Chromospheres and transition regions in F dwarfs.

Low resolution spectra in the wavelength region 1150-1000 A were obtained for five F stars using the SWP camera on the International Ultraviolet Explorer satellite. In four of these spectra emission lines from O I, C II, Si IV, and N V are visible. These lines are also prominent in the UV spectra of the quiet sun and cooler stars with chromospheric activity. The lines, with the exception of the O I line, originate in a transition region between the chromosphere and the corona. It was found that the surface flux in the emission lines of the stars observed is comparable to that in late type stars with chromopheric activity.