Variable H alpha line emission from the central star of the Helix Nebula

The central star of the Helix Nebula is a hot white dwarf with unexpected h ard X-ray emission. With an effective temperature of similar to 100,000 K, the star is a powerful source of H-ionizing radiation; the atmosphere of a stellar or planetary companion, if present, will be ionized and emit recomb ination lines. To probe the origin of hard X-ray emission from the Helix Ne bula's central star, we have obtained multi-epoch, high-dispersion spectra of the star and have found temporal variation in the Ha line profile over a time span of 1 week. The observed width and strength of the variable Ha em ission component are consistent with the hypothesized dMe companion propose d to explain the hard X-ray emission. A dMe companion, however, cannot expl ain the possible detection of variable He II and [N II] emission. Follow-up spectroscopic monitoring of the Helix Nebula central star is needed to bet ter establish the identification of the spectral lines and their temporal b ehavior in order to determine the origin of the optical variability and har d X-ray emission.