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Session 61 - Formation and Structure of the Milky Way.
Oral session, Tuesday, January 14
Harbour B,
The compact nonthermal radio source, Sgr A*, is thought to be at the dynamical center of the Galaxy. However, determining the location of Sgr A* on infrared images of the Galactic Center region has been a problem for over two decades. Previous attempts at aligning the radio and infrared reference frames in this region have been limited to accuracies of about 0.3 arcseconds. We present a new approach to this long-standing problem, which improves the alignment by about an order of magnitude.
We present detections of SiO masers from the inner circumstellar envelopes of giant and supergiant stars, that are seen in diffraction-limited infrared images of the Galactic Center region. The radio data allow measurements of the maser positions, relative to Sgr A*, with accuracies approaching milli-arcseconds. Since these masers trace their host stars to within a few milli-arcseconds, these relative positions can be used to calibrate the plate scale and rotation of the infrared images and, thus, to locate accurately the infrared position of Sgr A*. With current data we can align the radio and infrared reference frames in the Galactic Center region and locate the infrared position of Sgr A* to an accuracy of 0.03 arcseconds.
