Spectroscopy of high proper motion stars in the ground--based UV

Based on high quality spectral data (spectral resolution R>60000) within the wavelength range of 3550-5000 AA we determined main parameters (effective temperature, surface gravity, microturbulent velocity, and chemical element abundances including heavy metals from Sr to Dy) for 14 metal-deficient G-K stars with large proper motions. The stars we studied have a wide range of metallicity: [Fe/H]=-0.3 \div -2.9. Abundances of Mg, Al, Sr and Ba were calculated with non-LTE line-formation effects accounted for. Abundances both of the radioactive element Th and r-process element Eu were determined using synthetic spectrum calculations. We selected stars that belong to different galactic populations according to the kinematical criterion and parameters determined by us. We found that the studied stars with large proper motions refer to different components of the Galaxy: thin, thick disks and halo. The chemical composition of the star BD+80 245 located far from the galactic plane agrees with its belonging to the accreted halo. For the giant HD115444 we obtained [Fe/H]=-2.91, underabundance of Mn, overabundance of heavy metals from Ba to Dy, and, especially high excess of the r-process element Europium: [Eu/Fe]=+1.26. Contrary to its chemical composition typical for halo stars, HD115444 belongs to the disc population according to its kinematic parameters.Comment: 16 pages, 4 figures, 5 tables, "UV Universe-2010 (2nd NUVA Symposium) conference

Fermi surface nesting and possibility of orbital ordering in FeO

We study FeO, a Mott insulator in GGA and GGA+U approximations. In the GGA we find a multi-band metallic state with remarkable inter-band nesting between two $t_{2g}$ bands of Fermi surface, which signals possible instability towards an orbital ordered insulating phase. Such broken symmetry state, although has lower energy than the underlying homogeneous metallic state, but the gap magnitude is less than the experimentally observed optical gap. Therefore we incorporate the calculated value of on-site Coulomb repulsion U on orbital ordered state. We find that symmetry breaking and Coulomb correlations cooperate together to stabilize the system and give an insulating orbital ordered state, with the gap magnitude very close to the experimental value. We propose this method as a possible indication of orbital ordering in LDA and GGA calculations. We check our method with known examples of LiVO$_2$ and LaMnO$_3$.Comment: 4 pages, 4 figures, 1 tabl

Spectral investigation of new candidates to lambda Bootis type stars

We made detailed abundance analysis for ultimative test of membership of twenty λ Bootis type stars candidates. Atmosphere parameters, LTE abundances for ten elements (including C and O) and NLTE values for Na were determined. We are able to confirm or establish the membership for nine objects (HD 23258, HD 36726, HD 40588, HD 74911, HD 84123, HD 91130, HD 106223, HD 111604 and HD 290799). Six stars (HD 90821, HD 98772, HD 103483, HD 108765, HD 201184 and HD 261904) can be definitely ruled out as being member of the λ Bootis group whereas no ambiguous decision can be drawn for another five stars (HD 66684, HD 105058, HD 120500, HD 141851 and HD 294253). We also tryed to find apparent spectroscopic binaries which have two solar abundant components mimic one metal-weak star as proposed by Faraggiana & Bonifacio (1999)