Chemical composition of semi-regular variable giants. III.

摘要

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.