Illingworth, Garth Darrel
Description
Central velocity dispersions have been derived for
10 globular clusters from high dispersion (6.7A mm-1)
coude spectra of the integrated light. Two methods were
used. The first involved the comparison of the cluster
spectra with star spectra convolved with an appropriate
velocity distribution function. This is the method used
often for velocity dispersion determinations from spectra
of the integrated light of galaxies (e.g. Morton and
Chevalier 1972). Fourier techniques were used in...[Show more] the
second method. Power spectra were obtained from the
Fourier transformed spectral-intensity data of both the
stars and the clusters. The star power spectra were
multiplied by the transformed velocity distribution function
and compared with the cluster power spectra. The
advantages accruing from use of the Fourier method over
the direct comparison method are (1) use of much more of
the information contained in the original spectra;
(2) greater accuracy arising from the increased sensitivity
to changes in the velocity dispersion and (J) lessening
of the necessity for critical local matching in the star - cluster line strengths. Surface density distributions have been derived
from photoelectric surface photometry (using centered
apertures and small aperture drifts across the cluster)
and from star counts. These surface density distributions
were then compared with the theoretical distributions given
by King (1966a). These theoretical surface density distributions
are derived from self-consistent single mass models using a realistic velocity distribution function.
Two characteristic lengths, the core radius rc and
the tidal cutoff rt, obtained from the comparison of the
theoretical and observed surface density distributions are
then usBd, along with the velocity dispersion, to derive
masses for the 10 clusters. For comparison, masses are
also derived by the r 1/4 law/virial theorem method. The
mass-to-light ratio is obtained and the form of the luminosity
function in globular clusters is discussed.
Items in Open Research are protected by copyright, with all rights reserved, unless otherwise indicated.