SPICE -- modelling synthetic spectra of stars with non-homogeneous surfaces

Abstract: In the era of large time-domain spectro-photometric surveys, surface variations such as starspots, chemical inhomogeneities, pulsations, rotational distortions, and binary interactions can now be directly detected and modelled. Accurately interpreting these phenomena requires stellar spectral synthesis frameworks that go beyond the assumption of homogeneous surface properties. Yet most existing tools remain limited by this simplification, hindering their applicability to stars with complex surface structures. To address this need, we present SPICE (SPectral Integration Compiled Engine), an open-source Python package for generating high-resolution spectra and photometry from non-homogeneous stellar surface models. SPICE integrates angle-dependent specific intensities from each surface element, enabling forward modelling of both photometric and spectroscopic variability. Case studies demonstrate applications to spotted stars, Cepheid pulsations, and eclipsing binaries, making SPICE well-suited for analysing current and upcoming survey data. In addition, SPICE can directly import meshes from PHOEBE, enabling the modelling of complex binary configurations beyond these case studies.