AAS 197, January 2001
Session 6. Planetary Nebulae: Young and Old
Display, Monday, January 8, 2001, 9:30am-7:00pm, Exhibit Hall

## [6.11] Hot Molecular Hydrogen in M27 Observed by FUSE

S.R. McCandliss, K.R. Sembach, E.B. Burgh, D.J. Sahnow (JHU), FUSE Team

Recent FUSE observations of the very hot (~~140,000 K) central star of the planetary nebula M27 have revealed a far-UV spectrum unusually rich in molecular hydrogen absorption features. We have identified two velocity components, separated by \approx~45~km~s-1, with distinctly different ground state populations. The blueward component shows absorption lines originating from a highly excited ground state, with rotational levels (J\prime\prime) up to 15 and electronic levels (v\prime\prime) at least as high as 2. The velocity of the blue component is very close to the radial velocity of the nebula, while the redward component is cooler'' and is probably associated with foreground gas. We show a preliminary determination of the ground state population distribution of the highly excited blueward component. Possible excitation mechanisms can be constrained by groundbased observations of the infrared fluorescence along with upper limits to the far-UV fluorescence provided by a longslit sounding rocket observation.

This work is based in part on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University supported by NASA contract NAS5-32985. Additional data has been obtained from a Johns Hopkins sounding rocket mission (36.136 UG) supported by NASA grant NAG5-5122.