A plasmoid-model for mass loss from stars on the upper red giant branch: The mass loss rate is controlled by the number of density scale heights in the convection zone

Recent asteroseismic determinations of ΔM, the integrated mass loss on the red giant branch (RGB), for fields stars show a trend of ΔM decreasing as metallicity increases. This trend among field stars is inconsistent with many existing models of RGB mass loss. The present paper is motivated by a 'plasmoid' model of RGB mass loss in which magnetic flux loops, generated by a shear dynamo operating below the convection zone, are buoyed up to the stellar surface starting at the evolutionary stage right after the RGB 'kink'. This model leads us to examine correlations between, on the one hand, the average post-kink RGB mass loss rate, determined from ΔM and the post-kink RGB lifetime, and on the other hand, stellar properties which exist just after the end of the kink. For three distinct stellar samples, we find strong anti-correlations between the average post-kink RGB mass loss rate and the number of density scale heights in the convection zone. This leads us to propose that the number of density scale heights in the convection zone is a dominant factor in determining the rate of the mass loss process which sets in after the RGB kink.