The high radial velocity of an outer filament of the Helix nebula (NGC 7293)

Details The high radial velocity of an outer filament of the Helix nebula (NGC 7293) The high radial velocity of an outer filament of the Helix nebula (NGC 7293)

Feb 1987

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987mnras.224..885w&link_type=abstract

Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 224, Feb. 15, 1987, p. 885-893.

Astronomy and Astrophysics

Astronomy

27

Astronomical Spectroscopy, Flow Geometry, Flow Velocity, Nebulae, Radial Velocity, Stellar Mass Ejection, Asymptotic Giant Branch Stars, Filaments, H Alpha Line, High Speed, Red Giant Stars, Stellar Evolution

Scientific paper

An echele spectrograph was used to obtain a series of long-slit high-resolution line profiles of H-alpha and forbidden N Ii lines from the center of the Helix nebula (NGC 7293) to the filament 11 arcmin east. This filament shows a blue-shifted velocity of about 50 km/s with respect to the nebula mean velocity, i.e. larger than the approximately 25 km/s expansion of the bright helical ring. It is suggested that this feature may be part of a radially expanding ellipsoidal shell whose long axis is inclined towards the line-of-sight. Possible mechanisms for the formation of such a high-velocity feature are discussed. Collision of a hot fast wind and a cold red-giant wind cannot easily account for the presence of multiple shells nor the high radial velocity of the outer filament. A high-mass-loss high-velocity ejection event ('superwind') at the end of the red-giant phase of an AGB star is suggested as a more probable cause or the high-velocity outer structure.

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