The first radial velocity measurements of a microlensing event: no evidence for the predicted binary⋆,⋆⋆
Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de
Marseille) UMR 7326, 13388
2 Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
3 CNRS, Université Pierre et Marie Curie, UMR 7095, Institut d’Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France
4 Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
Received: 3 June 2015
Accepted: 4 July 2015
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.
Key words: techniques: radial velocities / planets and satellites: individual: OGLE-2011-BLG-0417 / gravitational lensing: micro / methods: observational / planets and satellites: detection
Based on observations made with ESO Telescope at the Paranal Observatory under program ID 092.C-0763(A) and 093.C-0532(A).
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2015