In this article I review surface abundances in stars which host planetary systems. Recent spectroscopic studies of stars with and without planetary systems have concluded that stars which host planets are more metal-rich than those without planets. We discover more subtle trends of different chemical elements as the number of detected exoplanets

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We present the abundance ratios [X/H] of a large set of chemical species with T_C from 75 to 1600 K in an almost complete set of 105 planet-host stars and in a volume-limited comparison sample of 88 stars without any known planets. The large range of different T_C covered by all the analyzed elements allows us to investigate possible anomalous

The observed enhancement of the Fe Kα line in three gravitationally lensed QSOs (MG J0414+0534, QSO 2237+0305, and H1413+117) is interpreted in terms of microlensing, even when equivalent X-ray continuum amplification is not observed. In order to interpret these observations, first we studied the effects of microlensing on quasar spectra produced

A comparison between the oscillation frequencies of six multi-periodic δ Scuti stars of the Pleiades cluster and the eigenfrequencies of rotating stellar models that match the corresponding stellar parameters has been carried out. The assumption that all the stars considered have some common parameters, such as metallicity, distance or age, is