Main sequences of open clusters with Hipparcos
نویسندگان
چکیده
Hipparcos observations of open clusters provide mean cluster parallax determinations with an unprecedented accuracy. Possible biases in the Hipparcos parallaxes exhibited by other authors has been analysed and proven not to exist. A comparison of observed (V; B ? V) diagrams of the Pleiades and Praesepe with theoretical isochrones has been performed. It does not exhibit disagreement with Hipparcos mean parallaxes when considering the uncertainties on the theoretical tracks and cluster chemical compositions.
منابع مشابه
The Problem of Hipparcos Distances to Open Clusters: I. Constraints from Multicolor Main Sequence Fitting
Parallax data from the Hipparcos mission allow the direct distance to open clusters to be compared with the distance inferred from main sequence (MS) fitting. There are surprising differences between the two distance measurements, which indicate either the need for changes in the cluster compositions or reddening, underlying problems with the technique of main sequence fitting, or systematic er...
متن کاملAnalysis of 7 Nearby Open Clusters Using Hipparcos Data
¿From Hipparcos data in 7 open cluster fields (Praesepe, IC 4756, NGC 2516, NGC 3532, NGC 6475, NGC 6633 and Stock 2) we have computed the membership of stars. The mean cluster distances have been derived from intermediate Hipparcos data. Cluster sequences in the HR diagram have been deduced from their distances, the photometry coming from the ‘Base des Amas’ (Mermilliod 1988). Comparison betwe...
متن کاملCorrelated Errors in Hipparcos Parallaxes towards the Pleiades and the Hyades
We show that the errors in the Hipparcos parallaxes towards the Pleiades and the Hyades open clusters are spatially correlated over angular scales of 2 to 3 degrees, with an amplitude of up to 2 mas. We suggest that this correlation on small angular scales is a generic feature of the Hipparcos parallaxes all over the sky. We predict the parallaxes of individual cluster members, πpm, from their ...
متن کاملParallaxes and proper motions for 20 open clusters as based on the new Hipparcos catalogue
Context. A new reduction of the astrometric data as produced by the Hipparcos mission has been published, claiming that the accuracies for nearly all stars brighter than magnitude Hp = 8 are improved, by up to a factor 4, compared to the original catalogue. As correlations between the underlying abscissa residuals have also been reduced by more than an order of magnitude to an insignificant lev...
متن کاملOB Associations , Open Clusters , and the Luminosity Calibration of the Nearer Stars
In the context of the luminosity calibration of the nearer stars I discuss the Hipparcos results on distances to nearby OB associations and open clusters. The shortcomings and assumptions in the analyses used to derive these results are pointed out and for the open clusters a comparison is made with results obtained from main sequence fitting. I conclude that given the considerable uncertaintie...
متن کامل