Left, from top to bottom: B, V, and I_C data used for temperature determinations. In the middle panel showing V data, points measured simultaneously with B measurements are marked in light blue, and points measured simultaneously with I_C measurements are marked in light red. Right: Enlarged view around discrepant V (upper panel) and V − I_C (lower panel) data; data points corrected by 0$\stackrel{\text{m}}{.}$05 are indicated by black crosses (for details, see the first paragraph of Sect. 4.3).