Chemical Yields from the First Stars

We examine the dependence of stellar yields on the metallicity Z of the stellar population. This effect may be important for the very first chemical enrichment from Population III stars, at very low Z. In the range of massive stars, mass loss rates varying with Z have remarkable effects. We also estimate chemical yields from Very Massive Objects (from 120 to 1000 Mo), which might have formed more easily in the very low-Z environment of the first stellar generations.Comment: 5 pages, 7 figures, to appear in The First Stars, Proceedings of the second MPA/ESO workshop, Eds.: Weiss, Abel, Hill, Springer, Heidelberg, 200

New Colour-Mass to Light Relations: the role of the Asymptotic Giant Branch phase and of interstellar dust

Colour-M/L (mass-to-light) relations are a popular recipe to derive stellar mass in external galaxies. Stellar mass estimates often rely on near infrared (NIR) photometry, considered an optimal tracer since it is little affected by dust and by the "frosting" effect of recent star formation episodes. However, recent literature has highlighted that theoretical estimates of the NIR M/L ratio strongly depend on the modelling of the Asymptotic Giant Branch (AGB) phase. We use the latest Padova isochrones, with detailed modelling of the Thermally Pulsing AGB phase, to update theoretical colour-M/L relations in the optical and NIR and discuss the consequences for the estimated stellar masses in external galaxies. We also discuss the effect of attenuation by interstellar dust on colour-M/L relations in the statistical case of large galaxy samples.Comment: 17 pages, 13 figures. MNRAS in pres

Star formation and chemical evolution in SPH simulations: a statistical approach

In Smoothed Particles Hydrodynamics (SPH) codes with a large number of particles, star formation as well as gas and metal restitution from dying stars can be treated statistically. This approach allows to include detailed chemical evolution and gas re-ejection with minor computational effort. Here we report on a new statistical algorithm for star formation and chemical evolution, especially conceived for SPH simulations with large numbers of particles, and for parallel SPH codes. For the sake of illustration, we present also two astrophysical simulations obtained with this algorithm, implemented into the Tree-SPH code by Lia & Carraro (2000). In the first one, we follow the formation of an individual disc-like galaxy, predict the final structure and metallicity evolution, and test resolution effects. In the second one we simulate the formation and evolution of a cluster of galaxies, to demonstrate the capabilities of the algorithm in investigating the chemo-dynamical evolution of galaxies and of the intergalactic medium in a cosmological context.Comment: 17 pages, 20 figures, accepted for publication on MNRA

A chemical evolution model for galaxy clusters

We develop a toy-model for the chemical evolution of the intracluster medium, polluted by the galactic winds from elliptical galaxies. The model follows the "galaxy formation history" of cluster galaxies, constrained by the observed luminosity function.Comment: 6 pages, 10 figures, to appear in the Proceedings of the Workshop "Chemical Enrichment of Intracluster and Intergalactic Medium", Vulcano, Italy, 14-18 May 2001, ASP Conference Serie

Accurate fundamental parameters for Lower Main Sequence Stars

We derive an empirical effective temperature and bolometric luminosity calibration for G and K dwarfs, by applying our own implementation of the InfraRed Flux Method to multi-band photometry. Our study is based on 104 stars for which we have excellent BVRIJHK photometry, excellent parallaxes and good metallicities. Colours computed from the most recent synthetic libraries (ATLAS9 and MARCS) are found to be in good agreement with the empirical colours in the optical bands, but some discrepancies still remain in the infrared. Synthetic and empirical bolometric corrections also show fair agreement. A careful comparison to temperatures, luminosities and angular diameters obtained with other methods in literature shows that systematic effects still exist in the calibrations at the level of a few percent. Our InfraRed Flux Method temperature scale is 100K hotter than recent analogous determinations in the literature, but is in agreement with spectroscopically calibrated temperature scales and fits well the colours of the Sun. Our angular diameters are typically 3% smaller when compared to other (indirect) determinations of angular diameter for such stars, but are consistent with the limb-darkening corrected predictions of the latest 3D model atmospheres and also with the results of asteroseismology. Very tight empirical relations are derived for bolometric luminosity, effective temperature and angular diameter from photometric indices. We find that much of the discrepancy with other temperature scales and the uncertainties in the infrared synthetic colours arise from the uncertainties in the use of Vega as the flux calibrator. Angular diameter measurements for a well chosen set of G and K dwarfs would go a long way to addressing this problem.Comment: 34 pages, 20 figures. Accepted by MNRAS. Landscape table available online at http://users.utu.fi/luccas/IRFM

From computational studies on the mechanism of the formation of organic meterocyclic compounds to spin crossover studies in Prussian Blue

Understanding with the use of computational tools the mechanism of reactions in organic chemistry or the electronic transitions in solid state is a quite challeng- ing problem. The main methods utilised for this research are Density Functional Theory (DFT) and time dependent DFT. The software utilised is GAUSSIAN03 for the reaction mechanism studies and CRYSTAL06 for the study of the spin crossover transition in a Prussian Blue analogue. In chapter 2, we investigate the first two reaction steps of the synthesis reaction mechanism of Dihydro-Imidazo-Phenathridinium (DIP) derivatives, which are a novel class of compounds that intercalate DNA, possessing anticancer properties. In chapter 3, we examine the last step of the DIP synthesis reaction, which is a hydride transfer, in particular it is considered the solvent effect on the excitation energies of the molecules involved in the hydride transfer. In chapter 4, we consider the hydride transfer reaction of heteroaryl-dimethylbenz- imidazoline derivatives (HDBMZ-H) with benzyl-carbamoylpyridinium (BCPY) and benzyl-nitrosoquinolinium (BNIQ) ions. In chapter 5, we study the spin crossover transition (SCO) in the CsFeII[CrIII(CN)6] Prussian Blue analogue. This transition can be induced experimentally by varia- tions of temperature or pressure and more light on this mechanism can be useful in information processing and display technologies. Those fields, in fact can benefit from the application of molecular electronic bistabilities in which the SCO phe- nomenon can be classified