THE ASTROSPHERE OF THE ASYMPTOTIC GIANT BRANCH STAR IRC+10216

Abstract

We have discovered a very extended shock structure (i.e., with a diameter of about 24′) surrounding the well-known carbon star IRC+10216 in ultraviolet images taken with the Galaxy Evolution Explorer satellite. We conclude that this structure results from the interaction of IRC+10216's molecular wind with the interstellar medium (ISM), as it moves through the latter. All important structural features expected from theoretical models of such interactions are identified: the termination shock, the astrosheath, the astropause, the bow shock, and an astrotail (with vortices). The extent of the astropause provides new lower limits to the envelope age (69,000 years) and mass (1.4 M☉, for a mass-loss rate of 2 × 10−5 M☉ yr−1). From the termination-shock standoff distance, we find that IRC+10216 is moving at a speed of about ≳91 km s−1 (1 cm−3/nISM)1/2 through the surrounding ISM.