To measure the ω(O − C) 2 values, given in Table 4, we have re-analyzed the **data** of Feast (1954) and Andersen (1975). This showed that the **data** of Andersen (1975) and those of our paper have similar quality while those of Feast (1954) have clearly lower quality, as already emphasised by Andersen (1975). For this reason, we omitted Feast's **data** in the remaining of this paper. We combined the newly obtained radial-velocity values ( Table 2) with those previously obtained by Anderson (1975). This gave a total of 62 radial-velocity values for each of the components to which we assigned equal weights. As can be seen in Table 4, we find an offset in average velocity V 0 between the two radial-velocity sets. This could be due to the difference in used spectral lines in the two studies, but it may also be that we find a downward trend in V 0 over time due to the presence of a third body. We have too few epochs to model any V 0 trend for the time being. For this reason, we shifted the **data** towards the CORALIE    Table 2 and the sine curve corresponds to the elements given in Table 4. The center-of-mass velocity is indicated by the dashed-dotted line.