The Unprecedented Light Variations of NGC 2346

The central star of the planetary nebula NGC 2346 is now well confirmed as a single-lined spectroscopic binary, with P = 16d (Méndez and Niemela 1981, Ap. J., 250, 240). Unexpected photometric variations were recently reported by L. Kohoutek (1982, IAU Circular 3667). From additional photoelectric measurements and visual estimates we have found that these variations are periodic, with the same period as the orbital motion of the A-type primary component. From previous observations we can ascertain that such variations did not exist before, and must have started in 1981. The light minimum occurs at phase 0.75, that is to say when the A-type component is moving towards us. Radial velocities measured on spectrograms obtained during the light minimum are more positive, by about 40 km s −1 , than expected from the orbital motion; while the radial velocities corresponding to the light maximum agree with what is expected from the orbital motion. The spectral type of the A-type star does not change significantly as a function of brightness.