MOA-2009-BLG-319Lb: A Sub-Saturn Planet Inside the Predicted Mass Desert

Abstract

We present an adaptive optics (AO) analysis of images from the Keck-II telescope NIRC2 instrument of the planetary microlensing event MOA-2009-BLG-319. The ∼10 year baseline between the event and the Keck observations allows the planetary host star to be detected at a separation of 66.5 ± 1.7 mas from the source star, consistent with the light curve model prediction. The combination of the host star brightness and light curve parameters yield host star and planet masses of M host = 0.514 ± 0.063M and mp = 66.0 ± 8.1M⊕ at a distance of DL = 7.0 ± 0.7 kpc. The star-planet projected separation is 2.03 ± 0.21 AU. The planet-star mass ratio of this system, q = (3.857 ± 0.029) × 10 −4 , places it in the predicted "planet desert" at 10 −4 < q < 4 × 10 −4 according to the runaway gas accretion scenario of the core accretion theory. Seven of the 30 planets in the Suzuki et al. ( 2016) sample fall in this mass ratio range, and this is the third with a measured host mass. All three of these host stars have masses of 0.5 ≤ M host /M ≤ 0.7, which implies that this predicted mass ratio gap is filled with planets that have host stars within a factor of two of 1M . This suggests that runaway gas accretion does not play a major role in determining giant planet masses for stars somewhat less massive than the Sun. Our analysis has been accomplished with a modified DAOPHOT code that has been designed to measure the brightness and positions of closely blended stars. This will aid in the development of the primary method that the Nancy Grace Roman Space Telescope mission will use to determine the masses of microlens planets and their hosts.

KMT-2019-BLG-0371 and the Limits of Bayesian Analysis

“…There have now been several events with direct measurements of the lens flux from high-resolution imaging (Batista et al 2015, Bhattacharya et al 2019, Terry et al 2020, Vandorou et al 2020. Comparing the inferred masses to the predictions from prior Bayesian estimates has often resulted in disagreements.…”

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

“…To measure the mass of a lens system, one needs two observables that yield mass-distance relations for the lens systems, i.e., any two of the angular Einstein radius 𝜃 E , the microlens parallax 𝜋 E and the apparent brightness of the lens system. The detection of lens brightness can be achieved by high angular resolution imaging when the source and lens are resolved (e.g., Alcock et al 2001;Kozłowski et al 2007;Batista et al 2015;Bennett et al 2015;Bhattacharya et al 2018;Vandorou et al 2020;Bennett et al 2020;Bhattacharya et al 2020;Terry et al 2020), but it is difficult for very faint VLM dwarfs. The measurements of 𝜃 E and 𝜋 E can yield the mass of a lensing object by (Gould 2000)…”

Revealing Short-period Exoplanets and Brown Dwarfs in the Galactic Bulge using the Microlensing Xallarap Effect with the \textit{Nancy Grace Roman Space Telescope}

“…The ability of Roman to measure θ E and D S has been studied in several papers. It is expected that most Roman events that the relative lens-source proper mo-tion µ rel can be measured via direct detection of lens light in the Roman images, which enables us to measure θ E (Bennett et al 2010(Bennett et al , 2020Bhattacharya et al 2018;P19;Terry et al 2020). D S for bright source events can potentially be measured by the direct parallax (astrometry) measurements in the Roman survey data (Gould et al 2015).…”