1999ApJ...524..824D

Based on the photometry of the classical open cluster M67 and the thorough membership survey, we made a color-magnitude diagram (CMD) of high-membership stars for the cluster. Apart from the stars fitted by a conventional isochrone (single-star evolutionary model) scheme, we noticed a number of features on the CMD that are usually ignored when constructing the corresponding single stellar population (SSP), especially the large number of blue stragglers. As for the study of the integrated properties of SSPs, we argue that the contributions from all ingredients in a single population of stars, such as the luminous blue stragglers, should be included. These bright blue objects may modify remarkably the spectral energy distribution (SED) in the blue and ultraviolet. In this paper we investigate their effects on the integrated light of single stellar populations. We will show in this work that, by using the observation of M67 in a multicolor intermediate-band system, we can assign adequate theoretical spectra to individual stars. The integrated spectrum of this cluster is dramatically different from the SSP built using isochrones only, which shows increasing enhancement toward shorter wavelengths (starting from about 5000 Å) of the spectrum. Taking this as a general case for SSPs, we can expect a considerable amount of modification to the integrated SEDs, which might cast new light on the analysis of the stellar content in the complex stellar systems.