Changes in the Radio Appearance of MWC 349A

We present new sensitive, high angular resolution 1.3, 2, and 6 cmobservations of the continuum emission from the peculiar emission-line star MWC349A, made with the Very Large Array. This radio emission is believed tooriginate in an ionized flow produced by the photoevaporation of a disk thatsurrounds the star. We determine for the first time the proper motion of thissource, which is consistent with that expected for the location of the sourcein the galaxy. Our analysis of the images, that include the new observations aswell as archive data covering a time interval of more than 20 years, indicatesthat the appearance of MWC 349A has been systematically changing over time. Thewell-defined ``hourglass'' shape that characterized the 2 and 1.3 cm appearanceof the source in the early 1980's has disappeared to be replaced by a more``square'' shape. We discuss if these changes can be accounted for byprecession of the MWC 349A disk or by intrinsic changes in the parameters ofthe disk, but could not reach a satisfactory explanation.Comment: 20 pages, 6 figure