Radiation drag near slowly rotating neutron stars

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Session 13 -- Models or Gas Flows and Spectral Formation
Display presentation, Monday, 30, 1994, 9:20-6:30

[13.03] Radiation drag near slowly rotating neutron stars

M. Coleman Miller (University of Chicago), Frederick K. Lamb (University of Illinois at Urbana-Champaign)

In a previous paper (Miller \& Lamb 1993) we showed that radiation forces are more important than general relativistic corrections to Newtonian gravitational forces in determining the motion of particles accreting onto a nonrotating, isotropically emitting neutron star if the luminosity is greater than $\sim$1\% of the Eddington critical luminosity $L_E^\infty$, even if the radius of the star is less than the radius of the innermost stable orbit. We also showed that at luminosities greater than $\sim 0.2L_E^\infty$, a substantial fraction of the accreting matter can transfer most of its angular momentum and gravitational binding energy to the radiation field before reaching the stellar surface.

Here we extend this work to include slow rotation of the gravitating mass and radiation source, as well as radiation from ring-like boundary layers. By ``slow rotation" we mean that the azimuthal velocity of the radiating source is $v/c\ll 1$ and that the dimensionless angular momentum of the gravitating mass is $j\equiv cJ/GM^2\ll 1$; for all neutron stars with measured rotation periods $j<1$, so this is a good approximation. We find that, compared to particle motion around nonrotating stars, the rate of radiation drag is decreased for prograde motion around rotating sources. However, because the drag time is increased, the total energy and angular momentum transfered from the particle to the radiation field can actually be increased compared to the nonrotating case. We conclude that in any disk-accreting neutron star source, radiation drag will have a significant qualitative effect on particle motion. This work was supported in part by NASA grant NAGW 830 at the University of Chicago and by NSF grant PHY 91-00283 and NASA grant NAGW 1583 at the University of Illinois.

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