Spitzer Opens New Path to Break Classic Degeneracy for Jupiter-Mass Microlensing Planet OGLE-2017-BLG-1140Lb

Abstract

We analyze the combined Spitzer and ground-based data for OGLE-2017-BLG-1140 and show that the event was generated by a Jupiter-class $(m_p\simeq 1.6M_{\mathrm{jup}})$ planet orbiting a mid-late M dwarf $(M\simeq 0.2M_{\odot })$ that lies $D_{LS}\simeq 1.0\mathrm{kpc}$ in the foreground of the microlensed, Galactic-bar, source star. The planet-host projected separation is $a_{\perp }\simeq 1.0\mathrm{au}$, i.e., well-beyond the snow line. By measuring the source proper motion ${\mu }_s$ from ongoing, long-term OGLE imaging, and combining this with the lens-source relative proper motion ${\mu }_{\mathrm{rel}}$ derived from the microlensing solution, we show that the lens proper motion ${\mu }_l={\mu }_{\mathrm{rel}}+{\mu }_s$ is consistent with the lens lying in the Galactic disk, although a bulge lens is not ruled out. We show that while the Spitzer and ground-based data are comparably well fitted by planetary (i.e., binary-lens, 2L1S) models and by binary-source (1L2S) models, the combination of Spitzer and ground-based data decisively favor the planetary model. This is a new channel to resolve the 2L1S/1L2S degeneracy, which can be difficult to break in some cases.

arXiv commentRevised version accepted for publication in The Astronomical Journal

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