期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 384, 期 4, 页码 1563-1566出版社
BLACKWELL PUBLISHING
DOI: 10.1111/j.1365-2966.2007.12806.x
关键词
stars : evolution; stars : fundamental parameters; stars : individual : HD 155358; planetary systems; stars : Population II
The nearby subgiant HD 155358 has very recently been announced by Cochran et al. to harbour two Jovian-mass planetary companions and to be the lowest metallicity exoplanet host star yet found. Here, we present a model atmosphere analysis and stellar evolutionary tracks for HD 155358, and demonstrate that it is actually a member of the ancient thick-disc population of the Milky Way (tau >= 12 Gyr). As such, HD 155358 is considerably rich in its alpha-chain nuclei, and hence only about a factor of 2 below the solar abundance in terms of these species. Yet, as a precursor to the thin disc and residing on the metal-poor end of the thin-disc metal abundance distribution, HD 155358 gives way to the principal possibility that any star of the thin-disc population of the Galaxy can be a potential exoplanet host. As opposed to this, the formation of planets and even planetary systems for HD 155358 and HD 37124 (another previously known thick-disc exoplanet host) is mentionable, as there is strong evidence for a vigorous starburst phase in the early Milky Way, and secondly, the direct census of an unbiased nearby thick-disc sample implies a minimum fraction of no less than 30 per cent multiple star systems (N >= 3) to originate from that epoch.
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