ISOSCELES project: A grid-based quantitative spectroscopic analysis of massive stars

TL;DR

The ISOSCELES project introduces a grid-based framework for more accurate spectroscopic analysis of massive stars by using hydrodynamic wind solutions instead of traditional approximations, improving parameter determination.

Contribution

It develops and validates a comprehensive grid of stellar atmosphere models based on hydrodynamic wind solutions, offering an improved alternative to the $eta$-law approximation for massive star analysis.

Findings

Successfully reproduces observed spectral profiles of six stars.

Demonstrates effectiveness of $ ext{delta}$-slow solutions for B supergiants.

Highlights differences between $eta$-law and hydrodynamic wind models.

Abstract

Massive stars play a fundamental role in galactic evolution through their strong stellar winds, chemical enrichment, and feedback mechanisms. Accurate modelling of their atmospheres and winds is critical for understanding their physical properties and evolutionary pathways. Traditional spectroscopic analyses often rely on the $\beta$-law approximation for wind-velocity profiles, which may not capture the complexity of observed phenomena. This study aims to introduce and validate the grId of Stellar atmOSphere and hydrodynamiC modELs for massivE Stars (ISOSCELES), a grid-based framework for the quantitative spectroscopic analysis of massive stars. The project leverages hydrodynamic wind solutions derived from the m-CAK theory, including both fast and $\delta$-slow solutions, to improve the accuracy of derived stellar and wind parameters. We constructed a comprehensive grid of models based on hydrodynamic wind solutions from the Hydwind code and synthetic spectral line profiles generated by the Fastwind code. The grid spans a broad parameter space covering OBA-type stars with solar metallicity. A semi-automatic fitting procedure was developed to analyse key spectral lines and derive the stellar and wind parameters. Applying ISOSCELES to six stars demonstrates its ability to reproduce observed spectral profiles with high fidelity. The $\delta$-slow solution proved effective for two early-type B supergiants. The grid also highlights the difference of using the $\beta$-law in modelling stellar winds compared with the m-CAK wind solutions. The ISOSCELES database represents a step forward in quantitatively analysing massive stars, offering an alternative to the $\beta$-law approximation. Future work will address the inclusion of UV lines and metallicity effects to further refine its applicability across diverse stellar populations.