Open AccessThe systemic velocities of four long‐period cataclysmic variable stars
Author(s) -
North R. C.,
Marsh T. R.,
Kolb U.,
Dhillon V. S.,
Moran C. K. J.
Publication year - 2002
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2002.05795.x
Subject(s) - physics , astrophysics , cataclysmic variable star , stars , luminosity , variable star , orbital period , light curve , orbit (dynamics) , astronomy , white dwarf , galaxy , engineering , aerospace engineering
Although a large number of orbital periods of cataclysmic variable (CV) stars have been measured, comparison of period and luminosity distributions with evolutionary theory is affected by strong selection effects. A test has been discovered that is independent of these selection effects and is based upon the kinematics of CVs. If the standard models of evolution are correct then long‐period ( P orb > 5 h) 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 for accurate radial velocities to be obtained. We find values of −1.7, 5.4, 15.4 and 1.8 km s −1 with uncertainties of the order of 3 km s −1 , referred to the dynamical local standard of rest, leading to a dispersion of ∼8 km s −1 . Calculation of a 95 per cent confidence interval gives the result 4 < σ γ < 28 km s −1 compared with a prediction of 15 km s −1 . We also have an improved determination of mass donor spectral type, K 2 and q for the four systems.