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The probabilistic nature of the IMF in stellar systems implies that clusters of the same mass and age do not present the same unique values of their observed parameters. Instead they follow a distribution. We address the study of such distributions in terms of their confidence limits that can be obtained by evolutionary synthesis models. These confidence(More)
This paper describes a new determination of the primordial helium abundance (Y P), based on the abundance analysis of five metal-poor extragalactic H ii regions. For three regions of the sample (SBS 0335–052, I Zw 18, and H 29) we present tailored photoionization models based on improved calculations with respect to previous models. In particular, we use(More)
In this paper we develop a new formalism for the theoretical study of stellar populations, which provides simple mathematical tools to account for the distributed nature of stellar population properties. This formalism is as accurate as large Monte Carlo simulations and as simple as standard synthesis models, being at the same time more powerful than either(More)
We present a review on the determination of the primordial helium abundance , Y p , based on the study of hydrogen and helium recombination lines in extragalactic H ii regions. We also discuss the observational determinations of the increase of helium to the increase of oxygen by mass ∆Y /∆O, and compare them with predictions based on models of galactic(More)
We present IACTalks, a free and open access seminars archive (http://iactalks.iac.es) aimed at promoting astronomy and the exchange of ideas by providing high-quality scientific seminars to the astronomical community. The archive of seminars and talks given at the Instituto de Astrofísica de Canarias goes back to 2008. Over 360 talks and seminars are now(More)
Context. Synthesis models predict the integrated properties of stellar populations. Several problems exist in this field, mostly related to the fact that integrated properties are distributed. To date, this aspect has been either ignored (as in standard synthesis models, which are inherently deterministic) or interpreted phenomenologically (as in Monte(More)
From deterministic to probabilistic population synthesis (why synthesis models are not what we thought they were, and how they can be much more than that) Abstract. For a number of reasons, the properties of integrated stellar populations are distributed. Traditional synthesis models usually return the mean value of such distribution, and a perfect fitting(More)
In this review we address the uncertainties implicit in evolutionary synthesis model computations. After describing the general structure of synthesis codes, we discuss several source of uncertainties that may affect their results. In particular, we discuss the uncertainties arising in the computation of isochrones from evolutionary tracks; those related to(More)
The stochastic nature of the IMF in young stellar clusters implies that clusters of the same mass and age do not present the same unique values of their observed parameters. Instead they follow a distribution. We address the study of such distributions, parameterised in terms of their confidence limits, in evolutionary synthesis models. These confidence(More)