New Models for the Spectral Evolution of Galaxies

Extract

Bruzual & Chariot (1991, BC91 hereafter) have supplemented the purely photometric isochrone synthesis models of Chariot & Bruzual (1991) with an updated library of stellar spectra and evolutionary tracks in order to compute the spectral evolution of stellar populations. BC91 used the evolutionary tracks of Maeder & Meynet (1989), with the main-sequence lifetimes for stars in the mass range 1.3 M⊙ ≤ m ≤ 2.5 M⊙, revised as prescribed by Maeder & Meynet (1991). BC91 included an accurate description of the late evolution of low and intermediate-mass stars as hot nuclei of planetary nebulae and through the white dwarf cooling sequence. While stars in these stages contribute negligibly to the optical/near-IR light, the self-consistent model of BC91 for an initial burst of star formation can account for the UV excess observed in quiescent early-type galaxies. Models that do not include post-AGB stars require additional star formation to account for this UV excess.