Volume 586, February 2016
|Number of page(s)||12|
|Section||Interstellar and circumstellar matter|
|Published online||05 February 2016|
A rotating helical filament in the L1251 dark cloud⋆
Hamburger Sternwarte, Universität Hamburg,
Gojenbergsweg 112, 21029
2 Ioffe Physical-Technical Institute, Polytekhnicheskaya Str. 26, 194021 St. Petersburg, Russia
3 St. Petersburg Electrotechnical University LETI, Prof. Popov Str. 5, 197376 St. Petersburg, Russia
4 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
5 Astronomy Department, King Abdulaziz University, PO Box 80203, 21589 Jeddah, Saudi Arabia
Received: 18 November 2015
Accepted: 22 December 2015
Aims. We derive the physical properties of a filament discovered in the dark cometary-shaped cloud L1251.
Methods. Mapping observations in the NH3(1, 1) and (2, 2) inversion lines, encompassing 300 positions toward L1251, were performed with the Effelsberg 100-m telescope at a spatial resolution of 40′′ and a spectral resolution of 0.045 km s-1.
Results. The filament L1251A consists of three condensations (α, β, and γ) of elongated morphology, which are combined in a long and narrow structure covering a 38′ × 3′ angular range (∼3.3 pc × 0.3 pc). Comparing the kinematics with the more extended envelope (∼61′ × 33′) emitting in 13CO, we find that: (1) the angular velocity of the envelope around the horizontal axis E → W is ΩEWCO ≈−2 × 10-14 rad s-1 (the line-of-sight velocity is more negative to the north); (2) approximately one half of the filament (combined α and β condensations) exhibits counter-rotation with ΩEWαβ ≈2 × 10-14 rad s-1; (3) one third of the filament (the γ condensation) co-rotates with ΩEWγ ≈−2 × 10-14 rad s-1; (4) the central part of the filament between these two kinematically distinct regions does not show any rotation around this axis; (5) the whole filament revolves slowly around the vertical axis S → N with ΩSNtot ≈7 × 10-15 rad s-1.
The opposite chirality (dextral and sinistral) of the αβ and γ condensations indicates magnetic field helicities of two types, negative and positive, which were most probably caused by dynamo mechanisms. We estimated the magnetic Reynolds number Rm ≳ 600 and the Rossby number ℛ < 1, which means that dynamo action is important.
Key words: ISM: clouds / ISM: molecules / ISM: kinematics and dynamics / radio lines: ISM / techniques: spectroscopic / line: profiles
FITS cube is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/586/A126
© ESO, 2016
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