On the temperature and the interstellar nature of coronal gas observed by Copernicus

More detailed scans of ions expected in interstellar absorption at temperatures of 100,000 to 1 million K have been made with Copernicus in five stars: Alpha Vir, Beta Cen, Lambda Sco, Mu Col, and HD 28497. Preliminary data show that the absorption due to O VI is stationary compared with the velocities of stellar absorption in the spectrum of the spectroscopic binary Lambda Sco, thus demonstrating its nonstellar nature. Ionization temperatures interpreted using steady-state or time-dependent assumptions yield values of 280,000 to 700,000 K. There is some evidence that a range of temperatures consistent with this spread may in fact exist in Alpha Vir. For this limited sample of data, there is no clear evidence for a generic association of low-column-density H2 and the O VI absorption. It is concluded that the O VI absorption refers to regions with temperatures exceeding 250,000 K. The only UV diagnostic for the gas appears to be the O VI features, though C IV may be useful in some cases.