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Is the Taurus B213 Region a True Filament?: Observations of Multiple Cyanoacetylene Transitions

We have obtained spectra of the J=2-1 and J=10-9 transitions of cyanoacetylene (\hc3n) toward a collection of positions in the most prominent filament, B213, in the Taurus molecular cloud. The analysis of the excitation conditions of these transitions reveals an average gas H$_2$ volume density of $(1.8\pm 0.7) \times10^{4} $ \cc. Based on column density derived from 2MASS and this volume density, the line of sight dimension of the high density portion of B213 is found to be $\simeq$ 0.12 pc, which is comparable to the smaller projected dimension and much smaller than the elongated dimension of B213 ($\sim$2.4 pc). B213 is thus likely a true cylinder--like filament rather than a sheet seen edge-on. The line width and velocity gradient seen in \hc3n are also consistent with Taurus B213 being a self-gravitating filament in the early stage of either fragmentation and/or collape.