results of $\ion{O}{iii}$ 52, 88 μm, $\ion{N}{iii}$ 57 μm, and $\ion{N}{ii}$ 122 μm lines. These ionized lines have been detected in the entire observed area, not only in the optically bright $\ion{H}{ii}$ region, but also in the molecular cloud direction and the region surrounding the Carina nebula. The electron density was derived from the $\ion{O}{iii}$ lines and two distinct components were seen in the electron density map. One is a component with a density of 100–350 cm-3, which encloses two $\ion{H}{ii}$ regions, Car I and Car II. The other is an extended diffuse component, in which the ratio of the $\ion{O}{iii}$ lines is nearly at the low electron density limit ($n_{\rm e} < 100$ cm-3). The observed $\ion{N}{iii}$/$\ion{O}{iii}$ line intensity ratio also supports low electron density of the extended gas component. The diffuse component was detected in the entire observed region, which corresponds to ~30 pc at the distance of the Carina nebula. The present LWS observations of the ionic lines indicate the existence of highly-ionized diffuse gas of low electron density extending around the Carina nebula.
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We have developed a new capacitive transimpedance amplifier (CTIA) that can be operated at 2 K, and have good performance as readout circuits of astronomical far-infrared array detectors. The circuit ...design of the present CTIA consists of silicon p-MOSFETs and other passive elements. The process is a standard Bi-CMOS process with 0.5 /spl mu/m design rule. The open-loop gain of the CTIA is more than 300, resulting in good integration performance. The output voltage swing of the CTIA was 270 mV. The power consumption for each CTIA is less than 10 /spl mu/W. The noise at the output showed a 1/f noise spectrum of 4 /spl mu/V//spl radic/Hz at 1 Hz. The performance of this CTIA nearly fulfills the requirements for the far-infrared array detectors onboard ASTRO-F, Japanese infrared astronomical satellite to be launched in 2005.
IRIS (Infrared Imaging Surveyor) is the first Japanese satellite dedicated solely to infrared astronomy. The telescope has 70-cm aperture, and is cooled down to 6 K with super-fluid helium assisted ...by two-stage Stirling cycle coolers. On the focal plane, the two instruments, the InfraRed Camera (IRC) and the Far-Infrared Surveyor (FIS), are mounted. IRC is a near- and mid-infrared camera for deep imaging-surveys in the wavelength region from 2 to 25 microns. FIS is a far-infrared instrument for a whole sky survey in the wavelength region from 50 to 200 microns. The diffraction-limited spatial resolution is achieved except in the shortest waveband. The point source sensitivity and the survey coverage are significantly improved compared to previous missions. The primary scientific objective is to investigate birth and evolution of galaxies in the early universe by surveys of young normal galaxies and starburst galaxies. IRIS is thrown by a Japanese M-V rocket into a sun-synchronous orbit, in which the cooled telescope can avoid huge emissions from the Sun and the Earth. The expected holding time of the super-fluid helium is more than one year. After consumption of the helium, the near-infrared observation can be continued by the mechanical coolers.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We present the results of mapping observations with ISO of O I 63 mu m, 145 mu m, N II 122 mu m, C II 158 mu m, Si II 35 mu m, and H sub(2) 9.66 mu m line emissions for the Carina nebula, an active ...star-forming region in the Galactic plane. The observations were made for the central 40' x 20' area of the nebula, including the optically bright H II region and molecular cloud lying in front of the ionized gas. Around the center of the observed area is the interface between the H II region and the molecular cloud which creates a typical photodissociation region (PDR). The C II 158 mu m emission shows a good correlation with the O I 63 mu m emission and peaks around the H II-molecular region interface. The correlated component has the ratio of C II 158 mu m to O I 63 mu m of about 2.8. We estimate from the correlation that about 80% of C II emission comes from the PDR in the Carina nebula. The photoelectric heating efficiency estimated from the ratio of the (C II 158 mu m + O I 63 mu m) intensity to the total far-infrared intensity ranges from 0.06 to 1.2%. O I 145 mu m is detected marginally at 10 positions. The average ratio of O I 145 mu m to O I 63 mu m of these positions is about 0.09 plus or minus 0.01 and is larger than model predictions. The observed C II 158 mu m to O I 63 mu m ratio indicates a relatively low temperature (<500 K) of the gas, while the large O I 145 mu m to 63 mu m ratio suggests a high temperature ( similar to 1000 K). This discrepancy cannot be accounted for consistently by the latest PDR model with the efficient photoelectric heating via polycyclic aromatic hydrocarbons (PAHs) even if absorption of O I 63 mu m by foreground cold gas is taken into account. We suggest that absorption of C II 158 mu m together with O I 63 mu m by overlapping PDRs, in which the heating via PAHs is suppressed due to the charge-up effect, may resolve the discrepancy. Quite strong Si II 35 mu m emission has been detected over the observed area. It shows a good correlation with N II 122 mu m, but the correlation with O I 63 mu m is very weak, indicating that Si II 35 mu m comes mainly from the diffuse ionized gas rather than the PDR. The ratio of Si II 35 mu m to N II 122 mu m is about 8 and Si of about 50% of the solar abundance relative to N should be present in the gas phase. The present results suggest that efficient dust destruction takes place and a large fraction of Si returns to the gas in the Carina star-forming region.
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Infrared (IR) dust emission from galaxies is frequently used as an indicator of star formation rate (SFR). However, the effect of the dust-to-gas ratio (i.e., amount of the dust) on the conversion ...law from IR luminosity to SFR has not so far been considered. Then, in this paper, we present a convenient analytical formula including this effect. In order to obtain the dependence on the dust-to-gas ratio, we extend the formula derived in our previous paper, in which a theoretical formula converting IR luminosity to SFR was derived. That formula was expressed as ${\rm SFR}/(M_\odot {\rm yr}^{-1})=\{ 3.3 10^{-10}(1- \eta )/(0.4-0.2f+0.6\epsilon )\} (L_{\rm IR}/L_\odot )$, where f is the fraction of ionizing photons absorbed by hydrogen, ϵ is the efficiency of dust absorption for nonionizing photons, η is the cirrus fraction of observed dust luminosity, and LIR is the observed luminosity of dust emission in the 8-1000-μm range. Our formula explains the IR excess of the Galaxy and the Large Magellanic Cloud. In the current paper, especially, we present the metallicity dependence of our conversion law between SFR and LIR. This is possible since both f and ϵ can be estimated via the dust-to-gas ratio, which is related to metallicity. We have confirmed that the relation between the metallicity and the dust-to-gas ratio is applied to both giant and dwarf galaxies. Finally, we apply the result to the cosmic star formation history. We find that the comoving SFR at $z\sim 3$ calculated from previous empirical formulae is underestimated by a factor of 4-5.
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The Small Magellanic Cloud (SMC) provides a unique laboratory for the study of the lifecycle of dust given its low metallicity (~1/5 solar) and relative proximity (~60 kpc). This motivated the ...SAGE-SMC (Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud) Spitzer Legacy program with the specific goals of studying the amount and type of dust in the present interstellar medium, the sources of dust in the winds of evolved stars, and how much dust is consumed in star formation. This program mapped the full SMC (30 deg2) including the body, wing, and tail in seven bands from 3.6 to 160 Delta *mm using IRAC and MIPS on the Spitzer Space Telescope. The data were reduced and mosaicked, and the point sources were measured using customized routines specific for large surveys. We have made the resulting mosaics and point-source catalogs available to the community. The infrared colors of the SMC are compared to those of other nearby galaxies and the 8 Delta *mm/24 Delta *mm ratio is somewhat lower than the average and the 70 Delta *mm/160 Delta *mm ratio is somewhat higher than the average. The global infrared spectral energy distribution (SED) shows that the SMC has approximately 1/3 the aromatic emission/polycyclic aromatic hydrocarbon abundance of most nearby galaxies. Infrared color-magnitude diagrams are given illustrating the distribution of different asymptotic giant branch stars and the locations of young stellar objects. Finally, the average SED of H II/star formation regions is compared to the equivalent Large Magellanic Cloud average H II/star formation region SED. These preliminary results will be expanded in detail in subsequent papers.
We investigate the possibility of searching for metal-poor high column density ( 10 super(23) cm super(-2)) clouds at high redshift (z) by using gamma ray burst afterglows. Such clouds could be ...related to primeval galaxies that may cause a burst of star formation. We show that a large part of hydrogen is in molecular form in such a high column density environment. Therefore, hydrogen molecules (H sub(2)) rather than hydrogen atoms should be searched for. Then we show that infrared H sub(2) lines are detectable for metal-poor ( 0.01 solar metallicity) high column density (logN sub(H) cm super(-2) 23.5) systems at high-z without suffering dust extinction. The optical properties of dust in infrared could also be constrained by observations of high column density systems. Some possible scenarios for producing high column density systems are finally discussed in the context of galaxy evolution.
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