We would like to find a way to improve the determination of galaxy star formation history from integrated light spectroscopy. To this end, several classes of chemically peculiar (CP) stars arise during the course of normal evolution in single stars a
nd noninteracting binary stars. An aging stellar population has periods of time in which CP stars contribute to the integrated light, and others in which the contributions fade. The HgMn stars, for example, occupy a narrow temperature range of 10500 to 16000 K, which maps to a narrow range of ages. Wolf-Rayet stars, He-poor stars, Bp-Ap stars, Am-Fm stars, and C stars all become very common in a normal stellar population at various ages between zero and several Gyr, fading in and out in a way that is analogous to features used in stellar spectral classification. We examine population fractions and light fractions in order to assess the feasibility of using CP stars as age tracers. We find that, even though CP stars do not usually dominate in number, there are enough of them so that the CP spectral features are detectable in high-quality integrated spectra of young and intermediate age stellar populations. The new technique should be calibratable and useful. Furthermore, using CP signatures as age dating tools sidesteps reliance on photometry that is susceptible to dust and Balmer features that are susceptible to nebular fill-in.
Spectral data on early type galaxies is analyzed for chemical abundance with an emphasis on obtaining detailed abundances for the elements O and Si in addition to C, N, Na, Mg, Ca, Fe, and Ba. The abundance trends with velocity dispersion fit preconc
eptions based upon previous Mg conclusions, namely that larger galaxies have a higher alpha element to iron peak ratio indicative of a higher ratio of Type II to Type Ia supernova products. The heaviest alpha elements, Ca and Ti, do not participate in this trend, although this fact does not necessarily alter the basic picture given the uncertainties in nucleosynthetic yields. Elements that likely have significant contributions from intermediate-mass stars, namely C, N, and Ba, also gain ground relative to Fe in massive galaxies at a modest level, with the Ba conclusion uncertain from our data alone.
In a sample of elliptical galaxies that span a large range of mass, a previously unused Ca index, CaHK, shows that [Ca/Fe] and [Ca/Mg] systematically decrease with increasing elliptical galaxy mass. Metallicity mixtures, age effects, stellar chromosp
heric emission effects, and low-mass initial mass function (IMF) boost effects are ruled out as causes. A [Ca/Fe] range of less than 0.3 dex is sufficient to blanket all observations. Feature gradients within galaxies imply a global Ca deficit rather than a radius-dependent phenomenon. Some, but not all, Type II supernova nucleosynthetic yield calculations indicate a decreasing Ca/Fe yield ratio in more massive supernovae, lending possible support to the hypothesis that more massive elliptical galaxies have an IMF that favors more massive stars. No Type II supernova nucleosynthetic yield calculations show significant leverage in the Ca/Fe ratio as a function of progenitor metallicity. Therefore, it seems unlikely that the Ca behavior can be explained as a built-in metallicity effect, and this argues against explanations that vary only the Type II to Type Ia supernova enrichment ratio.
