Synthetic Observed-Band Light Curves of Delta Cephei from MESA-RSP Models

Abstract

Observed-band light curves provide a stronger test of Cepheid pulsation models than period matching alone, because the measured photometric amplitude depends on the phase-dependent luminosity, temperature, radius, and passband transformation. We construct synthetic observed-band light curves for delta Cephei from nonlinear radial pulsation models computed with MESA-RSP and transform the model outputs L(phi), Teff(phi), and R(phi) into bolometric magnitudes and MIST bolometric-correction magnitudes in Bessell and Gaia passbands. The adopted AAVSO Johnson V-band template has peak-to-peak amplitude Delta V_obs = 0.8390 mag. The period-stable reference model with RSP alfam = 0.60 gives a MIST-BC V-band amplitude of only Delta V_syn approximately 0.0106 mag. Amplitude-enhanced models increase the synthetic amplitude, with RSP alfam = 0.425 giving 0.0302 mag, RSP alfam = 0.400 giving 0.0344 mag, and the accepted RSP alfam = 0.400, RSP alfat = 0.095 model giving 0.0367 mag. The final accepted model therefore reaches only 4.4 percent of the observed Johnson V-band amplitude. These results show that MIST-BC transformations are necessary for a physically meaningful observed-band comparison, but they do not remove the amplitude discrepancy in the present model sequence. The remaining mismatch indicates that the dominant limitation is the small nonlinear pulsation amplitude of the models rather than the bolometric-correction transformation itself.