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Eta Corvi (Eta Crv, η Corvi, η Crv) is an F-type main-sequence star, the sixth-brightest star in the constellation of Corvus.〔〔 〕 Two debris disks have been detected orbiting this star, one warm within a few astronomical units (AU) and another out at ~150 AU.〔 ==Properties== Eta Corvi is only about 30% of the Sun's age. The concentration of iron in its atmosphere is only about 93% that of the Sun's.〔 The projected rotational velocity at the equator (''v'' sin ''i'') is a brisk 68 km/s.〔 〕 A yellow-white main sequence star of spectral type F2V, it has an estimated surface temperature of 6950 K. It is 1.52 times as massive as the Sun and is 4.87 times as luminous. It is 59 light-years distant from our Solar System. The IRAS satellite detected an excess of infrared radiation from this star, beyond what would normally be expected for a stellar object of this class.〔 〕 Observations in the submillimetre band confirmed the presence of excess dust in orbit around the star having about 60% of the mass of the Moon and a temperature of 80 K. The data indicated a debris disk with an estimated maximum radius of 180 AU from the star, or 180 times the separation of Earth and the Sun.〔 〕 (Compare to the Kuiper belt, which extends out to 55 AU from the Sun.) Recent submillimeter observations confirm the presence of an outer flat, circumstellar disk of debris with an outer radius of 150 AU It is oriented at an inclination to the line of sight from the Earth. Most of the inner 100 AU of the disk is relatively free of material, which suggests it was cleared away by a planetary system.〔 In addition, infrared radiation which appears to be from an inner, hotter, debris disk within 3.5 AU of the star has been observed.〔 〕 Since the Poynting–Robertson effect would cause the dust in the outer disk to spiral in to the star within 20 million years, much younger than the age of the system, the observed presence of dust in the outer disk means that it must be constantly replenished. It is thought that this happens by the collisions of planetesimals orbiting at a distance of about 150 AU, which are repeatedly broken down into smaller and smaller pieces, eventually becoming dust.〔 The origin of the inner disk is not clear. It may have originated from planetesimals recently having moved from the outer regions of the system into the inner system, in a process similar to the Late Heavy Bombardment in the history of the Solar System, and subsequently being ground to dust by collisions.〔 〕 〔 〕 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「Eta Corvi」の詳細全文を読む スポンサード リンク
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