A new stellar library developed for stellar population synthesis modelling is presented. The library consists of 985 stars spanning a large range in atmospheric parameters. The spectra were obtained at the 2.5‐m Isaac Newton Telescope and cover the range λλ 3525–7500 Å at 2.3 Å (full width at half‐maximum) spectral resolution. The spectral resolution, spectral‐type coverage, flux‐calibration accuracy and number of stars represent a substantial improvement over previous libraries used in population‐synthesis models.

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.

In this paper we develop an evolutionary stellar population synthesis model to predict spectral energy distributions, SED's, for single-age, single-metallicity stellar populations, SSP's, at resolution ∼1.8Å in two narrow, but very important spectral regions around 4000Å and 5000Å. The input stellar database is composed of a subsample of ∼550 stars, selected from the original KPNO coude feed stellar spectral library of Jones. Therefore, this is the first time that an evolutionary model employs such an extensive empirical stellar spectral library, at such high resolution, for supporting its SED's predictions.A spectral library corresponding to simple old stellar populations with metallicities in the range −0.7 ≤ [F e/H] ≤ +0.2 is presented here, as well as an extensive discussion about the most popular system of absorption indices at intermediate resolution, the Lick system, showing the advantages of using the new model predictions. Also, for the first time is shown the behavior of the system of indices of Rose, at higher resolution, as a function of the age and metallicity of the stellar population.The newly synthesized model spectra can be used to analyze the observed galaxy spectrum in a very easy and flexible way, allowing us to adapt the theoretical predictions to the characteristics of the data instead of proceeding in the opposite direction as, for example, we should do when transforming the observational data for using model predictions based on a particular instrument-dependent system of indices at a specific resolution. The synthetic SSP spectra, with flux-calibrated response curve, can be smoothed to the same resolution of the observations, or to the measured galaxy internal velocity dispersion, allowing us to analyze the observed spectrum in its own system. Therefore we are able to utilize all the information contained in the data, at their spectral resolution. After performing this step, the entire observational spectrum can be compared at once, or the analysis can be done measuring a particular set of features in the two, the synthesized and the observational spectrum, rather than trying to correct the latter from broadening or instrumental effects.The SSP model spectra were calibrated at relatively high resolution with two well studied metal-rich globular clusters in our galaxy, 47 Tuc and NGC 6624, providing very good fits and being able to detect well known spectral peculiarities such as the CN anomaly of 47 Tuc. The model was also confronted to an early-type galaxy, NGC 3379, revealing its well known magnesium over iron overabundance, and showing how appropriate are the new model predictions, as well as the way in which they can be used, for studying the elemental ratios of these stellar systems. In fact, different models of different metallicities provide equal approaches to the galaxy spectrum: once H β is properly constrained, either we are able to fit the iron features (with a metallicity somewhat in the range -0.4≤[Fe/H]≤0) or the magnesium features (with a metallicity in the range 0≤[Fe/H]≤...

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We present synthetic spectral energy distributions (SEDs) for single-age, single-metallicity stellar populations (SSPs) covering the full optical spectral range at moderately high resolution [full width at half-maximum (FWHM) = 2.3 Å]. These SEDs constitute our base models, as they combine scaled-solar isochrones with an empirical stellar spectral library [Medium resolution INT Library of Empirical Spectra (MILES)], which follows the chemical evolution pattern of the solar neighbourhood. The models rely as much as possible on empirical ingredients, not just on the stellar spectra, but also on extensive photometric libraries, which are used to determine the transformations from the theoretical parameters of the isochrones to observational quantities. The unprecedented stellar parameter coverage of the MILES stellar library allowed us to safely extend our optical SSP SED predictions from intermediate-to very-old-age regimes and the metallicity coverage of the SSPs from super-solar to [M/H] = −2.3. SSPs with such low metallicities are particularly useful for globular cluster studies. We have computed SSP SEDs for a suite of initial mass function shapes and slopes. We provide a quantitative analysis of the dependence of the synthesized SSP SEDs on the (in)complete coverage of the stellar parameter space in the input library that not only shows that our models are of higher quality than those of other works, but also in which range of SSP parameters our models are reliable. The SSP SEDs are a useful tool to perform the analysis of stellar populations in a very flexible manner. Observed spectra can be studied by means of full spectrum fitting or by using line indices. For the latter, we propose a new line index system to avoid the intrinsic uncertainties associated with the popular Lick/IDS system and provide more appropriate, uniform, spectral resolution. Apart from constant resolution as a function of wavelength, the system is also based on flux-calibrated spectra. Data can be analysed at three different resolutions: 5, 8.4 and 14 Å (FWHM), which are appropriate for studying globular cluster, low-and intermediate-mass galaxies, and massive galaxies, respectively. Furthermore, we provide polynomials to transform current Lick/IDS line index measurements to the new system. We provide line index tables in the new system for various popular samples of Galactic globular clusters and galaxies. We apply the models to various stellar clusters and galaxies with high-quality spectra, for which independent studies are available, obtaining excellent results. Finally, we designed a web page from which not only these models and stellar libraries can be downloaded but which also provides a suite of on-line tools to facilitate the handling and transformation of the spectra.

We present models that predict spectra of old-and intermediate-aged stellar populations at 2.51Å (FWHM) with varying [α/Fe] abundance. The models are based on the MILES library and on corrections from theoretical stellar spectra. The models employ recent [Mg/Fe] determinations for the MILES stars and BaSTI scaled-solar and α-enhanced isochrones. We compute models for a suite of IMF shapes and slopes, covering a wide age/metallicity range. Using BASTI, we also compute "base models" matching The Galactic abundance pattern. We confirm that the α-enhanced models show a flux excess with respect to the scaled-solar models blue-ward ∼4500Å, which increases with age and metallicity. We also confirm that both [MgFe] and [MgFe] ′ indices are [α/Fe]-insensitive. We show that the sensitivity of the higher order Balmer lines to [α/Fe] resides in their pseudo-continua, with narrower index definitions yielding lower sensitivity. We confirm that the α-enhanced models yield bluer (redder) colours in the blue (red) spectral range. To match optical colours of massive galaxies we require both α-enhancement and a bottom-heavy IMF. The comparison of Globular Cluster line-strengths with our predictions match the [Mg/Fe] determinations from their individual stars. We obtain good fits to both full spectra and indices of galaxies with varying [α/Fe]. Using thousands of SDSS galaxy spectra we obtain a linear relation between a proxy for the abundance,

Abstract. We present SEDs for single-age, single-metallicity stellar populations (SSPs) covering the full optical spectral range at resolution (FWHM = 2.3Å). These SEDs can be regarded as our base models, as we combine scaled-solar isochrones with an empirical stellar spectral library (MILES), which follows the chemical evolution pattern of the solar neighbourhood. The models rely as much as possible on empirical ingredients as also employ extensive photometric libraries. Thanks to the unprecedented parameter coverage of the MILES library we synthesize SSP SEDs from intermediate-to very-old age regimes, and the metallicity from super-solar to [M/H] = −2.3, all for a suite of IMF shapes and slopes. We propose a new Line Index System (LIS), based on flux-calibrated spectra, to avoid the intrinsic uncertainties associated with the Lick/IDS system and provide more appropriate, uniform, spectral resolution.

We extend the spectral range of our stellar population synthesis models based on the MILES and CaT empirical stellar spectral libraries. For this purpose, we combine these two libraries with the Indo‐U.S. to construct composite stellar spectra to feed our models. The spectral energy distributions (SEDs) computed with these models and the originally published models are combined to construct composite SEDs for single‐age, single‐metallicity stellar populations (SSPs) covering the range λλ3465–9469 Å at moderately high and uniform resolution (full width at half‐maximum = 2.51 Å). The colours derived from these SSP SEDs provide good fits to Galactic globular cluster data. We find that the colours involving redder filters are very sensitive to the initial mass function (IMF), as well as a number of features and molecular bands throughout the spectra. To illustrate the potential use of these models, we focus on the Na i doublet at 8200 Å and with the aid of the newly synthesized SSP model SEDs, we define a new IMF‐sensitive index that is based on this feature, which overcomes various limitations from previous index definitions for low‐velocity dispersion stellar systems. We propose an index–index diagram based on this feature and the neighbouring Ca ii triplet at 8600 Å, to constrain the IMF if the age and [Na/Fe] abundance are known. Finally we also show a survey‐oriented spectrophotometric application which evidences the accurate flux calibration of these models for carrying out reliable spectral fitting techniques. These models are available through our user‐friendly website.