2009ApJ...695..930G

K 3-35 is a planetary nebula (PN) where H₂ O maser emission has been detected, suggesting that it departed from the proto-PNe phase only some decades ago. Interferometric VLA observations of the OH 18 cm transitions in K 3-35 are presented. OH maser emission is detected in all four ground state lines (1612, 1665, 1667, and 1720 MHz). All the masers appear blueshifted with respect to the systemic velocity of the nebula and have different spatial and kinematic distributions. The OH 1665 and 1720 MHz masers appear spatially coincident with the core of the nebula, while the OH 1612 and 1667 MHz ones exhibit a more extended distribution. We suggest that the 1665 and 1720 masers arise from a region close to the central star, possibly in a torus, while the 1612 and 1667 lines originate mainly from the extended northern lobe of the outflow. It is worth noting that the location and velocity of the OH 1720 MHz maser emission are very similar to those of the H₂ O masers (coinciding within 0".1 and ∼ 2 km/s, respectively). We suggest that the pumping mechanism in the H₂ O masers could be produced by the same shock that is exciting the OH 1720 MHz transition. A high degree of circular polarization (> 50%) was found to be present in some features of the 1612, 1665, and 1720 MHz emission. For the 1665 MHz transition at ∼ +18 km/s the emission with left and right circular polarizations (LCP and RCP) coincide spatially within a region of ∼ 0".03 in diameter. Assuming that these RCP and LCP 1665 features come from a Zeeman pair, we estimate a magnetic field of ∼ 0.9 mG within 150 AU from the 1.3 cm continuum peak. This value is in agreement with a solar-type magnetic field associated with evolved stars.