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Previous Results


December 2003
Using the Very Large Baseline Array (VLBA) of NRAO, we accurately determined the motions of water masers around two young stellar objects in the region W75N, located at 2000 parsec. Water masers are good indicators of energetic processes in star-forming regions, such as powerful outflows of material from young stars.

Both objects seem to be similar in spectral type (i.e., in mass and temperature), and they are separated by only 1400 astronomical units (AU). However, they show a strikingly different outflow geometry:

  • VLA 1 shows a collimated, jet-like outflow of about 2000 AU. The material is ejected from VLA 1 along this jet. This kind of geometry is typically seen in other regions.
  • VLA 2 is expelling gas in multiple directions, giving rise to a shell of 160 AU radius.

The bottom left panel of the figure shows the region enclosing sources VLA 1 (north) and VLA 2 (south). Here, the color map shows the radio-continuum at 1.3 cm (tracing ionized gas) from both sources, and crosses mark the position of the water masers. The other panels show close-ups of the masers around both sources. Arrow lengths and directions trace the motion of masers on the plane of the sky. Arrow colors show the velocity of masers along the line of sight (red = moving away from us; blue = moving towards us. See the scale on the right).

This difference in outflow geometry is surprising, being both sources so similar and so close to each other, which argues against this difference being due to the conditions of their surrounding medium.

We propose that the different shape of these outflows could be the result of the evolution of these young stars. Our results suggests the presence of non-collimated (e.g. approximately spherical) ejections of material in the earliest stages of stellar evolution, a possibility which is difficult to explain with present theories of star formation.

This work has been published in The Astrophysical Journal by J. M. Torrelles (IEEC), N. A. Patel (CfA), G. Anglada (IAA), J. F. Gómez (LAEFF), P. T. P. Ho (CfA), L. Lara (IAA), A. Alberdi (IAA), J. Cantó (UNAM), S. Curiel (UNAM), G. Garay (U. Chile), and L. F. Rodríguez (UNAM)