Deep Imaging Search for Planets Forming in the TW Hya Protoplanetary Disk with the Keck/NIRC2 Vortex Coronagraph

Abstract

Distinct gap features in the nearest protoplanetary disk, TW Hya (distance of 59.5 ± 0.9 pc), may be signposts of ongoing planet formation. We performed long-exposure thermal infrared coronagraphic imaging observations to search for accreting planets, especially within dust gaps previously detected in scattered light and submillimeter-wave thermal emission. Three nights of observations with the Keck/NIRC2 vortex coronagraph in L' (3.4–4.1 μm) did not reveal any statistically significant point sources. We thereby set strict upper limits on the masses of non-accreting planets. In the four most prominent disk gaps at 24, 41, 47, and 88 au, we obtain upper mass limits of 1.6–2.3, 1.1–1.6, 1.1–1.5, and 1.0–1.2 Jupiter masses (M_J), assuming an age range of 7–10 Myr for TW Hya. These limits correspond to the contrast at 95% completeness (true positive fraction of 0.95) with a 1% chance of a false positive within 1'' of the star. We also approximate an upper limit on the product of the planet mass and planetary accretion rate of M_pM ≾ 10^(-8) M^2_j yr^(-1) implying that any putative ~0.1 M J planet, which could be responsible for opening the 24 au gap, is presently accreting at rates insufficient to build up a Jupiter mass within TW Hya's pre-main-sequence lifetime.