A&A 402, 247-252 (2003)
DOI: 10.1051/0004-6361:20030266

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

H. Pöhnl¹, H. M. Maitzen¹ and E. Paunzen<sup>1, 2

1</sup>  Institut für Astronomie der Universität Wien, Türkenschanzstr. 17, 1180 Wien, Austria
²  Zentraler Informatikdienst der Universität Wien, Universitätsstr. 7, 1010 Wien, Austria

(Received 19 November 2002 / Accepted 28 January 2003 )

Abstract
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 from 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 2451 A 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 system 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 clusters and further strengthen the membership of the investigated CP2 stars.

Key words: stars: chemically peculiar -- stars: early-type -- open clusters and associations: general

Offprint request: H. M. Maitzen, maitzen@astro.univie.ac.at

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