THE ELEMENTAL COMPOSITION OF THE CORONA OF PROCYON - EVIDENCE FOR THEABSENCE OF THE FIP EFFECT

The chemical composition of the solar corona is not the same as that o f the underlying photosphere. In the corona, elements with a first ion ization potential (FIP) of less than or equal to 10 electron volts (fo r example, iron, magnesium, silicon, and calcium) are overabundant rel ative to those with an FIP of greater than or equal to 10 electron vol ts (for example, oxygen, neon, and sulfur) by factors of 3 to 10 with respect to the photosphere. The origin of this FIP effect is unknown. The launch of the Extreme Ultraviolet Explorer Satellite (EUVE) opened up the spectroscopic capability required to determine elemental abund ances in the coronae of other stars. Spectroscopic observations of the corona of the nearby F5 IV star Procyon obtained with EUVE have yield ed estimates of the relative abundances of high- and low-FIP species. The results provide evidence that Procyon, unlike the sun, does not ex hibit the FIP effect. Whether the sun or Procyon is more typical of th e general late-type stellar population is of fundamental interest to t he physics of stellar outer atmospheres and has a bearing on the origi n of cosmic rays.