PROBING THE CIRCUMSTELLAR ENVIRONMENTS OF VERY YOUNG LOW-MASS STARS USING WATER MASERS

We have used the VLA to search nearby very young low-mass stars for water maser emission. The sample consists of 26 low-luminosity IRAS sources embedded in dense molecular cores, a class of sources suspected to be newly forming low-mass stars on the order of a few hundred thousand years old. Three sources were detected: IRAS 16293 - 2422 in L1689, 05417 + 0907 in B35, and 16244 - 2432 in L1681B. The maser detection rate of 10% for the IRAS-dense cores is comparable to rates found in surveys of similar but typically higher luminosity sources. High spatial resolution maps show the region of maser emission is generally confined to an area smaller than approximately 0.5" (approximately 100 AU) near the star, and the velocities of individual components span intervals ranging from 20 to 40 km s-1. The maser velocities are too large to be due to gravitational motions in at least two of the sources, implying that the masers are associated with the winds from the young low-mass stars. Using the positions of the masers as probes of the wind's spatial structure provides a way to trace the collimation of the wind very close to the young star. Comparing the high spatial resolution maser data to lower resolution CO data shows no evidence for higher collimation close to the star-the stellar wind cavity appears to have similar collimation at 10(15) cm as at 10(17)-10(18) cm.