Oxygen Abundance and Energy Deposition in the Slow Coronal Wind

Abstract

Observations of the extended corona obtained with the Ultraviolet Coronagraph Spectrometer (UVCS) on board the Solar and Heliospheric Observatory (SOHO) during the solar minimum years 1996 and 1997 have been analyzed to derive the oxygen abundance in the outer corona. A comparison of the absolute coronal abundance, measured in the coronal regions surrounding the quiescent solar minimum streamers, to the heliospheric values confirms that these regions are the dominant sources of the slow solar wind. However, the inferred coronal abundances are consistent with the heliospheric values only in case the ion velocity distribution is anisotropic and enhanced across the coronal magnetic field. Thus this analysis also leads to the conclusion that energy is deposited in the slow coronal wind at least up to 2.7 R_solar and that the efficiency of energy deposition is likely to be related to the local coronal magnetic topology.