The Curious Case of 4U 182030: On the Resonant Trapping and Tidal Dissipation Rate of the White Dwarf Secondary
Snezana Prodan
University of Toronto
It has been suggested that the 170 day period in the light curve of the
low mass Xray binary 4U 182030 arises from the presence of a third
body with a large inclination to the binary orbit. We show that this long
period motion arises if the system is librating around the stable fixed
point in a Kozai resonance. We demonstrate that mass transfer drives the system toward this fixed point, and calculate, both analytically and via numerical integrations, that the period of libration is of order 170 days when the mutual inclination is near the Kozai critical value, which could indicate that the system might had suffered through Kozai migration. The nonzero eccentricity of the binary, combined with tidal dissipation, implies that the rate of change of the binary period would be slower than, or even of opposite sign to, that implied by standard mass transfer models. If the 170 day period results from libration, then, contrary to appearances, the orbital period of the inner binary is increasing with time; in that case, (e/0.009)^2Q/k_2 > 2.5x10^9, where k_2=0.01 is the tidal Love number and e=0.009 is the fiducial eccentricity of the inner binary. It appears unlikely that the observed negative period derivative results from the smaller than expected (but positive) value of period derivative combined with the previously suggested acceleration of the system in the gravitational field of the host globular cluster NGC 6624.
Date:  Monday, 24 October 2011 
Time:  15:00 
Where:  McGill University 
 Ernest Rutherford Physics Building, R.E. Bell Conference Room (room 103) 
Contact:  Robert Rutledge 
