The light curve model fitting of LMC Cepheids: MESA-RSP versus Stellingwerf's code predictions

TL;DR

This study tackles the challenge of convection treatment in Cepheid pulsations by calibrating the TC parameters of the 1D MESA-RSP code against observations and Stellingwerf models. Using 18 LMC Cepheids with multi-band photometry and Stellingwerf-derived stellar inputs, the authors tune α and α_m (and occasionally α_p, α_t, γ_r) across four fiducial TC sets to reproduce light-curve morphology and amplitudes, then validate against the Stellingwerf predictions for PL, PR, and PMR relations. A key finding is the emergence of distinct mass-luminosity relations for fundamental-mode and first-overtone Cepheids, suggesting ML is sensitive to mass and/or Teff range; no single TC parameter set reproduces all light curves, and correlations between TC parameters and global stellar properties are weak though subtle trends with period and Teff exist. The work confirms good agreement with Ragosta et al. 2019 for PL/PR/PMR relations and distances, highlights degeneracies among TC parameters, and underscores the potential value of incorporating radial-velocity data to break these degeneracies and advance accuracy in Cepheid distance scales.

Abstract

A major challenge in modeling classical Cepheids is the treatment of convection, particularly its complex interplay with pulsation. This inherently three-dimensional process is typically approximated in one-dimensional hydrocodes using dimensionless turbulent convection (TC) free parameters. Calibrating these parameters is essential for reproducing key observational features such as light-curve amplitudes, secondary bumps, and the red edge of the instability strip. In this work, we calibrate TC parameters adopted in the publicly available MESA-RSP code through comparison with both observational data of classical Cepheids and stellar parameter constraints from the Stellingwerf code. We compute multi-band (V, I, and Ks) MESA-RSP light curves for 18 observed Large Magellanic Cloud Cepheids, using stellar parameters determined from the Stellingwerf code. By fine-tuning the mixing-length and eddy viscosity parameters, we calibrate the TC treatment in MESA-RSP. We then compare the resulting period-luminosity (PL), period-radius (PR), and period-mass-radius (PMR) relations with predictions from the Stellingwerf models. We successfully reproduce multi-band light curves and obtain PL, PR, and PMR relations consistent with Ragosta et al. (2019). While in broad agreement with previous work, we explicitly identify distinct mass-luminosity (ML) relations for fundamental-mode and first-overtone Cepheids for the first time. This suggests that the macroscopic processes affecting the ML relation depend on stellar mass and/or effective temperature range. Although our study focuses on the calibration of TC parameters, we do not find a single set of parameter values that reproduces all light curves. No statistically significant correlation is found between stellar properties and convection parameters, although subtle trends with period and effective temperature may be present.

Figures (11)

• Figure 1: Location of the Cepheids selected in this work on the HRD. The IS edges are taken from deka24.
• Figure 2: The observed light curve (data points) for OGLE-LMC-CEP-1124 star is shown along with the best-fitting model predictions overlaid on all the computed models for this star. The $\chi^2$ values of the models range from 1.3 (best-fit model) to 49.4 (worst-fit model).
• Figure 3: Observed light curves (data points) are shown for the selected Cepheids with the best-fitting model predictions overplotted as continuous lines.
• Figure 4: Observed light curves (data points) are shown for five selected Cepheids with the best-fitting model predictions from mesa-rsp and Stellinwerf code over-plotted as continuous lines.
• Figure 5: This plot presents a comparison between the reddened distance moduli (in the $V, I$, and $K_{s}$ bands) and stellar radii derived in this work with those reported by R19. Each panel shows the respective comparison, including error bars on the distance moduli, showing the consistency and deviations across photometric bands and radius estimates.