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Maurizio Busso

Publications and source records attributed to Maurizio Busso.

24 records · Page 2Linked to original sources
arXiv2006

Technetium and the third dredge up in AGB stars II. Bulge stars

We searched for Technetium (Tc) in a sample of bright oxygen-rich asymptotic giant branch (AGB) stars located in the outer galactic bulge. Tc is an unstable element synthesised via the s-process in deep layers of AGB stars, thus it is a reliable indicator of both recent s-process activity and third dredge-up. We aim to test theoretical predictions on the luminosity limit for the onset of third dredge-up. Using high resolution optical spectra obtained with the UVES spectrograph at ESO's VLT we search for resonance lines of neutral Tc in the blue spectral region of our sample stars. These measurements allow us to improve the procedure of classification of stars with respect to their Tc content by using flux ratios. Synthetic spectra based on MARCS atmospheric models are presented and compared to the observed spectra around three lines of Tc. Bolometric magnitudes are calculated based on near infrared photometry of the objects. Among the sample of 27 long period bulge variables four were found to definitely contain Tc in their atmospheres. The luminosity of the Tc rich stars is in agreement with predictions from AGB evolutionary models on the minimum luminosity at the time when third dredge-up sets in. However, AGB evolutionary models and a bulge consisting of a single old population cannot be brought into agreement. This probably means that a younger population is present in the bulge, as suggested by various authors, which contains the Tc-rich stars here identified.

astro-ph↗
arXiv2003

Mid-infrared photometry of carbon stars and perspectives for surveys in the Magellanic Clouds from Dome-C

A preliminary analysis of the data from the MSX space infrared satellite, seems to confirm that the [8.8]-[12.5] micron color index is well correlated with the mass-loss rates in carbon stars of our Galaxy. The extension of this mid-infrared observation criterion to the Magellanic Clouds, with a small-size telescope, able to perform a continuous survey from Dome-C on the Antarctic Plateau, could be crucial to trace the local AGB population and evolution.

astro-ph↗
arXiv2000

Lead: Asymptotic Giant Branch production and Galactic Chemical Evolution

The enrichment of Pb in the Galaxy is followed in the framework of a detailed model of Galactic chemical evolution that already proved adequate to reproduce the chemical enrichment of O and of the elements from Ba to Eu. The stellar yields are computed through nucleosynthesis calculations in the Asymptotic Giant Branch (AGB) phase of low- and intermediate-mass stars, covering a wide range of metallicities. The physical parameters of the stellar structure were derived from full stellar evolutionary models previously computed. We show that low-mass AGB stars are the main producers of Pb in the Galaxy, with a complex dependence on metallicity and a maximum efficiency at [Fe/H] ~ -1. Our calculations succeed in reproducing the abundances of Pb isotopes in the solar system: the role attributed by the classical analysis of the s-process to the 'strong component', in order to explain more than 50% of solar 208Pb, is actually played by the high production of Pb in low-mass and low-metallicity AGB stars. We then follow the Galactic chemical evolution of Pb isotopes and give our expectations on the s-process contribution to each of them at the epoch of the solar system formation. Finally, we present new spectroscopic estimates of Pb abundance on a sample of field stars and compare them, together with a few other determinations available, with the predicted trend of [Pb/Fe] in the Galaxy.

astro-ph↗
arXiv2000

s- and r-process elements in two very metal-poor stars

New measurements of neutron-capture elements are presented for two very metal-poor stars ([Fe/H] ~ -3). One (LP 625-44) has an s-process signature believed to be due to mass transfer from a now-extinct metal-poor AGB companion, and the second (CS 22897-008) is one of a number of very metal-poor stars having high [Sr/Ba] ratios which is not expected from the r-process. In the s-process star, many elements including lead have been detected, providing strong constraints on the 13C pocket in the now-extinct AGB star. In the Sr-rich star, Zn, Y, and Zr are also seen to be overabundant, and several possible nucleosynthesis mechanisms are discussed.

astro-ph↗
arXiv1998

A New Astrophysical Interpretation of the Si and Ti Isotopic Compositions of Mainstream SiC Grains from Primitive Meteorites

Mainstream presolar SiC grains from primitive meteorites show a clear s-process signature in the isotopic composition of heavy trace elements. These grains most likely condensed in the winds of a variety of AGB stars. However, the non-solar and correlated Si and Ti isotopic compositions measured in these grains are inconsistent with a pure s-signature. We present a possible solution to this much-discussed problem by assuming a spread in the original composition of parent AGB stars due to small chemical inhomogeneities in the interstellar medium at the time of their birth. These inhomogeneities may naturally arise from variations in the contributions of each nuclide to the interstellar medium by the relevant stellar nucleosynthetic sites, SNII and different subtypes of SNIa.

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