Central Star of NGC 3132: A Visual Binary

Extract

A faint companion to HD 87892 (V=10.07, B-V=+0.09, U-B=+0.10, Sp.A2) has been discovered with the 3.6 m telescope (prime focus) of the European Southern Observatory at La Silla having the following parameters: separation ψ = 1″.65, position angle θ = 226°.3. The companion was detected on plates taken in the U system (IIIa-J baked + UG1) and appears to be about Δm_U ≃ 4.5 mag fainter than the main component; it is almost invisible in the nearly visual system having Δm_vis ≃ 4.8 mag. Contrary to the eccentric position of HD 87892 the companion lies in the axis of symmetry of the nebula. For the given reason the companion can be considered as the actual planetary nucleus. Assuming that its temperature is approximately T_* ≈ 10⁵ °K and the distance of the nebula d ≃ 0.9 kpc, the following parameters of the nucleus were estimated: L^*/L ≃ 110, R^*/R ≃ 0.035. The physical association of HD 87892 with its visual companion is probable. (Paper will appear in Astronomy and Astrophysics.)