Dipole nebula IC 2220, a southern reflection nebula around the variable red giant HD 65750

IC 2220 has been found to be a peculiar butterfly-shaped reflection nebula surrounding the bright variable M 3 III giant HD 65750 = HR 3126. The filaments of the nebula resemble the structure of a magnetic dipole field centered on the red giant. From UBV photometry of the star and the nebula, the (B -- V) and (U -- B) colors of the nebula are bluer by 0.23m and 0.99m, respectively, than those of the illuminating star. The high ultraviolet excess of the nebula may indicate that the red giant has a faint blue companion which is exciting the nebula, or that the grain properties in reflection nebulae around M- stars and B-stars are different. A very large closed loop which is visible in IC 2220 is tentatively interpreted as a giant prominence originating in the central star. The nebula and its central star possibly have the same distance (375 pc) as the open cluster NGC 2516, which is located only 1.7 deg from IC 2220 and which contains three more red giants in the heliumburning stage. There is also the possibility that the central star of IC 2220 could still be in its pre-main sequence stage of evolution. (auth)