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Spectroscopic direct detection of reflected light from extra-solar planets

J. H. C. Martins, P. Figueira, N. C. Santos, C. Lovis

Abstract
At optical wavelengths, an exoplanet's signature is essentially reflected light from the host star - several orders of magnitude fainter. Since it is superimposed on the star spectrum its detection has been a difficult observational challenge. However, the development of a new generation of instruments like ESPRESSO and next generation telescopes like the E-ELT put us in a privileged position to detect these planets' reflected light as we will have access to extremely high signal-to-noise ratio spectra. With this work, we propose an alternative approach for the direct detection of the reflected light of an exoplanet. We simulated observations with ESPRESSO@VLT and HIRES@E-ELT of several star+planet systems, encompassing 10h of the most favourable orbital phases. To the simulated spectra we applied the Cross Correlation Function to operate in a much higher signal-to-noise ratio domain than when compared with the spectra. The use of the Cross-Correlation Function permitted us to recover the simulated the planet signals at a level above 3 σnoise significance on several prototypical (e.g., Neptune type planet with a 2 days orbit with the VLT at 4.4 σnoise significance) and real planetary systems (e.g., 55 Cnc e with the E-ELT at 4.9 σnoise significance). Even by using a more pessimistic approach to the noise level estimation, where systematics in the spectra increase the noise 2-3 times, the detection of the reflected light from large close-orbit planets is possible. We have also shown that this kind of study is currently within reach of current instruments and telescopes (e.g., 51 Peg b with the VLT at 5.2 σnoise significance), although at the limit of their capabilities.

Keywords
techniques: radial velocities - planets and satellites: detection

Monthly Notices of the Royal Astronomical Society
Volume 436, Issue 2, Page 1215
2013 December

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia