The Populations of Carina. I. Decoding the Color--Magnitude Diagram

摘要: We investigate the color-magnitude diagram (CMD) of Carina dwarf spheroidal galaxy using data Stetson et al. (2011) and synthetic CMDs based on isochrones Dotter (2008), in terms parameters [Fe/H], age, [alpha/Fe], for cases when (i) [alpha/Fe] is held constant (ii) varied. The are well described by four basic epochs star formation, having [Fe/H] = -1.85, -1.5, -1.2, ~-1.15 ages ~13, 7, ~3.5, ~1.5 Gyr, respectively (for 0.1 (constant [alpha/Fe]) 0.2, 0.1, -0.2, -0.2 (variable [alpha/Fe])), with small spreads age order dex 1 - 3 Gyr. Within an elliptical radius 13.1 arcmin, mass fractions populations, at their times were (in decreasing order) 0.34, 0.39, 0.23, 0.04. This formalism reproduces five observed CMD features (two distinct subgiant branches old intermediate-age two younger, main-sequence components, color dispersion red giant branch (RGB)). youngest population less certain than those others, given it centrally concentrated may not be directly related to them. High-resolution spectroscopically analyzed RGB samples appear statistically incomplete compared selected radial velocity, which contain bluer stars comprising ~5 10% samples. conjecture these objects may, least part, members population. use simulations obtain insight into structure Carina's upper RGB.