Constraining the Nature of the PDS 70 Protoplanets with VLTI/GRAVITY

TL;DR

This study uses VLTI/GRAVITY to observe the PDS 70 protoplanets, revealing their orbital parameters, constraining their masses, and providing insights into their atmospheres and circumplanetary environments with unprecedented spatial resolution.

Contribution

First high-precision interferometric observations of PDS 70 b and c, constraining their orbits, masses, and atmospheric properties with sub-au resolution.

Findings

PDS 70 b has a nonzero eccentricity of 0.17.

PDS 70 c has a near-circular orbit.

An upper limit of 10 M_Jup was set for PDS 70 b's mass.

Abstract

We present K-band interferometric observations of the PDS 70 protoplanets along with their host star using VLTI/GRAVITY. We obtained K-band spectra and 100 $\mu$as precision astrometry of both PDS 70 b and c in two epochs, as well as spatially resolving the hot inner disk around the star. Rejecting unstable orbits, we found a nonzero eccentricity for PDS 70 b of $0.17 \pm 0.06$, a near-circular orbit for PDS 70 c, and an orbital configuration that is consistent with the planets migrating into a 2:1 mean motion resonance. Enforcing dynamical stability, we obtained a 95% upper limit on the mass of PDS 70 b of 10 $M_\textrm{Jup}$, while the mass of PDS 70 c was unconstrained. The GRAVITY K-band spectra rules out pure blackbody models for the photospheres of both planets. Instead, the models with the most support from the data are planetary atmospheres that are dusty, but the nature of the dust is unclear. Any circumplanetary dust around these planets is not well constrained by the planets' 1-5 $\mu$m spectral energy distributions (SEDs) and requires longer wavelength data to probe with SED analysis. However with VLTI/GRAVITY, we made the first observations of a circumplanetary environment with sub-au spatial resolution, placing an upper limit of 0.3~au on the size of a bright disk around PDS 70 b.