Abstract
The association between the Pencil nebula (RCW 37, NGC 2736), the Vela X-ray fragment D/D^ ' and the recently discovered new X-ray supernova remnant (RX J0852.0-4622) in Vela is investigated. [O III] 5007 Å line profiles of RCW 37 are presented that show the kinematics of this nebula for the first time. A partial velocity ellipse is present in the pv array of line profiles. The kinematics and morphology could suggest that the structure of RCW 37 is that of a thin curved sheet of optical emission that is undergoing a systematic expansion. A simple explanation for the data is that RX J0852.0-4622 has occured within the older, larger Vela SNR and that a portion of the supernova ejecta from RX J0852.0-4622 has impacted the pre-existing cold dense wall of the Vela SNR. The thin sheet of optical emission then traces out the inside edge of this shocked wall while the X-ray emission marks shock-heated gas. This model predicts that the distance to RX J0852.0-4622 will be that of the main Vela SNR which has been recently measured to be of order 250pc.
