Mira variable stars in the galactic bulge and halo

Abstract

This work aimed to study Miras in the bulge and halo of our galaxy, including those in globular clusters. The AAVSO International Variable Star Index VSX catalogue was used to retrieve Mira variable stars, while the information about globular clusters were taken from the Harris \citep{Harris1976}, McMaster catalogue \citep{33} and Holger Baumgardt \citep{34} table. Stellar characteristics such as metallicity, $T_{\rm eff}$, parallax and colors were obtained by Gaia EDR3 catalogue, Gaia DR3 VariSumarry, Gaia DR3 catalogue, 2MASS Point Source Catalogue, AllWISE, and ZTF catalogue. The UPSILoN program, color-color or color-magnitude diagrams were used to verify that our stars are indeed Miras-type variable stars and whether they are O or C type Miras. To deal with extinction, which affects stars mainly in the galactic bulge, we used IRSA DUST archive, OGLE-III and recalculation to the extiction-free Wesenheit magnitude. We obtained data for 1608 Miras in the bulge, of which 308 are located in 15 globular clusters. For the stars in the halo, we obtained data for 1954 Miras, of which 4 are located in 3 globular clusters. Miras in the bulge show a bimodal metallicity distribution with peaks at \text{--}0.4 dex and $+$0.5 dex, while Miras in the halo show only one peak at $+$0.5 dex. The period of Miras in the bulge is, on average, 30 days longer than for Miras in the halo, and O-type Miras are more abundant in the bulge than C-type Miras. The dependence of the logarithm of the base 10 period on magnitude in the infrared part of the spectrum gives us a linear dependence, with the dependence inverting when a filter is used in the optical part of the spectrum, because of the dust around the Miras.