  Recent X-ray observations of microquasars and Seyfert galaxies reveal the
broad emission lines in their spectra, which can arise in the innermost parts
of accretion disks. A theoretical analysis of observations and their
interpretations were discussed in a number of papers. We consider a radiating
annulus model to simulate spectral line shapes. That is a natural approximation
for narrow emitting circular rings without extra astrophysical assumptions
about emissivity laws. Recently Muller & Camenzind (2004) presented results of
their calculations and classified different types of spectral line shapes and
described their origin. We clarified their hypothesis about an origin of
doubled peaked and double horned line shapes. Based on results of numerical
simulations we showed that double peaked spectral lines arise almost for any
location of narrow emission rings (annuli) although Muller & Camenzind (2004)
suggested that such profiles arise for relatively flat space-times and typical
radii for emission region about 25 r_g. We showed that triangular spectral
lines could arise for nearest annuli and high inclination angles. We discuss a
possibility of appearance of narrow spectral line shapes as a result of
spiralling evolution of matter along quasi-circular orbits which could be
approximated by narrow annuli.
