On the far-infrared excess of Vega

Abstract

The Infrared Astronomy Satellite (IRAS) has recently detected a compact far-infrared emission source associated with Vega (α Lyrae)1. This flux appears to be thermal emission from dust heated by the visual/UV luminosity of Vega. Although circum-stellar dust is commonly associated with young, early-type stars2, the characteristics of the emission from Vega are quite atypical. The essential difference is the relatively low temperature of the dust for the observed source size. This low temperature implies that the dust grains producing the far-infrared emission must be very efficient 60/100-µm emitters and must, therefore, be much larger than typical interstellar and circumstellar dust grains. To place more limits on the properties of this far-infrared emission region, we observed Vega at 47 and 95 µm with the Kuiper Airborne Observatory (KAO) on the night of 12–13 August 1983. We report here confirmation of the IRAS results and that the source size may be as large as 46 arc s along some axis.