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Characterisation of young nearby stars : the Ursa Major group

This work presents a homogeneous set of stellar parameters for a larger sample of kinematic Ursa Major (UMa) group members with spectral types late-F to early-K. The UMa group is comprised of the stars in the UMa cluster in the Big Dipper constellation and of many co-moving stars spread over the whole sky. The definition of kinematic membership criteria has ever been difficult so that spectroscopic criteria should be added. Previous work indicated that the UMa group members are young with an age of roughly 300 Myrs. The youth leaves traces in the stellar spectrum, i.e. the Li I 6707.8 A absorption line, and activity features, e.g. partial filling-in of the core of the H alpha line due to chromospheric emission. Furthermore rotational line broadening is stronger than that of older stars. Additional to the youth indicators, iron abundance is an appropriate membership criterion in case it is different from that of other groups of stars. Spectroscopic properties of the UMa group already have been specified but resulting membership criteria are rather inconclusive. For this thesis, a sample of kinematic members was drawn from Montes et al. (2001a) and King et al.


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