Parallaxes and proper motions for 20 open clusters as based on the new Hipparcos catalogue

By F. V. Leeuwen. 2009

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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 level, our ability to determine reliable parallaxes and proper motions for open clusters should be improved. Aims. The new Hipparcos astrometric catalogue is used to derive mean parallax and proper motion estimates for 20 open clusters. The HR-diagrams of the nearest clusters are compared and combined to provide future input to sets of observational isochrones. Methods. Three different methods are applied, according to the proximity of the cluster, to compensate, where needed, for projection effects, spread in position along the line of sight, and the internal velocity dispersion of the cluster stars. Results. The new parallaxes have accuracies between 2 and 2.5 times higher than what had been derived from the original Hipparcos catalogue. At least two to three groups of clusters, mostly of similar ages, are observed to each occupy their own specific space in the HR diagram. A significant discrepancy in distance moduli from those obtained with isochrone-based main-sequence fitting remains, in particular for one of these groups, containing the Pleiades, NGC 2516, and Blanco 1. The difference in absolute magnitudes between this group and one containing the Hyades and Praesepe clusters appears to be correlated with systematic differences in the Stromgren Δc0 index between those groups. The same dependency has been known to exist for a long time, and is again confirmed by the Hipparcos data, in variations in absolute magnitudes for field stars of the same effective temperature. Conclusions. The positions of the cluster HR diagrams are consistent within different groups of clusters shown for example by the near-perfect alignment of the sequences for the Hyades and Praesepe, for Coma Ber and UMa, and for the Pleiades, NGC 2516, and Blanco 1. The groups are mutually consistent when systematic differences in Δc0 are taken into account, where the effect of these differences on the absolute magnitudes has been calibrated using field-star observations.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/5118354b1e11a749b6d3dc6889e5967e63ed98e2

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Citations in the corpus

ECLIPSING BINARY STARS AS BENCHMARKS FOR TRIGONOMETRIC PARALLAXES IN THE GAIA ERA (2016, background): “…problems, perhaps the most significant of which was the aberrant distance to the Pleiades which the Hipparcos parallax placed at 120.2±1.9 pc (van Leeuwen 2009) as compared to the broadly accepted distance of »135 pc from a variety of methods (e.g., Munari et al. 2004; Zwahlen et al. 2004;…”
Kinematics in Young Star Clusters and Associations with Gaia DR2 (2018, methodology): “Observed proper motions of stars in stellar systems can be affected by perspective and the motion of the center of the system (van Leeuwen 2009).”
Improved angular momentum evolution model for solar-like stars (2013, background): “Hyades The Hyades (Melotte 25) is a 628 ± 14 Myr old cluster (Delorme et al. 2011) located at a distance of 46.45 ± 0.5 pc (van Leeuwen 2009).”
New constraints on the chemical evolution of the solar neighbourhood and galactic disc(s) - improved astrophysical parameters for the Geneva-Copenhagen Survey (2011, methodology): “(which are less affected by activity stemming from the young age of this open cluster) from Crawford & Perry (1976) and adoptingE(B − V) = 0.04 (e.g., van Leeuwen 2009), we derive [Fe/H] = 0.00 ± 0.02 dex (σ = 0.10).”
Hubble Space Telescope Trigonometric Parallax of Polaris B, Companion of the Nearest Cepheid (2017, methodology): “However, van Leeuwen (2009), based on Hipparcos astrometry of over 50 Pleiads, found a mean cluster parallax of 8.32±0.13mas, larger by 0.97mas than the VLBI result.”
Microarcsecond Radio Astrometry (2013, background): “The Pleiades Distance Project seeks absolute parallaxes for up to 10 cluster stars in order to resolve the current cluster distance controversy and provide a solid foundation for many aspects of stellar astrophysics.”
Improving PARSEC models for very low mass stars (2014, background): “The models are initially shown in the theoretical H-R and massluminosity plots (top panels), for an age of log(age/yr) = 8.90 (van Leeuwen 2009) and a metallicity of Z = 0.02 [Carrera & Pancino (2011) presents [Fe/H] = 0.16, which corresponds to Z = 0.0244 with their adopted solar abundance].”
BANYAN. XI. The BANYAN Σ Multivariate Bayesian Algorithm to Identify Members of Young Associations with 150 pc (2018, background): “Its members are located at a distance of ≈ 150 pc (van Leeuwen 2009) and the cluster has a lithium depletion boundary age of 46+6−5 Myr (Dobbie et al. 2010).”