Query : 2003A&A...403..399C

2003A&A...403..399C - Astronomy and Astrophysics, volume 403, 399-412 (2003/5-4)

Theory of twisted trunks.


Abstract (from CDS):

Using the 2.6-m Nordic Optical Telescope we have observed a large number of elephant trunks in several HII regions. Here, we present a small selection of this material consisting of a few large, well-developed trunks, and some smaller ones. We find that: (i) the well-developed trunks are made up of dark filaments and knots which show evidence of twisted structures, (ii) the trunks are connected with essentially two filamentary legs running in V-shape, and (iii) all trunks have the maximum extinction in their heads. We advance a theory of twisted elephant trunks which is based on the presence of magnetic flux ropes in molecular clouds where hot OB stars are formed. If the rope contains a local condensation it may adopt a V-shape as the HII region around the hot stars expands. If, in addition, the magnetic field in the rope is sufficiently twisted, the rope may form a double helix at the apex of the V. The double helix is identified with the twisted elephant trunks. In order to illustrate the mechanisms behind the double helix we have constructed a mechanical analogy model of the magnetic flux rope in which the rope has been replaced by a bundle of elastic strings loaded by a weight. Experiments with the model clearly show that part of the bundle will transform into a double helix when the twist of the bundle is sufficiently large. We have also worked out a simple theoretical model of a mass-loaded magnetic flux rope. Numerical calculations show that a double helix will indeed form when the twist of the rope exceeds a certain critical limit. Numerical model calculations are applied to both the analogy model experiments and one of the well-developed elephant trunks. On the basis of our model we also suggest a new interpretation of the so called EGGs. The double helix mechanism is quite general, and should be active also in other suitable environments. One such environment may be the shell of supernova remnants. Another example is the expanding bubble outlined by the North Celestial Pole Loop.

Abstract Copyright:

Journal keyword(s): ISM: HII regions - ISM: kinematics and dynamics - ISM: magnetic fields - ISM: structure - ISM: supernova remnants

Simbad objects: 9

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Number of rows : 9
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
1 HD 7113 Em* 01 09 13.066 -73 11 38.92     11.7     ~ 119 0
2 IC 1805 OpC 02 32 50 +61 28.3   7.03 6.5     ~ 499 2
3 NGC 2244 OpC 06 32 11 +04 54.8           ~ 595 1
4 NAME Rosette Nebula HII 06 32 26.76 +04 47 37.1           ~ 472 1
5 [DB2002b] G141.33+34.45 MoC 08 49 02.2 +72 36 55           ~ 25 0
6 [DB2002b] G141.43+35.20 MoC 08 57 53.4 +72 16 26           ~ 20 0
7 [DB2002b] G142.27+36.17 MoC 09 06.1 +71 16           ~ 24 0
8 MBM 30 MoC 09 28 43.0 +70 24 55           ~ 27 0
9 M 16 OpC 18 18 45 -13 47.5   6.58 6.0     ~ 993 2

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