a) Broad range of SFHs designed to cover decreasing, increasing, and constant star-formation rates with time (labelled 1, 2, 3), and the SFH from Snaith et al. (2014, 2015), with a dip between 8.5 and 7 Gyr (thick blue curve labelled 4). SFH 5 is similar to 4 with noise removed (thin dark blue curve). b) The corresponding stellar densities as a function of [α/Fe]. SFHs like 1, 2, and 3 do not generate a dip in the [α/Fe] distribution. Only an SFH like 4 (or 5) with a drop and cessation in star formation in the specific time interval between ~10 to 7 Gyr can generate a distribution with a significant dip (blue curve). The short blue vertical lines indicate the time variation in Gyr for model 4 (thick blue curve). The peak at [α/ Fe] ~ 0.28 dex is due to the flattening of the variation of [α/Fe] visible in Fig. 1, which is not at all significant compared to the data used to generate the SFH (Snaith et al. 2014, 2015).