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Fig. 6

image

Carbon abundances A(C) of CEMP stars as a function of [Fe/H]. The stars in the present paper and in Caffau et al. (2013a) are shown with big and small circles, respectively. The other turn-off stars come from the literature (Sivarani et al. 2006; Frebel et al. 2005, 2006; Thompson et al. 2008; Aoki et al. 2008; Behara et al. 2010; Masseron et al. 2010, 2012; Yong et al. 2013; Cohen et al. 2013; Li et al. 2015). The CEMP-no turn-off stars are represented by filled blue squares. The CEMP-no giants are represented by two symbols: an open blue square for the measured value of the C abundance, and a filled blue square for the empirically corrected (for the first dredge-up) A(C) value. The CEMP-s or -rs stars are indistinctly represented by open red squares, but by open red triangles if they are also Pb-rich. When the Ba abundance is unknown the star is marked with a black cross. The upper limit marked as a violet star is the only “C-normal” star that appears in this plot: SDSS J1029+1729 (Caffau et al. 2012). The solid horizontal (black) lines represent the mean value of the carbon abundance for CEMP stars with [Fe/H] > −3.0 (A(C) = 8.25) and for CEMP stars with [Fe/H] < −3.4 (A(C) = 6.8) as derived by Spite et al. (2013). On the upper A(C)-band all the stars but four (HE 0007-1832, HE 022-4831, SDSS J0036-1043, and CS 22958-42) are Ba-rich. On the contrary, on the lower A(C)-band all the stars are CEMP-no.

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