Correcting MIST-PARSEC ZAMS Offsets: Abundance Scales and Boundary Conditions

1. Introduction

Stellar model grids are built on different physical assumptions, creating a systematic floor for stellar dating. This paper focuses on the MIST and PARSEC grids.

2. Physical Drivers and Abundance Scales

Table 1: Native Physical Parameters

The discrepancy in $T_{eff}$ arises from the choice of solar metallicity, mixing length, and atmospheric boundary conditions (Eddington vs. Krishna Swamy).

3. Results: The Systematic Floor

3.1. The Corrected Linear Formula

Table 2: ZAMS Effective Temperatures and Offsets

We derive an empirical fit with a maximum residual of 11 K: $\Delta T_{eff} \approx 41 (M/M_{\odot}) + 19$ K

Note: This fit is a first-order approximation for the 0.8–2.0 $M_{\odot}$ range.

4. Discussion

4.1. Implications for Stellar Dating

Applying our $\Delta T_{eff}$ of 100 K to solar-metallicity turn-off stars results in an age shift of approximately 1.2 Gyr for a 10 Gyr old population. This $\sim 10$ uncertainty is a dominant systematic floor in Galactic archaeology.

4.2. Comparison to Observations

Our derived correction aligns MIST and PARSEC predictions with the high-precision $T_{eff}$ scales observed in benchmark stars, bridging the gap between theoretical grids and precision asteroseismology.

5. Conclusion

By accounting for abundance-driven offsets, we provide a practical tool to reduce systematic errors.

References

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