Magnetic Field Clumping in Massive Star-Forming Regions as Determined   from Excited-State OH Absorption and Maser Emission
  We have observed six high-mass star-forming regions in the 2 Pi 3/2, J = 7/2 lines of OH using the GBT in order to investigate whether the magnetic field, and hence the density, measured in absorption differs from that implied by maser Zeeman splitting. We detect absorption in both the 13441 and 13434 MHz main lines in all six sources. Zeeman splitting in the F = 3-3 absorption line in W3(OH) implies a line-of-sight magnetic field strength of 3.0 +/- 0.3 mG. This is significantly less than full magnetic field strengths detected from OH maser Zeeman splitting, suggesting that OH maser regions may be denser than the non-masing OH material by a factor of several. Zeeman splitting is not detected in other sources, but we are able to place upper limits on B_parallel of 1.2 mG in G10.624-0.385 and 2.9 mG in K3-50. These results are consistent with a density enhancement of the masers, but other explanations for the lower magnetic field in absorption compared to maser emission are possible for these two sources. Absorption in one or both of the 13442 and 13433 MHz satellite lines is also seen in four sources. This is the very first detection of the 2 Pi 3/2, J = 7/2 satellite lines. Ratios of satellite-line to main-line absorption suggest enhancement of the satellite lines from local thermodynamic equilibrium values. Masers are seen in the F = 4-4 and 3-3 transitions of W3(OH) and the 4-4 transition of ON 1. A previously undetected 4-4 maser is seen near -44.85 km/s in W3(OH). 
Vincent L. Fish (NRAO), Mark J. Reid (CfA), Karl M. Menten (MPIfR)