The precataclysmic nucleus of Abell 41.

The present study is concerned with the discovery that the nucleus of the planetary nebula Abell 41 is a close binary with a period so short that it must become a cataclysmic variable in less than 2 x 10 to the 9th yr. The binary components are the hot primary (which excites the nebula) and a secondary of M-dwarf dimensions. The hemisphere of the secondary which faces the primary is heated to approximately 40,000 K. On a time scale of a few times 10,000 yr, the planetary is expected to dissipate, and the primary star will complete its contraction to white-dwarf dimensions. Then a long interval of inactivity will ensue, but the M dwarf must eventually be brought into contact with its Roche lobe because of loss of energy from the system by gravitational radiation.