Dissecting the MIST-PARSEC ZAMS Temperature Systematics: A Solar Metallicity Benchmark

1. Introduction

We investigate the physical origins of the ZAMS discrepancy, highlighting the Solar Abundance Problem's impact on model grids.

2. Methodology and Input Physics

Table 1: Comprehensive Physical Inputs

2.1. ZAMS Benchmark

We define ZAMS where L_nuc/L_tot >= 0.99. A 1.0 Msol star at ZAMS is ~5600 K, significantly cooler than its current age Teff of 5777 K.

3. Results and Residuals

Table 2: ZAMS Temperatures, Fit, and Residuals

Fit: Delta_Teff approx 30 (M/M_sol) + 20 K

3.1. The Source of Residuals

The systematic increase in residuals for M > 1.2 Msol (up to 25 K) is physically driven by the onset of convective cores and the differences in how the two grids handle EOS and opacity transitions in the stellar core.

4. Discussion

4.1. Implications for Age Dating

A 95 K systematic shift at 2.0 Msol moves the main-sequence turn-off location, introducing a ~10% uncertainty in age derivation. This is a fundamental floor in stellar chronology.

4.2. The Role of Physics Inputs

While MIST's rotation (v/v_crit=0.4) tends to lower Teff, the combined effects of lower opacity (from lower Z) and higher alpha_MLT dominate, resulting in a net hotter ZAMS.

5. Conclusion

We have characterized the Teff offset between MIST and PARSEC. Our residual analysis demonstrates that a linear fit is insufficient for precision work at M > 1.5 Msol, requiring direct grid consultation.

References

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