Roche tomography of cataclysmic variables - VI. Differential rotation of AE Aqr - Not tidally locked!

Abstract

We present Roche tomograms of the K4V secondary star in the cataclysmic variable AE Aqr, reconstructed from two datasets taken 9 days apart, and measure the differential rotation of the stellar surface. The tomograms show many large, cool starspots, including a large high-latitude spot and a prominent appendage down the trailing hemisphere. We find two distinct bands of spots around 22${}^{\circ }$ and 43${}^{\circ }$ latitude, and estimate a spot coverage of 15.4-17% on the northern hemisphere. Assuming a solar-like differential rotation law, the differential rotation of AE Aqr was measured using two different techniques. The first method yields an equator-pole lap time of 269 d and the second yields a lap time of 262 d. This shows the star is not fully tidally locked, as was previously assumed for CVs, but has a co-rotation latitude of $\sim 40^{\circ }$. We discuss the implications that these observations have on stellar dynamo theory, as well as the impact that spot traversal across the first Lagrangian point may have on accretion rates in CVs as well as some of their other observed properties. The entropy landscape technique was applied to determine the system parameters of AE Aqr. For the two independent datasets we find M${}_1$ = 1.20 and 1.17 M${}_{\odot }$, M${}_2$ = 0.81 and 0.78 M${}_{\odot }$, and orbital inclinations of $50^{\circ }$ to $51^{\circ }$ at optimal systemic velocities of γ = -64.7 and -62.9 kms${}^{-1}$.

arXiv comment17 pages, 18 figures, 5 tables, Accepted for publication in MNRAS

References in corpus (15)

• The Best Brown Dwarf Yet?: A Companion to the Hyades Eclipsing Binary V471 Tau
• The coronal structure of AB Dor determined from contemporaneous Doppler imaging and X-ray spectroscopy
• Doin' the twist: Secular changes in the surface differential rotation on AB Doradus
• The spin-orbit angles of the transiting exoplanets WASP-1b, WASP-24b, WASP-38b and HAT-P-8b from Rossiter-McLaughlin observations
• Spot patterns and differential rotation in the eclipsing pre-CV binary,V471 Tau
• Roche tomography of cataclysmic variables - IV. Starspots and slingshot prominences on BV Cen
• Roche tomography of cataclysmic variables: I. artefacts and techniques
• Roche tomography of cataclysmic variables -- II. Images of the secondary stars in AM Her, QQ Vul, IP Peg and HU Aqr
• Roche tomography of cataclysmic variables -- III. Starspots on AE Aqr
• High Dispersion Absorption-line Spectroscopy of AE Aqr
• The spotty donor star in the X-ray transient Cen X-4
• Spectroscopic Evidence for Starspots on the Secondary Star of SS Cygni
• Numerical simulation of the surface flow of a companion star in a close binary system
• Roche tomography of cataclysmic variables - V. A high-latitude star-spot on RU Pegasi
• Numerical Simulation of the Surface Flow on the Companion Star in a Close Binary System II. Construction of Doppler maps and application to Galactic supersoft X-ray sources

Cited by in corpus (13)

• Einstein@Home Discovery of the Gamma-ray Millisecond Pulsar PSR J2039-5617 Confirms Its Predicted Redback Nature
• Tracking the Stellar Longitudes of Starspots in Short-Period Kepler Binaries
• The crowded magnetosphere of the post common envelope binary QS Virginis
• Properties of the redback millisecond pulsar binary 3FGL J0212.1+5320
• Distances of CVs and related objects derived from Gaia Data Release 1
• Roche tomography of cataclysmic variables - VIII: The irradiated and spotted dwarf nova, SS Cygni
• X-ray observations of FO Aqr during the 2016 low state
• When the disc's away, the stars will play: dynamical masses in the nova-like variable KR Aur with a pinch of accretion
• A confined dynamo: magnetic activity of the K-dwarf component in the pre-cataclysmic binary system V471 Tauri
• The Identification of Hydrogen-Deficient Cataclysmic Variable Donor Stars
• Roche tomography of cataclysmic variables - VII. The long-term magnetic activity of AE Aqr
• Detection of an energetic flare from the M5V secondary star in the Polar MQ Dra
• 21 years of Astronomy at Warwick: celebrating the legacy of Prof. Tom Marsh