OGLE-2015-BLG-1670Lb: A Cold Neptune beyond the Snow Line in the Provisional WFIRST Microlensing Survey Field
Creators: name: Ranc, Clément
name: Bennett, David P.
name: Hirao, Yuki
name: Udalski, Andrzej
name: Han, Cheongho
name: Bond, Ian A.
name: Yee, Jennifer C.
name: Collaboration, The KMTNet
name: :
name: Albrow, Michael D.
name: Chung, Sun-Ju
name: Gould, Andrew
name: Hwang, Kyu-Ha
name: Jung, Youn-Kil
name: Ryu, Yoon-Hyun
name: Shin, In-Gu
name: Shvartzvald, Yossi
name: Zang, Weicheng
name: Zhu, Wei
name: Cha, Sang-Mok
name: Kim, Dong-Jin
name: Kim, Hyoun-Woo
name: Kim, Seung-Lee
name: Lee, Chung-Uk
name: Lee, Dong-Joo
name: Lee, Yong-Seok
name: Park, Byeong-Gon
name: Pogge, Richard W.
name: Collaboration, The MOA
name: :
name: Abe, Fumio
name: Barry, Richard K.
name: Bhattacharya, Aparna
name: Donachie, Martin
name: Fukui, Akihiko
name: Itow, Yoshitaka
name: Kawasaki, Kohei
name: Kondo, Iona
name: Koshimoto, Naoki
name: Li, Man Cheung Alex
name: Matsubara, Yutaka
name: Miyazaki, Shota
name: Muraki, Yasushi
name: Nagakane, Masayuki
name: Rattenbury, Nicholas J.
name: Suematsu, Haruno
name: Sullivan, Denis J.
name: Sumi, Takahiro
name: Suzuki, Daisuke
name: Tristram, Paul J.
name: Yonehara, Atsunori
name: Collaboration, The OGLE
name: :
name: Poleski, Radosław
name: Mróz, Przemek
name: Skowron, Jan
name: Szymański, Michał K.
name: Soszyński, Igor
name: Kozłowski, Szymon
name: Pietrukowicz, Paweł
name: Ulaczyk, Krzysztof
Publisher: name: arXiv
Year: 2018
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: 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 $A_\mathrm{max}\gtrsim200$, 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, $q=\left(1.00^{+0.18}_{-0.16}\right)\times 10^{-4}$, 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 $s\leftrightarrow1/s$ 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 $M_2=17.9^{+9.6}_{-8.8}\,\mathrm{M}_\oplus$ and the lens distance $D_\mathrm{L}=6.7^{+1.0}_{-1.3}\,\mathrm{kpc}$, corresponding to a Neptune-mass planet close to the Galactic bulge. Such events with a low absolute latitude ($|b|\approx 1.1\,\mathrm{deg}$) 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.
description: 30 pages, 8 figures, 5 tables. Typos corrected and section 3.2.3 added. Version accepted for publication in The Astronomical Journal