Data for Effective temperatures of cataclysmic-variable white dwarfs as a probe of their evolution

For 36 CVs, the white dwarf is recognisable through its broad Ly α absorption profile and we measure the white dwarf effective temperatures (Teff) by fitting the HST data assuming log g = 8.35, which corresponds to the average mass for CV white dwarfs (≃0.8 M⊙). Our results nearly double the number of CV white dwarfs with an accurate temperature measurement.

We find that CVs above the period gap have, on average, higher temperatures (〈Teff〉 ≃ 23 000 K) and exhibit much more scatter compared to those below the gap (〈Teff〉 ≃ 15 000 K). While this behaviour broadly agrees with theoretical predictions, some discrepancies are present: (i) all our new measurements above the gap are characterized by lower temperatures (Teff ≃ 16 000–26 000 K) than predicted by the present-day CV population models (Teff ≃ 38 000–43 000 K); (ii) our results below the gap are not clustered in the predicted narrow track and exhibit in particular a relatively large spread near the period minimum, which may point to some shortcomings in the CV evolutionary models.