Multi-epoch VLBA H2O maser observations towards the massive YSOs AFGL 2591 VLA 2 and VLA 3

We present multi-epoch Very Long Baseline Array (VLBA) H2O maser observations towards the massive young stellar objects (YSOs) VLA 2 and VLA 3 in the star-forming region AFGL 2591. Through these observations, we have extended the study of the evolution of the masers towards these objects up to a time-span of similar to 10 yr, measuring their radial velocities and proper motions. The H2O masers in VLA 3, the most massive YSO in AFGL 2591 (similar to 30-40 M-circle dot), are grouped within projected distances of less than or similar to 40 mas (less than or similar to 130 au) from VLA 3. In contrast to other H2O masers in AFGL 2591, the masers associated with VLA 3 are significantly blueshifted (up to similar to 30 km s(-1)) with respect to the velocity of the ambient molecular cloud. We find that the H2O maser cluster as a whole has moved westwards of VLA 3 between the 2001 and 2009 observations, with a proper motion of similar to 1.2 mas yr(-1) (similar to 20 km s(-1)). We conclude that these masers are tracing blueshifted outflowing material, shock excited at the inner parts of a cavity seen previously in ammonia molecular lines and infrared images, and proposed to be evacuated by the outflow associated with the massive VLA 3 source. The masers in the region of VLA 2 are located at projected distances of similar to 0.7 arcsec (similar to 2300 au) north from this source, with their kinematics suggesting that they are excited by a YSO other than VLA 2. This driving source has not yet been identified.