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Unique to the survey is its age-dating technique, which is based on a star's size. Ness and colleagues used high-quality Sloan survey spectra, which reveals a star's chemistry, with optical data collected by NASA's Kepler space telescope to develop a model that can be used to pinpoint a star's age.
"This is somewhat revolutionary because ages have previously been considered very hard to get, particularly from stellar spectra. They're important, but they're difficult," Ness said.
The key was a newly discovered relationship between a star's age and its ratio of carbon-to-nitrogen, concentrations of which can be ferreted out by analyzing a star's spectra.
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Older red giant stars have the highest carbon-to-nitrogen ratios and younger stars the lowest, Ness said.
Working with a sample of 2,000 stars, scientists studied how the ratios change based on a star's mass. They then incorporated the results into a computer model and used it to calculate masses and ages of all 70,000 red giant stars observed in Sloan's APOGEE (Apache Point Observatory Galaxy Evolution Experiment) survey.