Classical Cepheids and RR Lyrae (RR Lyr) are standard candles to measure galactic distances. Typically, fundamental-mode RR Lyr stars are used for distance measurements, and their accuracy is strongly limited by the dependence of absolute magnitudes on metallicity in both the optical and infrared bands.
With the distance inaccuracy of galaxies optimized to 1-2%, scientists from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) proposed using double-period RR Lyr stars to measure the distances of galaxies.
Five percent of RR Lyr stars pulse with more than one period. Double-period RR Lyr stars are unique because the two periods are connected to distinct stellar characteristics like mass and elemental abundance.
Scientists found that the two periods represent elemental abundance. Hence a period-luminosity relation independent of the elemental abundance was established. The period’s measurements were easier and more accurate than elemental abundance measurements.
This study offers a method through which scientists can obtain galactic distance from photometry alone.
Dr. DENG Licai, a senior researcher at NAOC and co-author of the study, said, “This will increase the sample of galaxies with high-precision distance by 20 or more.”
Journal Reference:
- Chen, X., Zhang, J., Wang, S. et al. The use of double-mode RR Lyrae stars as robust distance and metallicity indicators. Nature Astronomy (2023). DOI: 10.1038/s41550-023-02011-y