Enhanced density and magnetic fields in interstellar OH masers
  Aims: We have observed the 6030 and 6035 MHz transitions of OH in high-mass star-forming regions to obtain magnetic field estimates in both maser emission and absorption.   Methods: Observations were taken with the Effelsberg 100 m telescope.   Results: Our observations are consistent with previous results, although we do detect a new 6030 MHz maser feature near -70 km/s in the vicinity of W3(OH). In absorption we obtain a possible estimate of -1.1 +/- 0.3 mG for the average line-of-sight component of the magnetic field in the absorbing OH gas in K3-50 and submilligauss upper limits for the line-of-sight field strength in DR 21 and W3.   Conclusions: These results indicate that the magnetic field strength in the vicinity of OH masers is higher than that of the surrounding, non-masing material, which in turn suggests that the density of masing OH regions is higher than that of their surroundings. 
Vincent L. Fish (1), Mark J. Reid (2), Karl M. Menten (3), Thushara   Pillai (3) ((1) NRAO, (2) CfA, (3) MPIfR)