On the origin of orbital period change in WY Cancri: a genuine angular momentum loss?

TL;DR

This paper investigates whether the observed orbital period decrease in WY Cancri can be explained by angular momentum loss mechanisms such as magnetic braking or circumbinary disk interactions, finding these explanations unlikely due to required extreme conditions.

Contribution

The study assesses the plausibility of angular momentum loss as the cause of WY Cancri's period change, highlighting the improbability of necessary magnetic fields or wind loss fractions.

Findings

Magnetic braking requires a magnetic field >10,000 G, which is unusually strong.

Circumbinary disk interaction could explain the loss if 6% of stellar wind feeds the disk.

Extreme conditions are needed, making angular momentum loss an unlikely sole cause.

Abstract

WY Cancri is a short-period ($P$=0.829 d) eclipsing RS Canum Venaticorum stars, and both components are late-type stars. Recently, observations provided by photometric observations and light time minima show that the orbital period of WY Cancri is experiencing a secular decrease at a rate of ${\rm d} P/{\rm d}t=-1.2\times10^{-7}\rm d yr^{-1}$. In this Letter, we attempt to investigate if the period change of WY Cancri can originate from the angular momentum loss. In calculation, we assume that this source has a high wind loss rate of $\sim10^{-10} \rm M_{\odot} yr^{-1}$. To account for the observation, magnetic braking demands a strong surface magnetic field of $\gtrsim 10000$ G like Ap/Bp stars. Furthermore, if this source may be surrounded by a circumbinary disk, and 6% of the wind loss feeds the disk, tidal torque between the disk and the binary can offer the observed angular momentum loss rate. Such a strong magnetic field or an extremely high wind input fraction seem to be highly unlikely.