A research team led by Georgia State University astronomers has discovered some of the oldest stars in our solar neighborhood by determining their locations and velocities. A paper reporting the discovery is published in the Astronomical Journal.
Our Milky Way Galaxy is organized into spiral arms of giant stars that illuminate interstellar gas and dust. The Sun is in a finger called the Orion Spur. Overlaid is a graphic of galactic longitude in relation to our Sun. Image credit: NASA / Adler / University of Chicago / Wesleyan / JPL-Caltech.
Dr. Wei-Chun Jao, lead author of the study and a researcher in the Department of Physics and Astronomy at Georgia State University, and colleagues focused on very old stars called cool subdwarfs, which are much older and cooler in temperature than the Sun.
“The Milky Way is nearly 13 billion years old, and its oldest stars developed in the early stage of the Galaxy’s formation, making them about 6 to 9 billion years old,” the astronomers explained.
“They’re found in the halo, a roughly spherical component of the Galaxy that formed first, in which old stars move in orbits that are highly elongated and tilted.”
In this study, the scientists conducted a census of our solar neighborhood to identify how many young, adult and old stars are present.
They observed the stars over many years with the 0.9-m telescope at the U.S. Cerro Tololo Inter-American Observatory in the foothills of the Chilean Andes.
They used a technique called astrometry to measure the stars’ positions and were able to determine the stars’ motions across the sky, their distances and whether or not each star had a hidden companion orbiting it.
The team identified 22 new cool subdwarfs within 330 light-years, of which three are within 82 light-years, and an additional five subdwarfs from 330 to 522 light-years.
“Our work increases the known population of old stars in our solar neighborhood by 25%,” the researchers said.
Among the new subdwarfs, they discovered two old binary stars, even though older stars are typically found to be alone, rather than in pairs.
“We identified two new possible double stars — LSR 1610-0040 AB and LHS 440 AB,” Dr. Jao said.
“It’s rare for ‘senior citizens’ to have companions. Old folks tend to live by themselves. We then used the NASA/ESA Hubble Space Telescope to detect both stars in one of the binaries and measured the separation between them, which will allow us to measure their masses.”
“Finding old stars could also lead to the discovery of new planets,” he added.
“Maybe we can find some ancient civilizations around these old stars.”
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Wei-Chun Jao et al. 2017. The Solar Neighborhood. XLII. Parallax Results from the CTIOPI 0.9 m Program — Identifying New Nearby Subdwarfs Using Tangential Velocities and Locations on the H–R Diagram. AJ 154, 191; doi: 10.3847/1538-3881/aa8b64
