Florida Tech scientists earn NSF grant to study age of stars

November 19, 2008

Florida Tech Scientists Earn NSF Grant to Measure the Age of Stars MELBOURNE, FLA.--Terry Oswalt, Ph.D., head of the Florida Tech Department of Physics and Space Sciences, has won a National Science Foundation grant of more than $380,000 for a unique approach to learning stars' ages.

"How old is it? Is just about the most difficult question you can ask about a star," said Oswalt. He and his team will determine ages by studying the chromospheres, or outer atmospheres, of stars like the Sun. Chromospheric activity, like sunspots and the solar cycle, is known to correlate with age but the exact relation has not been explored beyond the age of the Sun.

"Stars, like people, become less active as they age. We're looking at stars like our Sun across a wide range of ages to see exactly how the faint features in their spectra, which are markers for activity, weaken with age," said Oswalt.

Oswalt is taking a new approach to calibrating and extending this age determination technique. He has selected a sample of stars like the Sun that happen to have "dead" companion stars known as white dwarfs. White dwarfs are the cooling embers of stars that have run out of fuel and are slowly cooling over time.

"Much as the coroner at a crime scene gauges the time of death by taking the victim's temperature, we get the so-called 'cooling age' of a white dwarf by taking its temperature," said Oswalt. This provides an independent check on the companion star's age, because stars in a pair were born at the same time. Using white dwarfs, which tend to be very old, Oswalt may be able to extend the activity-age relation for solar-type stars right up to the age of our galaxy, the Milky Way, about 10 billion years.

The research will take several years because to view markers for activity and to get the temperature of a white dwarf, each star's light must spread out into a spectrum. Very large telescopes are needed to gather enough light to do this -an hour or two for each star is required. Access time on the largest telescopes in the world is highly competitive. This means the typical astronomer is fortunate to win several nights in a given year.

A possible by-product of this research is a check on the ages of our Sun and the galaxy that have been obtained by other techniques. The research may also help to determine how much mass a white dwarf loses as it passes through the red giant stage. This is one of the most uncertain parts of stellar evolution theory.

The recycled material that stars put back into the galaxy as they die provides the heavy elements that form future planets. Oswalt's work, therefore, may help determine what stars are old enough to have planets and, perhaps, shed some light on how much time it takes for life to have evolved on them.
More than a dozen undergraduates to date have participated in Oswalt's project. Graduate students Merissa Rudkin and Kyle Johnston have undertaken dissertation projects directly related to it. Post-doc Silvia Catalan, who is expected to join the project in 2009, will focus on deriving independent age determinations by using stellar evolution models.

The Florida Tech Department of Physics and Space Sciences is home to the largest research telescope in Florida as well as one of the largest astronomy-related undergraduate programs in the United States. In fall 2008 it enrolled almost 200 students in physics and space sciences. About half are women or minorities.

Florida Institute of Technology

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