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The systemic velocities of four long-period cataclysmic variable stars

R. C. North·T. R. Marsh·U. Kolb·V. S. Dhillon·C. K. J. Moran
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Abstract

Although a large number of orbital periods of cataclysmic variable stars (CVs) have been measured, comparison of period and luminosity distributions with evolutionary theory is affected by strong selection effects. A test has been discovered which is independent of these selection effects and is based upon the kinematics of CVs (Kolb & Stehle, 1996). If the standard models of evolution are correct then long-period (P_orb > 5 hrs) CVs should be typically less than 1.5 Gyr old, and their line-of-sight velocity dispersion ($σ_γ$) should be small. We present results from a pilot study which indicate that this postulate is indeed true. Four long-period dwarf novae (EM Cyg, V426 Oph, SS Cyg and AH Her) were observed over a complete orbit, in order that accurate radial velocities be obtained. We find values of -1.7, 5.4, 15.4 and 1.8 km/s with uncertainties of order 3 km/s, referred to the dynamical Local Standard of Rest (LSR), leading to a dispersion of ~ 8 km/s. Calculation of a 95 per cent confidence interval gives the result 4 < σ_γ< 28 km/s compared to a prediction of 15 km/s. We also have an improved determination of mass donor spectral type, K_2 and q for the four systems.

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R. C. North, T. R. Marsh, U. Kolb, V. S. Dhillon, C. K. J. Moran. 2002-01-31. The systemic velocities of four long-period cataclysmic variable stars. https://doi.org/10.1046/j.1365-8711.2002.05795.x

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