Determine the Mg/Si ratio of the GJ 499 C primary

Determine the magnesium-to-silicon ratio of the primary star of GJ 499 C to test whether the brown dwarf’s inferred Mg-rich composition reflects its shared natal environment and to assess the phase-equilibrium cloud-formation interpretation.

Background

The retrieval for GJ 499 C yields an unusually high atmospheric Mg/Si ratio of approximately 1.9, dominated by forsterite (Mg₂SiO₄), with a smaller contribution from SiO. Under the phase-equilibrium framework discussed in the paper, such a ratio would imply a primary-star Mg/Si ratio greater than approximately 1.4 and would favor forsterite-dominated clouds.

Unlike the SDSS1416 system, the Mg/Si ratio of the GJ 499 C primary is not currently available. Measuring it would permit a direct benchmark comparison between the brown dwarf and its primary, thereby testing whether the inferred cloud composition and bulk chemical composition are physically consistent with the system’s formation history.

References

As for GJ 499 C, we do not know this ratio of its primary.

— Benchmark Brown Dwarfs as Chemical Laboratories: Linking System Bulk Properties to Atmospheric Retrievals  (2608.26029 - Kecskeméthy et al., 26 Aug 2026) in Section “The Mg/Si ratio”; reiterated in Section “Conclusions”