Speaker
Description
Traditional stellar astrophysics has long relied on the assumption of spherical symmetry, an approximation that breaks down for several stellar objects, e.g. rapid rotators and close binaries. In particular, for rapidly rotating stars, strong centrifugal forces induce substantial geometric deformation, producing an oblate stellar shape together with non-uniform surface gravities and temperatures. As a consequence, rotating stars exhibit pronounced latitudinal temperature gradients, characterized by hotter polar regions and cooler, bulged equatorial zones.
To bridge the gap between these physical effects and observational data, we present SPAMMS (Spectroscopic Patch Model for Massive Stars), a framework for 3D surface-based spectral synthesis. Unlike standard 1D convolution approaches, SPAMMS discretizes the distorted stellar surface into thousands of surface elements, modelling the distorted surface in 3D. For each element, the code computes local physical parameters ($T_{\rm eff}$ and $\log{g}$) and retrieves specific intensities from state-of-the-art atmospheric libraries -- including FASTWIND, TLUSTY, and ATLAS9 -- spanning a wide temperature range. The emergent stellar spectrum is then obtained through a rigorous numerical integration of these local intensities, each accounting for its projected radial velocity and line-of-sight projection effects. In this way, SPAMMS reproduces the observable spectra of rapidly rotating stars in a physically self-consistent manner.
The full potential of SPAMMS emerges when its spectroscopic modelling capabilities are combined with long-baseline interferometric observations. While spectroscopy probes the integrated flux distribution and surface velocity fields, interferometry provides the spatial resolution needed to directly constrain stellar oblateness and surface structure. The combination of these complementary observational techniques enables self-consistent determinations of key stellar parameters, including inclination, rotation rate, and surface temperature gradients. In the era of high-resolution spectroscopic and interferometric facilities, accounting for the intrinsically 3D nature of rapidly rotating stars using SPAMMS and interfometry data is no longer optional, but essential for understanding the structure and evolution of the most extreme stellar populations.
