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D. A. Boboltz (USNO), M. J. Claussen (NRAO)
We have produced the first images of the vibrational ground-state, v=0, J=1-0, SiO masers from four evolved stars. Both the ground-state and the first excited-state (v=1, J=1-0) transitions of 28SiO were observed toward a total of eight stars using the Very Large Array (VLA) in the A-configuration. All of the stars were previously known SiO excited-state maser sources, and seven of the stars had been recently shown to exhibit ground-state maser emission (Boboltz & Claussen, 2004, ApJ, 608, 480). Here we present the first high-resolution images of the ground-state masers toward the four stars (IRC+10011, o Cet, VY CMa, and NML Cyg) detected in our latest VLA observations. We compare these images with images of the v=1 masers recorded simultaneously to show that the ground-state masers occupy a region outside the typical SiO maser zone. We also show that there are remakable differences between the spatial distributions of the v=0 masers exhibited by the two Mira-type variables (IRC+10011 and o Cet) and those of the two supergiants (VY CMa and NML Cyg). For the two supergiants, it appears that the ground-state masers may be tracing outflows in the circumstellar envelopes of these stars.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.