Kinematics of the ionized gas in Puppis-Vela including the GUM nebula.

We present a high resolution spectroscopic study of the ionized gas in Puppis-Vela, which includes the Gum Nebula and the IRAS Vela Shell, in the emission lines of hydrogen alpha lambda 6563 A, (NII) lambda lambda 6548, 6584 A and the (OIII) lambda 5007 A. Line profiles were obtained at 18 positions well distributed over the entire region. Only the (NII) line profiles in the region of the IRAS Vela Shell show double peaked profiles, consistent with an expansion velocity of 10 +/- 2 km/s. The ionized gas associated with the 36 deg-diameter Gumm Nebula does not show any such systematic motions. This is consistent with, and provides further confirmation of, the results obtained from the IRAS Super Sky Flux (ISSA) maps (Srinivasan Sahu & Blaauw 1993) that the IRAS Vela Shell and the Gum Nebula are two separate structures but seen overlapping in projection. We detected no (OIII) lambda 5007A emission in any of the positions observed. From the (NII)/hydrogen alpha ratio, the temperatures derived at the 18 positions vary between 5,000 to 12,000 K.