STRUCTURE AND EVOLUTION OF MAGNETICALLY SUPPORTED MOLECULAR CLOUDS - EVIDENCE FOR AMBIPOLAR DIFFUSION IN THE BARNARD-1 CLOUD

Axisymmetric simulations have demonstrated that ambipolar diffusion in itiates the formation and contraction of protostellar cores in predomi nantly magnetically supported, self-gravitating, isothermal molecular model clouds. New, fully implicit, multifluid, adaptive-grid codes hav e reliably followed both the early, quasistatic, ambipolar-diffusion-c ontrolled phase of core formation as well as the later, dynamic contra ction phase of thermally and magnetically supercritical cores. In this paper we apply these results and present the first evolutionary, dyna mical model of any one specific molecular cloud. Using observational i nput on the structure of the B1 cloud, we first show that the ''intern al envelope'' of B (mass less-than-or-equal-to 600 M. within r less-th an-or-equal-to 2.9 pc, implying a mean density congruent-to 2 x 10(3) cm-3; and mean magnetic field along the line of sight = 16 + 3 muG) ca n be represented very well by a model in exact magnetohydrostatic equi librium. An evolutionary calculation then follows the ambipolar-diffus ion-induced formation and collapse of a supercritical protostellar cor e, whose predicted physical properties, including mass (13.4 M.), size (0.13 pc), mean density (1.3 x 10(5) cm-3), and mean magnetic field s trength along the line of sight (29.1 muG) are in excellent agreement with observed values for the NH3 core (M(core) = 13 M., R(core) = 0.15 pc, n(n,core) > 8 x 10(4) cm-3, and B(los) = 30 +/- 4 muG). Moreover, the calculated spatial profiles of the number density, column density , and magnetic field strength (hence, Alfven speed) compare well with observations. The model makes further predictions concerning the struc ture of the protostellar core of B1 that can be tested by higher spati al resolution observations.