[Paper Review] The Geneva-Copenhagen Survey of the Solar neighbourhood III. Improved distances, ages, and kinematics

Johan Holmberg, B. Nordström+1 more|arXiv (Cornell University)|Nov 24, 2008

Stellar, planetary, and galactic studiesPhysics and Astronomy27 references342 citations

TL;DR

This paper improves the astrophysical parameters of 16,682 F and G dwarfs in the Geneva-Copenhagen Survey by applying updated Hipparcos parallaxes, refining distances, ages, and kinematics. The revised data yield more accurate stellar masses, space motions, orbital parameters, and ages, with consistent age-velocity relations across multiple models, enhancing the reliability of Galactic disk evolution studies.

ABSTRACT

Ages, chemical compositions, velocity vectors, and Galactic orbits for stars in the solar neighbourhood are fundamental test data for models of Galactic evolution. We aim to improve the accuracy of the Geneva-Copenhagen Survey data by implementing the recent revision of the Hipparcos parallaxes. The new parallaxes yield improved astrometric distances for 12,506 stars in the GCS. We also check the GCS II scales of T_eff and [Fe/H] and find no need for change. Introducing the new distances, we recompute M_V for 16,086 stars, and U, V, W, and Galactic orbital parameters for the 13,520 stars that also have radial-velocity measurements. We also recompute stellar ages from the Padova stellar evolution models used in GCS I-II, using the new values of M_V, and compare them with ages from the Yale-Yonsei and Victoria-Regina models. Finally, we compare the observed age-velocity relation in W with three simulated disk heating scenarios to show the potential of the data. With these revisions, the basic data for the GCS stars should now be as reliable as is possible with existing techniques. Further improvement must await consolidation of the T_eff scale from angular diameters and fluxes, and the Gaia trigonometric parallaxes. We discuss the conditions for improving computed stellar ages from new input data, and for distinguishing different disk heating scenarios from data sets of the size and precision of the GCS.

Motivation & Objective

• Improve the accuracy of stellar distances, ages, and kinematics in the Geneva-Copenhagen Survey (GCS) using updated Hipparcos parallaxes.
• Address uncertainties in effective temperature and metallicity calibrations that affect age determinations in FG dwarfs.
• Recompute absolute magnitudes, space velocities (U, V, W), and Galactic orbital parameters using improved distance estimates.
• Assess the robustness of isochrone age determinations by comparing results from Padova, Yale-Yonsei, and Victoria-Regina stellar evolution models.
• Evaluate the potential of the GCS data to distinguish between different disk heating scenarios using the observed age-velocity relation in the W-component.

Proposed method

• Apply the revised Hipparcos parallaxes from van Leeuwen (2007) to compute improved astrometric distances for 12,506 stars in the GCS.
• Use the new parallaxes to verify and recalibrate photometric distances derived from uvbyβ photometry as established in GCS II.
• Exclude evolved cool stars with unreliable results using new selection criteria, particularly for stars with large parallax errors or no Hipparcos coverage.
• Recompute absolute magnitudes (MV) for 16,086 stars using the new distances and updated bolometric corrections.
• Derive U, V, W space velocities and Galactic orbital parameters for 13,520 stars with radial velocity measurements.
• Recompute stellar ages using the Padova stellar evolution models with updated MV values, and compare with results from Yale-Yonsei and Victoria-Regina models.

Experimental results

Research questions

• RQ1 How do updated Hipparcos parallaxes affect the accuracy of distances, absolute magnitudes, and kinematic parameters in the GCS?
• RQ2 To what extent do revised effective temperature and metallicity calibrations alter the derived stellar ages in FG dwarfs?
• RQ3 How consistent are the isochrone ages computed with Padova, Yale-Yonsei, and Victoria-Regina models using the new data?
• RQ4 Can the observed age-velocity relation in the W-component distinguish between different disk heating scenarios (e.g., secular heating, minor mergers, GMC interactions)?
• RQ5 What are the limitations of current data in resolving discrepancies between spectroscopic and photometric T_eff scales, and how can future data (e.g., Gaia) improve this?

Key findings

• The revised Hipparcos parallaxes significantly improve the accuracy of distances for 12,506 stars, reducing systematic errors in derived astrophysical parameters.
• Recomputed absolute magnitudes (MV) and space velocities (U, V, W) show improved consistency with dynamical models and orbital integrations.
• Stellar ages derived from Padova models using updated MV values are consistent with results from Yale-Yonsei and Victoria-Regina models, with no need for recalibration of T_eff or [Fe/H] scales.
• The observed age-velocity relation in the W-component shows a continuing rise in velocity dispersion throughout the disk's lifetime, consistent with radial migration models.
• Three simulated disk heating scenarios (GMCs, early heating with saturation, late minor merger) produce qualitatively distinct age-velocity relations, though statistical confidence limits require larger samples.
• The current data set remains the most reliable available for studying Galactic disk evolution, with further improvements expected only from Gaia parallaxes and improved T_eff calibration via interferometric angular diameters and 3D NLTE models.