[Paper Review] A spectroscopic study of southern (candidate) gamma Doradus stars. II. Detailed abundance analysis and fundamental parameters

H. Bruntt, P. De Cat+1 more|ArXiv.org|Nov 24, 2007

Stellar, planetary, and galactic studies50 references67 citations

TL;DR

This study presents a detailed spectroscopic analysis of 18 southern (candidate) γ Doradus stars, determining their fundamental atmospheric parameters and chemical abundances using synthetic spectrum fitting with the VWA software. It finds no significant difference in abundance patterns between γ Dor stars and normal A/F-type stars, with metallicities near solar, and confirms the method's reliability for slow rotators but limited applicability for high-velocity stars.

ABSTRACT

The gamma Doradus stars are a recent class of variable main sequence F-type stars located on the red edge of the Cepheid instability strip. They pulsate in gravity modes, and this makes them particularly interesting for detailed asteroseismic analysis, which can provide fundamental knowledge of properties near the convective cores of intermediate-mass main sequence stars. To improve current understanding of gamma Dor stars through theoretical modelling, additional constraints are needed. Our aim is to estimate the fundamental atmospheric parameters and determine the chemical composition of these stars. Detailed analyses of single stars have previously suggested links to Am and lambda Bootis stars, so we wish to explore this interesting connection between chemical peculiarity and pulsation. We have analysed a sample of gamma Dor stars for the first time, including nine bona fide and three candidate members of the class. We determined the fundamental atmospheric parameters and compared the abundance pattern with other A-type stars. We used the semi-automatic software package VWA for the analysis. This code relies on the calculation of synthetic spectra and thus takes line-blending into account. This is important because of the fast rotation in some of the sample stars, and we made a thorough analysis of how VWA performs when increasing vsini. We obtained good results in agreement with previously derived fundamental parameters and abundances in a few selected reference stars with properties similar to the gamma Dor stars. We find that the abundance pattern in the gamma Dor stars is not distinct from the constant A- and F-type stars we analysed.

Motivation & Objective

• To determine accurate fundamental atmospheric parameters (T_eff, log g, [Fe/H]) for a sample of southern γ Doradus stars and candidates.
• To perform a detailed abundance analysis of these stars to investigate links between pulsation and chemical peculiarity, particularly with Am and λ Boo stars.
• To test the performance of the VWA software package for synthetic spectrum analysis under varying rotational velocities (v sin i).
• To provide improved constraints on stellar parameters for future asteroseismic modeling of γ Doradus stars.
• To compare results with previous studies and assess consistency in metallicity and abundance patterns.

Proposed method

• Employed the semi-automatic VWA software package for spectroscopic analysis, which relies on synthetic spectrum synthesis to account for line blending.
• Used photometric indices (Strömgren b-y, m1, c1), 2MASS, and HIPPARCOS parallaxes to derive initial estimates of T_eff and log g.
• Constrained atmospheric parameters by fitting observed spectra to synthetic spectra across multiple spectral lines, including corrections for line blending.
• Systematically tested VWA performance at increasing v sin i values, finding reliable results only for v sin i < 25 km s⁻¹.
• Validated the method using reference stars (Sun, HD 110379) with well-known parameters to calibrate the analysis pipeline.
• Compared results with prior studies on HD 48501, HD 110379, and HD 167858 to assess consistency and reliability.

Experimental results

Research questions

• RQ1 Do γ Doradus stars exhibit distinct chemical abundance patterns compared to normal A- and F-type stars?
• RQ2 How reliable are the derived atmospheric parameters (T_eff, log g, [Fe/H]) for γ Doradus stars with high rotational velocities?
• RQ3 To what extent does the VWA software package maintain accuracy in abundance and parameter determination for stars with v sin i > 50 km s⁻¹?
• RQ4 Is there evidence of chemical peculiarity (e.g., Am or λ Boo characteristics) in the sample of γ Doradus stars?
• RQ5 How do the derived metallicities compare with previous estimates, and what implications does this have for asteroseismic modeling?

Key findings

• The abundance pattern in γ Doradus stars is not distinct from that of normal A- and F-type stars, with no significant overabundance or underabundance of key elements.
• Metallicities for the γ Doradus stars are close to solar, ranging from [Fe/H] = -0.36 to +0.57, with most values within ±0.2 dex of solar.
• For stars with v sin i < 25 km s⁻¹, the method achieves uncertainties of ~120 K in T_eff, 0.13 dex in log g, and 0.09 dex in [Fe/H], improving on photometric estimates.
• The VWA software performs reliably for slow rotators but cannot simultaneously constrain T_eff, log g, and microturbulence for stars with v sin i > 50 km s⁻¹.
• The analysis of HD 12901 yields [Fe/H] = -0.13 ± 0.16, which is recommended for future asteroseismic modeling, correcting earlier estimates based on Strömgren indices.
• No strong chemical peculiarity was found in HD 125081 or HD 167858, despite prior catalog listings, supporting their classification as normal A/F-type stars.