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The first radial velocity measurements of a microlensing event: no evidence for the predicted binary

I. Boisse, A. Santerne, J.-P. Beaulieu, W. Fakhardji, N. C. Santos, P. Figueira, S. G. Sousa, C. Ranc

Abstract
The gravitational microlensing technique allows the discovery of exoplanets around stars distributed in the disk of the galaxy towards the bulge. The alignment of two stars that led to the discovery is unique over the timescale of a human life, however, and cannot be re-observed. Moreover, the target host is often very faint and located in a crowded region. These difficulties hamper and often make impossible the follow up of the target and study of its possible companions. A radial-velocity curve was predicted for the binary system, OGLE-2011-BLG-0417, discovered and characterised from a microlensing event. We used the UVES spectrograph mounted at the VLT, ESO to derive precise radial-velocity measurements of OGLE-2011-BLG-0417. To gather high-precision radial velocities on faint targets of microlensing events, we proposed to use the source star as a reference to measure the lens radial velocities. We obtained ten radial velocities on the putative V = 18 lens with a dispersion of ~100 m s-1, spread over one year. Our measurements do not confirm the microlensing prediction for this binary system. The most likely scenario is that the putative V = 18 mag lens is actually a blend and not the primary lens which is 2 mag fainter. Further observations and analyses are needed to understand the microlensing observation and infer on the nature and characteristics of the lens itself.

Keywords
techniques: radial velocities - planets and satellites: individual:, OGLE-2011-BLG-0417 - gravitational lensing: micro - methods: observational - planets and satellites: detection

Astronomy and Astrophysics
Volume 582, Number of pages L11
2015 October

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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
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