First Extra-Solar Planets Detection by Chinese and Japanese Astronomers

Since the first planet was discovered around the solar-like star 51 Peg[1], planet hunters have unveiled more than 300 extrasolar planets by precise radial velocity monitoring. Statistical properties of planets around solar-like stars as well as their host stars have been widely investigated[2][3]. In general, the planetary companions are quite different from those in our solar system. The planets have minimum masses that range from 5 Earth masses to 20 Jupiter masses (here after MJ ) and are distributed in the range of orbital radii from 0.02 to 6 AU with orbital eccentricities of 0 to 0.9[4] and the period distribution shows a peak at 3 days. Despite that radial velocity method is more sensitive to massive companions, the frequency of the discovered planets increases with increasing mass[5].

After the first detection of a planet around a giant star by Frink et al.[6], hunting for extrasolar planets around giants and subgiants has gradually become a new frontier in extrasolar planet searches during recent years. By now, more than 20 planets and a few brown dwarfs have been discovered around such evolved stars. The growing number of planets is now allowing us to preliminarily unveil their properties. Researchers find that they show different properties from those in solar-like stars: high frequency of massive planets[7][5] and a lack of inner planets[8][9].

HD 173416

HD 173416b[10] with a mass of 2.7 MJ and a semimajor axis a=1.16 AU is the first planet candidate discovered from the Xinglong-Okayama Planet Search Program. Since many planets exist within 0.6 AU around low-mass dwarfs, the lack of inner planets around evolved intermediate-mass stars may reflect different histories of formation and evolutions of the planetary systems around them.


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