Both stars were considered unusual because they were thought to have had a lower luminosity than is normal for main sequence stars of their age and surface temperature. That is, they lie below the main sequence curve on the Hertzsprung-Russell diagram for newly formed stars. However, this was challenged, after using the much more accurate parallaxes from the Hipparcos catalogue (ESA, 1997), it was calculated that the stars actually have higher luminosities and so are shifted upwards, crossing them into the main sequence. Most stars will evolve above this curve as they age. ζ1 has an intermediate level of magnetic activity in its chromosphere with an erratic variability. ζ2 is more sedate, showing a much lower level of activity with a 10-year cycle. Although the kinematics of this system suggest that they belong to a population of older stars, the properties of their stellar chromospheres suggests that they are only about 2 billion years old.