IRA S-selected Galactic star-forming regions – I. New $6_{16} rightarrow 5_{23}$ water maser detections in molecular cores north of Dec. $+15^circ

The results are presented of a survey, performed with the Medicina 32-m parabolic reflector, of a sample of IRAS-selected sources associated with molecular clouds for water masers at $22 \ {\rm GHz} (6_{16} \rightarrow 5_{23})$. The final aim is to study the occurrence of maser emission from star-forming regions in the very early stages of evolution. The whole sample consists of 1409 IRAS sources selected by applying Emerson's colour criteria. In the present paper, results are given for sources with declinations greater than $+15^\circ$, belonging to two subsamples that satisfy more restrictive colour criteria which should identify ultracompact H ii regions (subsample A, 288 sources) and H ii regions (subsample B, 133 sources). The main result of the present study is that 59 IRAS sources in the samples are water maser emitters, 11 of which are new detections from the present survey.