OGLE-2016-BLG-1195Lb: A Sub-Neptune Beyond the Snow Line of an M-dwarf Confirmed by Keck AO

TL;DR

This paper confirms the existence of a sub-Neptune exoplanet beyond the snow line of an M-dwarf using high-resolution Keck AO imaging, and highlights the importance of accounting for systematics in photometric data analysis.

Contribution

It provides direct imaging confirmation of a planetary system initially detected by microlensing and critically reanalyzes extit{Spitzer} data to address potential systematic errors.

Findings

Confirmed the planet's mass and orbit using Keck AO imaging.

Identified potential systematic errors in extit{Spitzer} photometry affecting previous analyses.

Highlighted the importance of careful data detrending in microlensing and space-based photometry.

Abstract

We present the analysis of high resolution follow-up observations of OGLE-2016-BLG-1195 using Laser Guide Star Adaptive Optics with Keck, seven years after the event's peak. We resolve the lens, measuring its flux and the relative source-lens proper motion, thus finding the system to be a $M_{\rm p} = 10.08\pm 1.18\ M_{\rm \oplus}$ planet orbiting an M-dwarf, $M_{\rm L} = 0.62\pm 0.05\ M_{\odot}$, beyond the snow line, with a projected separation of $r_\perp=2.24\pm 0.21$ AU at $D_{\rm L} = 7.45\pm 0.55$ kpc. Our results are consistent with the discovery paper, which reports values with 1-sigma uncertainties based on a single mass-distance constraint from finite source effects. However, both the discovery paper and our follow-up results disagree with the analysis of a different group that also present the planetary signal detection. The latter utilizes \textit{Spitzer} photometry to measure a parallax signal claiming the system is an Earth-mass planet orbiting an ultracool dwarf. Their parallax signal though is improbable since it suggests a lens star in the disk moving perpendicular to Galactic rotation. Moreover, microlensing parallaxes can be impacted by systematic errors in the photometry. Therefore, we reanalyze the \textit{Spitzer} photometry using a Pixel Level Decorrelation (PLD) model to detrend detector systematics. We find that we can not confidently recover the same detrended light curve that is likely dominated by systematic errors in the photometric data. The results of this paper act as a cautionary tale that a careful understanding of detector systematics and how they influence astrophysical constraints is crucial.