All Figures

	Figure 1: Colour-colour-diagram of COMBO-17-classified stars: 1332 stars and 9 white dwarfs with T>10 000 K have been classified in the S11 field in the range of R=[16,23]. The object COMBO-17 J1143 marked here by a circle displays large template fitting residuals that are also reflected by its offset from the stellar locus.
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In the text

Figure 2: Colour-colour-diagram of white dwarfs: large symbols show all known ultra-cool white dwarfs, where COMBO-17 J1143 is marked by a circle. Its original SDSS photometry is shown as the data point with error bars. Normal white dwarfs are shown as small symbols (sample by Kleinman et al. 2004). Objects which are redder than normal white dwarfs in r-i have M dwarf companions while bluer ones show CIA in optical bands.

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In the text

Figure 3: The SED of COMBO-17-J1143 (black data points) compared to the spectra of all known ultra-cool white dwarfs (grey lines) except for LHS 1402. COMBO-17 photometry is shown with horizontal error bars indicating filter width and vertical error bars representing the respective flux error. The spectra have been normalised with respect to the measured flux in the three filters B, V and R. COMBO-17 J1143 is most similar to LHS 3250 and SDSS J0947.

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In the text

	Figure 4: Finding chart for COMBO-17 J114356.08-0144032 taken from a 5-h R-band image obtained with WFI at the 2.2 m-telescope at La Silla in February 2000. The frame is on a side. North is up and East is on the left.
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In the text