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tokens: star discovered by Caffau et al. (2011a ). The other symbols are literature data. The black and yellow dashed lines delimit the low-carbon band. Details can be found in Bonifacio et al. (2018) . 6.3 <italic>α</italic> and neutron-capture elements Figure 6 shows the abundance ratios of [Mg/Fe] and [Ca/Fe] as a function of [Fe/H] for our sample of stars using the solar abundances from Lodders et al. (2009) . Literature data from Roederer et al. (2014) are also shown, which contain results from a rather large sample of evolved and main sequence stars. We were able to measure magnesium in the five stars. Among them, SDSS J081554.26+472947.5 seems to have a rather low [Mg/Fe] abundance ratio and a subsolar [Ca/Fe] upper limit abundance. This is due to our high upper limit of [Fe/H]. In fact, by adopting the very low [Fe/H] determined by González Hernández et al. (2020) , we obtain [Mg/Fe] = 1.62 dex in excellent agreement with the [Mg/Fe] = 1.66 dex abundance that these latter authors obtained. The stellar parameters we adopted for SDSS J081554.26+472947.5 are close to those used by González Hernández et al. (2020) with a difference of 15 K on the temperature, a difference of 0.6 dex in log g that has no strong effect (typically 0.1 to 0.15 dex on the neutral Ca and Mg) on the determination of the abundance of neutral species, and the same micro-turbulent velocity. We found three stars with subsolar values for calcium, confirming the existence of stars with low [ α /Fe] ratios as already suggested by Bonifacio et al. (2018) . However, we reiterate the fact that in very metal-poor stars, under the LTE hypothesis, the resonance line that we used to determine the abundance of calcium leads to an underestimation of the calciumabundance ( Spite et al. 2012 , and references therein). For turnoff stars, the amplitude of the effect is rather small. Spite et al. (2012) computed a correction of the order of +0.1 dex in a turnoff star with [Fe/H] = −3.2 dex. Figure 7 shows the [Mg/Ca] ratio as a function [Fe/H] (upper panel) and as a function of [Mg/H] (lower panel). We have added the literature data from Roederer et al. (2014) for comparison. The [Mg/Ca] ratio found in our sample of stars ranges from +0.2 to +0.5 dex. This ratio is slightly higher than the abundance ratio found in the [Fe/H] range of –2 to –3 dex. At lower metallicities, the results from Roederer et al. (2014) show that the spread in the [Mg/Ca] ratio increases as [Fe/H] decreases with values ranging from negative abundance ratios to highly enhanced [Mg/Ca] ratios. From our measurements, the [Mg/Ca] ratio seems to increase as [Fe/H] decreases. The result for SDSS J081554.26+472947.5 found by González Hernández et al. (2020) seems to corroborate this point. The increase of the [Mg/Ca] ratio is also visible when the ratio is plotted as a function of [Mg/H]. However, a high value of [Mg/Ca] at very low [Mg/H] is not found in all the stars. In particular, SDSS J102915+17292, the normal