Molecular and Atomic Excitation Stratification in the Outflow of the Planetary Nebula M27

Details Molecular and Atomic Excitation Stratification in the Outflow of the Planetary Nebula M27 Molecular and Atomic Excitation Stratification in the Outflow of the Planetary Nebula M27

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005aas...20717519m&link_type=abstract

American Astronomical Society Meeting 207, #175.19; Bulletin of the American Astronomical Society, Vol. 37, p.1447

Astronomy and Astrophysics

Astronomy

Scientific paper

The velocity structure of outward moving atomic and molecular material in the planetary nebula M27 (the Dumbbell) as revealed by STIS and FUSE absorption line spectroscopy and Dwingeloo 21 cm observations is presented. Comparisons are made to the velocity profiles of Hα , [N II] λ 6584 and [O III] λ 5007 emission observed by Meaburn et al. (2005, 1992) and CO (2-1) 230 GHz emission observed by Bachiller et al. (2002). Highly excited molecular hydrogen is found at velocities between -30 and -35 km s-1, blueshifted from the central star (RV ≈ -40 km s-1). The molecular hydrogen appears at a transition velocity demarcating a high ionization, low velocity flow (-10≲ vhi ≲ -30 km s-1) from a low ionization zone, high velocity flow (-30≲ vlow ≲ -50 km s-1). H I absorption is found in the low ionization zone, consistent with four velocity components between -35 and -59 km s-1. Molecular hydrogen ro-vibrational excitation shows statistically significant deviation from pure thermal excitation at a temperature of 2040 K. It is incompatable with the excitation expected from continuum fluorescence, but may be compatable with expectations for the recently discovered Lyα fluorescence pumping of hot thermal molecular discussed by Lupu et al. (this meeting).
In addition, the line of sight nebular material produces no reddening of the stellar continuum. This is at odds with the dust extinction (E(bv) ≈ 0.1) inferred from Hα /Hβ line ratios. I discuss dissociation channels for molecular hydrogen (or its ion) that might result in a preferential enhancement of Hα /Hβ , relative to that expected from radiative recombination, and thereby mimic the effect of extinction. The consequence of low dust content, atomic and molecular excitation and velocity statification are discussed in the context of molecular clump formation models for planetary nebulae.
This work is supported by NASA grant NNGO4GK82G to the Johns Hopkins University.

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