High‐Mass Protostellar Candidates. I. The Sample and Initial Results

We describe a systematic program aimed at identifying and characterizingcandidate high-mass proto-stellar objects (HMPOs). Our candidate sampleconsists of 69 objects selected by criteria based on those established byRamesh & Sridharan (1997) using far-infrared, radio-continuum and molecularline data. Infrared-Astronomical-Satellite (IRAS) andMidcourse-Space-Experiment (MSX) data were used to study the larger scaleenvironments of the candidate sources and to determine their total luminositiesand dust temperatures. To derive the physical and chemical properties of ourtarget regions, we observed continuum and spectral line radiation at millimeterand radio wavelengths. We imaged the free-free and dust continuum emission atwavelengths of 3.6 cm and 1.2 mm, respectively, searched for H2O and CH3OHmaser emission and observed the CO 2-1 and several NH3 lines toward all sourcesin our sample. Other molecular tracers were observed in a subsample. Thepresented results indicate that a substantial fraction of our sample harborsHMPOs in a pre-UCHII region phase, the earliest known stage in the high-massstar formation process.Comment: 16 pages, 11 eps-figures. Astrophysical Journal, in pres