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HD 189733, also catalogued as V452 Vulpeculae, is a binary star system approximately 63 light-years away in the constellation of Vulpecula (the Fox). The primary star is suspected to be an orange dwarf star, while the secondary star is a red dwarf star. Given that this system has the same visual magnitude as HD 209458, it promises much for the study of close transiting extrasolar planets. The star can be found with binoculars 0.3 degrees east of the Dumbbell Nebula (M27). As of 2005, it has been confirmed that an extrasolar planet orbits the primary star within the system.〔 == Stellar system == ''HD 189733 A'' is an orange dwarf star of the spectral type K1.5V. The star has a mass of 81 percent that of the Sun, a radius 76 percent, and a luminosity of 33 percent. The star is between 89 and 102 percent as enriched in iron as the Sun, making the star more than 600 million years old. The star has starspots which affect its luminosity by 1.5 percent in visible light. As a result, it is listed in the General Catalogue of Variable Stars as a BY Draconis variable with the variable star designation ''V452 Vul''. Discovered in 2006 by the infrared 2MASS astronomical survey, 2MASS J20004297+2242342 or ''HD 189733 B'' is a dim red dwarf star of spectral type M. The companion was observed at a separation of 216 astronomical units away from the primary star. Orbiting in a clockwise orbit (which is nearly perpendicular to the orbital plane of transiting planet HD 189733 b), the orbital period is estimated around 3,200 years long.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「HD 189733」の詳細全文を読む スポンサード リンク
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