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The properties of pre-eruptive structures and coronal mass ejections (CMEs)are characterized by those of their footpoints, the latter of which thusattract great interest. However, how to identify the footpoints of pre-eruptivestructures and how to identify the footpoints with ground-based instruments,still remain elusive. In this work, we study an arc-shaped structure intrudingin the sunspot umbra. It is located close to the (pre-)eruptive flux ropefootpoint and is thus expected to help identify the footpoint. We analyse thisarc-shaped structure, which we name as "sunspot scar", in a CME event on 2012July 12 and in two CME events in observationally-inspired MHD simulationsperformed by OHM and MPI-AMRVAC. The sunspot scar has a more inclined magneticfield with a weaker vertical component and a stronger horizontal componentrelative to that in the surrounding umbra and manifests as a light bridge inthe white light passband. The hot field lines anchored in the sunspot scar arespatially at the transition between the flux rope and the background coronalloops, and temporally in the process of the slipping reconnection which buildsup the flux rope. The sunspot scar and its related light bridge mark the edgeof the CME flux rope footpoint, and especially, the edge of the pre-eruptiveflux rope footpoint in the framework of "pre-eruptive structures being fluxropes". Therefore, they provide a new perspective for the identification ofpre-eruptive and CME flux rope footpoints, and also new methods for studyingthe properties and evolution of pre-eruptive structures and CMEs withphotospheric observations only.

Identifying Footpoints of Pre-eruptive and Coronal Mass Ejection Flux Ropes with Sunspot Scars