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22-08-2019
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Maser astrometry in CASA

Submitter: Sophia Vaughan
Description: The Milky Way is only one of millions upon millions of galaxies in the universe, but it does have one unique property; it is the only galaxy which is observed from within. This does mean that it is harder to tell what type of galaxy the Milky Way is although the stars are close enough so that we can measure their properties and kinematics. In order to determine the structure and type of the Milky Way, the distances and velocities of many stars need to be known very accurately and precisely. This information can then be used to reconstruct the properties of the Galaxy. The challenge is to determine with extreme accuracy an object's position on the sky. This is needed in order to get a good measure of the object's parallax distance and its velocity component in the plane of the sky. There are certain types of object that make this task feasible though, one of these types of object is known as a maser, for which we can actually do VLBI astrometry.

Today’s daily image shows a map of three sources on the sky with zoomed in images of each of the sources. All the positions of these sources are known from previously analysed data in L. H. Quiroga-Nuñez et. al A&A 625, A70 (2019). However, the images you see are the first ever images made of masers using new VLBI tasks in the CASA package. The black crosses on each of the images indicate the known positions of all the sources which demonstrates this software can be used to find the positions of masers. In fact, the accuracy of the relative position of the maser calculated from this image agrees with previous measurements to within the measured accuracy ±63μas in Right Ascension and ±25μas in Declination, even though not all corrections have been applied yet.
Copyright: Sophia Vaughan
 
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