On the evolutionary status of chemically peculiar stars of the upper main sequence

Authors:
H. Poehnl,
H.M. Maitzen,
E. Paunzen (Institut fuer Astronomie der Universitaet Wien, Austria)

Comments: 7 pages, 1 figure, accepted by A&A

We present further evidence that the magnetic chemically peculiar stars (CP2)
of the upper main sequence already occur at very early stages of the stellar
evolution, significantly before they reach 30% of their life-time on the main
sequence. This result is especially important for models dealing with dynamo
theories, angular momentum loss during the pre- as well as main sequence and
evolutionary calculations for CP2 stars. Results form the literature either
derived for objects in the Hyades and the UMa cluster or from the Hipparcos
mission contradict each other. A way out of this dilemma is to investigate
young open clusters with known ages and accurate distances (error < 10%),
including CP2 members. Up to now, four open clusters fulfill these
requirements: IC 2391, IC 2602, NGC 2451A and NGC 2516. In total, 13 CP2 stars
can be found within these clusters. We have used the measurements and
calibrations of the Geneva 7-color photometric systems to derive effective
temperatures and luminosities. Taking into account the overall metallicity of
the individual clusters, isochrones and evolutionary tracks were used to
estimate ages and masses for the individual objects. The derived ages (between
10 and 140 Myr) are well in line with those of the corresponding cluster and
further strengthens the membership of the investigated CP2 stars.

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