[Paper Review] Metallicities for 13 nearby open clusters from high-resolution spectroscopy of dwarf and giant stars. Stellar metallicity, stellar mass, and giant planets

N. C. Santos, C. Lovis+3 more|ArXiv.org|Nov 14, 2008

Stellar, planetary, and galactic studies39 references53 citations

TL;DR

This study presents high-resolution spectroscopic analysis of iron abundances in 39 giant and 16 dwarf stars across 13 nearby open clusters, finding metallicities predominantly near solar. It demonstrates that metallicity measurements for giants are highly sensitive to the choice of spectral line list, necessitating careful line selection to align giant star metallicities with those of dwarfs, with implications for disentangling metallicity and stellar mass effects on giant planet formation.

ABSTRACT

We present a study of accurate stellar parameters and iron abundances for 39 giants and 16 dwarfs in the 13 open clusters IC2714, IC4651, IC4756, NGC2360, NGC2423, NGC2447 (M93), NGC2539, NGC2682 (M67), NGC3114, NGC3680, NGC4349, NGC5822, NGC6633. The analysis was done using a set of high-resolution and high-S/N spectra obtained with the UVES spectrograph (VLT). These clusters are currently being searched for planets using precise radial velocities. For all the clusters, the derived average metallicities are close to solar. Interestingly, the values derived seem to depend on the line-list used. This dependence and its implications for the study of chemical abundances in giants stars are discussed. We show that a careful choice of the lines may be crucial for the derivation of metallicities for giant stars on the same metallicity scale as those derived for dwarfs. Finally, we discuss the implications of the derived abundances for the metallicity- and mass-giant planet correlation. We conclude that a good knowledge of the two parameters is necessary to correctly disentangle their influence on the formation of giant planets.

Motivation & Objective

• Address the uncertainty in stellar metallicity measurements for giant stars, particularly in the context of planet formation studies.
• Quantify the impact of different spectral line lists on derived metallicities for giant stars compared to dwarfs.
• Assess the role of stellar mass and metallicity in the formation of giant planets by analyzing metallicity and mass in open clusters hosting planets.
• Provide accurate stellar parameters and iron abundances for 55 stars in 13 open clusters to support ongoing radial velocity planet searches.
• Clarify whether the metallicity-giant planet correlation observed in field dwarfs also applies to evolved giant stars.

Proposed method

• Acquired high-resolution, high signal-to-noise ratio spectra using the UVES spectrograph at the VLT's 8.2-m Kueyen telescope.
• Performed detailed spectroscopic analysis using multiple line lists to derive stellar parameters (Teff, log g, [Fe/H]) for both dwarf and giant stars.
• Calibrated metallicity measurements across different line lists to assess systematic biases in giant star abundance determinations.
• Compared derived metallicities of giant stars with those of dwarfs in the same clusters to evaluate consistency across spectral types.
• Used high-precision radial velocity monitoring data from ongoing surveys to contextualize metallicity results in planet-hosting environments.
• Applied standard model atmospheres and radiative transfer techniques to derive iron abundances from observed line profiles.

Experimental results

Research questions

• RQ1 How does the choice of spectral line list affect the derived metallicity of giant stars compared to dwarfs?
• RQ2 Are the metallicities of giant stars in open clusters systematically offset when derived with different line lists, and can this be corrected?
• RQ3 Does the metallicity-giant planet correlation observed in field dwarfs also hold for giant stars in open clusters?
• RQ4 How do stellar mass and metallicity jointly influence the frequency of giant planets in evolved stars?
• RQ5 Can accurate stellar mass estimates for giant stars help reconcile discrepancies in planet formation theories across different stellar types?

Key findings

• All 13 open clusters studied have average metallicities close to solar, with [Fe/H] values ranging from approximately -0.12 to +0.14 dex.
• Metallicity measurements for giant stars are significantly dependent on the spectral line list used, introducing systematic offsets of up to 0.1 dex.
• Careful selection of spectral lines is essential to ensure that metallicities derived for giant stars are on the same scale as those for dwarfs.
• NGC2423, one of the most metal-rich clusters in the sample ([Fe/H] ≈ +0.14 ± 0.06), hosts a giant planet, consistent with the metallicity-planet correlation.
• NGC4349, one of the most metal-poor clusters ([Fe/H] ≈ -0.12 ± 0.06), hosts a giant star with a high mass (3.9 ± 0.3 M⊙), suggesting mass may compensate for low metallicity in planet formation.
• Stellar mass and metallicity appear to jointly influence giant planet frequency, indicating that both parameters must be accurately known to disentangle their individual effects.