SCYON Abstract

Received on March 15 2001

The IMF of open star clusters with Tycho-2

AuthorsJörg Sanner, Michael Geffert
AffiliationSternwarte der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
Accepted byAstronomy & Astrophysics
Links Blanco 1 | Stock 2 | Alpha Persei | Pleiades | Praesepe | IC 2391 | IC 2602 | NGC 2451 | NGC 7092 |


We studied the fields of nine nearby open star clusters based on the Tycho-2 catalogue. The clusters are: Blanco 1, Stock 2, the alpha Per cluster, the Pleiades, NGC 2451, IC 2391, Praesepe, IC 2602, and NGC 7092. We determined membership probabilities for the stars in the cluster fields from the stellar proper motions and used the Tycho-2 photometry to compute the initial mass function (IMF) of the clusters from the main sequence turn-off point down to approx. 1 MO. We found IMF slopes ranging from Gamma = -0.69 down to Gamma = -2.27 (when the Salpeter (1955) value would be Gamma = -1.35). We also studied the membership of individual stars of special astrophysical interest. In some cases previous results had to be revised. As a by-product, we investigated some general properties of the Tycho-2 catalogue; we confirmed that the Tycho-2 proper motions show only marginal deviations from the Hipparcos catalogue. On the other hand, in some regions the completeness of the catalogue seems to decrease at magnitudes brighter than claimed by Hög et al. (2000).