Hubble Space Telescope search for the transit of the Earth-mass exoplanet α Centauri Bb

Demory, Brice-Olivier ; Ehrenreich, David ; Queloz, Didier ; Seager, Sara ; Gilliland, Ronald ; Chaplin, William J. ; Proffitt, Charles ; Gillon, Michael ; Günther, Maximilian N. ; Benneke, Björn ; Dumusque, Xavier ; Lovis, Christophe ; Pepe, Francesco ; Ségransan, Damien ; Triaud, Amaury ; Udry, Stéphane

In: Monthly Notices of the Royal Astronomical Society, 2015, vol. 450, no. 2, p. 2043-2051

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    Summary
    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 characterization of this population of objects. We present the results of a search for the transit of the Earth-mass exoplanet α Centauri Bb with the Hubble Space Telescope (HST). We observed α Centauri B twice in 2013 and 2014 for a total of 40h. We achieve a precision of 115ppm 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 α Centauri Bb with the orbital parameters published in the literature at 96.6 per cent confidence. We find in our data a single transit-like event that could be associated with another Earth-sized planet in the system, on a longer period orbit. Our programme demonstrates the ability of HST to obtain consistent, high-precision photometry of saturated stars over 26h of continuous observations