KMT-2018-BLG-0029Lb: A Very Low Mass-Ratio Spitzer Microlens Planet

At q = 1.81 ± 0.20 × 10⁻⁵, KMT-2018-BLG-0029Lb has the lowest planet-host mass ratio q of any microlensing planet to date by more than a factor of two. Hence, it is the first planet that probes below the apparent “pile-up” at q = 5–10 ×10⁻⁵. The event was observed by Spitzer, yielding a microlens-parallax π_E measurement. Combined with a measurement of the Einstein radius θ_E from finite-source effects during the caustic crossings, these measurements imply masses of the host M_(host) = 1.14^(+0.10)_(−0.12)M⊙ and planet M_(planet) = 7.59^(+0.75)_(−0.69)M⊕, system distance D_L = 3.38^(+0.22)_(−0.26) 3.38^(+0.22)_(−0.26) kpc and projected separation a⊥ = 4.27^(+0.21)_(−0.23) 4.27^(+0.21)_(−0.23) AU. The blended light, which is substantially brighter than the microlensed source, is plausibly due to the lens and could be observed at high resolution immediately

MOA-2020-BLG-135Lb: A New Neptune-class Planet for the Extended MOA-II Exoplanet Microlens Statistical Analysis

We report the light-curve analysis for the event MOA-2020-BLG-135, which leads to the discovery of a new Neptune-class planet, MOA-2020-BLG-135Lb. With a derived mass ratio of $q=1.52_{-0.31}^{+0.39} \times 10^{-4}$ and separation $s\approx1$, the planet lies exactly at the break and likely peak of the exoplanet mass-ratio function derived by the MOA collaboration (Suzuki et al. 2016). We estimate the properties of the lens system based on a Galactic model and considering two different Bayesian priors: one assuming that all stars have an equal planet-hosting probability and the other that planets are more likely to orbit more massive stars. With a uniform host mass prior, we predict that the lens system is likely to be a planet of mass $m_\mathrm{planet}=11.3_{-6.9}^{+19.2} M_\oplus$ and a host star of mass $M_\mathrm{host}=0.23_{-0.14}^{+0.39} M_\odot$, located at a distance $D_L=7.9_{-1.0}^{+1.0}\;\mathrm{kpc}$. With a prior that holds that planet occurrence scales in proportion to the host star mass, the estimated lens system properties are $m_\mathrm{planet}=25_{-15}^{+22} M_\oplus$, $M_\mathrm{host}=0.53_{-0.32}^{+0.42} M_\odot$, and $D_L=8.3_{-1.0}^{+0.9}\; \mathrm{kpc}$. This planet qualifies for inclusion in the extended MOA-II exoplanet microlens sample.Comment: 22 pages, 6 figures, 4 tables, submitted to the AAS Journal