Integralinių žvaigždžių spiečių parametrų tikslumas. Stochastiniai efektai

Star clusters are important tools to probe the star formation history in their host galaxy. The physical parameters (age, mass, extinction, and metallicity) of star clusters with integrated broad-band photometry are traditionally derived using the Simple Stellar Population models (SSP). However, parameters are inaccurate because the models do not take the stochastic sampling of star mass in clusters into account. A method to derive the parameters of unresolved star clusters by taking the stochastic sampling of star mass in clusters into account has been developed and shown to give more accurate results than SSP models. The method makes possible the derivation of star cluster parameters, including metallicity, based on broad-band optical and ultraviolet passband photometry in the cases of photometric errors as large as 0.05 mag and 0.15 mag, respectively. Using 203 star clusters in the M31 galaxy, the importance of the metallicity effects has been demonstrated. The metallicity derived for 36 massive M31 star clusters is in a good agreement with the metallicity derived using spectroscopy taken from literature. For 747 star clusters in the M33 galaxy, available optical data have been supplemented with our near-infrared data measured on 2MASS images, and their age, mass, and extinction have been derived. A typical disruption time of star clusters in the M33 galaxy is found to ~300 Myr, i.e., comparable to what is observed in the M31 galaxy