BLUE STRAGGLERS IN GALACTIC OPEN CLUSTERS

摘要

Stellar population synthesis is a powerful tool for the study of complex stellar systems, which is based on the results of single-star evolution theory. Although being very successful in many aspects, there are still some problems unsolved, especially when the effects of the physically interactive binary stars are prominent. As the basic building blocks of evolutionary population synthesis, single stellar population (SSP) models exclude effects of interactive binary systems. In this work, we present a series of synthesized spectra of SSPs based on photomet-ric observations of the galactic open clusters. It is shown that blue straggler stars (BSs) in these clusters, which are considered rooted in close binary systems or collision encounters, provide a considerable amount of enhancement at the ultraviolet and blue part of the spectra. These bright blue objects will modify the integrated spectral energy distribution (ISED) of the host cluster that is usually regarded as a prototype of a SSP, and will alter the age prediction of the unresolved cluster when observed photometrically, therefore greatly influence our understandings of stellar systems when high metallicity intermediate age populations become important. When measured in (B - V) color, the uncertainty in age estimation amounts up to 30%. In this work, 26 open clusters of ages ≥ 1 Gyr are analyzed.