Based on extensive statistical-equilibrium calculations, we performed a non-LTE analysis of the K i 7699 equivalent-width data of metal-deficient stars for the purpose of clarifying the behavior of the photospheric potassium abundance in disk/halo stars. While the resulting non-LTE abundance corrections turned out to be considerably large, amounting to 0.2-0.7 dex, their effect on the [K/Fe] vs. [Fe/H] relation is not very important, since these corrections do not show any significant metallicity dependence. Hence, we again confirmed the results of previous LTE studies, that [K/Fe] shows a gradual systematic increase toward a lowered metallicity up to [K/Fe] ∼ 0.3-0.5 at [Fe/H] ∼ −1 to −2, such as in the case of α elements.

We report on chemical abundances for 15 old metal-rich stars in the solar neighborhood based on high-resolution, high signal-to-noise ratio observations. It is found that [O/Fe], [S/Fe], and probably [Ba/Fe] decrease with increasing metallicity, while the remaining elements, C, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, and Ni, generally have solar [X/Fe] ratios irrespective of metallicity. The kinematic data indicate a slight lag in the Galactic rotation for most stars. In combination with their low maximum distance perpendicular to the Galactic plane, Z max , we suggest that most of the sample stars originate from the inner thin disk. This suggestion is supported by the similar abundance pattern of these stars as that of thin-disk stars. The connection of the old metal-rich stars with the old population of the inner disk suggests an inside-out formation of the disk. One exceptional case in our sample is HD 190360. It is suspected to be a thick-disk star based on the enhanced O, S, Mg, and Si abundances as well as the special kinematics, V LSR ¼ À40 km s À1 and Z max ¼ 1:0 kpc. It shows that stars from a population other than the thin disk exist among old metal-rich stars in the solar neighborhood. The location of these stars, presently in the solar neighborhood, may indicate that orbit diffusion effects of old stars are quite significant.

No abstract

Abstract. We obtain abundances of α, iron peak and neutron capture (n-capture) process elements in four Ba stars HD 26886, HD 27271, HD 50082 and HD 98839 based on high resolution, high signal-to-noise spectra. We find that all of these Ba stars are disk stars. Their α and iron peak elements are similar to the solar abundances. The n-capture process elements are overabundant relative to the Sun. In particular, the second peak slow neutron capture process (s-process) elements, Ba and La, are higher than the first peak s-process elements, Y and Zr. Analyzing the abundances of four sample stars, the heavy-element abundances of the strong Ba star HD 50082 are higher than those of other three mild Ba stars. The stellar mass of the strong Ba star HD 50082 is 1.32 M (+0.28, −0.22 M ), which is consistent with the average mass of strong Ba stars (1.5 M ). For mild Ba star HD 27271, we derive 1.90 M (+0.25, −0.20 M ), consistent with the average mass of mild Ba stars (1.9 M , with 0.6 M white dwarf companion). For mild Ba star HD 26886, the derived 2.78 M (+0.75, −0.78 M ) is consistent with the average 2.3 M of mild Ba stars with 0.67 M companion white dwarfs within the errors. Mass of mild Ba star HD 98839 is high to 3.62 M , which inspires more thoughts on the formation of Ba star phenomenon. Using our angular momentum conservation theoretical model of wind accretion of Ba binary systems, we obtain the theoretical heavy-element abundances of Ba stars that best fit our data. The results show that the observed abundances of the typical strong Ba star HD 50082 and the typical mild Ba star HD 27271 are consistent with the theoretical results very well. This suggests that their heavy-element abundances were caused by accreting the ejecta of AGB stars, the progenitors of the present white dwarf companions, through stellar wind. However, wind accretion scenario cannot explain the observed abundance pattern of the mild Ba star HD 26886 with shorter orbital period (P = 1263.2 d). The mild Ba star HD 98839 with high mass (up to 3.62 M ) and very long orbital period (P > 11 000 d) may be either a star with the heavy elements enriched by itself or a "true Ba" star.

We obtain high-resolution and high signal-to-noise ratio spectra of 39 red clump giants selected from the Hipparcos Catalogue. We determine their atmospheric parameters, iron abundances, a-element enhancements, and masses. We find that the sample can be divided into a metal-poor group and a metal-rich group. The majority of the stars are metal-rich ( ) with mass around 2 , while the metal-poor group has lower surfacegravity and lower mass. The variation of a-element abundances with [Fe/H] agrees with that of local G and K disk dwarfs. We also show that the metallicity is weakly correlated with the I-band absolute magnitude and the VϪI color, in agreement with Udalski's recent findings. We make the high-resolution spectra available over the internet for interested readers.

No abstract

No abstract

Abstract. We present observations of ten metal-poor halo stars with the metallicity range −2.3 < [Fe/H] < −1.4 and derive their stellar parameters, acquire some elemental abundances relative to iron and discuss the relation between the abundance ratio and the metallicity. It was found that oxygen abundances are nearly constant at a level of 0.6 dex for our metal-poor halo stars when the non-LTE correction is considered. The α-elements (Mg, Si, Ca and Ti) are overabundant relative to Fe and decrease with increasing metallicity. We also obtained a significant underabundant non-LTE [Na/Fe] ratio from Na  D lines which have a large deviation from the LTE assumption. Scandium is marginally overabundant with respect to iron and tends to decrease with increasing metallicity like the α-elements. A nearly solar value of [Cr/Fe] ratio and underabundant [Mn/Fe] ratio are obtained.