IM Normae: The Death Spiral of a Cataclysmic Variable?

We present a study of the orbital light curves of the recurrent nova IM Normae since its 2002 outburst. The broad “eclipses” recur with a 2.46 hr period, which increases on a timescale of 1.28(16) × 106 yr. Under the assumption of conservative mass transfer, this suggests a rate near 10−7 M ⊙ yr−1, and this agrees with the estimated accretion rate of the postnova, based on our estimate of luminosity. IM Nor appears to be a close match to the famous recurrent nova T Pyxidis. Both stars appear to have very high accretion rates, sufficient to drive the recurrent-nova events. Both have quiescent light curves, which suggest strong heating of the low-mass secondary, and very wide orbital minima, which suggest obscuration of a large “corona” around the primary. And both have very rapid orbital period increases, as expected from a short-period binary with high mass transfer from the low-mass component. These two stars may represent a final stage of nova—and cataclysmic variable—evolution, in which irradiation-driven winds drive a high rate of mass transfer, thereby evaporating the donor star in a paroxysm of nova outbursts.

A Brown Dwarf Companion to the Nova-like Variable RW Tri

The orbital period of Nova-like variable RW Tri is expected to experience a long-term evolution due to a stable mass transfer from the red dwarf to the white dwarf. By adding 297 new eclipse timings obtained from our own observations and a cross-identification of many databases, we fully reinvestigated the variations in orbital period of RW Tri, based on a total of 658 data points spanning over 80 years. The new O-C diagram demonstrates a more complicate pattern than a pure sinusoidal modulation shown in the previous O-C analyses. The best fit of the O-C variations is a quadratic-plus-sinusoidal curve with a period of 22.66 (2) years and a typical decrease rate of P˙ = −2d.32(4) × 10−9 yr−1. To explain secular orbital period decrease, the magnetic braking effect is required to cause the orbital angular moment loss in RW Tri with a mass ratio less than unity, while a conserved mass transfer is also enough for RW Tri with a mass ratio larger than unity. No matter what the mass ratio is, a slightly enhanced mass transfer rate, 2.4–5.3 × 10−9 M⊙ yr−1, derived from our O-C diagram, providing an evidence supporting the disk instability model and the standard/revised models of cataclysmic variable evolution, is almost the same as that obtained from the light-curve modeling. This further confirms our observed orbital period decrease and the controversial system parameter, mass transfer rate. Our updated O-C analysis further verifies the claimed cyclical changes of orbital period with a period range of 21–24 years, which is approximately one half of the results in the literature. In accordance with the light-travel time effect, this periodical variation shown in our new O-C diagram indicates a brown dwarf hidden in RW Tri at a coplanar orbit. Note that the large scatter in the data range of 0–3 × 104 cycles requires the high-precision photometry in the longer base line in the future.

Sudden and steady orbital period changes across six classical Nova Eruptions: the end of hibernation and two serious challenges for the magnetic braking model of cataclysmic variable evolution

ABSTRACT I report on two new measures of the sudden change in the orbital period (P) across the nova eruption (ΔP) and the steady period change in quiescence ($\dot{P}$) for classical novae (CNe) RR Pic and HR Del, bringing a total of six such measures for CNe, all in a final report of my large and long observing program. The fractional changes (ΔP/P) in parts-per-million (ppm) are −290.71 ± 0.28 (QZ Aur), −472.1 ± 4.8 (HR Del), −4.46 ± 0.03 (DQ Her), +39.6 ± 0.5 (BT Mon), −2003.7 ± 0.9 (RR Pic), and −273 ± 61 (V1017 Sgr). These results are in stark opposition to the Hibernation Model for the evolution of cataclysmic variables (CVs), which requires ΔP/P> + 1000 ppm to get the required drop in the accretion rate to produce hibernation. The hibernation model cannot be salvaged in any way. My program has also measured the first long-term $\dot{P}$ for CNe, with −2.84 ± 0.22 (QZ Aur), +4.0 ± 0.9 (HR Del), +0.00 ± 0.02 (DQ Her), −2.3 ± 0.1 (BT Mon), and +1.25 ± 0.01 (RR Pic) in units of 10−11 d per cycle. These can be directly compared to the predictions of the magnetic braking model, where the long-term average $\dot{P}$ is a single universal function of P. The measured values are +5.3, −94, 0.00, +6.9, and −190 times that predicted by the model, so the predictions are always greatly wrong. Further, the effects of the ΔP averaged over the eruption cycle are usually much larger than the magnetic braking effects. To get a realistic model of CV evolution, we must add the physics of the ΔP and $\dot{P}$ variations.

Observational Studies of Cataclysmic Variable Evolution: Of Samples, Biases and Surprises

I present, brief status reports on three large observational projects that are designed to test our current understanding of the evolution of cataclysmic variables (CVs): The spectroscopic selection of new CVs in the Hamburg Quasar Survey, the search for pre-CVs based on Sloan colours and UK Schmidt/6dF multiobject spectroscopy, and the identification of CVs that descended from supersoft X-ray binaries using a HST/STIS far-ultraviolet spectroscopic survey.