Exploring inside-out Doppler tomography: magnetic cataclysmic variables^⋆

¹ South African Astronomical Observatory, PO Box 9, Observatory 7935, Cape Town South Africa
e-mail: ejk@saao.ac.za
² Astrophysics, Cosmology and Gravity Centre (ACGC), Department of Astronomy, University of Cape Town, Private Bag X3, 7701 Rondebosch, South Africa

Received: 15 June 2016
Accepted: 25 August 2016

Abstract

Context. Doppler tomography of magnetic cataclysmic variables is a valuable tool for the interpretation of the complex spectroscopic emission line profiles observed for these systems.

Aims. We present the results of applying our inside-out velocity projection and flux modulation mapping techniques to the Doppler tomography of magnetic cataclysmic variables.

Methods. The inside-out projection reverses the standard velocity direction by transposing the zero-velocity origin to the outer circumference and the maximum velocities to the origin of the velocity space. The inside-out tomogram is constructed by directly projecting phase-resolved spectra onto the inside-out framework. In addition, our flux modulation mapping technique extracts any information related to the modulation of the line flux by utilising consecutive half-phase tomograms. We apply this to both the standard and the inside-out techniques.

Results. Our test cases, the polars HU Aqr and V834 Cen, and the intermediate polar PQ Gem, were chosen because of their known accretion characteristics, namely ballistic, magnetic and curtain dominated accretion, respectively. In all three cases the inside-out tomogram better exposes low-velocity emission details which are overly compacted in the standard tomogram. This is especially apparent for the mid-inclination V834 Cen where the almost blob-like blended lower velocity emission in the standard tomogram is more exposed in the inside-out tomogram, making it easier to distinguish between the ballistic and magnetically confined accretion flows that are evident in the trailed spectra. Similarly, the inside-out tomogram enhances high velocity emission details which are washed out in the standard tomogram. This is particularly effective in revealing the high velocity magnetic accretion flows in the polars HU Aqr and V834 Cen. The addition of our flux modulation technique gives a significant improvement in reproducing the trailed input spectra adding more confidence to the interpretation of the Doppler maps. Furthermore, amplitude and phase maps are constructed that further reveal amplitude and phasing characteristics of the emission components in the three test cases.