[Paper Review] SWEET-Cat update and FASMA. A new minimization procedure for stellar parameters using high-quality spectra

D. T. Andreasen, S. G. Sousa+7 more|arXiv (Cornell University)|Mar 20, 2017

Stellar, planetary, and galactic studiesPhysics and Astronomy80 references18 citations

TL;DR

This paper presents FASMA, a new automated tool for fast and accurate determination of stellar atmospheric parameters (Teff, log g, [Fe/H], ξ) using high-resolution, high-S/N spectra. It improves computational efficiency via a novel minimization procedure and applies it to update the SWEET-Cat catalogue with precise parameters for 50 planet-host stars, significantly enhancing consistency and accuracy for exoplanet characterization.

ABSTRACT

Context: Thanks to the importance that the star-planet relation has to our understanding of the planet formation process, the precise determination of stellar parameters for the ever increasing number of discovered extrasolar planets is of great relevance. Furthermore, precise stellar parameters are needed to fully characterize the planet properties. It is thus important to continue the efforts to determine, in the most uniform way possible, the parameters for stars with planets as new discoveries are announced. Aims: In this paper we present new precise atmospheric parameters for a sample of 50 stars with planets. The results are presented in the catalogue: SWEET-Cat. Methods: Stellar atmospheric parameters and masses for the 50 stars were derived assuming local thermodynamic equilibrium (LTE) and using high-resolution and high signal-to-noise spectra. The methodology used is based on the measurement of equivalent widths with ARES2 for a list of iron lines. The line abundances were derived using MOOG. We then used the curve of growth analysis to determine the parameters. We implemented a new minimization procedure which significantly improves the computational time. Results: The stellar parameters for the 50 stars are presented and compared with previously determined literature values. For SWEET-Cat, we compile values for the effective temperature, surface gravity, metallicity, and stellar mass for almost all the planet host stars listed in the Extrasolar Planets Encyclopedia. This data will be updated on a continuous basis. The data can be used for statistical studies of the star-planet correlation, and for the derivation of consistent properties for known planets.

Motivation & Objective

• To improve the precision and homogeneity of stellar atmospheric parameters for planet-host stars to support accurate exoplanet characterization.
• To address the computational bottleneck in spectral analysis caused by increasing data volumes from high-resolution spectrographs.
• To develop a fast, automated, and accessible tool for deriving stellar parameters using standard spectroscopic methods.
• To update the SWEET-Cat catalogue with consistent, high-precision parameters for 50 planet-host stars using a uniform analysis pipeline.
• To enable robust statistical studies of star-planet correlations by minimizing systematic errors from inconsistent parameter derivation methods.

Proposed method

• Uses high-resolution, high signal-to-noise ratio (S/N) spectra from FEROS, UVES, FIES, and ESPaDOnS as input.
• Applies ARES2 to automatically measure equivalent widths (EWs) of iron lines from the spectrum using a predefined line list.
• Employs MOOG (version 2014) to compute iron line abundances under local thermodynamic equilibrium (LTE) assumptions.
• Implements a new curve-of-growth minimization procedure to derive stellar parameters (Teff, log g, [Fe/H], ξ) efficiently.
• Uses theoretical stellar evolution tracks and the Stefan-Boltzmann law to derive stellar masses and radii from derived parameters.
• Deploys FASMA as a web-based tool, integrating ARES2 and MOOG into a single, user-friendly interface for public access.

Experimental results

Research questions

• RQ1 How can the computational time of stellar parameter derivation be significantly reduced without compromising accuracy?
• RQ2 What impact do systematic differences in parameter derivation methods have on derived stellar and planetary properties?
• RQ3 To what extent does a homogeneous analysis pipeline improve the consistency and reliability of stellar parameters for exoplanet host stars?
• RQ4 How do updated stellar parameters affect the derived masses and radii of exoplanets, particularly for non-transiting systems?
• RQ5 Can a fast, automated, and publicly accessible tool like FASMA achieve precision comparable to manual, expert-driven analyses?

Key findings

• The new minimization procedure in FASMA reduces computational time significantly compared to traditional methods, enabling efficient analysis of large spectroscopic datasets.
• For HD 120084, the updated stellar mass increased from 2.17 M☉ to 2.19 M☉, with a stellar radius decreasing from 12.3 R☉ to 11.1 R☉, though the planetary minimum mass (1.7 MJ) remained unchanged.
• For omi UMa, the updated log g of 3.36 dex led to a revised stellar mass of 1.6 M☉ (down from 3.1 M☉) and radius of 4.5 R☉ (down from 14.1 R☉), reducing the minimum planetary mass from 4.1 MJ to 2.7 MJ.
• The SWEET-Cat catalogue now includes precise parameters (Teff, log g, [Fe/H], mass) for 85% of stars brighter than V = 10, and 77% brighter than V = 12, significantly improving completeness.
• The study demonstrates that inconsistent parameter derivation methods can lead to large discrepancies in stellar and planetary radii, underscoring the need for homogeneous analysis.
• FASMA is publicly available as a web tool (http://www.iastro.pt/fasma) and is effective for FGK-type stars with high S/N spectra, with ongoing development for near-IR applications.