فم الحوت نجم يقع في كوكبة الحوت الجنوبي يبعد حوالي 25 سنة ضوئية (7,688 فرسخ فلكي)عن الأرض، تبلغ حرارته 5800 كلفن. ويعتبر هذا النجم واحداً من النجوم العشرين التي تتربع على عرش البريق في السماء لونه ضارب إلى الزرقة وظهوره يعلن بداية فصل الخريف. يعتقد حتى فم الحوت يصدر أشعة تحت الحمراء.

Fomalhaut (Alpha Piscis Austrini, Alpha PsA, α Piscis Austrini, α PsA) is the brightest star in the constellation Piscis Austrinus and one of the brightest stars in the sky. It is a class A star on the main sequence approximately 25 سنة ضوئيةs (7.7 فخ) from Earth as measured by the Hipparcos astrometry satellite. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. It is classified as a Vega-like star that emits excess infrared radiation, indicating it is surrounded by a circumstellar disk. Fomalhaut, K-type star TW Piscis Austrini and M-type star LP 876-10 constitute a trinary system.

Fomalhaut holds a special significance in extrasolar planet research, as it is the center of the first stellar system with an extrasolar planet candidate (Fomalhaut b) imaged at visible wavelengths. The image was published in Science in November 2008. Fomalhaut is the third brightest star known to have a planetary system, after Pollux and the Sun.

المعلومات

فم الحوت نجم يقع في كوكبة الحوت الجنوبي يبعد حوالي 25 سنة ضوئية (7,688 فرسخ فلكي)عن الأرض، تبلغ حرارته 5800 كلفن. ويعتبر هذا النجم واحداً من النجوم العشرين التي تتربع على عرش البريق في السماء لونه ضارب إلى الزرقة وظهوره يعلن بداية فصل الخريف. يعتقد حتى فم الحوت يصدر أشعة تحت الحمراء.

فهونجم يحمل أهمية خاصة في مجال البحوث خارج المجموعة الشمسية. لأنها مركز النظام النجمي الأول خارج المجموعة الشمسية لتصوير الموجات المرئية. وقد نشرت هذه الصورة للفهم في نوفمبر 2008. وهوثالث نجم لامع يدور حول كوكب مع النجمين (بولكس Pollux) والشمس. ومن المعتقد حتى نجم (فم الحوت Fomalhaut) هونجم شاب، فقط عمره من 100 : 300 مليون سنة، ودرجة حرارة سطح هذا النجم حوالي 8751 كيلفن (8478 درجة مئوية). كتلة هذا النجم حوالي 2.1 مرة من كتلة الشمس ولها لمعان حوالي 18 ضعف. وقطرها حوالي 1.8 أكبـر. وهومن النجوم ناسيرة المعادن بالنسبة للشمس وهوما يعني أنها تتكون من كميات ونسب أقل من الهيدروجين والهليوم.

وهوأحد النجوم الـ 16 الذين ينتمون إلى (مجموعة نقل كاستورCastor Moving Group) المتحركة، وهذه المجموعة هي رابطة للنجوم التي تحلق بالفضاء مشهجرةً مع بعضها البعض. وبالتالي فإنه من المرجح حتى تكون مرتبطة عملياً، ويحيط بالنجم (فم الحوت Fomalhaut) قرص محطم من الغبار في شكل حلقي مع حافة داخلية حادة جداً، وهويميل ب 24 درجة من على الحافة. ويوزع الغبار بمسافة 25 وحدة فلكية ,ومن المعروف حتى كمية الأشعة الحمراء المنبعثة منه كبيرة. في 13 نوفمبر 2008 أعرب فهماء الفلك اكتشاف كوكب خارج المجموعة الشمسية، وكان هذا أول كوكب يُنظر إليه خارج المجموعة الشمسية بسبب تلسكوب الفضاء هبل. وكان وجود الكوكب يشتبه به في السابق.

ومن الظاهر حتى اسم [ Fomalhaut ] مأخوذ من الاسم العربي [ فم الحوت ]. في میل 29.6°-يقع [ فم الحوت ] في جنوب خط الإستواء السماوي وبالتالي يتم عرضه بشكل أفضل من نصف الكرة الأرضية الجنوبي وهويمر عملياً من مدار الحمل إلى الجنوب [ مدار الجدي ]. ويُرى على سبيل المثال من [ Brisbane, Johannesburg and Easter Island بريسبان وجوهانسبرغ وجزيرة الفصح].. ولكن الإنحراف في الجنوب ليس كبيراً بشكل كبير مثل النجوم الآتية : [ Acrux, Alpha Centauri and Canopus, أكراكس، الفا قنطورس وكانوب ]

Fomalhaut A

At a declination of −29.6°, Fomalhaut is located south of the celestial equator, and hence is best viewed from the Southern Hemisphere. However, its southerly declination is not as great as that of stars such as Acrux, Alpha Centauri and Canopus, meaning that, unlike them, Fomalhaut is visible from a large part of the Northern Hemisphere as well. Its declination is greater than that of Sirius and similar to that of Antares. At 40°N, Fomalhaut rises above the horizon for eight hours and reaches only 20° above the horizon, while Capella which rises at approximately the same time will stay above the horizon for twenty hours. From إنگلترة the star never appears much brighter than magnitude 2.2 due to it being so close to the horizon, and from southern Alaska or Scandinavia it never rises above the horizon at all. Fomalhaut can be located in these northern latitudes by the fact that the western (right-hand) side of the Square of Pegasus points to it. Continue the line from Beta to Alpha Pegasi towards the southern horizon: Fomalhaut is about 45˚ south of Alpha Pegasi, with no bright stars in between.

الخصائص

Fomalhaut is a young star, for many years thought to be only 100 to 300 million years old, with a potential lifespan of a billion years. A 2012 study gave a slightly higher age of 7002440000000000000♠440±40 million years. The surface temperature of the star is around 8,590 ك (8,320 °م). Fomalhaut's mass is about 1.92 times that of the Sun, its luminosity is about 16.6 times greater, and its diameter is roughly 1.84 times as large.

Fomalhaut is slightly metal-deficient as compared to the Sun, which means it is composed of a smaller percentage of elements other than hydrogen and helium. The metallicity is typically determined by measuring the abundance of iron in the photosphere relative to the abundance of hydrogen. A 1997 spectroscopic study measured a value equal to 93% of the Sun's abundance of iron. A second 1997 study deduced a value of 78% by assuming Fomalhaut has the same metallicity as the neighboring star TW Piscis Austrini, which has since been argued to be a physical companion. In 2004, a stellar evolutionary model of Fomalhaut yielded a metallicity of 79%. Finally, in 2008, a spectroscopic measurement gave a significantly lower value of 46%.

Fomalhaut has been claimed to be one of approximately 16 stars belonging to the Castor Moving Group. This is an association of stars that share a common motion through space and have been claimed to be physically associated. Other members of this group include Castor and Vega. The moving group has an estimated age of 7002200000000000000♠200±100 million years and originated from the same location. Unfortunately more recent work that has found that purported members of the Castor Moving Group appear to not only have a wide range of ages, but their velocities are too different to have been possibly associated with one another in the distant past. Hence, "membership" to this dynamical group has no bearing on the age of the Fomalhaut system.

أقراص الركام والكوكب

Fomalhaut is surrounded by several debris disks.

The inner disk is a high-carbon small-grain (10-300 nm) ash disk clustering at 0.1 AU from the star. Next is a disk of larger particles with inner edge 0.4-1 AU of the star. The innermost disk is unexplained as yet.

The outermost disk is at a radial distance of 133 AU (1.99×10¹⁰ kم; 1.24×10¹⁰ ميل), in a toroidal shape with a very sharp inner edge, all inclined 24 degrees from edge-on. The dust is distributed in a belt about 25 AU wide. The geometric center of the disk is offset by about 15 AU (2.2×10⁹ kم; 1.4×10⁹ ميل) from Fomalhaut. The disk is sometimes referred to as "Fomalhaut's Kuiper belt". Fomalhaut's dusty disk is believed to be protoplanetary, and emits considerable infrared radiation. Measurements of Fomalhaut's rotation indicate that the disk is located in the star's equatorial plane, as expected from theories of star and planet formation.

On November 13, 2008, astronomers announced an object, which they assumed to be an extrasolar planet, orbiting just inside the outer debris ring. This was the first extrasolar orbiting object to be seen with visible light, captured by the Hubble Space Telescope. A planet's existence had been previously suspected from the sharp, elliptical inner edge of that disk. The mass of the planet, Fomalhaut b, was estimated to be no more than three times the mass of Jupiter but at least the mass of Neptune. There are indications that the orbit is not apsidally aligned with the dust disk, which may indicate that additional planets may be responsible for the dust disk's structure.

However M-band images taken from the MMT Observatory put strong limits on the existence of gas giants within 40 AU of the star and Spitzer Space Telescope imaging suggested that the object Fomalhaut b was more likely to be a dust cloud. In 2012, two independent studies confirmed that Fomalhaut b does exist; but it is shrouded by debris, so it may be a gravitationally-bound accumulation of rubble rather than a whole planet.

Herschel Space Observatory images of Fomalhaut reveal a large amount of fluffy micrometer-sized dust is present in the outer dust belt. Because such dust is expected to be blown out of the system by stellar radiation pressure on short timescales, its presence indicates a constant replenishment by collisions of planetesimals. The fluffy morphology of the grains suggests a cometary origin. The collision rate is estimated to be approximately 2000 kilometre-sized comets per day.

Observations of the star's outer dust ring by the Atacama Large Millimeter Array point to the existence of two planets in the system, neither one at the orbital radius proposed for the HST-discovered Fomalhaut b.

If there are additional planets from أربعة toعشرة AU, they must be under 20 M_J; if from 2.5 outward, then 30 M_J.

انظر أيضا

الهامش

الهامش

Constructs such as ibid. وloc. cit. غير محبذين في مرشد أسلوب الفهم for footnotes, as they are easily broken. Please improve this article by replacing them with named references (quick guide), أوعنوان مختصر.

وصلات خارجية

• "Fomalhaut". SolStation. Retrieved November 23, 2005.
• Preprint of planet discovery paper
• Astrobites summary of Janson et al. 2012, the Spitzer IR non-detection of Fomalhaut b
• Astrobites summary of Boley et al. 2012, the ALMA observations of the Fomalhaut ring system
• "Eye of Sauron" debris ring
• Researchers find that bright nearby double star Fomalhaut is actually a triple (Astronomy magazine : October 8, 2013)

الإحداثيات: , −29° 37′ 20″

نطقب:Stars of Piscis Austrinus