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D. Galán-Diéguez

Publications and source records attributed to D. Galán-Diéguez.

2 recordsLinked to original sources

SPAMMS: 3D spectroscopic modeling of stellar surfaces. II. Implementation of Kurucz and TLUSTY model atmospheres

Context. Accurate stellar spectra are essential to derive stellar properties. Traditional model atmospheres often oversimplify phenomena that break spherical symmetry, such as rotational deformation or multiplicity. The Spectroscopic PAtch Model for Massive Stars (SPAMMS) accounts for these effects, but its applicability has been limited by the spectral types covered by its model atmosphere grids. Aims. We aim to extend the parameter space of the model atmosphere grids available to SPAMMS, enabling spectral synthesis across a broader range of stellar types. Methods. We computed specific intensities, $I\left(λ,μ\right)$, for $101$ emergent angles using PRISMAS (Pipeline of Radiative Intensity Synthesis for Meshed Atmospheric Surfaces), and pre-computed LTE and non-LTE atmospheres from two ATLAS9-Kurucz grids and the TLUSTY-based OSTAR2002 and BSTAR2006 models. Results. The intensity grids cover effective temperatures from $3500$ to $55000\,\mathrm{K}$ and surface gravities from $0.0$ to $5.0\,\mathrm{dex}$, spanning O- to K-type stars. They include metallicities from $0$ to $30\,\mathrm{Z_\odot}$ and microturbulent velocities of $1$, $3$, $5$, and $10\,\mathrm{km\,s^{-1}}$. The spectral range extends from $3000$ to $9000\,\mathring{\mathrm{A}}$ with $Δλ=0.01\,\mathring{\mathrm{A}}$. As a proof of concept, we modelled with SPAMMS a rapidly rotating B-type star and an eclipsing Algol-type binary. Conclusions. The new LTE-Kurucz and NLTE-TLUSTY grids substantially expand the parameter space accessible to SPAMMS. The code can now generate synthetic spectra for a broader range of stellar types and geometries, including rapidly rotating and multiple systems -- providing a more comprehensive framework for modelling non-spherical stellar surfaces.

astro-ph.SR↗

The lack of fast rotators in Cyg OB2. I. Insights from spectral reclassification of its B0 population

Context. Cygnus OB2, in the Cygnus X complex -- one of the most active star-forming regions of the Galaxy -- hosts hundreds of O- and B-type stars at different evolutionary stages. This association provides a unique laboratory to study massive star evolution and dynamics. However, despite extensive studies, the absence of a fast-rotating group ($v\sin{i}>200\,\mathrm{km\,s^{-1}}$) among the O-type population of Cygnus OB2 challenges current models of massive star evolution. Aims. Stellar rotation strongly impacts spectral line shapes of O-type stars, and high rotation can potentially lead to misclassifications. We investigate whether some stars in Cygnus OB2, classified at low spectral resolution as B0, are actually rapidly rotating late-O types. Such cases could explain the observed lack of fast rotators in Cygnus OB2. Methods. Accounting for rotation, we reclassified the known B0 population in Cygnus OB2, using the MGB tool and both the new and pre-existing optical spectroscopy. Finally, we computed the projected rotational velocities using iacob-broad. Results. About $19\,\%$ of the initial B0 population in Cygnus OB2 are, in fact, late-O types. Only six stars in the entire dataset show $v\sin{i}>200\,\mathrm{km\,s^{-1}}$, with just one new O-type star exceeding this threshold. Conclusions. In our study of Cygnus OB2, we continue to find a notable lack of fast rotators among its O-type population. We propose a combination of three factors as the most likely explanation: (i) the young age of Cygnus OB2 may imply that fast rotators have not been produced yet due to binary interactions; (ii) fast rotators may have been dynamically ejected from the core as runaway stars; and (iii) local star formation conditions may hinder binary formation (reducing spin-up interactions) or result in slower rotational velocities at birth.

astro-ph.SR↗