AAS 205th Meeting, 9-13 January 2005
Session 74 ISM II
Oral, Tuesday, January 11, 2005, 10:00-11:30am, California

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[74.03] The Magnetic field in the wall of the Local Bubble and the Coalsack dark cloud

B-G Andersson (CAS/JHU), S.B. Potter (SAAO)

We present high sampling-density polarimetry of stars in the direction of the Southern Coalsack dark cloud, comprising data on >400 stars. Combining the polarization measurements with distance information for both the stars and the intervening extinction we can decompose the origin of the polarization into three regions along the line of sight;

1) the wall of the local bubble,

2) the Coalsack cloud, and

3) material likely associated with the Carina arm.

Having separated the polarization into these components, and taking radiative transfer effects into account, we use the Chandrasekhar-Fermi method - supported by density estimates from C~I excitation measurements and estimates of the turbulent velocity from Ultra-High Resolution Spectroscopy - to derive magnetic field components in the plane of the sky of 8+5-3 microGauss for the wall of the local bubble and 93±23 microGauss for the Coalsack.

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