Evolved Stars
At the end of its life our Sun will expand as a red giant star, possibly swallowing the inner planets of the solar system. Such red giants are common in the galaxy, and often have shells of gas containing silicon monoxide around them. Silicon monoxide is one of the molecules that exhibits masing behaviour (the microwave equivalent of a laser), producing very intense, very tiny spots of radio emission at wavelengths of 7 mm and 3.5 mm. These spots can be studied using very long baseline interferometry. Their morphology, location and Doppler shifts can be measured with exquisite precision, giving us a very precise probe of the turbulent environment in the circumstellar region.
Haystack scientists are using VLBI to make images of silicon monoxide shells around evolved stars, an example of which is shown here. By tracing the motions and properties of the masers, a more complete understanding of the processes generating and sustaining the stellar atomosphere is sought. Only VLBI has the angular resolution to discern detail on such small scales, a tiny fraction of the stellar diameter.
SiO maser spots (rainbow colors) observed at 3-millimeter wavelength show a nearly complete circumstellar ring surrounding the pulsating red giant star R Cassiopeia. The central red disk is a computer-generated image to show the size and orientation of the star with respect to the masers. The smaller red spots are masers moving toward Earth, and blue spots are masers moving away from Earth.
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