The central star of the planetary nebula Abell 78

The ultraviolet spectrum of the nucleus of Abell 78, one of the two planetaries known to contain zones of nearly pure helium, is studied. The line spectrum and wind velocities are examined, the determination of interstellar extinction for assessing circumstellar dust is improved, and the temperature, luminosity, and core mass are derived. The results for A78 are compared with results for A30, and it is concluded that the dust distributions around the two central stars are quite different. The temperature of the A78 core is not as high as previously believed, and almost certainly lies between 67,000 K and 130,000 K. The most likely temperature range is 77,000-84,000 K. The core mass lies between 0.56 and 0.70 solar mass, with the most likely values between 0.56 and 0.58 solar mass.