Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986msngr..46...18f&link_type=abstract
The Messenger, vol. 46, p. 18-19
Astronomy and Astrophysics
Astrophysics
Dwarfs:Halo Stars, Halo Stars:Dwarfs, Halo Stars:Spectra, Spectra:Halo Stars
Scientific paper
The determination of detailed elemental abundances in the atmosphere of stars is interesting for many branches of Astrophysics. The huge amount of information obtained with high resolution spectroscopy is useful, for example, to test the model of nucleosynthesis in the stars during their life as weil as the final stages of nucleosynthesis of the elements in stars. This last case does not seem to be directly linked with abundance determination in stars. Still, at the end of their life, the massive stars expelled processed material into the interstellar medium. Then, the atmosphere of stars which will be formed from the interstellar matter will contain the signature of the matter expelled by the stars. The analysis of stars of different age will give some hints for the understanding of these last stages and for the chemical evolution of the Galaxy. The differential study of dwarf stars relative to the sun gives very accurate results. Moreover, the study of halo dwarfs can give clues on the early evolution of the Galaxy. However, halo dwarfs are faint and the limiting magnitude of the instrument is crucial for such studies. At ESO, high resolution spectroscopy was possible only with the 1.4 m CAT + CES. The detector was a RETICON array of 1,870 photodiodes (15 um x 700 um). The limiting visual magnitude was about 7. It was, in principle, possible to obtain fainter stars by long exposures but the so-called "cosmic rays" made the choice hazardous. Multiple exposures of the same object could also be done but the time needed to obtain good spectra for a large sampie of stars was quite long and prohibitive. Thus, this instrumentation was typically used for disk dwarfs. The resolving power was of the order of 100,000. Only the brightest halo dwarfs were then observable.
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