CAPOS XII. PIGS bulge field stars

Bulge membership was defined via orbital confinement using an apocenter cut and the high-density locus in the (E_J_, L_z_) plane, with uncertainties estimated using Monte Carlo simulations. We identified 98 stars as genuine bulge members. The metallicity distribution spans -2.5<=[Fe/H]<=-0.4, with a median [Fe/H]=-1.71, offset to higher metallicity than the inner halo (median [Fe/H]=-1.96).

The sample follows a high-alpha sequence with slopes d[Si/Fe]/d[Fe/H]=-0.020^+0.012^_-0.051_ and d[Mg/Fe]/d[Fe/H]=-0.097^+0.062^_-0.133_. Fe-peak tracers show [Ni/Fe]~0, while [Mn/Fe] declines with [Fe/H] with a mild upturn at higher metallicity. We detect no significant [Si/Fe] gradients with Rapo or Zmax (+0.010^+0.018^_0.000_ and +0.006^+0.022^_-0.011_dex/kpc, respectively).

The results are insensitive to the assumed {OMEGA}p, yielding indistinguishable memberships. The chemo-orbital evidence favors an in situ origin within the inner Galaxy for the metal-poor bulge field, enriched at early times and later rearranged by secular bar evolution, with a minor contribution from halo stars at the most metal-poor end.