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C. K. Henry, E. M. Sion (Villanova Un.)
We consider the thermal history of the magnetic white dwarf in the Hyades, pre-cataclysmic, eclipsing-spectroscopic binary, V471 Tauri. With Teff=35,000K, (Mwd = 0.8 M\odot), its cooling age is only 7.8\times 106 years compared with the mean cooling age of Hyades single white dwarfs of 9\times 107 years. If its formation was essentially coeval with the single Hyades degenerates, then V471 Tauri is ~3,000K hotter than their average Teff (19,680K). This amount of heating by accretion is in the same regime as that experienced, on average, by white dwarfs in cataclysmic variables (Sion 1999, PASP, 111, 532). We compare the positions of the Hyades degenerates in the HRD with a Bondi-Hoyle locus of constant accretion, as discussed by Castellani and Panagia (1971). We consider several possible phyical explanations for the puzzling cooling history of the V471 Tauri degenerate. These include the possiblity of an ancient nova with limit cycle evolution, steady proton-proton nuclear burning providing its surface luminosity, and radial accretion heating maintaining its observed Teff. For steady hydrogen burning, an accretion rate \dot{M} = 10-11 Ls/Xh = 2.3\times 10-12 M\odot/yr is sufficient to account for the present Teff. As a test of two of these three scenarios, we are carrying out a quasi-static evolutionary calculation of radial accretion onto the white dwarf. This research is supported by NSF grant AST99-09155 to Villanova University and by NASA ADP grant NAG5-8388.