In 1998 he participated actively to the the first colloquium of the Observatoire de Paris « Galaxy evolution: connecting the distant universe with the local fossil record ». He remained active in this topic, both by the comparison of the chemical composition of ancient stars to that of “Damped Lyman alpha” systems, observed at high redshift, at an epoch contemporary to that of the formation of halo stars, and by the study of more and more primitive halo stars.
- Piercarlo Bonifacio
- Director of UMR8111/GEPI
Since 2001, Piercarlo has a strong collaboration with GEPI: initially as member of the ESO Large Programme LP165.N-276 « First Stars », directed by R. Cayrel, he came to spend one year at GEPI (2001-2002), to tighten his collaboration with the 5 GEPI researchers participating in the LP, R. Cayrel , M. and F. Spite, V. Hill and P. François. With Monique Spite he has provided the reduction and interpretation of the data of dwarf and sub-giant stars, while the other members were mainly dedicating their attention to giant stars. At the end of the LP, Piercarlo obtained the creation of a European research structure, a « Marie Curie excellence Team », composed of 5 researchers named "Cosmological Impact of the First Stars » (CIFIST ), hosted by GEPI because of its link with the ESO-LP. The structure started its operation in 2005 and was completed in September 2009. It has been highly productive on several topics. The first is that it extended the ESO LP to even more primitive objects selected from the SDSS survey, which is several magnitudes deeper than previous surveys. The observation of the lithium plateau at lower metallicities has allowed to see the appearance of a slope and a dispersion, which are absent at the mean metallicities of the halo, with [Fe/H] in the range -1.3 to -2.5. A second one is the 3D hydrodynamical approach to stellar atmospheres, with the creation of a library of 3D models, covering stars of all ages and metallicities. In this approach, the coherence between the atmospheric kinematics and the hydrodynamical modeling of the convective zone is assured, this eliminates the use of free parameters such as mixing length, micro- and macro- turbulence. An interesting application of this approach has been to take into account the convective asymmetry of the lithium lines, which resulted in a major re-evaluation of the 6Li/7Li ratios in the halo stars. This advance has been made possible by the hiring of Hans Ludwig by CIFIST.
Another aspect of Piercarlo’s activities is his involvement in astrophysical instrumentation. This is particularly important for the pôle instrumental of GEPI. Piercarlo is the Project Scientist of the multi-object spectrograph OPTIMOS-EVE for the E-ELT (ESO). The involvement of GEPI in E-ELT instrumentation is clearly a major aspect, both for the purely technological interest and for the guaranteed time for astronomical observations, which may result from this.
Another project, at the moment potential, but of great interest as added value to the GAIA mission, is that of a multi-fibre spectrograph for the prime focus of the Canada-France-Hawaii telescope, aimed at bridging the lack of data from the « radial-velocity-spectrograph » of GAIA, for stars fainter than 17th magnitude. Such a spectrograph will avoid to lose one component of the velocity when proper motions are still measurable, Piercarlo is coordinating a team of 6 engineers and three researchers of GEPI as well as 2 british engineers for the fibre positioner, for a feasibility study of this instrument.
This finishes this short description of the present and past activities of our new director, to whom we wish new successes in his present role.