UC Berkeley

GBT Measurements of the Zeeman Effect in the Eridanus/Orion Region

Tim Robishaw

Carl Heiles

The Orion Molecular Cloud Complex

Heiles 1997

Hat Creek 85 ft

9 years of Zeeman data

Distance ~535 pcBower, Sandstrom, Goldston

in prep.

Starlight Polarization Orientations

Breger 1976, Vrba et al. 1988

Starlight Polarization Orientations

Breger 1976, Vrba et al. 1988

The GBT Is a Zeeman Machine!

Off-Axis DesignMinimizes Blockage

Minimizes Sidelobes!!

The GBT Is a Zeeman Machine!

The GBT Is a Zeeman Machine!

Verschuur’s Indictment

1993 BAAS 1821993 BAAS 1831995 ApJ 451: 6241995 ApJ 451: 645

Verschuur’s Indictment

Verschuur’s Indictment

3 hours

The GBTHat Creek85 foot

3 hours

OH

OH

Summary• The GBT can be used as a Zeeman detector• Apparent HI self-absorption samples the

molecular component of the filament• LOS B field measured in emission changes sign

across axis of filament– Detections consistent with previous HI emission

measurements: they were reliable!

• Field reverses within central half-degree of filament (~ 4.5 pc)

• Highest resolution data for modeling of helical magnetic field structure