Paper detail

On the detectability of a predicted mesolensing event associated with the high proper motion star VB 10

Extrapolation of the astrometric motion of the nearby low-mass star VB 10 indicates that sometime in late December 2011 or during the first 2-3 months of 2012, the star will make a close approach to a background point source. Based on astrometric uncertainties, we estimate a 1 in 2 chance that the distance of closest approach ρ_{min} will be less than 100mas, a 1 in 5 chance that ρ_{min}<50mas, and a 1 in 10 chance that ρ_{min}<20mas. The latter would result in a microlensing event with a 6% magnification in the light from the background source, and an astrometric shift of 3.3 mas. The lensing signal will however be significantly diluted by the light from VB 10, which is 1.5mag brighter than the background source in B band, 5 mag brighter in I band, and 10 mag brighter in K, making the event undetectable in all but the bluer optical bands. However, we show that if VB 10 happens to harbor a \sim 1 M_J planet on a moderately wide (\approx 0.18AU-0.84AU) orbit, there is a chance (1% to more than 10%, depending on the distance of closest approach and orbital period and inclination) that a passage of the planet closer to the background source will result in a secondary event of higher magnification. The detection of secondary events could be made possible with a several-times-per-night multi-site monitoring campaign.