AN ATMOSPHERIC ANALYSIS OF THE CARBON-RICH WHITE-DWARF G35-26

We present the first detailed spectral analysis of the DQ white dwarf G35-26 (Gr 469, WD 0203 + 207). Based on the published spectra, we determine that the dominant atmospheric constituent is He and that the temperature lies between 11,000 K and 14,000 K, the hydrogen abundance is between n(H)/n(tot) = 0.01 and 0.005, and the carbon abundance is close to n(C)/n(tot) = 0.03. The breadth of Hβ and Hγ and the virtual absence of Hδ suggests a high gravity - between log (g) = 9 and log (g) = 9.5. If this gravity is correct, it gives G35-26 the highest mass (1.2-1.33 M⊙) yet observed for a single white dwarf, if it is placed on the zero-temperature Hamada-Salpeter (H-S) relation. O+Ne+Mg white dwarfs in the range 1.2-1.37 M⊙ are predicted by theory, and G35-26 might be the first such object discovered, providing unique study opportunities. Given an H-S radius, the distance is between 33 and 69 pc. Based on the abundances that we find, there is no inconsistency in assuming that the hydrogen was accreted from the interstellar medium and that the carbon is due to dredge-up, since accretion of the observed amounts of C would leave detectable amounts of N, O, and Ca in the photosphere, whereas accretion of N, O, and Ca along with the H would not. At the moment no further progress is likely in the analysis of G35-26 until better spectra are made and an accurate parallax is measured.