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

¹ Centro Multidisciplinario de Física, Vicerrectoría de Investigación, Universidad Mayor, 8580745 Santiago, Chile
² Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111, Valparaíso, Chile
³ Departamento de Espectroscopía, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque S/N, BF1900FWA La Plata, Buenos Aires, Argentina
⁴ Instituto de Astrofísica de La Plata, CCT La Plata, CONICET-UNLP, Paseo del Bosque S/N, BF1900FWA La Plata, Buenos Aires, Argentina

^★ Corresponding author: ignacio.araya@umayor.cl

Received: 14 May 2025
Accepted: 3 October 2025

Abstract

Context. 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 β-law approximation for wind-velocity profiles, which may not capture the complexity of observed phenomena.

Aims. 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 δ-slow solutions, to improve the accuracy of derived stellar and wind parameters.

Methods. 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.

Results. Applying ISOSCELES to six stars demonstrates its ability to reproduce observed spectral profiles with high fidelity. The δ-slow solution proved effective for two early-type B supergiants. The grid also highlights the difference of using the β-law in modelling stellar winds compared with the m-CAK wind solutions.

Conclusions. The ISOSCELES database represents a step forward in quantitatively analysing massive stars, offering an alternative to the β-law approximation. Future work will address the inclusion of UV lines and metallicity effects to further refine its applicability across diverse stellar populations.