Emission line tomography of the short period cataclysmic variables CC Scl and V2051 Oph

Abstract

We present time series spectroscopy of two short period cataclysmic variables, CC Scl and V2051 Oph, to test the efficiency of Doppler-tomography-based methods in constraining orbital parameters of evolved cataclysmic variables. We find that the Ca II triplet lines offer superior diagnostics, revealing emission components from the mass donors and sharp images of the accretion discs. Furthermore, we use Monte Carlo methods to estimate the uncertainties from ensembles of Doppler maps.We compare our new methods against traditional radial velocity methods and show that they offer a valid route towards system parameter determination. Our analysis of CC Scl suggests a low mass ratio of q = 0.08 ± 0.03 with a primary velocity of K1 = 37 ± 14 km s-1. This mass ratio is in between the pre- and post-period minimum status, however our K1 solution favours a post-period minimum system. Our derived parameters for V2051 Oph (q = 0.18 ± 0.05, K1 = 97 ± 10 km s-1) are in agreement with the eclipse solution (q = 0.19 ± 0.03), offering a direct validation of our methods.