A survey of OH masers towards high mass protostellar objects ^*,**

¹ The University of Manchester, School of Physics and Astronomy, Sackville Street Building, PO Box 88, Manchester M60 1QD, UK e-mail: G.Fuller@manchester.ac.uk
² Al-Azhar University, Faculty of Science, Astronomy Department, PO Box 11884, Naser City, Cairo, Egypt
³ The University of Manchester, Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL, UK

Received: 21 August 2006
Accepted: 18 December 2006

Abstract

Context.Masers are important tracers of the early evolution of young high mass stars, but the relationship between different types of maser and the evolutionary state of the exciting source remains unclear.

Aims.To determine whether OH masers are common towards candidate high mass protostellar objects.

Methods.We present a survey of OH maser emission towards a sample of high mass protostellar objects made using the Nançay and GBT telescopes.

Results.OH maser emission was detected towards 63 objects with 36 new detections. There are 56 star-forming regions and 7 OH/IR candidates. Nearly half of the detected sources have OH flux densities 1 Jy. There is no evidence that sources with OH masers have a different range of luminosities from the non-maser sources. The results of this survey are compared with previous H₂O and class II CH₃OH maser observations of the same objects. Some of the detected sources are only associated with OH masers and some sources are only associated with the 1720 MHz OH maser line. The velocity range of the maser emission suggests that the water maser sources may be divided into two groups. The detection rates and velocity range of the OH and Class II CH₃OH masers support the idea that there is a spatial association of the OH and Class II CH₃OH masers. The sources span a wide range in R, the ratio of the methanol maser peak flux to OH 1665 MHz maser peak flux, however there are only a few sources with intermediate values of R, , which has characterised previous samples. The majority of the sources are either methanol-favoured or OH-favoured. Sources which have masers of any species, OH, water or methanol, have redder [ 100 μm–12 μm] IRAS colours than those without masers. However, there is no evidence for different maser species tracing different stages in the evolution of these young high mass sources.

Conclusions.The detection of OH masers towards 26% of a sample of 217 sources should remove any doubt about the existence of OH maser emission towards these objects or this early evolutionary stage. Previous observations which have shown that the OH maser emission from similar sources traces the circumstellar disks around the objects. This combined with the sensitivity of the OH emission to the magnetic field, make the newly detected sources interesting candidates for future follow-up at high angular resolution.