We present a new model of molecular cloud cores that originate from filamentary clouds that are threaded by helical magnetic fields .
Only modest toroidal fields are required to produce elongated cores , with intrinsic axis ratios in the range 0.1 \stackrel { < } { \sim } q \stackrel { < } { \sim } 0.9 and mean projected axis ratios in the range 0.3 \stackrel { < } { \sim } \langle p \rangle \stackrel { < } { \sim } 1 .
Thus many of our models are in good agreement with the observed shapes of cores ( Myers et al 1991 , Ryden 1996 ) , which find axis ratios distributed about the mean values \langle p \rangle \approx 0.5 - 0.6 and q \approx 0.4 - 0.5 .
We find that the Bonnor-Ebert critical mass is reduced by about 20 % by the helical field threading our models .
We also find that models are generally most elongated when the mass is significantly less than the Bonnor-Ebert critical mass for unmagnetized cores .