[Paper Review] Abundance analysis of targets for the COROT / MONS asteroseismology missions II. Abundance analysis of the COROT main targets

H. Bruntt, I. Bikmaev+14 more|arXiv (Cornell University)|Mar 18, 2004

Stellar, planetary, and galactic studies54 citations

TL;DR

This study presents a detailed abundance analysis of nine bright F and G-type stars selected as primary targets for the COROT asteroseismology mission, using high-resolution spectroscopy and three independent analysis methods. The key contribution is the precise determination of stellar atmospheric parameters (Teff, log g, [Fe/H]) to within 70–100 K, 0.1–0.2 dex, and 0.1 dex for slow rotators, with consistent results across methods and strong agreement with external data, enabling improved modeling of target stars for space-based asteroseismology.

ABSTRACT

One of the goals of the ground-based support program for the COROT and Roemer satellite missions is to characterize suitable target stars for the part of the missions dedicated to asteroseismology. We present the detailed abundance analysis of nine of the potential COROT main targets using the semi-automatic software VWA. For two additional COROT targets we could not perform the analysis due to the high rotational velocity of these stars. For five stars with low rotational velocity we have also performed abundance analysis by a classical equivalent width method in order to test the reliability of the VWA software. The agreement between the different methods is good. We find that it is necessary to measure abundances extracted from each line relative to the abundances found from a spectrum of the Sun in order to remove systematic errors. We have constrained the global atmospheric parameters Teff, log g, and [Fe/H] to within 70-100 K, 0.1-0.2 dex, and 0.1 dex for five stars which are slow rotators (v sin i < 15 km/s). For most of the stars stars we find good agreement with the parameters found from line depth ratios, H-alpha lines, Strömgren indices, previous spectroscopic studies, and also log g determined from the HIPPARCOS parallaxes. For the fast rotators v sin i > 60 km/s it is not possible to constrain the atmospheric parameters.

Motivation & Objective

• To improve the characterization of candidate target stars for the COROT and MONS asteroseismology missions by determining accurate atmospheric parameters and elemental abundances.
• To assess the reliability of the semi-automatic VWA software for abundance analysis by comparing it with classical equivalent width methods.
• To constrain stellar parameters (Teff, log g, [Fe/H]) using abundance consistency across multiple spectral lines and external data sources.
• To identify and correct systematic errors in abundance determinations, particularly for elements with complex hyperfine structure like Mn.
• To evaluate the impact of stellar rotation on parameter determination, especially for fast rotators where spectral lines are blended.

Proposed method

• High-resolution spectroscopy was obtained using the ELODIE spectrograph on the 1.93 m telescope at Observatoire de Haute-Provence, covering 3800–6800 Å at R = 45,000.
• Three independent abundance analysis methods were employed: the semi-automatic VWA software, classical equivalent width analysis, and synthetic spectrum fitting.
• Atmospheric parameters were derived by minimizing abundance trends with excitation potential and reducing line-to-line scatter, using a grid of 1D LTE model atmospheres.
• Abundances were referenced to solar values from Grevesse & Sauval (1998), with systematic errors removed by comparing to solar spectra.
• Parameter constraints were validated using Strömgren photometry, Hα lines, line depth ratios, and Hipparcos parallaxes.
• Systematic errors were investigated by comparing results from different methods and identifying issues such as incomplete hyperfine structure data in VALD for Mn.

Experimental results

Research questions

• RQ1 How accurately can the VWA software determine elemental abundances in F and G-type stars compared to classical equivalent width methods?
• RQ2 To what extent do derived atmospheric parameters (Teff, log g, [Fe/H]) agree across different observational techniques such as photometry, line depth ratios, and Hipparcos parallaxes?
• RQ3 What is the impact of stellar rotation on the reliability of abundance and parameter determination, particularly for fast rotators (vsini > 60 km s⁻¹)?
• RQ4 How do systematic errors—such as incomplete hyperfine structure data in VALD—affect abundance determinations, especially for Mn?
• RQ5 Can the consistency of abundance patterns across multiple elements rule out the presence of chemically peculiar stars among the COROT targets?

Key findings

• For five slow rotators (vsini < 15 km s⁻¹), the atmospheric parameters were constrained to T_eff within 70–100 K, log g within 0.1–0.2 dex, and [Fe/H] within 0.1 dex.
• The three abundance analysis methods (VWA, equivalent width, and synthetic fitting) showed excellent agreement, validating the reliability of the VWA software for these targets.
• No evidence was found for chemically peculiar stars, as abundance patterns showed no significant anomalies across elements.
• For Mn, a systematic underestimation was observed due to incomplete hyperfine structure data in the VALD database, indicating a need for improved atomic data.
• For fast rotators (vsini > 60 km s⁻¹), such as HD 46304 and HD 174866, abundance analysis was not feasible due to line blending, and parameter constraints were unreliable (T_eff uncertain by ±200 K, log g by ±0.5 dex).
• The metallicity [Fe/H] was determined to 0.10 dex accuracy for slow rotators and 0.20 dex for fast rotators, including uncertainties from model assumptions and solar abundance zero points.