[Paper Review] The Geneva-Copenhagen survey of the Solar neighbourhood: Ages, metallicities, and kinematic properties of 14,000 F and G dwarfs

B. Nordström, M. Mayor+7 more|ArXiv.org|May 11, 2004

Stellar, planetary, and galactic studiesPhysics and Astronomy74 references927 citations

TL;DR

This study presents a comprehensive analysis of ~14,000 F and G dwarf stars in the Solar neighbourhood using high-precision radial velocities, photometry, parallaxes, and proper motions to derive accurate ages, metallicities, kinematics, and Galactic orbits. It reveals significant observational and theoretical biases distorting age distributions and confirms the 'G-dwarf problem,' radial metallicity gradients, and ongoing kinematic heating of the thin disk, challenging simple closed-box models of Galactic chemical evolution.

ABSTRACT

We present and discuss new determinations of metallicity, rotation, age, kinematics, and Galactic orbits for a complete, magnitude-limited, and kinematically unbiased sample of 16,682 nearby F and G dwarf stars. Our 63,000 new, accurate radial-velocity observations for nearly 13,500 stars allow identification of most of the binary stars in the sample and, together with published data complete the kinematic information for 14,139 stars. A major effort has been devoted to the determination of new isochrone ages for all stars for which this is possible. Particular attention has been given to a realistic treatment of statistical biases and error estimates, as standard techniques tend to underestimate these effects and introduce spurious features in the age distributions. We demonstrate, however, how strong observational and theoretical biases cause the distribution of the observed ages to be very different from that of the true age distribution of the sample. Our first results confirm the lack of metal-poor G dwarfs relative to closed-box model predictions (the ``G dwarf problem''), the existence of radial metallicity gradients in the disk, the small change in mean metallicity of the thin disk since its formation and the substantial scatter in metallicity at all ages, and the continuing kinematic heating of the thin disk with an efficiency consistent with that expected for a combination of spiral arms and giant molecular clouds. Distinct features in the distribution of the V component of the space motion are extended in age and metallicity, corresponding to the effects of stochastic spiral waves rather than classical moving groups, and may complicate the identification of thick-disk stars from kinematic criteria. (abridged)

Motivation & Objective

• To determine accurate ages, metallicities, and kinematic properties for a complete, magnitude-limited sample of 14,000 F and G dwarf stars in the Solar neighbourhood.
• To correct for observational and theoretical biases that distort age distributions and introduce spurious features in stellar population analyses.
• To investigate the age-metallicity, age-velocity, and metallicity-velocity relations in the Galactic disk using a large, high-precision dataset.
• To re-evaluate the 'G-dwarf problem' using a rigorously selected and well-characterized sample of stars.
• To provide a benchmark dataset for future studies, including upcoming missions like GAIA, by simulating selection effects and observational errors.

Proposed method

• Combined new radial-velocity measurements from the CORAVEL and other instruments with existing Hipparcos parallaxes, Tycho-2 proper motions, and $uvby\beta$ photometry for 14,139 stars.
• Applied revised calibrations to derive effective temperatures and metallicities from $uvby\beta$ photometry, improving accuracy over previous estimates.
• Used isochrone fitting with updated evolutionary models to determine stellar ages, with careful treatment of statistical biases and error propagation.
• Implemented a rigorous statistical framework to account for selection effects, observational errors, and biases in age distribution estimation.
• Analyzed kinematic properties using space motions (U, V, W) and Galactic orbital parameters to study dynamical evolution and heating of the disk.
• Revisited key Galactic disk relations—age-metallicity, age-velocity, and metallicity-velocity—using the full sample and corrected for systematic effects.

Experimental results

Research questions

• RQ1 How do observational and theoretical biases affect the inferred age distribution of F and G dwarfs in the Solar neighbourhood?
• RQ2 To what extent does the observed metallicity distribution of G dwarfs deviate from predictions of the closed-box model, and what does this imply for Galactic chemical evolution?
• RQ3 What is the nature and origin of the observed kinematic structure in the V-component of space motion, particularly its extension in age and metallicity?
• RQ4 How do the age-velocity and metallicity-velocity relations constrain models of dynamical heating in the Galactic disk?
• RQ5 Can the distribution of stars in age-metallicity space be reconciled with simple models of disk evolution, or do they require more complex, time-dependent enrichment histories?

Key findings

• The observed age distribution is strongly distorted by selection and measurement biases, with standard techniques underestimating scatter and introducing spurious features.
• The age-metallicity relation shows substantial scatter at all ages, indicating that chemical enrichment in the thin disk is not uniform and cannot be described by a simple closed-box model.
• The metallicity distribution of G dwarfs shows a deficit of metal-poor stars relative to closed-box model predictions, confirming the 'G-dwarf problem'.
• A radial metallicity gradient is confirmed in the Galactic disk, with metallicity decreasing with increasing Galactocentric radius.
• The mean metallicity of the thin disk has changed only slightly since its formation, suggesting a long-term, stable chemical evolution process.
• Kinematic heating of the thin disk continues over time, with a rate consistent with contributions from spiral arms and giant molecular clouds, and distinct features in the V-velocity distribution are linked to stochastic spiral waves rather than classical moving groups.