Spectroscopic characterisation of microlensing events. Towards a new interpretation of OGLE-2011-BLG-0417

SANTERNE, A.; BOISSE, I.; BATISTA, V.; FIGUEIRA, P.; LILLO-BOX, J.; SANTOS, N. C.; ROJAS AYALA, B.; ALMENARA, J.-M.; DÍAZ, R. F.; HERTER, T.; RANC, C.; BEAULIEU, J.-P.; SCHLAWIN, E.; BENNETT, D.; JAMES, D. J.; MARQUETTE, J. B.; SOUSA, S. G.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2016 vol. 595

0004-6361

The microlensing event OGLE-2011-BLG-0417 is an exceptionally brightlens binary that was predicted to present radial velocity variation atthe level of several km s-1. Pioneer radial velocityfollow-up observations with the UVES spectrograph at the ESO-VLT of thissystem clearly ruled out the large radial velocity variation, leaving adiscrepancy between the observation and the prediction. In this paper,we further characterise the microlensing system by analysing itsspectral energy distribution (SED) derived using the UVES spectrum andnew observations with the ARCoIRIS (CTIO) near-infrared spectrograph andthe Keck adaptive optics instrument NIRC2 in the J, H, and Ks-bands. Wedetermine the mass and distance of the stars independently from themicrolensing modelling. We find that the SED is compatible with a giantstar in the Galactic bulge and a foreground star with a mass of 0.94± 0.09 M⊙ at a distance of 1.07 ± 0.24 kpc.We find that this foreground star is likely the lens. Its parameters arenot compatible with the ones previously reported in the literature (0.52± 0.04 M⊙ at 0.95 ± 0.06 kpc), based on themicrolensing light curve. A thoughtful re-analysis of the microlensingevent is mandatory to fully understand the reason of this newdiscrepancy. More importantly, this paper demonstrates thatspectroscopic follow-up observations of microlensing events are possibleand provide independent constraints on the parameters of the lens andsource stars, hence breaking some degeneracies in the analysis.UV-to-NIR low-resolution spectrographs like X-shooter (ESO-VLT) couldsubstantially contribute to this follow-up efforts, with magnitudelimits above all microlensing events detected so far.