The statistical properties of circumstellar disks around young stars are important for constraining theoretical models for the formation and early evolution of planetary systems. In this brief review, I survey the literature related to ground-based and Spitzer-based infrared (IR) studies of young stellar clusters, with particular emphasis on tracing the evolution of primordial (“protoplanetary”...

We revisit the observed frequencies of carbon-enhanced metal-poor (CEMP) stars as a function of the metallicity in the Galaxy, using data from the literature with available high-resolution spectroscopy. Our analysis excludes stars exhibiting clear overabundances of neutron-capture elements and takes into account the expected depletion of surface carbon abundance that occurs due to CN processing...

We present in this contribution our set of multiwavelength synthesis models including the evolution of single and binary stars. The main results we have obtained can be summarized as follows: (a) massive close-binary systems will start to experience mass transfer episodes after the first 4 Myr of the starburst evolution; (b) as a result of these mass transfer processes, stars of relatively low ...

We consider the dynamical evolution of a disk of stars orbiting a central black hole. In particular, we focus on the effect of the stellar mass function on the evolution of the disk, using both analytic arguments and numerical simulations. We apply our model to the ring of massive stars at ≃ 0.1pc from the Galactic Center, assuming that the stars formed in a cold, circular disk, and find that o...

Formation of massive stars by accretion requires a high accretion rate of Ṁ∗ > 10 −4 M⊙/yr to overcome the radiation pressure barrier of the forming stars. Here, we study evolution of protostars accreting at such high rates, by solving the structure of the central star and the inner accreting envelope simultaneously. The protostellar evolution is followed starting from small initial cores until...

We have carried out a study of the early type stars in nearby OB associations spanning an age range of ∼ 3 to 16 Myr, with the aim of determining the fraction of stars which belong to the Herbig Ae/Be class. We studied the B, A, and F stars in the nearby (≤ 500 pc) OB associations Upper Scorpius, Perseus OB2, Lacerta OB1, and Orion OB1, with membership determined from Hipparcos data. We also in...

The discrepancy between the observed abundances of He in the interstellar medium and those predicted by stellar and galactic chemical evolution remains largely unexplained. In this paper, we attempt to shed some light on this unsolved problem by presenting a quantitative comparison of the He abundances recently measured in six planetary nebulae (IC 289, NGC 3242, NGC 6543, NGC 6720, NGC 7009, N...

We review the properties of massive star evolution in different environments, where the major environmental factor is metallicity. Comparisons between evolutionary models and observations of massive OB, WR stars and related objects are presented. We also review several observations asking for future improvements of stellar models and theoretical developments in this respect. We summarize evolut...

We present preliminary results of stellar structure and nucleosynthesis calculations for some early stars. The study (still in progress) seeks to explore the expected chemical signatures of second generation lowand intermediate-mass stars that may have formed out of a combination of Big Bang and Pop III (Z=0) supernovae material. Although the study is incomplete at this stage, we find some impo...

Aims. N-body simulations give us a rough idea of how the shape of a simulated object appears in three-dimensional space. From an observational point of view this may give us a misleading picture as a stellar system consists of both bright and faint stars. The faint stars may be the most common stars in the system but the morphological information obtained by observations of an object may be dom...