Studies on properties of planet-host stars and on formation conditions of planets based on analyses of chemical compositions.

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Abundance analyses of 13 elements (C to Zn) were carried out for 73 planet-host starsand 18 comparison stars. Comparison of [Fe/H] with a total metallicity [M/H] which includes abundances of Fe and 13 elements yielded the result that [M/H] corresponds to about 0.75 of [Fe/H] value, and suggested that [M/H] should be used as a metallicity concerning a condition for planet formation in the metal-deficient region. One hot Jupiter was detected around one intermediate-mass giant by planet survey, and its mass was turned out to be a new lower limit of planets being formed around intermediate-mass stars. It is found that about 10 stars of the giant sample may have planet around them, and that Fe abundances distribute around the solar value, which is different from dwarfs case. As for the related studies, behaviors of sulfur and silicon of alpha elements and existence of chromosphere were investigated in the sample of metal-poor dwarfs and giants. Sulfur shows a flat trend with +0.4 dex against [Fe/H] in a lower metallicity region. Silicon shows a behavior similar to sulfur, but it is confirmed that NLTE analyses are necessary for abundance analyses based on near infrared absorption lines. As for chromosphere, it is confirmed observationally that chromosphere exists in dwarfs and giants commonly independent of metallicity.