All Figures

	Figure 1: Theoretical SDSS color grid for DQ white dwarfs. Thick continuous lines are lines of constant carbon abundance from [C/He] = -8.0 ( top) to -4 ( bottom), step 1.0. Thin dashed: lines of constant from 4400 K ( right) to 13 000 K ( left) in steps of 200 K. Crosses show the observed DQ stars from Harris et al. (2003) and Kleinman et al. (2004).
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In the text

	Figure 2: Comparison of effective temperatures determined from the photometry with results from DB05.
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In the text

	Figure 3: Two examples of the spectral fitting for objects with molecular features of different strengths. Top: SDSS J171341.76+324009.1, bottom: SDSS J032054.11-071625.4. Note that the name used above the panels is the internal SDSS-MJD-PLATE-FID designation of the SDSS project, which can be cross-identified using Tables 1 and 2. Vertical axis is relative intensity on an arbitrary scale.
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In the text

	Figure 4: Comparison of carbon abundances from spectral fitting with results from DB05.
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In the text

	Figure 5: Carbon abundance versus effective temperatures. Full circles are the results from this paper. We have added as open circles the results from DB05 for those objects not in our sample.
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In the text

Figure A.1: Spectral fit for DQ white dwarfs.


In the text

Figure A.1: continued.


In the text

Figure A.1: continued.


In the text

Figure A.1: continued.


In the text

Figure A.1: continued.


In the text

Figure A.1: continued.


In the text

Figure A.1: continued.


In the text

Figure A.1: continued.


In the text

Figure A.1: continued.


In the text