Abstract
Abstract We present the MOA Collaboration light-curve data for the planetary microlensing event OGLE-2015-BLG-0954, which was previously announced in a paper by the KMTNet and OGLE Collaborations. The MOA data cover the caustic exit, which was not covered by the KMTNet or Optical Gravitational Lensing Experiment (OGLE) data, and they provide a more reliable measurement of the finite source effect. The MOA data also provide a new source color measurement that reveals a lens-source relative proper motion of μ rel = 11.8 ± 0.8 mas yr−1, which compares to the value of μ rel = 18.4 ± 1.7 mas yr−1 reported in the KMTNet-OGLE paper. This new MOA value for μ rel has an a priori probability that is a factor of ≳100 times larger than the previous value, and it does not require a lens system distance of D L < 1 kpc. Based on the corrected source color, we find that the lens system consists of a planet of mass orbiting a star at an orbital separation of and a distance of .
Highlights
Statistical analyses of exoplanetary microlensing samples have indicated that planets with roughly Neptune masses are more common than Jupiters (Gould et al 2010; Sumi et al 2010; Cassan et al 2012; Shvartzvald et al 2016), and the recent analysis of a larger sample, by the MOA Collaboration (Suzuki et al 2016), has indicated a break, and likely a peak, in the exoplanet mass ratio function at a mass ratio of q ∼ 10−4
Statistical analyses of the exoplanets found by microlensing have focused on the planetary parameters that are most measured in microlensing events, the mass ratio, q, and the separation, s, in Einstein radius units
For most planetary microlensing events, θE can be directly determined from finite source effects, which provides a measurement of the source radius crossing time, t*
Summary
Gravitational microlensing has a unique niche among methods for studying exoplanet systems (Bennett 2008; Gaudi 2012) because of its sensitivity to planets extending down to low masses (Bennett & Rhie 1996) beyond the snow line (Mao & Paczyński 1991; Gould & Loeb 1992), where planet formation is thought to be the most efficient (Ida & Lin 2005; Kennedy et al 2006; Lecar et al 2006; Kennedy & Kenyon 2008; Thommes et al 2008), according to the leading core accretion planet formation theory (Lissauer 1993; Pollack et al 1996). The step in the statistical analysis of wide-orbit sample exoplanetary microlens systems will be to include the constraints from measurements of θE, πE, and the host-star brightness for large statistical samples, such as those of Suzuki et al (2016) This will enable us to expand our analysis beyond the mass ratio and the separation in Einstein radius units to determine the exoplanet mass function as a function of the hoststar mass, as well as a function of Galactocentric distance. MOA-2014-BLG-262 is the event with the situation most similar to the event that we discuss in this paper (Bennett et al.2014) This was a relatively short-duration event with a clear signal of a planetary mass ratio companion, but the best-fit model implied a very large relative proper motion, μrel = 19.6 ± 1.6 mas yr−1.
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