Comparison of observed inner disk abundance ratios (wrt. C₂H₂) with chemical models (upper panel) and cometary observations (lower panel) for IRS 46 and GV Tau. In both panels detections (diamonds) and upper limits (arrows) for IRS 46 (black) and GV Tau (red) are indicated. Upper panel: abundance ratios in the disk model by Markwick et al. (2002) at 5 AU (green triangle), from the reference disk model at 1 AU by Najita et al. (2011) (blue square) and at a O/C = 1 (blue cross), and from the disk model by Agúndez et al. (2008) at 1 AU (green square) and 3 AU (green cross). Lower panel: observed range of cometary abundance ratios from Mumma & Charnley (2011, green bar and stars).