Physical structure of a coronal streamer in the closed-field region as observed from UVCS/SOHO and SXT/YOHKOH

We analyze a coronal helmet streamer observed on 1996 July 25 using instrum ents aboard two solar spacecraft, the Ultraviolet Coronagraph Spectrometer (UVCS) on board Solar and Heliospheric Observatory (SOHO) and the Soft X-Ra y Telescope (SXT) on board Yohkoh. We derive temperatures and electron dens ities at 1.15 R. from SXT/Yohkoh observations. At this height, the streamer temperature is about log T (K) = 6.28 +/- 0.05, and the electron density i s about log n(e)(cm(-3)) = 8.09 +/- 0.26, while at 1.5 R. a temperature of log T (K) = 6.2 and a density of log n(e)(cm(-3)) = 7.1 are obtained by UVC S/SOHO. Within the measurement uncertainty this suggests a constant tempera ture from the base of the streamer to 1.5 R.. Electron density measurements suggest that the gas in the streamer core is close to hydrostatic equilibr ium. Comparison with potential field models for the magnetic field suggests a plasma beta larger than 1 in the closed-field region in the streamer. In deriving electron densities and temperatures from the SXT/Yohkoh data, we include the effects of abundance anomalies on the SXT filter response. We u se the elemental abundances derived from the UVCS/SOHO observations to esti mate the first ionization potential and gravitational settling effects. We then give the set of abundances for the solar corona, which agrees with our observations. In addition, we analyzed the SXT data from 6 consecutive day s. We found that from 1996 July 22 to July 27, the physical properties of t he streamer are nearly constant. We conclude that we may be observing the s ame loop system over 6 days.