AKARI IRC Survey of the Large Magellanic Cloud: Outline of the Survey and Initial Results
Hasegawa, Tetsuo; Onaka, Takashi; Tamura, Motohide; Nakada, Yoshikazu; Tanabé, Toshihiko; Ita, Yoshifusa; Matsuura, Mikako; Usui, Fumihiko; Koo, Bon-Chul; Sakon, Itsuki; Kaneda, Hidehiro; Shimonishi, Takashi; Kawamura, Akiko; Takahashi, Hidenori; Wada, Takehiko; Kato, Daisuke
Japan, South Korea
Abstract
We observed an area of 10deg2 of the Large Magellanic Cloud using the Infrared Camera (IRC) on board AKARI. The observations were carried out using five imaging filters (3, 7, 11, 15, and 24μm) and adispersion prism (2-5μm, λ / Δλ sim 20) equipped in the IRC. This paper describes an outline of our survey project, and presents some initial results using imaging data that detected over 5.9 × 105 near-infrared and 6.4 × 104 mid-infrared point sources. The 10 σ detection limits of our survey are about 16.5, 14.0, 12.3, 10.8, and 9.2 in Vega-magnitude at 3, 7, 11, 15, and 24μm, respectively. The 11 and 15μm data, which are unique to AKARI IRC, allow us to construct color-magnitude diagrams that are useful to identify stars with circumstellar dust. We found anew sequence in the color-magnitude diagram, which is attributed to red giants with luminosity fainter than that of the tip of the first red-giant branch. We suggest that this sequence is likely to be related to the broad emission feature of aluminum oxide at 11.5μm. The 11 and 15μm data also indicate that the ([11]-[15]) color of both oxygen-rich and carbon-rich red giants once becomes blue, and then turns red again in the course of their evolution, probably due to a change in the flux ratio of the silicate or silicon carbide emission feature at 10 or 11.3μm to the 15μm flux.