What is the mass of the brown dwarf/red dwarf boundary in super metal-rich objects?

Question

I am trying to make a red dwarf with twice the metallicity of the Sun. What could its theoretical minimum mass be in Jupiter masses?

Answer 1

About 72-73 Jupiter masses.

The stellar/brown dwarf boundary is (slightly) metallicity dependent - it gets lower for higher metallicities. The exact value would depend on who's models you adopted and most do not consider the high metallicity you want. However, the scaling with metallicity from the solar-metallicity case should be almost model-independent.

The most recent work looks like the SANDee models by Gerasimov et al. (2024). The hydrogen burning limit for a metallicity [Fe/H]$=+0.3$ (about twice the solar value) is $0.069M_\odot$ (or 72 Jupiter masses). This can be compared with a H-burning limit from the same models that is 4% more massive for a solar-metallicity object.

Note that whether a low mass "star" above this limit is actually undergoing fusion will depend on its age, since the onset of nuclear fusion takes longer and longer as you approach the brown dwarf limit.