Radio and infrared observations of optically invisible Type II hydroxyl masers

Abstract

We have measured accurate positions at 1612 MHz for 52 Type II OH masers. In many cases we have also determined the angular sizes of the masers at the peak of the OH line profile. We have also measured the 10-micron flux for many of the objects and the 2--10-micron flux distribution for eight of them. The masers display a wide range of 10-micron fluxes for a given OH line peak flux. The infrared flux distributions can be matched approximately by blackbody distributions for temperatures ranging from about 400 to 800 K. Consideration of the kinematics of the Type II OH masers suggests that most of the angular sizes (and upper limits) are consistent with a linear diameter of the region responsible for the peak of the OH line profile in the range 3000--5000 AU.