The Intriguing Polar EU Cancri in the Eyes of Kepler K2

TL;DR

This paper analyzes the Kepler K2 light curve of the faint polar EU Cnc, revealing a stable, large-amplitude pulse likely from an accretion region, and discusses its potential classification as a low-accretion-rate polar.

Contribution

First detailed Kepler light curve analysis of EU Cnc, revealing stable accretion features and proposing its classification as a low-accretion-rate polar.

Findings

Large-amplitude, stable pulse lasting half the orbit

Weak dips at the start and end of the orbital hump

Consistent low state over observational history

Abstract

We present the light curve of EU Cnc, the first published analysis of a Kepler light curve of a polar. Although EU Cnc was extremely faint during campaign 16 and 18 its light curve showed a large-amplitude pulse that lasted for half of each orbit, which we interpret to be light from an accretion region that rotates behind the limb of the white dwarf for half of the orbit. Remarkably, the pulse profile showed no appreciable variability in either campaign. Additionally, we note weak dips of unknown origin with a depth of ~10% at the beginning and end of the orbital hump. The K2 waveform is consistent with all previously reported variations on the orbital timescale, suggesting that EU Cnc has possibly been at the same low state for its entire observational history. We then explore the possibility that EU Cnc's unusual combination of a low mass-transfer rate and consistent light curve indicates the possibility that EU Cnc might be a low-accretion-rate polar (LARP).