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Newly formed stars are expected to be surrounded by rotating disks of molecular gas, from which planets may later coalesce. Radio frequency spectral lines from methanol appear to be the best tracers for such disks but this technique has yet to be fully exploited because they lie outside the standard radio observing bands. The Australian radio imaging array (ATCA) covers these spectral lines, but with limited spatial resolution. Pioneering work has revealed clear evidence for these star-fprming disks in a few cases. In the upper left image the blue and red dots indicate the positions of approaching and receding methanol maser emission sites, super-imposed on a broad-band radio image showing outflowing gas in the star-forming region known as G339.88-1.26. The inferred rotating molecular disk has also been seen at infra-red wavelengths (10 microns) using the ESO 3.6m telescope. as explained in the text, MERLIN and the European VLBI Network will be the ideal instruments to study such systems in detail. |
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The lower left plot shows the distribution of 6.6 and 12.2 GHz
methanol maser sites in NGC7538, another star-forming region where
a rotating molecular disk is seen on an angular scale of only
20 milliarcseconds. Here the symbol size is proportional to the radial velocity and implies a linear velocity gradient that arises from just that part of the disk directly in front of the star. Observations were made using the European VLBI Network and the Very Long Baseline Array (VLBA) in the USA. |