IC-349 - BARNARD MEROPE NEBULA

IC 349 is the brightest area in the Pleiades reflection nebulosity, by a factor of about 15. Discovered visually by Barnard in 1890, it is a difficult object because it is only about 30 '' from 23 Tau, of V=4.2 . It is fan-shaped with the axis pointing very nearly toward 23 Tau. I ts blue color and the fact that its spectrum appears identical to that of the star shows that it also is a reflection nebula. The general Pl eiades nebulosity is the result of a chance encounter between the clus ter and a molecular cloud at a relative cross motion of about 12 km s( -1). It is proposed that the semistellar object at the head of IC 349 is part of that cloud and is being dissipated in the radiation field o f 23 Tau as it approaches that star. The relative velocity vector is o btained from the proper motion and radial velocity of the cluster, and the CO radial velocity of the nearby Tau-Aur clouds; the proper motio n of IC 349 is inferred from the proper motions of the cloud T Tauri s tars. The shape of the fan of IC 349 is compatible with a model in whi ch small dust particles ejected from the nucleus are being swept backw ard by the combined effects of radiation pressure from 23 Tau and drag exerted by intercluster gas. It is unknown whether the nucleus is a d ust-shrouded pre-main-sequence star or a dense concentration of gas an d dust several hundred A.U. in diameter. (C) 1996 American Astronomica l Society.