Publications of the Astronomical Society of the Pacific, Vol. 117, No. 833 (July 2005), pp. 711-720 (10 pages) ABSTRACT The shape of the line bisector for the prototype spectral line Fe i λ6253 was ...

This determines the gradient of the required line. Use B\((6,3)\) and \(m\). The perpendicular bisector passes through the midpoint of AC. This determines the point on the required line.