Top: comparison of the three observed epochs of TW Hya: 2010a (cyan, thin line), 2010b (gray, medium line), and 2013 (black, thick line). The oxygen line (left) is a triple line blend, and the calcium line (right) is blended with an H⁰ Paschen series line and an absorption artifact from the telluric correction of that line, which we fit out before determining the integrated flux. Bottom: residual spectra after subtraction of epoch 2 from epoch 3.