OH masers at 1612 and 1720 MHz in star-forming regions

Masers at the ground-state OH satellite transitions near 1612 and 1720 MHz are occasionally found in star-forming regions, accompanying the dominant m aser of OH at 1665 MHz. The satellite lines can then be valuable diagnostic s of physical conditions in star-forming regions if we can first ascertain that all maser species truly arise from the same site. For this purpose, ne wly measured satellite line positions with subarcsecond accuracy are report ed here, and compared with masers of main-line OH at 1665 MHz, with methano l masers at 6668 MHz, and with ultracompact H II regions. We confirm that m ost of the satellite-line OH masers that we have measured are associated wi th star-forming regions, but a few are not: several 1612-MHz masers are ass ociated with late-type stars, and one 1720-MHz maser is associated with a s upernova remnant. The 1720-MHz masers in star-forming regions are accounted for by a pumping scheme requiring high densities, and are distinctly diffe rent from those in supernova remnants where the favoured pumping scheme ope rates at much lower densities.