OGLE-2015-BLG-1670Lb: A Cold Neptune beyond the Snow Line in the Provisional WFIRST Microlensing Survey Field

Abstract

We present the analysis of the microlensing event OGLE-2015-BLG-1670, detected in a high-extinction field, very close to the Galactic plane. Due to the dust extinction along the line of sight, this event was too faint to be detected before it reached the peak of magnification. The microlensing light-curve models indicate a high-magnification event with a maximum of A max 200, very sensitive to planetary deviations. An anomaly in the light curve has been densely observed by the microlensing surveys MOA, KMTNet, and OGLE. From the light-curve modeling, we find a planetary anomaly characterized by a planet-to-host mass ratio, q = 1.00 +0.18 −0.16 × 10 −4 , at the peak recently identified in the mass-ratio function of microlensing planets. Thus, this event is interesting to include in future statistical studies about planet demography. We have explored the possible degeneracies and find two competing planetary models resulting from the s ↔ 1/s degeneracy. However, because the projected separation is very close to s = 1, the physical implications for the planet for the two solutions are quite similar, except for the value of s. By combining the light-curve parameters with a Galactic model, we have estimated the planet mass M 2 = 17.9 +9.6 −8.8 M ⊕ and the lens distance D L = 6.7 +1.0 −1.3 kpc, corresponding to a Neptune-mass planet close to the Galactic bulge. Such events with a low absolute latitude (|b| ≈ 1.1 deg) are subject to both high extinction and more uncertain source distances, two factors that may affect the mass measurements in the provisional Wide Field Infrared Survey Telescope fields. More events are needed to investigate the potential trade-off between the higher lensing rate and the difficulty in measuring masses in these low-latitude fields.

OGLE-2018-BLG-0532Lb: Cold Neptune with Possible Jovian Sibling

“…Here we analyze OGLE-2018-BLG-0532, whose lensing system contains at least one planet, a cold Neptune with mass ratio = q ´-1.0 0.2 10 4 ( ) , i.e., right at the somewhat arbitrary "low mass-ratio" boundary of Udalski et al (2018) and near the upper end of the possible "pileup" noted by Jung et al (2019). We note that Ranc et al (2019) have reported a planet that also straddles this boundary, with q=(1.00±0.17)×10 −4 . That is, both of these planets would meet the sample conditions of the Jung et al (2019) study.…”

“…They had argued for a sharp break in the mass-ratio function at q brk ∼0.56×10 −4 and/or a "pile up" of cold Neptunes just above the putative break point. Both of these planets (the other being OGLE-2015Ranc et al 2019), have mass-ratio estimates whose error bars straddle q=1.0×10 −4 . This places them near the upper end of the putative "pileup."…”

OGLE-2019-BLG-0825: Constraints on the Source System and Effect on Binary-lens Parameters Arising from a Five-day Xallarap Effect in a Candidate Planetary Microlensing Event

“…We follow a standard empirical error-bar normalization process (Yee et al 2012) intended to estimate proper uncertainties for the lensing parameters in the light-curve modeling. This process, described below, hardly affects the best-fit parameters (Ranc et al 2019). We renormalize the photometric error bars using the formula…”

OGLE-2014-BLG-0319: A Sub-Jupiter-Mass Planetary Event Encountered Degeneracy with Different Mass Ratios and Lens-Source Relative Proper Motions

“…Finally, we find the final best-fit model fitting all the renormalized light curves. We note that the best-fit model parameters and the final results are not sensitive to moderate changes of the renormalization factors (Ranc et al 2019). The data sets and the renormalization coefficients used in our analysis are summarized in Table 1.…”