Explain the discrepancy in helium-layer masses relative to Zenati et al. (2019)

Determine the physical causes of the discrepancy between the helium-envelope masses predicted by the MESA-constructed carbon–oxygen white dwarf models in this study and those reported by Zenati, Toonen, and Perets (2019), particularly for low-mass white dwarfs (e.g., the 0.5 solar-mass model where the present work finds about 50% less helium). Identify which differences in input physics, modeling assumptions, or evolutionary treatments account for the divergent helium-layer masses.

Background

The authors construct carbon–oxygen white dwarf models with realistic composition profiles using MESA and quantify the total helium mass and the mass above the He/C transition layer as a function of white dwarf mass. They compare their results to those of Zenati et al. (2019) and find broad agreement for higher masses within the overlapping range but significant differences at the low-mass end.

Specifically, for a 0.5 solar-mass white dwarf, this paper obtains roughly half the helium mass reported by Zenati et al. (2019). The authors explicitly note that the origin of this discrepancy is not understood, highlighting the need to identify the modeling or physical differences responsible for the divergent outcomes.