We have developed a new stellar population synthesis model designed to study earlytype galaxies. It provides optical and near-infrared colors, and line indices for 25 absorption lines. It can synthesize single age, single metallicity stellar populations or follow the galaxy through its evolution from an initial gas cloud to the present time. The model incorporates the new isochrones of the Padova group and the latest stellar spectral libraries. We have applied our model to new data for a set of three early-type galaxies, to find out whether these can be fitted using single-age old metal-rich stellar populations, as is normal practice when one uses other stellar models of this kind. The model is extensively compared with previous ones in the literature to establish its accuracy as well as the accuracy of this kind of models in general.Using the evolutionary version of the model we find that we cannot fit the most metal-rich elliptical galaxies if we keep the IMF constant and do not allow infall of gas. We do however reproduce the results of Arimoto & Yoshii (1986) for the evolution of the gas, and produce colors, and, for the first time with this type of models, absorption line-strengths. It is in fact possible to fit the data for the elliptical galaxies by varying the IMF with time. Our numerical model is in good broad agreement with the analytical simple model. We prefer however to calculate the evolution of the gas numerically instead of using the simple model, since it offers more flexibility, and even improved insight, when comparing with observations. In the present paper we describe the model, and compare a few key observables with new data for three early-type standard galaxies. However the data, as well as our fits, will be discussed in much more detail in a second paper , where some conclusions will be drawn about elliptical galaxies on the basis of this model.

We present here the results of applying a new chemo-evolutionary stellar population model developed by ourselves in a previous paper to new high quality observational data of the nuclear regions of two representative elliptical galaxies and the bulge of the Sombrero galaxy. Here we fit in detail ∼20 absorption lines and 6 optical and near-infrared colors following two approaches: fitting a single-age singlemetallicity model and fitting our full chemical evolutionary model. We find that all of the iron lines are weaker than the best fitting models predict, indicating that the iron-abundance is anomalous and deficient. We also find that the Ca I index at 4227Å is much lower than predicted by the models. We can obtain good fits for all the other lines and observed colors with models of old and metal-rich stellar populations, and can show that the observed radial gradients are due to metallicity decreasing outward. We find that good fits are obtained both with fully evolutionary models and with single-age single-metallicity models. This is due to the fact that in the evolutionary model more than 80% of stars form within 1.5 Gyr after the formation of the galaxies. The fact that slightly better fits are obtained with evolutionary models indicates these galaxies contain a small spread in metallicity.

This paper represents a collective effort to provide an extensive electronic database useful for the interpretation of the spectra and evolution of galaxies. A broad variety of empirical and theoretical data are discussed here, and the data are made fully available in the AAS CD-ROM Series, Vo. 7. Several empirical stellar libraries are part of this database. They cover the ultraviolet spectral range observed with IUE, optical data from different ground-based telescopes, and ground-based infrared data. Spectral type coverage depends on the wavelength, but it is mostly complete for types O and M and luminosity classes V to I. A large metallicity range is covered as well. Theoretical libraries of selected spectral indices of cool stars and of stellar continuum fluxes in the temperature range 2000 K to 50,000 K, as well as Wolf-Rayet energy distributions are presented. Several libraries of star clusters and early-type galaxies have been selected for this database. We discuss an extensive set of empirical spectra templates covering the wavelength region from 1200 - 9800 A, as well as narrow-band line indices in a large number of passbands. Bench-mark spectra of nearby galaxies for model tests are included as well. We compiled numerous evolutionary models and isochrones for stars of all mass ranges of interest, wide metallicity range, and for all evolutionary phases, including the pre-main-sequence phase. The majority of the models have been computed by the Geneva and Padova groups. Evolutionary synthesis models computed by several independent groups are made available. They can be applied to old and young systems, and are optimized with respect to different aspects of input physics. The model predictions include stellar (colors, magnitudes, absorption features) and nebular (emission-line fluxes) properties. Finally, we present models of ionized gas to be used for the interpretation of active galactic nuclei and young star-forming galaxies. The community is encouraged to make use of this electronic database and to perform a critical comparison between the individual datasets

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Abstract. In this article we compare and contrast the predictions of models we have published previously, with the most recent observational data on the G-dwarf/K-dwarf metallicity distribution in the local Galaxy, as well as with up to date plots showing the relation between the Be and B abundances of local stars and their Fe abundances. We show how the data clearly support models in which infall to the plane has not declined secularly during the disc lifetime, and that the best fits are to models in which the accretion rate has tended to a slow increase. These models, devised to give the best possible account of the G-dwarf metallicity distribution, turn out to give an even better account of the K-dwarf distribution. They also do surprisingly well at predicting the observed plots of Be and B vs. Fe in the disc.

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We discuss several lines of evidence indicating that gas is Ñowing into the solar neighborhood and go on to o †er a theoretical framework to explain this phenomenon, which is important for any model of the chemical and dynamical evolution of the Galaxy. We derive a theoretical age distribution for the G dwarf stars in the solar neighborhood that Ðts well the distribution observed recently in the generally increasing trend of the amplitude of oscillation with time, leading to star formation peaks at several epochs. Our model is based on the interference between two e †ects : the variable rate of gas inÑow to the solar vicinity due to the density wave pattern in the disk, and the arrival of gas from the local intergalactic medium broken cyclically by star formation processes. The model is shown to be consistent with a scenario in which low-metallicity gas falls continually to the Galactic plane from the intergalactic medium, notably in the form of high-velocity clouds.

We present here a new theoretical model designed to explain the interstellar dust grain size distribution function (IDGSDF), and compare its results with previous observationally derived distributions and with previous theoretical models. The range of grain sizes produced in the late stages of stars with different masses is considered, and folded into a model which takes into account the observed changes in the historical local star formation rate. Stars in different mass ranges reach their grain producing epochs at times whose mass dependence is quantifiable, and the range of grain sizes produced has also been estimated as a function of stellar mass. The results show an IDGSDF which has a global slope comparable to the observationally derived plot and three peaks at values of the grain radius comparable to those in the observationally derived distribution, which have their ultimate origin in three major peaks which have been observed in the SFR over the past 15 Gyr. The model uses grain-grain interactions to modify pre-existing size distributions at lower grain sizes, where collisions appear more important. The interactions include disruption by collisions as well as coagulation to form larger grains. The initial distributions are given a range of initial functions (flat, Gaussian, fractal) for their physical parameters, as well as geometrical forms ranging from spherical to highly elongated. The particles are constrained in an imaginary box, and laws of inelastic collisions are applied. Finally we combine the two models and produce an IDGSDF which is a notably good match to the observational fit, and specifically at small grain radii reproduces the data better than the "SFR model" alone.