A SOHO/UVCS study of coronal outflows at the edge of an active region complex

Abstract

Context. In the past, active regions (ARs) have been suggested as a possible source of the slow solar wind. Their role as solar wind contributors has recently been supported by HINODE observations at low coronal levels.Aims. Our purpose is to determine whether outflows at the edges of ARs can be detected in higher layers of the corona, supporting the low-corona evidence for the occurrence of wind streams from ARs.Methods. Data acquired by SOHO/UVCS on January 2, 1998, at altitudes ranging from 1.5 to 2.3 solar radii at mid latitudes, were used to infer the physical properties of an AR complex at the time of its limb passage. To this end, the Doppler dimming technique was applied to UVCS observations of the H i Lyα and O vi doublet lines at 1031.9 and 1037.6 A.Results. Outflow speeds (and electron densities) were inferred: outflows, at speeds increasing with height, turn out to be confined within a narrow channel at the edge of closed loop systems within the AR. Our results are compared with those obtained by other authors with different techniques. Conclusions. Our results support the assumption that ARs are sources of slow wind. To our knowledge these are the first direct measurements of AR flows in the intermediate corona. Tentative profiles of the speed vs. heliocentric altitudes at heliocentric distances between ≈ 1.5 and ≈ 2.3 solar radii show that AR flows are faster than streams from equatorial coronal holes.