Radio Mapping of Type I Post-Main-Sequence Nebulae

Type I post-main-sequence nebulae appear to be characterised by a range of unusual, and in certain cases extreme physical characteristics, including high velocity (and possibly high mass) outflows, and anomalous He, N, and C abundances; a feature which is almost certainly indicative of high mass nebular projenitors (cf. Renzini and Voli, 1981). The nature of the flows in these sources is not fully understood, although our own extensive NIR mapping and optical spectroscopy reveals that many contain extremely compact ionised cores, wherein high excitation winds extend to velocities of ~ 103 km.sec-1(and in certain cases very much greater). The primary nebular mass appears to expand at very much lower velocities, although even here it is clear that dense, mass condensations are being accelerated to velocities of order ~ 102 km. sec-1 or greater; an order of magnitude larger than characterising the broad range of PMS nebulae. These condensations appear to display a lower range of excitations than the high velocity flows, perhaps reflecting the inclusion of dense HI condensations (and corresponding UV shadow zones), and dominate the lower excitation nebular structures [OI], [NII] and [OII]. The result, as noted in figure 1 for M2–9, is that [NII] and Ha line profiles differ appreciably.