Star formation histories in NGC 147 and NGC 185

Frontiers in Theoretical and Applied Physics/UAE 2017

Golshan, R. Hamedani^1,2 ; Javadi, A.^1 ; Van Loon, J.Th.^3

School of Astronomy, Institute for Research in Fundamental Sciences (IPM), Tehran

19395-5531, Iran^1

Department of Physics, Isfahan University of Technology, Isfahan

84156-83111, Iran^2

Lennard-Jones Laboratories, Keele University, Staffordshire

ST5 5BG, United Kingdom^3

关键词: Asymptotic giant branch;    Interstellar gas;    Long period variables;    Mass functions;    Near-infrared photometry;    Star formation rates;    Star formations;    Stellar evolutions;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/869/1/012087/pdf
DOI  :  10.1088/1742-6596/869/1/012087

来源: IOP

【 摘 要 】

NGC 147 and NGC 185 are two of the most massive satellites of the Andromeda galaxy (M 31). With similar mass and morphological type dE, they possess different amounts of interstellar gas and tidal distortion. The question therefore is, how do their histories compare? We present the first reconstruction of the star formation histories of NGC 147 and NGC 185 using long-period variable stars (LPVs). LPVs are low- to intermediate-mass stars at the asymptotic giant branch, which their luminosity is related to their birth mass. Combining near-infrared photometry with stellar evolution models, we construct the mass function and hence the star formation history. For NGC 185 we found that the main epoch of star formation occurred 8.3 Gyr ago, followed by a much lower, but relatively constant star formation rate. In the case of NGC 147, the star formation rate peaked only 7 Gyr ago, staying intense until ∼ 3 Gyr ago, but no star formation has occurred for at least 300 Myr. Despite their similar masses, NGC 147 has evolved more slowly than NGC 185 initially, but more dramatically in more recent times.