The Star Blended with the MOA-2008-BLG-310 Source Is Not the Exoplanet Host Star

Abstract

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, ${\mu }_{\mathrm{rel}}$, 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 $M_h=0.21_{-0.09}^{+0.21}{M}_{\odot }$, a planet mass of $m_p=23.4_{-9.9}^{+23.9}{M}_{\oplus }$ at a projected separation of $a_{\perp }=1.12_{-0.17}^{+0.16},$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.

Submitted to AJ on March 18, 2017

References in corpus (21)

• Wide-Field InfrarRed Survey Telescope-Astrophysics Focused Telescope Assets WFIRST-AFTA 2015 Report
• Discovery of a Jupiter/Saturn Analog with Gravitational Microlensing
• Microlens OGLE-2005-BLG-169 Implies Cool Neptune-Like Planets are Common
• A Low-Mass Planet with a Possible Sub-Stellar-Mass Host in Microlensing Event MOA-2007-BLG-192
• The Exoplanet Mass-Ratio Function from the MOA-II Survey: Discovery of a Break and Likely Peak at a Neptune Mass
• On the Location of the Snow Line in a Protoplanetary Disk
• Identification of the OGLE-2003-BLG-235/MOA-2003-BLG-53 Planetary Host Star
• The First Circumbinary Planet Found by Microlensing: OGLE-2007-BLG-349L(AB)c
• Triple Microlens OGLE-2008-BLG-092L: Binary Stellar System with a Circumprimary Uranus-type Planet
• The SAMI Galaxy Survey: Towards a unified dynamical scaling relation for galaxies of all types
• Gas dynamics in the Milky Way: a low pattern speed model
• Revisiting the microlensing event OGLE 2012-BLG-0026: A solar mass star with two cold giant planets
• Mapping stellar kinematics across the Galactic bar: HST measurements of proper motions in 35 fields
• OGLE-2012-BLG-0950Lb: The First Planet Mass Measurement from Only Microlens Parallax and Lens Flux
• Near-Infrared Spectroscopy of the Y0 WISEP J173835.52+273258.9 and the Y1 WISE J035000.32-565830.2: the Importance of Non-Equilibrium Chemistry
• Evidence for a planetary mass third body orbiting the binary star KIC 5095269
• The Varying Light Curve and Timings of the Ultra-short Period Contact Binary KIC 9532219
• OGLE-2008-BLG-355Lb: A Massive Planet around A Late type Star
• Microlensing by Kuiper, Oort, and Free-Floating Planets
• Discovery of a Gas giant Planet in Microlensing Event OGLE-2014-BLG-1760
• OGLE-2012-BLG-0724Lb: A Saturn-mass Planet around an M-dwarf

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• A Likely Detection of a Two-Planet System in a Low Magnification Microlensing Event
• Bayesian Approach for Determining Microlens System Properties with High-Angular-Resolution Follow-up Imaging
• OGLE-2017-BLG-0406: $Spitzer$ Microlens Parallax Reveals Saturn-mass Planet orbiting M-dwarf Host in the Inner Galactic Disk
• OGLE-2013-BLG-1761Lb: A Massive Planet Around an M/K Dwarf
• OGLE-2015-BLG-1670Lb: A Cold Neptune beyond the Snow Line in the Provisional WFIRST Microlensing Survey Field
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• KMT-2019-BLG-0371 and the Limits of Bayesian Analysis
• OGLE-2013-BLG-0911Lb: A Secondary on the Brown-Dwarf Planet Boundary around an M-dwarf
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• OGLE-2015-BLG-1649Lb: A gas giant planet around a low-mass dwarf
• OGLE-2016-BLG-0156: Microlensing Event With Pronounced Microlens-Parallax Effects Yielding Precise Lens Mass Measurement
• Casting Light on Degeneracies: A Comprehensive Study of Lightcurve Variations in Microlensing Events OGLE-2017-BLG-0103 and OGLE-2017-BLG-0192