Technical Memo: A Cross-Calibration Table for MIST v1.2 and PARSEC v1.2S at Solar Metallicity

1. Purpose and Scope

Observational astronomers often need to compare results derived from different stellar model grids. This memo provides a ready-to-use conversion baseline for solar metallicity, eliminating the need for researchers to re-compute full evolutionary tracks for basic cross-checking.

Scope:

• Grids: MIST v1.2 (Choi et al. 2016) vs. PARSEC v1.2S (Bressan et al. 2012, 2014 Release).
• Metallicity: Solar (Z approx 0.014-0.015).
• Phase: Zero Age Main Sequence (ZAMS), defined as L_nuc/L_tot >= 0.99.

2. Systematic Input Physics Differences

The offset between these grids is driven by well-documented differences in input physics. We summarize them here for reproducibility.

Table 1: Key Input Physics Parameters

3. The Cross-Calibration Baseline

The following table provides the ZAMS Teff values for both grids. The "Residual" column represents the deviation from a simple linear fit, highlighting the non-linear physics of stellar interiors.

Table 2: ZAMS Effective Temperatures and Conversion Residuals

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

3.1. Physical Interpretation of Residuals

The positive residuals for M > 1.0 Msol (peaking at +25 K for 1.5 Msol) are not random errors. They represent the systematic floor caused by the onset of convective cores and the transition to CNO-cycle dominance. This non-linearity is a fundamental feature of stellar structure that a simple linear scaling cannot fully capture.

4. Usage Guide for Observers

1. For Quick Estimates: Use the linear fit Delta_Teff approx 30M + 20 K to translate between grids.
2. For Precision Work: Use the "Residual" column in Table 2 to manually correct your linear estimate. For example, at 1.5 Msol, add an extra 25 K to your linear prediction to match the MIST-PARSEC offset.
3. Age Dating Context: Be aware that a ~95 K systematic shift at the turn-off (2.0 Msol) can introduce a ~10% uncertainty in age derivation if the wrong grid physics are assumed.

5. Conclusion

This memo provides a transparent, physics-informed baseline for cross-referencing MIST and PARSEC. By explicitly tabulating the residuals, we offer a practical tool for observers to manage the systematic uncertainties inherent in model selection.

References

1. Choi, J., et al. 2016, ApJ, 823, 102 (MIST)
2. Bressan, A., et al. 2012, MNRAS, 427, 127 (PARSEC)
3. Asplund, M., et al. 2009, ARA&A, 47, 481