Oxygen abundance in streamers above 2 solar radii

Abstract. Oxygen abundance in streamers has been evaluated by several authors [see e. g. 1, 2, 3] who found, in the core of streamers, an oxygen abundance lower by a factor 3-4 than in the lateral branches (legs). All estimates were made at heliocentric distances h 2 2 R . In this paper we analyze UVCS observations of two streamers, observed during solar minimum, at altitudes h 2 4 R with the purpose of deriving the oxygen abundance, relative to hydrogen, and its latitude dependence within streamers, in the range 2 4 h 4 R . To this end, electron densities have been derived from LASCO data, taken at the time of the UVCS observations, and the radial temperature profile has been taken from literature. These parameters allow us, after the collisional contribution to the OVI 1032, 1037 Å line intensities has been identified, to determine the oxygen abundance that reproduces the observed collisional components. Our results are compared with previous abundance determinations and the relationship between coronal and in situ abundances is also discussed