Collapse and Fragmentation Models of Prolate Molecular Cloud Cores. II. Initial Differential Rotation

Details Collapse and Fragmentation Models of Prolate Molecular Cloud Cores. II. Initial Differential Rotation Collapse and Fragmentation Models of Prolate Molecular Cloud Cores. II. Initial Differential Rotation

May 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...498..236d&link_type=abstract

Astrophysical Journal v.498, p.236

Astronomy and Astrophysics

Astronomy

7

Stars: Binaries: General, Hydrodynamics, Ism: Clouds, Stars: Formation

Scientific paper

The prevalence of companions to pre-main-sequence stars and the emerging observational evidence for binary and multiple protostellar condensations suggest that fragmentation during protostellar collapse is a mechanism that may occur frequently in the star formation process. Here a second-order accurate hydrodynamic code has been used to investigate the gravitational (postmagnetic) collapse and fragmentation of low-mass (~1 M&sun;), small (~0.05 pc) molecular cloud cores, starting from moderately centrally condensed (Gaussian), prolate (2:1 and 4:1 axial ratios) configurations with varying thermal energies ( alpha ) and degrees of differential rotation (nu = 1/3 and 2/3). To facilitate comparisons with previous collapse calculations of uniformly rotating prolate cloud cores (Sigalotti & Klapp), all the models were made to start with a ratio of rotational to gravitational energy of beta ~ 0.036. The results indicate that prolate clouds are highly susceptible to binary fragmentation and that with respect to uniformly rotating initial conditions, differential rotation plays no role in either determining or enhancing fragmentation in initially slowly rotating clouds. In contrast to the fragmentation criteria previously established by Boss and Myhill, the results also indicate that clouds with alpha = 0.56 and varied prolateness collapse in a similar fashion, producing intermediate central condensations of oblate spheroidal shape before fragmenting into either a binary (2:1 clouds) or multiple protostellar core (4:1 clouds). The models with alpha <= 0.45 all produced binary systems after having formed intermediate central condensations, which might be of prolate ellipsoidal (2:1 clouds) or narrow cylindrical (4:1 clouds) shape. The mass and separation of the binary fragments increase with decreasing alpha and with an increase of both the degree of differential rotation and the cloud elongation. The results imply that for initial low beta , the degree of cloud prolateness has a greater effect on the outcome than does differential rotation.

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