RR Lyrae Variables Population in M31 and its Satellites

Nahathai Tanakul and Ata Sarajedini

We briefly present results of RR Lyrae observations in M31 and its satellite galaxies using archival imaging from the Hubble Space Telescope. Published data for M31, M33, and several M31 dwarf spheroidal galaxies are also used to study the global properties of RR Lyrae stars in these systems.
From the properties of RR Lyrae stars, we find that the majority of M31 and M33 RRLs are of Oosterhoff I type, while those in M31 dSphs are of Oosterhoff intermediate type. The main parameter affecting these Oosterhoff types is likely to be metallicity. Metallicity also plays a role in the lack of RRLs among the High Amplitude Short Period (HASP, defined as those with P≲0.48 d and A_V≥0.75 mag) variables in M31 dSphs. This difference in the properties of RRLs between the parent galaxy and its satellites, as well as the lack of RRLs in the HASP region in dSphs, is also present in the Milky Way. Therefore, systems like these dSphs are unlikely to be the main building blocks of the M31 and Milky Way halo.

Proceedings of the Polish Astronomical Society, vol. 6, 93-98 (2018)

Download full article as PDF file: