2016A&A...586A.126L

We derive the physical properties of a filament discovered in the dark cometary-shaped cloud L1251. 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 0.045km/s. 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'x3' angular range (∼3.3pcx0.3pc). Comparing the kinematics with the more extended envelope (∼61'x33') emitting in ¹³CO, we find that: (1) the angular velocity of the envelope around the horizontal axis E-W is Ω^EW_CO≃-2x10^–14rad/s (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 Ω^EW_αβ≃2x10^–14rad/s; (3) one third of the filament (the γ condensation) co-rotates with Ω^EW_γ≃-2x10^–14rad/s; (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 Ω^SN_tot≃7x10^–15rad/s. 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 R_m≳600 and the Rossby number R<1, which means that dynamo action is important.