AKARI observations of circumstellar dust in the globular clusters NGC 104 and NGC 362

Abstract

We report on preliminary results of AKARI observations of two globular clusters, NGC 104 and NGC 362. Imaging data covering areas of about 10×10 arcmin2 centered on the two clusters were obtained with the Infrared Camera (IRC) at 2.4, 3.2, 4.1, 7.0, 9.0, 11.0, 15.0, 18.0, and 24.0 μm. We used IRC 11.0νm to 2MASS Ks 2 μm flux-density ratio (F 11/F2) and IRC 24.0 μm to 7.0 μm flux-density ratio (F24/F7) as diagnostics of circumstellar dust emission. Dust emissions are mainly detected from variable stars, obviously on the asymptotic giant branch, but some variable stars that reside below the tip of the first-ascending giant branch also show dust emissions. We found eight red sources with the F24/F7 ratio being greater than unity in NGC 362. Six out of the eight have no 2MASS counterparts. However, we found no such source in NGC 104. © 2007. Astronomical Society of Japan.