Caffau, E. and Bonifacio, P. and Spite, M. and Spite, F. and Monaco, L. and Sbordone, L. and Francois, P. and Gallagher, A. and Plez, B. and Zaggia, S. and Ludwig, H.-G. and Cayrel, R. and Koch, Andreas and Steffen, M. and Salvadori, S. and Klessen, R.S. and Glover, S. and Christlieb, N. (2016) TOPoS: III. An ultra iron-poor CEMP multiple system. Astronomy and Astrophysics, 595: L6. ISSN 1432-0746
Abstract
Aims. One of the primary objectives of the TOPoS survey is to search for the most metal-poor stars. Our search has led to the discovery of one of the most iron-poor objects known, SDSS J092912.32+023817.0. This object is a multiple system, in which two components are clearly detected in the spectrum. Methods. We have analysed 16 high-resolution spectra obtained using the UVES spectrograph at the ESO 8.2 m VLT telescope to measure radial velocities and determine the chemical composition of the system. Results. Cross correlation of the spectra with a synthetic template yields a double-peaked cross-correlation function (CCF) for eight spectra, and in one case there is evidence for the presence of a third peak. Chemical analysis of the spectrum obtained by averaging all the spectra for which the CCF showed a single peak found that the iron abundance is [Fe/H]=–4.97. The system is also carbon enhanced with [C/Fe]=+3.91 (A(C) = 7.44). From the permitted oxygen triplet we determined an upper limit for oxygen of [O/Fe]< +3.52 such that C/O > 1.3. We are also able to provide more stringent upper limits on the Sr and Ba abundances ([Sr/Fe] < +0.70, and [Ba/Fe] < +1.46, respectively).