Astronomers discovered 32 new variable stars while observing the field of the globular cluster Palomar 2 with the Indian Astronomical Observatory (IAO). The new variables discovered are mostly RR Lyrae stars and cluster members. The discovery is detailed in a paper published on the arXiv pre-print repository on August 16.
Variable stars could provide important insights into stellar structure and evolution. They may also aid in our understanding of the universe’s distance scale. The so-called RR Lyrae (RRL) variables, in particular, are a powerful tool for studying the morphology, metallicity, and age of galaxies, particularly those with low surface brightness. RRLs are pulsating horizontal branch stars of spectral class A or F, with a mass roughly half that of the sun.
A team of astronomers led by Armando Arellano Ferro of Mexico’s National Autonomous University (UNAM) has discovered dozens of new variables. The discovery was made as a result of long-term observations of the Palomar 2 field with the IAO’s 2.0-m telescope. Palomar 2 is a distant globular cluster located 100,000 light years away in the constellation Auriga, and no variables have been discovered in this stellar grouping thus far.
“A CCD VI imaging time-series of 11 years is used to investigate the light curves of stars in the Palomar 2 field…. The data were collected using the 2.0-m telescope at the Indian Astronomical Observatory (IAO), Hanle, India, between December 12, 2010 and February 12, 2021 “The researchers wrote about it in their paper.
Ferro’s team discovered 32 variables in total. They discovered 20 RR Lyrae variables of the RRab type and one of the RRc type thanks to IAO, and they identified 10 more variables and one red-giant branch (RGB) star by analysing data from ESA’s Gaia satellite. Six of the ten variable stars were confirmed to be RRab stars.
Based on Gaia-DR3 (Data Release 3) proper motions and variable placement in the corresponding intrinsic color-magnitude diagram, the astronomers performed a membership analysis of the identified variable stars (CMD). As a result, they discovered that 18 of them belong to the Palomar 2 cluster.
Furthermore, based on the data gathered, the researchers discovered that Palomar 2 is approximately 86,000 light years away from Earth, making it closer than previously estimated. The results also indicate that the metallicity of the cluster is -1.39, which is consistent with previous studies.
According to the paper, the average period of the Palomar 2 member RRab stars is about 0.55 days. This suggests that Palomar 2 belongs to the Oosterhoff type I (Oo I) cluster. Oo I clusters, on average, contain RR Lyrae stars with higher metallicity and shorter pulsation periods.
