OGLE-2018-BLG-0799Lb: a Sub-Saturn-Mass Planet Orbiting a Very Low Mass Dwarf

Abstract

We report the discovery and analysis of a sub-Saturn-mass planet in the microlensing event OGLE-2018-BLG-0799. The planetary signal was observed by several ground-based telescopes, and the planet-host mass ratio is 𝑞 = (2.65 ± 0.16) × 10 −3 . The ground-based observations yield a constraint on the angular Einstein radius 𝜃 E , and the microlens parallax 𝜋 E is measured from the joint analysis of the Spitzer and ground-based observations, which suggests that the host star is most likely to be a very low-mass dwarf. A full Bayesian analysis using a Galactic model indicates that the planetary system is composed of an 𝑀 planet = 0.22 +0.19 −0.06 𝑀 𝐽 planet orbiting an 𝑀 host = 0.080 +0.080 −0.020 𝑀 , at a distance of 𝐷 L = 4.42 +1.73 −1.23 kpc. The projected planet-host separation is 𝑟 ⊥ = 1.27 +0.45 −0.29 AU, implying that the planet is located beyond the snowline of the host star. However, because of systematics in the Spitzer photometry, there is ambiguity in the parallax measurement, so the system could be more massive and farther away.

OGLE-2014-BLG-0319: A Sub-Jupiter-Mass Planetary Event Encountered Degeneracy with Different Mass Ratios and Lens-Source Relative Proper Motions

“…the degeneracy be-tween models A and C for this event. This degeneracy was also found in Zang et al (2020). In this degeneracy, one can constrain the source size which is relatively large compared with the caustic and the other can not, which is also demonstrated in Zang et al (2020).…”

“…This degeneracy was also found in Zang et al (2020). In this degeneracy, one can constrain the source size which is relatively large compared with the caustic and the other can not, which is also demonstrated in Zang et al (2020). This is qualitatively possible for planetary-caustic events with no sharp caustic-crossing features.…”

OGLE-2016-BLG-1093Lb: A Sub-Jupiter-mass Spitzer Planet Located in Galactic Bulge

“…Koshimoto & Bennett (2020) have suggested that systematics in the Spitzer light curve may bias the resulting parallax measurements. Such systematics have been seen at the level of 1-2 instrumental flux units (Gould et al 2020;Hirao et al 2020;Zang et al 2020), and so are most likely to play a significant role in events with small changes in flux as measured by Spitzer.…”

“…As a check, we also conduct the Spitzer-"only" test for the full Spitzer dataset. We conduct this Spitzer-"only" analysis following the formalism laid out in Gould et al (2020) but using a full planet model as in Zang et al (2020). Specifically, we fix the seven parameters of the model (t 0 , u 0 , t E , ρ, α, s, q) to their ground-based values, vary π E,N and π E,E on a grid, and fit only the Spitzer data with the color-constraint applied.…”

The effect of late giant collisions on the atmospheres of protoplanets and the formation of cold sub-Saturns

“…If confirmed by future observations, including direct imaging, radial velocity, and WFIRST surveys, CSS would defy classic formation models predicting that their progenitors should have grown into Jupiter-mass planets (Suzuki et al 2018;Zang et al 2020;Terry et al 2021). Suzuki et al (2018) in particular showed that detailed population synthesis models (Ida & Lin 2004;Mordasini, Alibert, & Benz 2009;Ida, Lin, & Nagasawa 2013) predict an order of magnitude fewer CSS planets than observed with the early microlensing surveys.…”