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SATO BUN'EI The Korean Astronomical Society 2005 Journal of The Korean Astronomical Society Vol.38 No.2
We have carried out a precise Doppler survey of G-type giants aiming to unveil the properties of planetary systems in intermediate-mass stars ($1.5-5M_{\bigodot}$). G-type giants are promising targets for Doppler planet searches around massive stars, because they are slow-rotators and have many sharp absorption lines in their spectra and their surface activities are relatively low in contrast to their younger counterparts on the main-sequence (B-A stars). We are now monitoring radial velocities of about 300 late G-type (including early K-type) giants using HIgh Dispersion Echelle Spectrograph (HIDES) at Okayama Astrophysical Observatory. We have achieved a Doppler precision of about 6-7 m/s over a time span of 3 years using an iodine absorption cell. We found that most of the targets have radial velocity scatters of ${\sigma}{\~} 10-20 m\;s^{-1}$ over 1-3 years, with the most stable reaching levels of 6-8 m $s^{-1}$. Up to now, we have succeeded in discovering the first extrasolar planet around a G-type giant star HD 104985, and also found several candidates showing significant radial velocity variations, suggesting the existence of stellar and substellar companions. Observations have continued to establish their variability.
Kambe, Eiji,Ando, Hiroyasu,Sato, Bun’ei,Izumiura, Hideyuki,Sekii, Takashi,Paulson, Diane B.,Yanagisawa, Kenshi,Masuda, Seiji,Shibahashi, Hiromoto,Hatzes, Artie P.,MARTI´C, Milena,LEBRUN, Jean-Claude,M Astronomical Society of Japan 2008 Publications of the Astronomical Society of Japan Vol.60 No.1
An improvement of the radial-velocity measurement accuracy is crucial for the detection of tiny stellar oscillationsand exoplanets. Through the analysis of week-long extensive observations of solar-type stars (Procyon in 2000, 2002, and 2006/2007 and τ Cet in 2002 and 2006/2007), we have carefully examined, revised, and finelytuned the widely used multiple Gaussian IP fitting method for the spectrograph, HIDES. By determining a necessaryand sufficient number of free parameters in the model as well as introducing an iterative process in the radial-velocityanalysis, we can reach a precision of below 3ms<SUP>-1</SUP>, which is much smaller than the precision of 6ms<SUP>-1</SUP> officially announced so far for HIDES. We also make our technique refined for the 2002 McDonald Procyon data. Even with our revised method, slow radial velocity variations with an amplitude of about 10ms<SUP>-1</SUP> are left in the Procyon data. We emphasize that it is neither due to particular observing instruments nor radial-velocity analysis, and thus could be due to stellar origin. The analysis presented here makes the foundations of our next scientific analysis of the radial-velocity variations of Procyon, which will be presented in our forthcoming papers.