Consistency of the proposed azimuthal C/O variation in HD 100546

Determine whether the proposed azimuthal carbon-to-oxygen ratio variation in the gas phase of the HD 100546 protoplanetary disk is consistent with the system’s other molecular-line observations.

Background

The paper discusses prior observations of HD 100546 that revealed azimuthal asymmetries in CS, CO, HCO+, HCN, CN, and C2H emission. A previous interpretation attributed the CS–CO asymmetry to an azimuthally varying gas-phase C/O ratio caused by more efficient freeze-out in the shadowed region.

The consistency of that interpretation with the broader set of molecular observations had not been established. The authors identify this as an unresolved issue in the context of the difficulty of explaining the different molecular-line behaviors with a single physical-chemical model; the present study instead focuses on the better-characterized shadowed disk HD 143006.

References

For instance, it is unclear if the proposed azimuthal C/O variation is consistent with the other molecular data.

— Molecules in the shadows of the protoplanetary disk HD 143006: Evidence for C/O $\gtrsim 1$ from simultaneously modeling fourteen ALMA lines  (2609.26433 - Terwisga et al., 22 Sep 2026) in Section 1, Introduction