Photo-centre offsets associated with the CO bandhead emission. This figure was constructed by co-adding the time averaged differential phase observations obtained on the date 2013-03-04 using the UT1-UT3 baseline across the first 3 CO bandheads. The uncertainty in the differential phase is represented by the rms of the continuum measurements. The smaller model offset (solid line) corresponds to an inner disc radius of 5 stellar radii (0.2 AU) and an outer radius of 1.0 AU (0.7 mas). The larger offset (dashed line) was calculated for an inner radius of 10 stellar radii (0.4 AU) and an outer radius of 4.0 AU (2.7 mas, sizes calculated assuming a distance of 1.5 kpc).