ABSTRACTwhich falls in the planetary-mass regime. This is the first discovery of a planetary companion orbiting a G-type giant star.

By using the high-dispersion spectra of 14 bright planet-harboring stars (along with 4 reference stars) observed with the new coudé echelle spectrograph at Okayama Astrophysical Observatory, we investigated the abundances of volatile elements (C, N, O, S, Zn; low condensation temperature T c ) in order to examine whether these show any significant difference compared to the abundances of other refractory elements (Si, Ti, V, Fe, Co, Ni; high T c ) which are known to be generally overabundant in those stars with planets, since a T c -dependence is expected if the cause of such a metal-richness is due to the accretion of solid planetesimals onto the host star. We found, however, that all elements we studied behave themselves quite similarly to Fe (i.e., [X/Fe]≃ 0) even for the case of volatile elements, which may suggest that the enhanced metallicity in those planet-bearing stars is not so much an acquired character (by accretion of rocky material) as rather primordial.

Intermediate resolution phase-resolved spectra of WZ Sge were obtained on five consecutive nights (July 23 -27) covering the initial stage of the 2001 superoutburst. Double-peaked emission lines of HeII at 4686 A, which were absent on July 23, emerged on July 24 together with emission lines of CIII / NIII Bowen blend. Analyses of the HeII emission lines using the Doppler tomography revealed an asymmetric spiral structure on the accretion disk. This finding demonstrates that spiral shocks with a very short orbital period can arise during the initial stage of an outburst and may be present in all SU UMa stars.

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