Distance measurement based on RR Lyrae variable stars
This paper summarizes the applications of RR Lyrae variable stars for distance measurements in the last 20 years.RR Lyrae stars are low-mass,metal-poor stars located in the overlap region of the pulsation instability strip and the horizontal branch.Due to the presence of radial pulsations,there are periodic brightness variations in RR Lyrae stars.RR Lyrae stars can be easily identified because of their sawtooth-shaped light curves.Based on the shape of the light curve,RR Lyrae stars can be mainly classified into fundamental mode(RRab),first-overtone mode(RRc)and double-mode(RRd)sub-types.With the development of large-scale time-domain telescopes,the current sample of RR Lyrae stars based on 1-meter-class telescopes is almost complete,with a number of about 300000 stars.RR Lyrae stars are good standard candles due to the tight relationship between luminosity and period and metallicity.The distance measurements based on RR Lyrae stars have also been optimized,gradually shifting from relying on visible metallicity-luminosity relations to infrared period-metallicity-luminosity relations.The zero points of the period-metallicity-luminosity relations for the RR Lyrae stars have been significantly optimized thanks to the improvement of the geometric distance of the Large Magellanic Cloud and the Gaia parallax.RRab stars and RRc stars were used to measure distances with an accuracy of about 5％for a single object and up to 2％for multiple objects.RRab stars have been the best distance tracer of old population for the last decades.On the basis of a large sample of RRab stars,the structure of the Galactic halo,bulge,and the Magellanic Clouds is refined,and the distances to globular clusters and dwarf galaxies are more accurately measured.In 2023,based on LAMOST and SDSS low resolution spectra,RRd stars were found to have period-luminosity relations that do not depend on metallicities.It is the only valuable object in standard candles that is independent of metallicities,and can break the bottleneck of the lack of metallicity in photometry-based distance measurements.RRd stars open the way to bulk measurements of high-precision distances to galaxies.Based on multiple RRd stars,the distance accuracy can be up to 1％which is better than distance accuracy based on RRab stars or tip of red giant branch stars.At the same time,RRd stars can also provide the metallicity of the objects to help optimize the accuracy of RRab star-based distances.With the future Chinese Space Station Telescope and other instruments,the number of RRd stars will increase to tens of thousands.RRd stars will be used to determine high-precision distances to hundreds of galaxies or dwarf galaxies with an error of about 1％,increasing that sample by a factor of 20,and will then be able to optimize the Hubble constant from multiple distance ladders.
万方数据
维普
