Astron. Astrophys. 332, L5-L8 (1998) Available formats: HTML | PDF | (gzipped) PostScript small.htm Letter to the Editor Helical structures in a Rosette elephant trunk *
Per Carlqvist 1,
Helmuth Kristen 2 and
Gösta F. Gahm 2
Received 2 December 1997 / Accepted 13 January 1998 Abstract We discuss small-scale, helical, interstellar filaments on the basis of optical observations of an elephant trunk in the Rosette nebula. The trunk studied is composed of a number of sinusoidal or serpentine-like dark filaments, preferentially in the outer part of the trunk, where their wavelength is 7-9 times the trunk radius. The diameters are down to the limit of resolution of 1.0 arcsec , corresponding to 1600 au , and ranging up to about 6400 au . At some positions filament crossings give rise to enhanced extinction. We suggest that the sinusoidal filaments are helices lined up by magnetic fields. We derive average extinctions of 0.5-1.0 in the filaments, implying molecular densities of . From existing data on the Rosette H II region, we conclude that the surrounding kinetic and dynamic pressure and the background radiation field suffice to balance even the denser filaments and to exert drag forces on the trunk as a whole, consistent with evidence of stretching of the trunk. The helical magnetic structures imply the presence of electric currents along the trunk axis. These currents should form a nearly force-free geometry and are consistent with a model consisting of 4-7 helical cables on the surface of a cylinder and which produce the observed wavelength of the helices. We suggest that the Rosette elephant trunks form an interconnected system of rope-like structures which are relics from filamentary skeletons of magnetic fields in the primordial cloud. Key words: ISM: clouds ISM: H ii regions ISM: individual objects: Rosette nebula ISM: kinematics and dynamics ISM: magnetic fields
* Based on observations collected at the Nordic Optical Telescope, La Palma, Spain Send offprint requests to: Per Carlqvist © European Southern Observatory (ESO) 1998 Online publication: March 10, 1998 |