Smoke Signals From IRC +10216: 1. Milliarcsecond Proper Motions of the Dust

摘要

The results of a 7-epoch interferometric imaging study, at wavelengths in thenear-infrared K-band, of the carbon star IRC +10216 are presented. The use ofnon- and partially-redundant aperture masking techniques on the 10-m Keck-Itelescope has allowed us to produce images of the innermost regions of thecircumstellar dust envelope with unprecedented detail. With roughly twice theresolving power of previous work, the complex asymmetric structures reportedwithin the central 0.5 arcsec (20 stellar radii) have been imaged at the sizescale of the stellar disk itself (about 50 mas). A prominent dark lane at aposition angle of approximately 120 deg is suggested to be an optically thickdisk or torus of dust which could help to explain IRC +10216's well-knownbipolarity at a position angle of 20 deg. Observations spanning more than apulsational cycle (638 days) have revealed significant temporal evolution ofthe nebula, including the outward motion of bright knots and clumps.Registering these displacements against the compact bright core, which wetentatively identify as marking the location of the star, has allowed us todetermine the apparent angular velocity at a number of points. The magnitudesof the proper motions were found to be in agreement with current estimates ofthe stellar distance and radial velocity. Higher outflow speeds were found forfeatures with greater separation from the core. This is consistent withacceleration taking place over the region sampled by the measurements, howeveralternate interpretations are also presented. Although a number of changes ofmorphology were found, none were clearly interpreted as the condensation of newdust over the pulsation cycle.