Volume 562, February 2014
|Number of page(s)||37|
|Section||Galactic structure, stellar clusters and populations|
|Published online||03 February 2014|
1 Laboratoire Univers et Particules de Montpellier, UMR 5299 CNRS & Université Montpellier II, Place Bataillon, 34095 Montpellier, France
2 V.A. Ambartsumian Byurakan Astrophysical Observatory & Isaac Newton Institute of Chile, Armenian Branch, 0213 Aragatsotn Marz, Armenia
3 Observatoire de Lyon, CRAL, UMR 5574 CNRS & Université de Lyon I,9 av. Charles André, 69230 Saint-Genis Laval, France
4 Université Paul Sabatier & Institut de Recherche en Astrophysique et Planétologie, UMR 5277 CNRS & UPS,14 Av. Edouard Belin, 31400 Toulouse, France
Received: 4 October 2013
Accepted: 19 November 2013
The population of cool carbon (C) stars located far from the galactic plane is probably made of debris of small galaxies such as the Sagittarius dwarf spheroidal galaxy (Sgr), which are disrupted by the gravitational field of the Galaxy. We aim to know this population better through spectroscopy, 2MASS photometric colours, and variability data. When possible, we compared the halo results to C star populations in the Fornax dwarf spheroidal galaxy, Sgr, and the solar neighbourhood. We first present a few new discoveries of C stars in the halo and in Fornax. The number of spectra of halo C stars is now 125. Forty percent show Hα in emission. The narrow location in the JHK diagram of the halo C stars is found to differ from that of similar C stars in the above galaxies. The light curves of the Catalina and LINEAR variability databases were exploited to derive the pulsation periods of 66 halo C stars. A few supplementary periods were obtained with the TAROT telescopes. We confirm that the period distribution of the halo strongly resembles that of Fornax, and we found that it is very different from the C stars in the solar neighbourhood. There is a larger proportion of short-period Mira/SRa variables in the halo than in Sgr, but the survey for C stars in this dwarf galaxy is not complete, and the study of their variability needs to be continued to investigate the link between Sgr and the cool halo C stars.
Key words: stars: carbon / Galaxy: halo / Galaxy: stellar content
Based on observations made with the NTT and 3.6 m telescope at the European Southern Observatory (La Silla, Chile; programs 084.D-0302 and 070.D-0203), with the TAROT telescopes at La Silla and at Observatoire de la Côte d’Azur (France), and on the exploitation of the Catalina Sky Survey and the LINEAR variability databases.
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2014
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