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VLBI measures the depth of the Cygnus X star-forming region

Submitter: Huib van Langevelde
Description: The Cygnus X region contains a number of well-studied high-mass star forming regions, but not only regions of embedded star formation (as can be seen in this MSX 8micron image), but also many O and B stars and young supernova remnants. Supposedly all of this activity is related to the “Local Spur”, as most high mass star formation is related to the spiral structure of the Milky Way. In fact, it has been argued that the Cygnus X region has a common origin, a super bubble or a giant Strömgren sphere. However, the question whether this is all happening in a single “mini-starburst” structure depends on disentangling the depth effects in the picture above.

Using the EVN for methanol masers and the VLBA for water masers, it has been possible to measure direct parallax distances (insets) for all the well-known high-mass star forming complexes with 10% accuracy. From the methanol masers it is clear that W75N, DR21, DR20 and IRAS20290+4052 are all part of the Cygnus X North complex, at a common distance of 1.4 kpc, indeed in the “local spur”. However, the water masers in AFGL2591 show a parallax that puts this region 3.3 kpc, associating it with more distant star-forming regions seen in projection, maybe located in the Perseus arm. Moreover, the individual three-dimensional space velocities measured at the same time, seem to rule out that even the molecular clouds in the Cygnus X North region originate from a single event, as has been proposed in the past.

These EVN and VLBA measurements are published in a paper by Kazi Rygl (INAF, Rome) and collaborators, including Huib van Langevelde and Kalle Torstensson from JIVE (Rygl et al., 2012, A&A 539 79). This study demonstrates the enormous potential of VLBI to disentangle the scale and dynamics of star formation in the Galaxy. Measurements on the Cygnus X region continue in order to try to determine the depth effects of individual clouds in the Cygnus X North complex.

Copyright: published in A&A
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