Please see Gagné et al. (2018) for the details of the BANYAN Σ classifier and Gagné et al. (2026) for the updated BANYAN Σ models, and please acknowledge both papers when you use results from this tool.

The stored BANYAN Σ results in MOCAdb include an Obs column describing the observables used for the stored results of this star: pm is the minimum set of observables, equatorial coordinates and proper motion; rv is the radial velocity; and plx is the parallax or photometric distance. The YA(%) result is the total membership probability for all possible young associations combined, in percent. Most of the time, this is concentrated in a single association, but for some ambiguous members it can be distributed across more than one. When this happens, all_prob_yas contains more than one moca_aid key with its relative share of the total association probability, in percent. For example, all_prob_yas: BPMG(60); ABDMG(40), with YA(%): 90%, means the total association probability is divided 60/40 between BPMG and ABDMG; the absolute BPMG probability is 54%, and the ABDMG probability is 36%.

The priors of BANYAN Σ are adjusted such that a selection threshold of 90% in total association probability will recover 90% of the true members across associations when using input measurements with a precision similar to Gaia; see Section 6 of Gagné et al. 2018. The contamination rate even at a 90% probability threshold varies widely between associations and is usually worse for the nearest associations or those with larger UVW models. When choosing a threshold other than 90%, the recovery rate also becomes association-dependent.