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arXiv · 2608.04211

Custom Colors: A Module for Computing Synthetic Photometry On-the-Fly in Stellar Evolution Calculations, Integrated with MESA and Usable with Other Stellar Evolution Codes

Niall Miller·Meridith Joyce·Philip Mocz
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Abstract

Stellar evolution simulations predict physical quantities such as luminosity, whereas broadband photometric observations measure flux in specific bandpasses; converting the predicted stellar state to magnitudes requires interpolating a stellar atmosphere model at the surface parameters, convolving the resulting spectral energy distribution (SED) with filter transmission curves, and applying a photometric zero-point correction. We introduce Custom Colors, which performs this conversion from the stellar model. It is integrated into MESA as MESA Custom Colors, and available as the Python package SED_Model for external applications. At each timestep, the module interpolates a user-specified atmosphere grid at the current T_eff, log g, [M/H], applies geometric dilution at a user-specified distance, convolves the SED with each requested filter transmission curve, and appends observer-frame magnitudes to standard MESA output files. We demonstrate the module across six diverse use cases: TP-AGB evolution, nonlinear RR Lyrae pulsation, starspot-modified photospheres, white dwarf cooling, blue-loop evolution, and rotational spot modulation based on an external YREC SPOTS grid. These cases draw on Kurucz/ATLAS9, BT-Settl, and Koester DA atmosphere grids and filter systems including Roman WFI, LSST ugrizy, Gaia, and extended Johnson UBVRIJHKLMN. Two of these demonstrations compare the module directly with observational data: a 0.6M_dot DA white dwarf cooling track follows the broad Gaia DR3 cooling locus from M_G ~ 8.5 to 15mag without intermediate color transformation, and an RSP model recovers the Kepler light curve of FN Lyr (KIC6936115) to 1.1% in period and 0.2% in amplitude.

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Niall Miller, Meridith Joyce, Philip Mocz. 2026-08-04. Custom Colors: A Module for Computing Synthetic Photometry On-the-Fly in Stellar Evolution Calculations, Integrated with MESA and Usable with Other Stellar Evolution Codes. https://arxiv.org/abs/2608.04211

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