1 Department of Astronomy and Astronomical Observatory, Odessa National University, T.G. Shevchenko Park, 65014 Odessa;
Isaac Newton Institute of Chile, Odessa Branch, Ukraine
e-mail: email@example.com; firstname.lastname@example.org; email@example.com
2 GEPI, Observatoire de Paris-Meudon, 92125 Meudon Cedex, France
3 Tavrian National University, Yaltinskaya 4, 330000 Simferopol, Crimea, Ukraine
4 WIYN Observatory, 950 N Cherry Ave, Tucson, AZ 85719, USA
Received: 19 October 2011
Accepted: 20 March 2012
Aims. We derive the stellar atmosphere parameters and chemical element abundances of four stars classified as semi-regular variables of type “d” (SRd). These stars should presumably belong to the Galactic halo population.
Methods. Elemental abundances are derived by applying both local thermodynamical equilibrium and non-local thermodynamical equilibrium analyses to high resolution (R ≈ 80 000) spectra obtained with the CFHT ESPaDOnS spectrograph. We determine the abundances of 27 chemical elements in VW Dra, FT Cnc, VV LMi, and MQ Hya.
Results. The stars of our present program have a chemical composition that is inconsistent with their presumable status as metal-deficient halo giants. All studied SRd giants have relative-to-solar elemental abundances that are typical of the thick/thin Galactic disk stars. We find that all objects of this class for which spectroscopic follow up analyses have been completed show a dichotomy in the amplitudes of their photometric variations. Specifically, the disk objects have small amplitudes, while halo SRd stars have much larger amplitudes, which indicates that amplitude is obviously related to the metallicity of the star.
Key words: stars: abundances / stars: variables: general / stars: late-type / stars: fundamental parameters
Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.
Figures 2 and 3 are available in electronic form at http://www.aanda.org
© ESO, 2012