I report two new measures of the sudden change in the orbital period (P) across the nova eruption (ΔP) and the steady period change in quiescence (P- ) for classical novae (CNe) DQ Her and BT Mon. The fractional changes (ΔP/P) in parts per million (ppm) are -4.46 ± 0.03 for DQ Her and +39.6 ± 0.5 for BT Mon. For BT Mon, the ΔP/P value is not large enough (i.e. >1580 ppm) to allow for hibernation in this system. The negative ΔP/P for DQ Her is a confident counterexample of the hibernation model for the evolution of cataclysmic variables. Further, published models of period changes by nova eruptions do not allow for such a negative value, so some additional mechanism is required, with this perhaps being due to asymmetric ejection of material. My program has also measured the first long-term P- for CNe, with 0.00 ± 0.02 for DQ Her and -2.3 ± 0.1 for BT Mon, all with units of 10-11 d cycle-1. These can be directly compared to the predictions of the magnetic braking model, where the long-term average P- is a single universal function of P. The predicted values are -0.027 for DQ Her and -0.33 for BT Mon. For both novae, the measured P- is significantly far from the predictions for magnetic braking. Further, the observed ΔP for BTMon imposes an additional positive period change of +0.60 ×10-11 d cycle-1 when averaged over the eruption cycle, so this system actually has a long-term rise in P.
Publication Source (Journal or Book title)
Monthly Notices of the Royal Astronomical Society
Schaefer, B. (2020). Sudden and steady orbital period changes across the classical nova eruptions of DQ Her and BT Mon. Monthly Notices of the Royal Astronomical Society (3), 3323-3342. https://doi.org/10.1093/mnras/stz3325