The Intermediate Polar EI UMa: A Pre-Polar Cataclysmic Variable
Abstract
We present optical and X-ray time-series photometry of EI UMa that reveal modulation at 746 and 770 s, which we interpret as the white dwarf spin and spin-orbit sidebands. These detections, combined with previous X-ray studies, establish EI UMa as an intermediate polar. We estimate the mass accretion rate to be ~ 3.6 x 10^{17} g s^{-1}, which is close to, and likely greater than, the critical rate above which dwarf nova instabilities are suppressed. We also estimate the white dwarf to have a large magnetic moment mu > (3.4 +/- 0.2) x 10^{33} G cm^3. The high mass accretion rate and magnetic moment imply the existence of an accretion ring rather than a disk, and along with the relatively long orbital period, these suggest that EI UMa is a rare example of a pre-polar cataclysmic variable.
Cite
@article{arxiv.0802.3542,
title = {The Intermediate Polar EI UMa: A Pre-Polar Cataclysmic Variable},
author = {Tamara W. Reimer and William F. Welsh and Koji Mukai and F. A. Ringwald},
journal= {arXiv preprint arXiv:0802.3542},
year = {2009}
}
Comments
To be published in The Astrophysical Journal