Extra-solar planet search by radial velocity measurements of stars

点击翻译按钮获取中文摘要

In this three-year project, we have completed the extra-solar planet search program, that is, we tried to pick up the planet candidates by radial velocity observation of 300 G-giants with Subaru telescope (HDS), and followed up the radial velocity variations of these candidates with HIDES high dispersion spectrograph at Okayama Astrophysical Observatory, NAOCCES at Xinglong station in China, and HOES at Hugen san in Korea. As a result, we discovered 5 exoplanets and 1 brown dwarf, whose results were published in refereed journals. In addition to this, we submitted a paper on the discovery of 4 exoplanets. It is quite rare even in the world that one group accomplished the discovery of about 10 exoplanets, and we are now in a good position to discuss on the planet formation in intermediate mass stars. In a preliminary analysis, orbital periods of these planets are shown to be longer than 100days, and there seems to be a lower limit in orbital period for stars of intermediate mass range, … More which is a different situation from the planets around dwarf stars like the Sun. If this is true, it gives a certain limit on planet formation scenario. Increase of these sample might lead to give a firm foundation on this scenario. It is also shown that metallicity in the planet hovering stars is higher than that in non-hovering stars, which is a confirmation of the previous works.Scientists of Japan, China, and Korea had two workshops at Hakone in Japan in 2006 and at Lijiang in China in 2007, respectively. In these meeting, we presented the observational results and discussed on the observational plans, and developed the software concerning radial velocity reduction. In particular, we achieved a tremendous progress in improving accuracy of radial velocity measurement. Previous precision, 5m/s at Okayama and 9m/s at Hugen san are much improved into 2m/s and 4m/s, respectively. Our intensive discussion during these workshops could lead to the mutual understandings that it is important that instrumental profile (IP) of the spectrograph should not change over the relevant wavelength, and the sampling points for IP should be increased in a sense of over sampling, that is, use of CCD with a small pixel size. Accuracy at Xinglong in China was not improved into less than 10m/s, but we are confident about how to improve radial velocity accuracy in futur.Based on these results, we are considering increase in number of exoplanets around G-giants and based on the reinforced statistical data we try to understand planet formation Less