OGLE-2019-BLG-0960 Lb: the Smallest Microlensing Planet

Abstract

We report the analysis of OGLE-2019-BLG-0960, which contains the smallest mass-ratio microlensing planet found to date (q = 1.2–1.6 × 10−5 at 1σ). Although there is substantial uncertainty in the satellite parallax measured by Spitzer, the measurement of the annual parallax effect combined with the finite source effect allows us to determine the mass of the host star (M L = 0.3–0.6 M ⊙), the mass of its planet (m p = 1.4–3.1 M ⊕), the projected separation between the host and planet (a ⊥ = 1.2–2.3 au), and the distance to the lens system (D L = 0.6–1.2 kpc). The lens is plausibly the blend, which could be checked with adaptive optics observations. As the smallest planet clearly below the break in the mass-ratio function, it demonstrates that current experiments are powerful enough to robustly measure the slope of the mass-ratio function below that break. We find that the cross-section for detecting small planets is maximized for planets with separations just outside of the boundary for resonant caustics and that sensitivity to such planets can be maximized by intensively monitoring events whenever they are magnified by a factor A > 5. Finally, an empirical investigation demonstrates that most planets showing a degeneracy between (s > 1) and (s < 1) solutions are not in the regime ( ∣ log s ∣ ≫ 0 ) for which the “close”/“wide” degeneracy was derived. This investigation suggests that there is a link between the “close”/“wide” and “inner/outer” degeneracies and also that the symmetry in the lens equation goes much deeper than symmetries uncovered for the limiting cases.

Scaling K2. V. Statistical Validation of 60 New Exoplanets From K2 Campaigns 2–18

“…We find that the light curve of OGLE-2016-BLG-1093 is qualitatively similar to that of KMT-2019-BLG-0842Lb (Jung et al 2020) or OGLE-2019-BLG-0960Lb (Yee et al 2021), both of which have much smaller mass ratios (q < 10 −4 ) than our best-fit solution. Following the formalism of Hwang et al (2022)…”

Systematic KMTNet Planetary Anomaly Search. IV. Complete Statistical Sample of 2019 Prime-Field Microlensing Planets

“…The 2L1S modeling yields two degenerate solutions with ∆χ 2 = 3.7, and the top panels of Figure 3 display the caustic structures and the source trajectories. The topology of the degeneracy is similar to the topology of the planetary event, OGLE-2019-BLG-0960 (Yee et al 2021). The two solutions both have s > 1 and appear to be major-image perturbations.…”

Analytic Simplifications to Planetary Microlensing under the Generalized Perturbative Picture

“…Firstly, resonant-topology lenses have a relatively large sphere of influence in the source plane, as the size of the resonant caustic scales as q 1/3 . In the case of semi-resonant lenses where central and planetary caustics are in close proximity to each other but do not merge into a single resonant caustic, there are extended regions of excess magnification or suppressed magnification between the central and planetary caustics (e.g., Abe et al 2013;Yee et al 2021). These scenarios with s → 1 have become increasingly common pathways to planet detections with pure-survey strategies (e.g., Zang et al 2022).…”

“…Practical utilities aside, an important consequence of the Chang-Refsdal approximation of GG97 is the existence of degeneracies for planetary caustic perturbations, commonly referred to as the inner-outer degeneracy (Han et al 2018). However, observed degeneracies that reference the inner-outer degeneracy rarely have well-isolated planetary caustics (Yee et al 2021). Moreover, the equation underlying the inner-outer degeneracy was recently found ) and proved to be valid also for perturbations associated with central and resonant caustics, exactly where the Chang-Refsdal approximation breaks down.…”