Free Access
Volume 572, December 2014
Article Number A10
Number of page(s) 14
Section Extragalactic astronomy
Published online 18 November 2014

Online material

Appendix A: Solving the SFH using BaSTI isochrones

The SFH solutions presented in Sect. 4 were derived by adopting the Dartmouth isochrone set. To determine the effect of a change in isochrones on the SFH solution, we also derived the SFH of Carina using the Teramo/BaSTI isochrone set (Pietrinferni et al. 2004). The best-fitting SFH results for the Teramo isochrones are shown in Figs. A.1 and A.2 and can be directly compared with Figs. 7 and 8. The star formation rates as a function of age and metallicity derived from the SFH solution using the BaSTI isochrones are given in Tables 2 and 3.

thumbnail Fig. A.1

Full SFH solution as a function of age and metallicity for each of the 3 annuli within the Carina dSph adopting the Teramo isochrone set.

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Figure A.3 shows the model CMD in comparison to the observed CMD for each annulus of Carina. The SFH in Fig. A.2 is roughly consistent with the solution derived using the Dartmouth isochrone. The ages derived using the Teramo isochrone are are systematically shifted toward older ages, which is a well-known effect caused by the difference in adopted colour transformations between the two sets of isochrones. However, in both solutions, two main episodes of star formation are visible, showing a similar extent in age and metallicity. Therefore, our choice of isochrone set does not lead to considerable differences in the interpretation of the episodic SFH of Carina.

thumbnail Fig. A.2

Star formation history (left) and CEH (right) of the 3 different annuli within the Carina dSph adopting the Teramo isochrone set.

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thumbnail Fig. A.3

Observed (top row) and best-fit (middle row) CMD for the different annuli within Carina adopting the Teramo isochrone set. The bottom row shows the difference between the observed and best-fit CMD, expressed as a function of the uncertainty in each CMD bin.

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thumbnail Fig. A.4

Spectroscopic abundances of individual stars in the Carina dSph, with ages derived from the SFH determined using the Teramo isochrone set. The top-left panel shows the age-metallicity relation for individual stars from Ca ii triplet spectroscopy (red) and HR (blue) observations. The abundances of [Mg/Fe] b), [Ca/Fe] c) and [Ba/Fe] d) are also shown, with colours indicating the age of individual stars. Triangles indicate stars without a statistical age estimate. For these stars only a rough age is given, based on the closest distance from evolutionary features in the SFH.

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Using the best-fit SFH results, we also derived the probability distribution for the age of individual stars from spectroscopic observations. Stars with spectroscopic metallicities [Fe/H] ≤ − 2.5 were treated as having [Fe/H] = −2.5 when determining ages, since BaSTI isochrones only extends to this metallicity. The spectroscopic abundances of Ca ii triplet and HR samples are shown in Fig. A.4 derived using the Teramo isochrones. Comparison with Fig. 13 shows that very similar trends as a function of age are recovered, although the ages determined using the Teramo isochrones are consistently older by approximately 1 Gyr as a result of the age difference in the SFH.

© ESO, 2014

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