Hubble Space Telescope search for the transit of the Earth-mass exoplanet α Centauri B b
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 B b with the Hubble Space Telescope (HST). We observed α Centauri B twice in 2013 and 2014 for a total of 40 h. 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 α Centauri B b 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 26 h of continuous observations.
© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 March 25. Received 2015 March 16; in original form 2014 November 6. First published online April 30, 2015 We are indebted to Shelly Meyett and Tricia Royle for their assistance in the planning and executing of these observations. We thank Tom Ayres for his help in preparing our phase 2 programme, as well as Adrian Barker, Samantha Thompson and Julien de Wit for discussions. We also thank the anonymous referee for a detailed and helpful review that improved the paper. We are grateful to STScI Director Matt Mountain for awarding Director's Discretionary Time for both programmes. Based on observations made with the NASA/ESA HST, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programme PID13180 and 13927. Support for this programme was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. This work has been carried out within the frame of the National Center for Competence in Research PlanetS supported by the Swiss National Science Foundation (SNSF). DE, CL, FP, and SU acknowledge the financial support of the SNSF. AT is a Swiss National Science Foundation fellow under grant number P300P2-147773.
Submitted - 1503.07528v1.pdf
Published - MNRAS-2015-Demory-2043-51.pdf