* Astronomy

Title: The Star Blended with the MOA-2008-BLG-310 Source Is Not the Exoplanet Host Star
Author: A. Bhattacharya, D. P. Bennett, J. Anderson, I. A. Bond, A. Gould, V. Batista, J. P. Beaulieu, P. Fouque, J. B. Marquette, R. Pogge

High resolution Hubble Space Telescope (HST) image analysis of the MOA-2008-BLG-310 microlens system indicates that the excess flux at the location of the source found in the discovery paper cannot primarily be due to the lens star because it does not match the lens-source relative proper motion, rel, predicted by the microlens models. This excess flux is most likely to be due to an unrelated star that happens to be located in close proximity to the source star. Two epochs of HST observations indicate proper motion for this blend star that is typical of a random bulge star, but is not consistent with a companion to the source or lens stars if the flux is dominated by only one star, aside from the lens. We consider models in which the excess flux is due to a combination of an unrelated star and the lens star, and this yields 95% confidence level upper limit on the lens star brightness of I_L>22.44 and V_L>23.62. A Bayesian analysis using a standard Galactic model and these magnitude limits yields a host star mass M_h = 0.21 ^{+0.21}_{-0.09} solar masses, a planet mass of m_p = 23.4 ^{+23.9}_{-9.9} earth masses at a projected separation of a_\perp = 1.12^{+0.16}_{-0.17} AU. This result illustrates excess flux in a high resolution image of a microlens-source system need not be due to the lens. It is important to check that the lens-source relative proper motion is consistent with the microlensing prediction. The high resolution image analysis techniques developed in this paper can be used to verify the WFIRST exoplanet microlensing survey mass measurements.

Read more (1590kb, PDF)