The Magnetic Field of the H~II Region NGC 6334A
  We have studied the polarization characteristics and Faraday rotation of the
extragalactic radio source J17204$-$3554, that appears projected on the north
lobe of the galactic H II region NGC 6334A. From observations made with the
Very Large Array at 6.0 and 3.6 cm in three different epochs (1994, 1997, and
2006), we estimate a rotation measure of +5100$\pm$900 rad m$^{-2}$ for the
extragalactic source. This large rotation measure implies a line-of-sight
average magnetic field of $B_\parallel \simeq +36\pm6$ $\mu$G, the largest
obtained by this method for an H II region. NGC 6334A is significantly denser
than other H II regions studied and this larger magnetic field is expected on
the grounds of magnetic flux conservation. The ratio of thermal to magnetic
pressure is $\sim$5, in the range of values determined for more diffuse H II
regions.
