SIMBAD references

A new model atmosphere analysis for the peculiar DQ white dwarf discovered by Carollo et al. (2002A&A...393L..45C) is presented. The effective temperature and carbon abundance have been estimated by fitting both the photometric data (UB_JVR_FI_NJHK) and a low resolution spectrum (3500<λ<7500Å) with a new model grid for helium-rich white dwarfs with traces of carbon (DQ stars). We estimate T_eff≃5120±200K and log[C/He]≃-5.8±0.5, which make GSC2U J131147.2+292348 the coolest DQ star ever observed. This result indicates that the hypothetical transition from C₂ to C₂H molecules around T_eff=6000K, which was inferred to explain the absence of DQ stars at lower temperatures, needs to be reconsidered.