H. M. Qiu

Chemical abundances of old metal-rich stars in the solar neighborhood

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, Zmax, 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, VLSR = -40 km s-1 and Zmax = 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.

High-resolution spectroscopic observations of Hipparcos red clump giants: Metallicity and mass determinations

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, α-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 (Z > 0.3 Z☉) with mass around 2 M☉, while the metal-poor group has lower surface gravity and lower mass. The variation of α-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 V-I color, in agreement with Udalskis recent findings. We make the high-resolution spectra available over the internet for interested readers.

The abundance patterns of Sirius and Vega

On the basis of high-resolution echelle spectra obtained with the Coude Echelle Spectrograph attached to the 2.16 m telescope at the Beijing Astronomical Observatory (Xinglong, China) for Sirius and Vega, we performed an elemental abundance analysis of 29 ions, in which 23 elements are included, with Teff = 9880, log g = 4.40, [Fe/H] = 0.50, and ξt = 1.85 km s-1 for Sirius and Teff = 9430, log g = 3.95, [Fe/H] = -0.57, and ξt = 1.50 km s-1 for Vega. The results show different abundance patterns for these two stars. The iron peak elements seem to be enhanced by about 1.0 dex in Sirius relative to Vega. Comparison with previous investigations is present.

Chemical Abundances of 15 Extrasolar Planet Host Stars

Based on high-resolution, high signal-to-noise ratio spectra, we have derived accurate metallicities for 15 extrasolar planet host stars, as well as differential abundances for 16 other elements. The companions of three stars, HD 29587, HD 98230, and possibly HD 190228, have been shown to have masses in the brown dwarf regime and give an average value of the metallicities [Fe/H] = -0.44 ± 0.17. If we exclude these three stars, the rest of the sample stars are metal-rich relative to the Sun, covering the range from -0.12 to 0.41, with an average [Fe/H] value of 0.16 ± 0.17. The stars with planets show a slight overabundance pattern for [Na/Fe], [Mg/Fe], [Al/Fe], and [Sc/Fe]. On the other hand, [C/Fe], [O/Fe], [Si/Fe], [Ca/Fe], [Ti/Fe], [V/Fe], [Cr/Fe], [Ni/Fe], and [Ba/Fe] are approximately solar in the sample. The stars with planets also show underabundances for [K/Fe] and slight overabundances for [Mn/Fe], but stars with brown dwarfs show a contrary trend for these two elements. An interesting result is that sulfur displays enhanced values of [S/Fe], ranging from 0.04 to 0.40 through the sample. These results are used to investigate the connection between giant planets and high metallicity and to probe the influence of this process on the other elements.

On the Abundance of Potassium in Metal-Poor Stars

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 0.2–0.7dex, their effect on the [K/Fe] vs. [Fe/H] relation is not very important, since these corrections do not show anysignificant dependenceon the metallicity. 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. 5a t [Fe/H] ∼− 1t o−2, such as in the case of α elements.

Chemical abundances of 10 metal-poor halo stars

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.

Equivalent Widths in the Spectrum of Sirius

The equivalent widths of total 546 lines (26 elements are included) in the spectrum of the bright Am star Sirius from 380 to 930 nm are tabulated. The high-resolution, high signal-to-noise ratio spectrum was obtained with the Coude Echelle Spectrograph attached to the 2.16 m telescope at Beijing Astronomical Observatory (Xinglong, China). Here we also give the results of the equivalent widths comparison between our measurements and those of Strom et al. and Sadakane & Ueta.

Equivalent Widths of 15 Extrasolar-Planet Host Stars

We present the equivalent widths of 15 extrasolar-planet host stars. These data were based on the high-resolution, high signal-to-noise ratio spectra obtained with the 2.16m telescope at Xinglong station. The error in the Xinglong equivalent width is estimated by a comparison of these data with those given in previous studies of common stars. The discovery of planets around main sequence stars provides us a most important oppor- tunity to understand the theories of the planetary system and stars. Much has been done in the way of detailed analysis of the chemical abundance of the extrasolar-planet host stars, that will lead to useful information on how systems with large planets have formed. In Zhao et al. (2002), we presented accurate metallicities and abundance ratios of many elements for 15 extrasolar-planet host stars with the aim of finding out whether all our sample stars follow the same planet-high metallicity relation and how this process acts on dierent elements by examining the ratios between elements with the same nucleosynthesis history. In this work, the equivalent widths for these stars are given, and these data are compared with other studies for the stars in common.

Lithium abundances in 11 solar-type stars

We present determinations of fundamental parameters and lithium abundances in eleven solar-type stars through observations of the Li I λ6707.8Å. The correlations between the abundance of lithium and that of other elements (Ca, K and Fe) are also discussed. The analysis of our data indicates that the maximum lithium abundance decreases with decreasingTeff, and also decreases with increasing age. The sun is just one of the stars with low lithium abundance. One of the sample stars shows a high lithium abundance of as much as 2.34 dex. The plot of lithium abundance versus [Ca/H] is similar to that versus [Fe/H]. Lithium seems depleted more quickly than potassium in the cool solar-type stars. The correlation between the lithium abundance and the other stellar characteristics, such as absolute visual magnitude, does not seem very strong. The large scatter present at each color cannot be uniquely attributed to different initial compositions or to pure age effect. Other complex mechanisms may exist to provide different amounts of lithium depletion for stars with properties similar to the sun.

Abundance of α-elements in red clump giants

Abstract Based on high-resolution, high signal-to-noise ratio spectra, we have analysed the abundance of five α elements (Mg, Si, S, Ca, Ti) in 17 red clump giants. The results show that the giants can be divided into two categories, one metal-rich, with metallicity [Fe/H]≥ 0.0, the other metal-poor, with [Fe/H]≤ −0.3. The abundances of the five elements in both categories increase with increasing metallicity. The results indicate that, for both categories, the nucleosynthesis and the evolution of iron and the five elements are probably in step.