Study recovers lost carbon stars

All of the “lost” Smith carbon stars have been found by a Central Michigan University faculty member, a student and a collaborator from the Space Telescope Institute. In 1956, H. and E. Smith, a husband and wife team of astronomers, published a list of 186 carbon stars they discovered while observing in South Africa. However, when astronomers created a master list of carbon stars in the 1970s, these objects were omitted. The Smiths had not published accurate positions but only a rough map of the stars’ positions in the sky, and they could not be located. These objects became known informally as the “lost carbon stars.”

During the summer of 2004, Wayne Osborn, a faculty member in CMU’s physics department, CMU undergraduate Jason Smolinski and D. J. MacConnell, a Space Telescope Institute expert on carbon stars, spent a week at the astronomical plate archive at Harvard College Observatory reviewing the Smiths’ original photographs and verifying information. The Smiths had marked the stars on the photos, and Osborn’s team carefully measured their positions.

“We were able to identify all the carbon stars plotted by the Smiths on their map with known stars, and 180 turned out to be true carbon stars.” said Osborn. “Five stars turned out to be other very red stars but not true carbon stars, while one star plotted on the map had no corresponding star marked on either of the two photographs of this field. But our review of the photographs also revealed nine additional carbon stars that the Smiths had found, but which they had not plotted on their map.”

Carbon stars have long been of interest to astronomers because of their large intrinsic brightness and extreme red color. More recently, they have received attention because they have been shown to be in the last stages of evolution.

Osborn and his colleagues believe their study significantly improved the listings of known carbon stars in the galaxy. A paper on their work is being published in Baltic Astronomy, the standard publication for work on carbon stars. The project was supported by a $2,170 American Astronomical Society small research grant.

From Central Michigan University

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