Research

High-precision chemical abundance analysis of the HAT-P-1 stellar binary

We performed a detailed study on chemical abundances of the HAT-P-1 binary system using strictly line-by-line differential analysis, based on high-resolution, high signal-to-noise ratio Keck/HIRES spectra. The secondary star in the HAT-P-1 stellar binary is known to host a transiting giant planet (Bakos et al. 2007) while no planets have yet been detected around the primary star.

We determined the stellar parameters of the binary stars and measured differential abundance ratios of 23 elements with extremely high precision. The results demonstrate that these two stars are identical in elemental abundances: Δ[X/Fe] = +0.001 ± 0.006 dex (σ= 0.008 dex). When comparing the two HAT-P-1 components relative to each other, the slope of Δ[X/Fe] vs. condensation temperature (Tc) is almost zero. From the fact that the two HAT-P-1 components share the identical chemical compositions, we conclude that the presence of giant planets does not necessarily imply differences in the chemical compositions of the host stars.

The detailed chemical composition of the terrestrial planet host Kepler-10

We conducted a detailed abundance analysis of the terrestrial planet host Kepler-10 and fourteen of its stellar twins. Stellar parameters and chemical abundances of Kepler-10 and the stellar twins were obtained with extremely high precision using a strictly line-by-line differential analysis of high quality CFHT, HET and Magellan spectra.

When compared to most thick disk twins, Kepler-10 shows depletion in the refractory elements relative to the volatile elements, which could be due to the formation of rocky planets in the Kepler-10 system. The average abundance pattern corresponds to ~ 13 Earth masses, while the two known planets in Kepler-10 system have a combined ~ 20 Earth masses.

Our results demonstrate that although several factors (e.g., planet signature, stellar age, stellar birth location and Galactic chemical evolution etc.) could lead to or affect the chemical pattern when exploring the abundance trends with condensation temperature, we find that the trends give further support for the planetary signature hypothesis.

The Hyades open cluster is chemically inhomogeneous

We presented a strictly line-by-line differential analysis of 16 solar-type stars in the Hyades open cluster based on high resolution, high S/N spectra obtained from McDonald 2.7m telescope in order to determine how chemically homogeneous an open cluster is, a crucial ingredient for Galactic archaeology and the concept of chemical tagging (e.g. Freeman & Bland-Hawthorn 2002). We derived stellar parameters and differential chemical abundance for 20 elements with uncertainties as low as ~ 0.01 – 0.02 dex.

Our main results including: (1) the observed abundance dispersions are a factor of 1.5 - 2 larger than the average measurements errors for most of elements, (2) there are positive correlations, of high statistical significance, between essentially all pairs of elements.

Our results indicate that the Hyades is chemically inhomogeneous, in contradiction with common wisdom of open clusters. The possible scenario of these abundance variations could be (1) inhomogeneous chemical evolution in the proto-cluster environment (2) supernova ejection in the proto-cluster cloud (3) pollution of metal-poor gas before complete mixing. Our results provide a vital challenge to the current view of Galactic archeology.

To be continued...