The nature of the cometary knots in the Helix planetary nebula (NGC 7293)

Details The nature of the cometary knots in the Helix planetary nebula (NGC 7293) The nature of the cometary knots in the Helix planetary nebula (NGC 7293)

Feb 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998mnras.294..201m&link_type=abstract

Monthly Notices of the Royal Astronomical Society, vol. 294, p. 201

Astronomy and Astrophysics

Astronomy

73

Planetary Nebulae, Cometary Atmospheres, Charge Coupled Devices, Astronomical Photography, Radial Velocity

Scientific paper

The system of cometary knots in the Helix planetary nebula (NGC 7293) has been systematically observed using ground-based images and long-slit, high-resolution spectroscopy. The global expansion of the system of knots is around 14 km/s, some 17 km/s less than for the overrunning gas, and they are distributed in a thick central disk. The velocity field of the system of knots is similar to that of molecular (CO) emission but with a lower expansion velocity. Most knots are external to the central forbidden O III 5007-A-emitting region, but some still show localized forbidden O III 5007-A-emission from their heads. The kinematical structure of two of the latter knots as revealed by profiles of the forbidden O I 6300-A, N II 6584-A, O III 5007-A, and H-alpha emission lines is considered in detail and compared with their CO emission line profiles. The interstellar absorption by the core of a further knot is derived from a forbidden O III 5007-A HST image combined with MES forbidden O III 5007-A profiles. Accurate masses, densities and ages are determined as a consequence.

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