Evolution Of The Stellar Population Synthesis

Age and metallicity are the most important parameters for stellar populations, but they are often found to be degenerated. Previous studies showed that it is difficult to break this degeneracy by broad-band colours alone, so one aim of this thesis is to present several kinds of parameters using the evolutionary population synthesis (EPS) technique to solve the problem. Furthermore, Binary stars have been neglected in most studies of the integrated light of the stellar populations with the EPS methods. However in real clusters and galaxies over 50% stars are in binaries, and binary interaction can result in some important classes of objects, such as blue straggles (BSs) and subdwarf B stars (sdB, also referred as extreme horizontal branch [EHB]) which contribute significantly to the integrated light. Therefore the second aim of this thesis is to include binary stars in EPS models.Our EPS studies (i.e. YEPS) are divided into two parts: one is for the single stellar populations (SSPs), the other part is for the binary stellar populations (BSPs). First, we present the integrated color indices, the spectral energy distributions (ISEDs) and 21 Lick/IDS absorption-line indices for an extensive set of instantaneous burst SSPs. The ages of the SSPs are 1 ≤τ≤19Gyr and the metallicities -2.3≤ [Fe/H]≤0.3. Second, applying a set of absorption-line indices to the Merit Function for Galactic and M31 globular clusters and the circumnuclear region of M32, we obtain their age and metallicity. At last, we include binary interactions in our EPS models to investigate the effects on the integrated colours, ISEDs and Lick absorption feature indices. In our constructed BSPs approximately 50 per cent of stellar systems are binary systems with orbital periods less than 100 yr.