HD 136164 Ab IR spectrum with VLTI/GRAVITY

Young, low-mass brown dwarfs orbiting early-type stars, with low mass ratios (q<~0.01), appear to be intrinsically rare and present a formation dilemma: could a handful of these objects be the highest-mass outcomes of "planetary" formation channels (bottom up within a protoplanetary disk), or are they more representative of the lowest-mass "failed binaries" (formed via disk fragmentation or core fragmentation)? Additionally, their orbits can yield model-independent dynamical masses, and when paired with wide wavelength coverage and accurate system age estimates, can constrain evolutionary models in a regime where the models have a wide dispersion depending on the initial conditions.

We present new interferometric observations of the 16Myr substellar companion HD136164Ab (HIP75056Ab) made with the Very Large Telescope Interferometer (VLTI)/GRAVITY and an updated orbit fit including proper motion measurements from the Hipparcos-Gaia Catalog of Accelerations. We estimate a dynamical mass of 35{+/-}10MJ (q~0.02), making HD136164Ab the youngest substellar companion with a dynamical mass estimate. The new mass and newly constrained orbital eccentricity (e=0.44{+/-}0.03) and separation (22.5{+/-}1au) could indicate that the companion formed via the low-mass tail of the initial mass function.