  We investigate the effects of cosmological constant on the characteristic
peaks in the iron line profile in the black hole accretion disk X-ray spectrum.
Our results show that for a fixed mass black hole, the peaks become less
pronounced and closer together with increasing cosmological constant. This
effect is mainly due to the slower rotational velocity of Keplerian orbits at
large radii in the Schwarzschild-de Sitter spacetime as compared to those for
the Schwarzschild spacetime. This change of the iron line profile is similar to
that obtained from increasing the outer radius of the accretion disk size or
reducing the emission intensity power law exponent in the accretion disk
emissivity models.
