UW’s WIYN Open Cluster Study records 100,000th measurement


For 20 years, astronomers from the University of Wisconsin–Madison have gazed up at the broad canvas of stars and galaxies in the night sky above the mountains west of Tucson, Arizona, searching for pairs of stars dancing around one another.

Marking a milestone achievement in their analysis of binary stars, UW–Madison astronomy professor and WIYN Open Cluster Study (WOCS) project lead Bob Mathieu and his team of students recently recorded their 100,000th spectrum measurement with UW’s WIYN Telescope at the Kitt Peak Observatory.

“How such stars evolve is interesting in its own right, but is also essential to know if we want to understand the evolution of planets and the possibilities of life elsewhere in our galaxy,” Mathieu says.

The WIYN Observatory in Arizona is a 3.5 meter instrument owned and operated by the WIYN Consortium, consisting of the National Optical Astronomy Observatories, or NOAO, the University of Wisconsin – Madison, Yale University, and Indiana University.

According to Mathieu, most stars form not as one but instead as a pair, making our own sun an exception. Some of those stars that the WOCS study focuses on have similar masses to our own Sun, but with different ages, providing opportunities to answer questions about the Sun’s life trajectory, says Mathieu.

“The essential finding is that suns and their companions do not evolve independently, and eventually dramatically change their life paths from those of single stars like the Sun,” Mathieu says.

Stars sometimes transfer mass from one star onto another. As one evolves into a red giant it “dumps” all of its outer material onto the other star, leaving behind its core as a white dwarf, and transforming its partner into a star hotter and brighter than our own, called a “blue straggler.”

Closer pairs of stars may marge, wiping out orbiting planets and any life that may exist on them, leaving behind another blue straggler. And in chaotic gravitational dances, sometimes two pairs of stars collide, with similar disruptive effects on nearby planets and life.

The study of the dynamic interactions between the stars that lead to so many alternative pathways of stellar evolution is something we’ve led here at Wisconsin, and that we can be proud of,” Mathieu says, referring to the sharing, merging and colliding pairs of binary stars on which his focuses. “In terms of what questions remain to be answered, we have established that these processes happen. How they happen is the next frontier.”