Search results for "Giant star"
showing 5 items of 15 documents
CS 29497-004 abundances
2017
We report an abundance analysis for the highly r-process-enhanced (r-II) star CS 29497-004, a very metal-poor giant with solar system Teff=5013K and [Fe/H]=-2.85, whose nature was initially discovered in the course of the HERES project. Our analysis is based on high signal-to-noise ratio, high-resolution (R~75000) VLT/UVES spectra and MARCS model atmospheres under the assumption of local thermodynamic equilibrium, and obtains abundance measurements for a total of 46 elements, 31 of which are neutron-capture elements. As is the case for the other ~25 r-II stars currently known, the heavy-element abundance pattern of CS 29497-004 well-matches a scaled solar system second peak r-process-elemen…
ESPRESSO radial velocities of HE0107-5240
2020
The vast majority of the known stars of ultra low metallicity ([Fe/H]<-4.5) are known to be enhanced in carbon, and belong to the 'low-carbon band' (A(C)=log(C/H)+12~7.6). It is generally, although not universally, accepted that this peculiar chemical composition reflects the chemical composition of the gas cloud out of which these stars were formed. The first ultra-metal-poor star discovered, HE 0107-5240, is also enhanced in carbon and belongs to the 'low-carbon band'. It has recently been claimed to be a long-period binary, based on radial velocity measurements. It has also been claimed that this binarity may explain its peculiar composition as being due to mass transfer to a former AGB …
Post-AGB candidates in LMC and SMC SALT spectra
2020
We selected a sample of post-AGB candidates in the Magellanic Clouds on the basis of their near- and mid-infrared colour characteristics. Fifteen of the most optically bright post-AGB candidates were observed with the South African Large Telescope in order to determine their stellar parameters and thus to validate or discriminate their nature as post-AGB objects in the Magellanic Clouds. The spectral types of absorption-line objects were estimated according to the MK classification, and effective temperatures were obtained by means of stellar atmosphere modelling. Emission-line objects were classified on the basis of the fluxes of the emission lines and the presence of the continuum. Out of…
Near-infrarred spectro-interferometry of red giant and supergiant stars
2015
Las estrellas supergigantes rojas son estrellas frías y muy masivas que se encuentran en la fase previa a las estrellas Wolf-Rayet y a las supernovas. Presentan extensas atmósferas y fuertes vientos estelares que dan lugar a una importante pérdida de masa. El mecanismo que da lugar a estos vientos y a las extensas atmósferas es actualmente tema de debate. Además, la estimación de los parámetros fundamentales de este tipo de estrellas y su posterior localización en el diagrama HR es de gran importancia para calibrar los modelos de evolución estelar, y entender cómo la pérdida de masa afecta a su evolución. En esta tesis hemos estudiado una muestra representativa de estrellas supergigantes ro…
The Gaia-ESO Survey: impact of extra mixing on C and N abundances of giant stars
2018
The GES survey using FLAMES at the VLT has obtained high-resolution UVES spectra for a large number of giant stars, allowing a determination of the abundances of the key chemical elements C and N at their surface. The surface abundances of these chemical species are well-known to change in stars during their evolution on the red giant branch after the first dredge-up episod, as a result of extra-mixing phenomena. We investigate the effects of thermohaline mixing on C and N abundances using the first comparison between the GES [C/N] determinations with simulations of the observed fields using a model of stellar population synthesis. We explore the effects of thermohaline mixing on the chemic…