Stagnated Outflow of O⁺⁵ Ions in the Source Region of the Slow Solar Wind at Solar Minimum

Abstract

Using recent coordinated UVCS and LASCO measurements by Strachan and coworkers to constrain the heating parameters of a one-dimensional single-fluid minor ion model, we calculate the outflow velocity profile of O⁺⁵ ions in the flow tube overlying the helmet streamer, which has been supposed to be the source region of the slow solar wind at least during solar minimum. The background solar wind parameters and the flow tube geometry are taken from a recent two-dimensional magnetohydrodynamic solar wind model. We show that in this slow-wind source region the O⁺⁵ outflow speed varies nonmonotonically with increasing heliocentric distance. There is a local minimum of the outflow speed near the streamer cusp point (about 3 R_solar), which is below the current observational sensitivity. This type of ion outflow in the slow solar wind is termed ``stagnated outflow'' in this paper. We also show that the observed effective temperature in the perpendicular direction (to the magnetic field) and the outflow speed of the O⁺⁵ ions can be used to put limits on their parallel thermal temperature.