Stars over 12 billion years old found in globular cluster

(ORDO NEWS) — Astronomers at the Indian Astronomical Observatory (IAO) have discovered 32 new variable stars while observing the Palomar 2 globular cluster in the constellation Auriga.

The variables mainly refer to RR Lyrae stars, a class of pulsating stars of spectral class A or F, which are old low-mass giants over 12 billion years old with the same luminosity. The discovery is reported in a preprint published on the arXiv website.

21 variables were found using the IAO 2m telescope during the observation period from December 12, 2010 to February 12, 2021. Another 11 variables were found in the analysis of data obtained by the ESA Gaia spacecraft.

RR Lyrae stars, as a rule, they are located in globular clusters. Palomar 2 is a globular cluster about 100,000 light-years distant, but so far no variable has been observed in this group of stars.

The astronomers performed an membership analysis of the identified variable stars based on the proper motions of Gaia-DR3 and the location of the variables on the corresponding color-magnitude diagram (CMD).

As a result, it was revealed that 18 of them are members of the Palomar-2 cluster. In addition, scientists were able to refine the distance to the globular cluster, which turned out to be 86,000 light-years, which is closer than previously thought.

The average period of the Palomar 2 variables is about 0.55 days. This indicates that Palomar 2 should be classified as an Oosterhoff Type I (Oo I) cluster. Such clusters contain RR Lyrae stars with higher metallicity and shorter pulsation periods on average.

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