Abstract
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 (alpha, beta, and gamma) of elongated morphology, which are combined in a long and narrow structure covering a 38' x 3' angular range (similar to 3.3 pc x 0.3 pc). Comparing the kinematics with the more extended envelope (similar to 61' x 33') emitting in (CO)-C-13, we find that: (1) the angular velocity of the envelope around the horizontal axis E -> W is Omega(EW)(CO) approximate to -2 x 10(-14) rad s(-1) (the line-of-sight velocity is more negative to the north); (2) approximately one half of the filament (combined alpha and beta condensations) exhibits counter-rotation with Omega(EW)(alpha beta) approximate to 2x10(-14) rad s(-1); (3) one third of the filament (the gamma condensation) co-rotates with Omega(EW)(gamma) approximate to -2x10(-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 Omega(SN)(tot) approximate to 7x10(-15) rad s(-1). The opposite chirality (dextral and sinistral) of the alpha beta and gamma 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 R-m greater than or similar to 600 and the Rossby number R < 1, which means that dynamo action is important.