2010MNRAS.407.1070M

Accurate BVR_CI_C light and colour curves of the Mira variable in the dust-free symbiotic system K4-46 are presented and discussed. They cover several consecutive pulsations cycles. The Mira mean period is 284.2d, the reddening sums to E(B - V) = 0.35 and the distance is 10kpc. Absolute spectrophotometry at both maximum and minimum brightness of the Mira is presented. The rich emission line and continuum spectrum of the HII region ionized by the hard radiation of the white dwarf dominates at Mira minimum. From its photoionization analysis, it is found that the HII region extends to a radius of 210au, has a mass 1.8x10^–4 M_☉ and it is ionized by a white dwarf of 158000K temperature and 0.06R_☉ radius, stably burning hydrogen at its surface. The derived [Fe/H] = -0.45 well match the ambient metallicity expected at K4-46 at its 15kpc galactocentric distance, and the overabundances in N, Ne and He are those expected if the HII region is fed by the wind of the Mira and polluted by nuclearly processed material lost by the white dwarf companion.