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The universe is huge and contains hundreds of billions of galaxies. For galaxies close to us, we determine distances mostly using classical Cepheids and RR Lyr stars. RR
The universe is huge and contains hundreds of billions of galaxies. For galaxies close to us, we determine distances mostly using classical Cepheids and RR Lyr stars. RR Lyr stars are pulsating variables that are 100 times brighter than our Sun and more than twice as old. They can be used as a standard candle to measure distances to galaxies because of the close relationship between the vibratory period and luminosity of the same number of elements.
Based on this information, astronomers from the National Astronomical Observatory of the Chinese Academy of Sciences (NAOC) have proposed the dual-period use of RR Lyr stars to measure distances to galaxies with an optimized distance error of 1-2%.
Their findings were recently published in a journal Nature Astronomy .
About 5% of RR Lyr stars vibrate in more than one period. Dual period RR Lyr stars are unique because the two periods are associated with stellar properties such as mass and element abundance.
Distance and element count measurements for dwarf galaxies and globular clusters. Credit: NAOC
Lead author of the study, Dr. “We found that elemental excess can be represented by two epochs, and thus we establish an elemental excess-independent relationship between epoch and luminosity,” said CHEN Xiaodian.
Compared to element number measurements, period measurements are simple and accurate.
NAOC Senior Scientist and co-author of the study, Dr. “Our work provides a method by which distance measurements to nearby galaxies can be obtained using only photometry, without relying on spectroscopic observations,” said DAN Leekay. “This would increase the sample of galaxies with high precision distance by a factor of 20 or more.”
Two-period RR Lyr stars are valuable probes that not only provide reliable distances but also element abundance information.
In the coming years, the China Space Station Telescope and Vera S. Rubin Observatory will discover tens of thousands of binary RR Lyr stars in nearby galaxies. Using a distance measurement method based on the double periods of RR Lyr stars, we expect to see an intuitive 3D map of the Local Group and obtain a fairly accurate Hubble constant.
Source: Port Altele
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