OGLE-2017-BLG-1434Lb: Eighth q<1×10⁻⁴ Mass-Ratio Microlens Planet Confirms Turnover in Planet Mass-Ratio Function

Udalski, A.; Ryu, Y.-H.; Sajadian, S.; Gould, A.; Mróz, P.; Poleski, R.; Szymański, M. K.; Skowron, J.; Soszyński, I.; Kozłowski, S.; Pietrukowicz, P.; Ulaczyk, K.; Pawlak, M.; Rybicki, K.; Iwanek, P.; Albrow, M. D.; Chung, S.-J.; Han, C.; Hwang, K.-H.; Jung, Y.; Shin, I.-G.; Shvartzvald, Y.; Yee, J. C.; Zang, W.; Zhu, W.; Cha, S.-M.; Kim, D.-J.; Kim, H.-W.; Kim, S.-L.; Lee, C.-U.; Lee, D.-J.; Lee, Y.; Park, B.-G.; Pogge, R. W.; Bozza, V.; Dominik, M.; Helling, C.; Hundertmark, M.; Jørgensen, U. G.; Longa-Peña, P.; Lowry, S.; Burgdorf, M.; Campbell-White, J.; Ciceri, S.; Evans, D.; Figuera Jaimes, R.; Fujii, Y. I.; Haikala, L. K.; Henning, T.; Hinse, T. C.; Mancini, L.; Peixinho, N.; Rahvar, S.; Rabus, M.; Skottfelt, J.; Snodgrass, C.; Southworth, J. and von Essen, C. (2018). OGLE-2017-BLG-1434Lb: Eighth q<1×10⁻⁴ Mass-Ratio Microlens Planet Confirms Turnover in Planet Mass-Ratio Function. Acta Astronomica, 68(1) pp. 1–42.

DOI: https://doi.org/10.32023/0001-5237/68.1.1

Abstract

We report the discovery of a cold Super-Earth planet (m_p=4.4±0.5 M_⊕) orbiting a low-mass (M=0.23±0.03) M_⊙ dwarf at projected separation a_⊥=1.18±0.10 a.u., i.e., about 1.9 times the distance the snow line. The system is quite nearby for a microlensing planet, D_L=0.86±0.09 kpc. Indeed, it was the large lens-source relative parallax π_rel=1.0 mas (combined with the low mass M) that gave rise to the large, and thus well-measured, "microlens parallax" π_E∝(π_rel/M)^1/2 that enabled these precise measurements. OGLE-2017-BLG-1434Lb is the eighth microlensing planet with planet-host mass ratio q<1×10^-4.

We apply a new planet-detection sensitivity method, which is a variant of "V/V_max", to seven of these eight planets to derive the mass-ratio function in this regime. We find dN/d lnq ∝ q^p, with p=1.05^+0.78_-0.68, which confirms the "turnover" in the mass function found by Suzuki et al. relative to the power law of opposite sign n=-0.93±0.13 at higher mass ratios q≳2×10^-4. We combine our result with that of Suzuki et al. to obtain p=0.73^+0.42_-0.34.

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