| A search for water maser emission at 22.2GHz has been performed towards 160 IRAS sources selected using the Wood & Churchwell color criteria to identify high-mass star forming regions. The aim of the survey is to verify the existence of a substantial variation of the maser detection rate within the Wood & Churchwell sample, and to estimate its possible contamination due to spurious sources. Out of the whole sample, water maser emission was found in 11 sources, 2 of which being new detections. The success rate of the survey is very low: 7%. We find a strong dependence of the maser occurrence on the IRAS flux density at 60μm: the rate drops from ~24% for sources brighter than 100Jy to ~1% for weaker ones. These results, combined with those found in previous surveys, indicate that it is very unlikely that the population of weak IRAS sources with shallow far-infrared continuum spectra is associated with high-mass star forming regions. Since these sources account for about half of the total number of the IRAS PS located inside the Wood & Churchwell color box, we believe that the predicted population of OB-type stars may have been overestimated by a factor up to 50%. |
