L

+8 +6 +4 +2 0 -2 -4 Right Ascension Offset Act (arcmin)

Figure 3.18 Rotation of the dense core L1251A. The size of each filled square is proportional to the radial velocity, as gauged from the 1.3 cm line of NH3. The star symbol marks the position of the embedded source IRAS 22290+7458.

correspond to Q, the cloud's angular velocity. For tipped axes that form an angle i with the line of sight, the gradient would be Q/ sin i.

These results must be viewed with some caution. For example, the projected motion of a molecular outflow can also create gradients in the radial velocity. However, this effect cannot be dominant, as similar velocity gradients are seen in cores with and without young stars. Assuming, then, that the observations are indicative of true rotation, we may gauge its dynamical significance. A dense core of mass M and diameter L has a rotational kinetic energy given by Tiot = (1/20) ML2Q2, if the object is idealized as a uniform-density sphere. The result for a prolate configuration of average diameter L and modest axial ratio is the same within a factor of two. Since the potential energy in the spherical case is W = (6/5) GM2/L, we can estimate the ratio of Trot to \W\:

q2L3

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