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第4回「あかり」国際会議 (2017年10月17-20日. 東京大学), 文京区, 東京, The 4th AKARI International Conference: The Cosmic Wheel and the Legacy of the AKARI archive: from galaxies and stars to planets and life (October 17-20, 2017. The University of Tokyo), Bunkyo-ku, Tokyo, Japan, We introduce a general-purpose surface brightness correction method for compact extended sources imaged in the slow-scan pointed-observation mode of the Far-Infrared Surveyor (FIS) aboard the AKARI infrared astronomical satellite. Our method recovers correct surface brightness maps by rescaling archived raw FIS maps using the surface-brightness-dependent inverse FIS response function. The flux of a target source is then automatically corrected for as the simple sum of surface brightnesses within the adopted target perimeter (i.e., standard contour photometry). This correction method is contrasted with the previous aperture photometry method for point sources, which directly corrects for the target flux with a flux-dependent scaling law. The new surface brightness correction method is applicable to objects of any shape from unresolved point sources to resolved extended objects, as long as the target is not deemed diffuse, i.e., the total extent of the target source does not exceed much more than a single FIS scan width of about 10 min. The new correction method takes advantage of the well-defined shape (i.e., the scale-invariance) of the point spread function, which enables us to adopt a power-law FIS response function. We analyze the point source photometric calibrator data using the FIS AKARI Slow-Scan Tool and constrain the parameters of the adopted power-law FIS response function. We conclude that the photometric accuracy of the new correction method is better than 10% error based on comparisons with the expected fluxes of the photometric calibrators, and that resulting fluxes without the present correction method can lead to differences more than a factor of two., 形態: カラー図版あり, Physical characteristics: Original contains color illustrations, 資料番号: AA1730026053, レポート番号: JAXA-SP-17-009E

SPICA Science Conference from Exoplanets to Distant Galaxies: SPICA's New Window on the Cool Universe (June 18-21, 2013. Ito Hall, the University of Tokyo), Bunkyou-ku, Tokyo, Japan, We present the preliminary results of the flux calibration for extended sources observed with the Far-Infrared Surveyor (FIS) onboard the AKARI satellite. The circumstellar shells of evolved stars (particularly of AGB and post-AGB stars) retain the fossil record of their mass loss in the form of dust/gas density distributions and these shells have the potential to verify/constrain many theoretical aspects of stellar evolution and mass loss. Hence, it is critical to have an accurate surface brightness and flux calibration. The FIS has four photometric bands between 50-180 μm with two types of Ge:Ga array detectors. The Ge:Ga array is long known to have a slow transient response and FIS has already been characterized for point sources. To calibrate for extended sources, we used a method in which photometry is done in a contour aperture of the 3σ detection threshold above the background to encompass more than the PSF core. We show that the revised slow transient corrections for the short wavelength band have a similar functional form as for the point source corrections, whereas for the long wavelength band two distinct functional forms dependent on the source brightness., 形態: カラー図版あり, Physical characteristics: Original contains color illustrations, 資料番号: AA1730027055, レポート番号: JAXA-SP-17-010E

We performed a far-IR imaging survey of the circumstellar dust shells of 144 evolved stars as a mission programme of the AKARI infrared astronomical satellite using the Far-Infrared Surveyor (FIS) instrument. With this survey, we deliver far-IR surface brightness distributions of roughly 10' x 40' or 10' x 20' areas of the sky around the target evolved stars in the four FIS bands at 65, 90, 140, and 160 microns. Our objectives are to characterize the far-IR surface brightness distributions of the cold dust component in the circumstellar dust shells, from which we derive the amount of cold dust grains as low as 20 K and empirically establish the history of the early mass loss history. In this first installment of the series, we introduce the project and its aims, describe the observations, data reduction, and surface brightness correction process, and present the entire data set along with the results of integrated photometry measurements (i.e., the central source and circumstellar dust shell altogether). We find that (1) far-IR emission is detected from all but one object at the spatial resolution about 30" - 50" in the corresponding bands, (2) roughly 60 - 70 % of the target sources show some extension, (3) previously unresolved nearby objects in the far-IR are now resolved around 28 target sources, (4) the results of photometry measurements are reasonable with respect to the entries in the AKARI/FIS Bright Source Catalogue, despite the fact that the targets are assumed to be point-sources when catalogue flux densities were computed, and (5) an IR two-color diagram would place the target sources in a roughly linear distribution that may correlate with the age of the circumstellar dust shell and can potentially be used to identify which targets are more extended than others., To be published in PASJ AKARI Special Issue: 25 pages, 5 figures, 5 tables (and 28 supplementary figures available only in PASJ on-line)