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Alpha Centauri star system.
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Earth-sized world found next door

Scientists have found an Earth-sized planet circling a neighbour star just four light-years away.
No need to brush up on extraterrestrial etiquette quite yet, however. The planet, which flies around its parent star 10 times closer than Mercury orbits the Sun, which means its surface temperature would be more than 2000C - far too hot for liquid water to exist on the surface. Water is believed to be necessary for life.
But the newly found planet orbiting Alpha Centauri B, a Sun-like star roughly 25 trillion miles away, could have better-positioned siblings.

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Earth-sized world discovered in nearby Alpha Centauri star system.

It is a world so close that E.T. could phone home in just four years. Astronomers have discovered the lowest-mass planet yet orbiting a Sun-like star. It orbits Alpha Centauri B, a member of the stellar system that is our Solar Systems nearest neighbour. Although nearly identical to Earth in mass, the planet is much closer to its star than Mercury is to the Sun, meaning that it is a scorched and barren rock. Nevertheless, its astronomical proximity to Earth will undoubtedly stir dreams of interstellar exploration, particularly as astronomers search Centauri for more hospitable worlds.
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Alpha Centauri Bb
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Today a European planet-hunting team announced their discovery of an alien world about the same mass as Earth. This alone would be noteworthy, for of all the "exoplanets" now known beyond our solar system, only a very few, and very recently, have been shown to at all resemble our own. But there is more to the story. This particular exoplanet resides in a three-day orbit around the dusky orange star Alpha Centauri B, a member of the Sun's closest neighbouring stellar system. There are two other stars in the system as well, the yellow Sun-like star Alpha Centauri A and the red dwarf star Proxima Centauri.
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Alpha Centauri Bb
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U orbiti najblie zvijezde otkriven Zemljin blizanac

Europski su astronomi otkrili da oko nama najblie zvijezde Alpha Centauri krui planet cija je masa gotovo jednaka Zemljinoj
To je istovremeno i najlaki planet koji je ikada otkriven. Istraivanja su obavljena uz pomoc instrumenta HARPS postavljenom na 3,6 metarskom teleskopu promatracnice La Silla u Cileu.
Alpha Centauri je jedna od najsvjetlijih zvijezda na junom nebu i najblia je Suncevom sustavu - udaljena je samo 4,3 svjetlosne godine. Ovaj se sustav zapravo sastoji od tri zvijezde - Alpha Centauri A i B koje su slicne Suncu i krecu po orbitama jedna blizu druge te jedne udaljenije, bljede, crvene Proxima Centauri. O mogucnosti da u tom sustavu postoje planeti i eventualno ivot znanstvenici nagadaju jo od 19. stoljeca, medutim, cak ni vrlo precizna istraivanja nisu nita uspjela otkriti. Sve do danas.

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Title: Oscillations in the Habitable Zone around Alpha Centauri B
Authors: Duncan Forgan

The Alpha Centauri AB system is an attractive one for radial velocity observations to detect potential exoplanets. The high metallicity of both Alpha Centauri A and B suggest that they could have possessed circumstellar discs capable of forming planets. As the closest star system to the Sun, with well over a century of accurate astrometric measurements (and Alpha Centauri B exhibiting low chromospheric activity) high precision surveys of Alpha Centauri B's potential exoplanetary system are possible with relatively cheap instrumentation. Authors studying habitability in this system typically adopt habitable zones (HZs) based on global radiative balance models that neglect the radiative perturbations of Alpha Centauri A.
We investigate the habitability of planets around Alpha Centauri B using 1D latitudinal energy balance models (LEBMs), which fully incorporate the presence of Alpha Centauri A as a means of astronomically forcing terrestrial planet climates. We find that the extent of the HZ is relatively unchanged by the presence of Alpha Centauri A, but there are variations in fractional habitability for planets orbiting at the boundaries of the zone due to Alpha Centauri A, even in the case of zero eccentricity. Temperature oscillations of a few K can be observed at all planetary orbits, the strength of which varies with the planet's ocean fraction and obliquity.

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Title: Recalculating the Orbit of alpha-Centauri AB
Authors: Suryadi Siregar, Hanindyo Kuncarayakti (Astronomy Research Division and Bosscha Observatory, Bandung Institute of Technology)

The two main components of the closest star system, alpha-Centauri AB(RA 14h39m, Dec-6050', J2000.0) is indubitably one of the most studied visual double stars. This paper presents the results of our recalculation of orbital and physical parameters of the system using Thiele-van den Bos method, based on observational data from year 1900 to 2002. Despite some significant discrepancies, in general our results confirmed previous results of orbital parameter determinations using different method.

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Title: Doppler imaging of the helium-variable star a Cen
Authors: David A. Bohlender, J.B. Rice, P. Hechler

The helium-peculiar star a Cen exhibits line profile variations of elements such as iron, nitrogen and oxygen in addition to its well-known extreme helium variability. New high S/N, high-resolution spectra are used to perform a quantitative measurement of the abundances of the star and determine the relation of the concentrations of the heavier elements on the surface of the star to the helium concentration and the magnetic field orientation. Doppler images have been created using programs described in earlier papers by Rice and others. An alternative surface abundance mapping code has been used to model the helium line variations after our Doppler imaging of certain individual helium lines produced mediocre results. We confirm the long-known existence of helium-rich and helium-poor hemispheres on a Cen and we measure a difference of more than two orders of magnitude in helium abundance from one side of the star to the other. Helium is overabundant by a factor of about 5 over much of the helium-rich hemisphere. Of particular note is our discovery that the helium-poor hemisphere has a very high abundance of helium-3, approximately equal to the helium-4 abundance. a Cen is therefore a new member of the small group of helium-3 stars and the first well-established magnetic member of the class. For the three metals investigated here, there are two strong concentrations of abundance near the equator consistent with the positive magnetic maximum and two somewhat weaker concentrations of abundance where the helium concentration is centred and roughly where the negative peak of the magnetic field would be found. Another strong concentration is found near the equator and this is not explainable in terms of any simple symmetry with the helium abundance or the apparent magnetic field main polar locations.

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What alien worlds orbit our nearest star?

Simulations of the conditions in the Alpha Centauri star system suggest Earth-like planets might exist there, but gas giants are unlikely.

The Alpha Centauri dual star system is thought to host rocky Earth-mass worlds, but this assumes they could form in the turbulent conditions associated with the opposing gravitational tugs of paired star systems.
Rocky planets are created from the merger of moon-sized planetary embryos which, in turn, form from the accretion of kilometre-sized planetesimals. However, there is no guarantee that such embryos could form in turbulent conditions.

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Title: Planetesimal Accretion in Binary Systems: Could Planets Form Around Alpha Centauri B ?
Authors: Ji-Wei Xie, Ji-Lin Zhou, Jian Ge

Stellar perturbations affect planet-formation in binary systems. Recent studies show that the planet-formation stage of mutual accretion of km-sized planetesimals is most sensitive to binary effects. In this paper, the condition for planetesimal accretion is investigated around Alpha CenB, which is believed to be an ideal candidate for detection of an Earth-like planet in or near its habitable zone(0.5-0.9 AU). A simplified scaling method is developed to estimate the accretion timescale of the planetesimals embedded in a protoplanetary disk. Twenty-four cases with different binary inclinations(i_B=0, 0.1, 1.0, and 10 deg), gas densities(0.3,1,and 3 times of the Minimum Mass of Solar Nebula, MMSN hereafter), and with and without gas depletion, are simulated. We find: (1)...(2)...(3)...(4)...(see the paper for details). In other words, our results suggest that formation of Earth-like planets through accretion of km-sized planetesimals is possible in Alpha CenB, while formation of gaseous giant planets is not favourable.

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