Mapping Magnetic Fields from Hat Creek

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Session 35 -- Hat Creek
Display presentation, Tuesday, 9:30-6:30, Pauley Room

[35.01] Mapping Magnetic Fields from Hat Creek

A. Goodman (Harvard University), C. Heiles (UC Berkeley), P. Myers (Harvard-Smithsonian Center for Astrophysics), R. G\" usten (MPI, Bonn)

Near the end of its days, the 85-foot telescope at Hat Creek had gotten so good at H I Zeeman observing that one might even say the spectra were being ``mass-produced.'' In a typical integration time of 10 hours, it was possible to measure fields on the order of 5 to 10 $\mu$G in a broad range of interstellar cloud environments. At this meeting, we will describe two magnetic field studies which were both completed just prior to the demise of the 85-foot.

Goodman and Heiles (1993, ApJ, in prep.) presents more than 50 independent Zeeman measurements of the field associated with the Ophiuchus dark cloud complex. The H I spectra in Ophiuchus show self-absorption features whose LSR velocities match those of the denser molecular gas in the region. The average field strength associated with the self-absorption features is $\sim 9$ $\mu$G, with a dispersion $\sim 4$ $\mu$G. The field strengths measured in Ophiuchus imply that magnetic and kinetic energy are similar for the gas associated with the field.

Myers, Goodman, Heiles and G\" usten (1993, ApJ, in prep.) presents over 30 measurements of the H I Zeeman effect in high-latitude clouds. Many of the measurements are in the Ursa Major high-latitude cloud complex, where more than 20 independent observations serve to map out the structure of the line-of-sight field. Field strengths in Ursa Major run to almost 20 $\mu$G, and the field and column density structure appear correlated. One of the most interesting results of this work is that despite the fact that high-latitude clouds are typically far out of virial equilibrium (gravitational energy $<<$ kinetic energy), kinetic and magnetic energy appear to be comparable in these clouds, as they do in star-forming clouds, which are much closer to virial equilibrium.

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