A Study of Water Masers

Molecular outflows and HII regions are both connected to star forming regions. Moreover, these regions are commonly related to H2O masers, although this relation is not completely understood. HII regions tend to be particularly diffuse, while masers arise from population inversion in optically thick environments. In addition, water masers are frequently observed to be coexistent with CO outflows and are linked through energetics: the mechanical energy of the CO outflow and the maser emission energy are both thought to be powered by a stellar wind from a young stellar object (YSO). Because masers are excellent tracers of the three-dimensional velocity field in which they lie, spatial distributions of H2O masers can test current theories of outflow systems.

Current star formation theories (Forster & Caswell 1989, Genzel & Downes 1977) suggest that as a YSO forms from a massive protostar, H2O masers form near the core while OH masers form within the circumstellar material. For this reason, we chose to use half of our summer student observing time to look at the 6_16 - 5_23 maser transition in water molecules (22 GHz, 1.3 cm, K band). The water maser regions were chosen based on a study published in 1995 by G. Tofain et al. and suggested by an NRAO staff scientist, Greg Taylor.

As in the first epoch of observations by Tofani et al., the VLA is in A-configuration this summer. The first observation ran from 5:30 to 7:00 LST on 16 July 1999, during which we observed 4 sources: AFGL5142, S233, S235B and NGC2071. The second run observed these same four sources and four additional ones (NGC281W, AFGL5180, Mon-R2, GGD-4) from 4:30 to 7:30 LST on 22 July 1999. By self-calibrating and imaging the data in AIPS, we hope to pursue a study in the proper motions of these masers, thereby lending some insight into the molecular outflows in star-forming regions.

Questions? E-mail Colleen Schwartz.