New detections of OH sources towards the 6.7 GHz methanol masers

Toruń Centre for Astronomy, Nicolaus Copernicus University, ul. Gagarina 11, PL–87100 Toruń, Poland

Send offprint request to: M. Szymczak

Received: 29 May 2000
Accepted: 14 September 2000

Abstract

A sample of 6.7 GHz methanol masers has been searched for OH maser emission at 1665 and 1667 MHz using the 32 m Toruń radio telescope. Eight new OH sources were detected. They are generally weak at radio and infrared wavelengths. In the northern hemisphere sample of 68 methanol sources the OH maser emission is associated with 49 sources. Generally OH masers do not arise in weak FIR sources. The ratio of OH to CH₃OH maser flux densities increases for objects with blue FIR colour and probably reflects evolutionary changes in the star-forming regions.