Z. W. Li

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.

Multi-spacecraft Observations of the 2008 January 2 CME in the Inner Heliosphere

We perform a detailed analysis of a coronal mass ejection (CME) on 2008 January 2. The combination of the Solar and Heliospheric Observatory and the twin STEREO spacecraft provides three-point observations of this CME. We track the CME in imaging observations and compare its morphology and kinematics viewed from different vantage points. The shape, angular width, distance, velocity, and acceleration of the CME front are different in the observations of these spacecraft. We also compare the efficiency of several methods, which convert the elongation angles of the CME front in images to radial distances. The results of our kinematic analysis demonstrate that this CME experiences a rapid acceleration at the early stage, which corresponds to the flash phase of the associated solar flare in time. Then, at a height of about 3.7 solar radius, the CME reaches a velocity of 790 km s?1 and propagates outward without an obvious deceleration. Because of its propagation direction away from the observers, the CME is not detected in situ by either ACE or STEREO.

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.

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.

Lithium in G Dwarfs

We present determinations of fundamental parameters and lithium abundances of 10 G dwarfs. The analysis of our data shows that the maximum lithium abundance decreasess with decreasingT eff , but with a large scatter. One of the sample stars shows a high lithium abundance as much as 2.34 dex. The correlation between the lithium abundance and absolute visual magnitude or stellar age, does not seem very good. The scatter cannot be uniquely attributed to different initial compositions or to pure age effect.