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RE: Alpha Centauri planets
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VLT to Search for Planets in Alpha Centauri System

ESO has signed an agreement with the Breakthrough Initiatives to adapt the Very Large Telescope instrumentation in Chile to conduct a search for planets in the nearby star system Alpha Centauri. Such planets could be the targets for an eventual launch of miniature space probes by the Breakthrough Starshot initiative.
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alpha Centauri A and B
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Title: Close stellar conjunctions of alpha Centauri A and B until 2050 - An mK = 7.8 star may enter the Einstein ring of alpha Cen A in 2028
Author: P. Kervella, F. Mignard, A. Mérand, F. Thévenin

The rapid proper motion of the alpha Cen pair (3.7 arcsec/yr) and its location close to the galactic plane on a rich stellar background combine to make them excellent candidates for stellar conjunctions with distant stars. Adding new astrometry to archival data, we have refined the orbital parameters, barycentric proper motion and parallax of alpha Cen and compute its apparent trajectory on sky over the coming decades. We present a catalogue of the expected close conjunctions until 2050. An exceptional event will take place in early May 2028, when alpha Cen A will come within 0.015 +/- 0.135 arcseconds of the mK = 7.8 star 2MASS 14392160-6049528 (hereafter S5). In terms of impact parameter and contrast, this is the most favorable stellar conjunction of alpha Cen within at least the next three decades. With an angular diameter of LD = 0.47 +/- 0.05 mas, it is likely that S5 is a red giant or supergiant located at several kiloparsecs. The approached stars will act as moving light probes in transmission through the environment of alpha Cen. The observation of these close conjunctions holds great promises to search for planets and other low mass objects in the alpha Cen system using photometry and astrometry. The relativistic deflection of the approached star images will be in the milliarcsecond range. The small impact parameter of the conjunction with S5 means that this star has a probability of 45% of entering the Einstein ring of alpha Cen A. The gravitational amplification of the flux of S5 could reach a factor five for the combination of the two lensed images. The proper motion, orbital parameters and parallax of alpha Cen will be measurable with an extreme accuracy from differential astrometry with the S stars. This will be valuable, for example to prepare the Breakthrough Starshot initiative to send interstellar nanocrafts to alpha Centauri.

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RE: Alpha Centauri
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Twin Earths may lurk in our nearest star system

There could be two Earth-like planets within cosmic spitting distance of our own. Both are likely too close to their star to host life, but the discovery opens the possibility of other planets in the system with more temperate climates.
Alpha Centauri is a binary star system just 4.3 light years away from our own. In 2012 astronomers announced that the system had a planet, which they dubbed Alpha Centauri Bb as it was apparently orbiting the smaller of the stars, Alpha Centauri B.

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Alpha Centauri Bb
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Title: Hubble Space Telescope search for the transit of the Earth-mass exoplanet Alpha Centauri Bb
Author: Brice-Olivier Demory (Cavendish Laboratory), David Ehrenreich, Didier Queloz, Sara Seager, Ronald Gilliland, William J. Chaplin, Charles Proffitt, Michael Gillon, Maximilian N. Guenther, Bjoern Benneke, Xavier Dumusque, Christophe Lovis, Francesco Pepe, Damien Segransan, Amaury Triaud, Stephane Udry

Results from exoplanet surveys indicate that small planets (super-Earth size and below) are abundant in our Galaxy. However, little is known about their interiors and atmospheres. There is therefore a need to find small planets transiting bright stars, which would enable a detailed characterisation of this population of objects. We present the results of a search for the transit of the Earth-mass exoplanet Alpha Centauri Bb with the Hubble Space Telescope (HST). We observed Alpha Centauri B twice in 2013 and 2014 for a total of 40 hours. We achieve a precision of 115 ppm per 6-s exposure time in a highly-saturated regime, which is found to be consistent across HST orbits. We rule out the transiting nature of Alpha Centauri Bb with the orbital parameters published in the literature at 96.6% confidence. We find in our data a single transit-like event that could be associated to another Earth-size planet in the system, on a longer period orbit. Our program demonstrates the ability of HST to obtain consistent, high-precision photometry of saturated stars over 26 hours of continuous observations.

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Russian astronomers spot second planet in Alpha Centauri system

St. Petersburg astronomers have spotted one more planet circling a star in the Alpha Centauri system just 4.36 light-years away from the Solar System. The discovery was announced on Wednesday at a scientific conference Journees-2014 held at the Pulkovo Observatory in St. Petersburg.
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Alpha Centauri culminates each year at midnight on 24 April

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Alpha Centauri A
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A cool discovery about the Suns next-door twin

ESA's Herschel space observatory has detected a cool layer in the atmosphere of Alpha Centauri A, the first time this has been seen in a star beyond our own Sun. The finding is not only important for understanding the Sun's activity, but could also help in the quest to discover proto-planetary systems around other stars.
The Sun's nearest neighbours are the three stars of the Alpha Centauri system. The faint red dwarf, Proxima Centauri, is nearest at just 4.24 light-years, with the tight double star, Alpha Centauri AB, slightly further away at 4.37 light-years.

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Alpha Centauri Bb
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New planet is nearest one to our Solar System

An astronomer involved in the discovery of the new exoplanet spoke to BBC Radio 5 live about its significance.
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RE: Alpha Centauri
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Title: An Earth mass planet orbiting Alpha Centauri B
Authors: Xavier Dumusque, Francesco Pepe, Christophe Lovis, Damien Ségransan, Johannes Sahlmann, Willy Benz, François Bouchy, Michel Mayor, Didier Queloz, Nuno Santos and Stéphane Udry

Exoplanets down to the size of Earth have been found, but not in the habitable zone, i.e. the distance to the parent star where water, if present, would be liquid. There are planets in the habitable zone of stars cooler than our Sun, but for obvious reasons, such as tidal locking, strong stellar activity, are unlikely to harbour water-carbon life as we know it. The detection of a habitable Earth-mass planet orbiting a star similar to our Sun is extremely difficult because such a signal is completely overwhelmed by stellar perturbations. Here we report the detection of the smallest minimum mass planet detected so far around a solar-type star. This planet, orbiting our neighbour star Alpha Centauri B, is also the closest one to the solar system found to date. This result represents a major step towards the detection of Earth twins in the immediate vicinity of the Sun.

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Alpha Centauri Bb
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ESO's HARPS instrument finds Earth-mass exoplanet orbiting Alpha Centauri B

European astronomers have discovered a planet with about the mass of the Earth orbiting a star in the Alpha Centauri system - the nearest to Earth. It is also the lightest exoplanet ever discovered around a star like the Sun. The planet was detected using the HARPS instrument on the 3.6-metre telescope at ESO's La Silla Observatory in Chile. The results will appear online in the journal Nature on 17 October 2012.
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