An Astrometric Planetary Companion Candidate to the M9 Dwarf TVLM 513–46546

Abstract

Astrometric observations of the M9 dwarf TVLM 513–46546 taken with the VLBA reveal an astrometric signature consistent with a period of 221 ± 5 days. The orbital fit implies that the companion has a mass m p  = 0.35−0.42 M J , a circular orbit ( e  ≃ 0), a semimajor axis a  = 0.28−0.31 au, and an inclination angle i  = 71°−88°. The detected companion, TVLM 513 b , is one of the few giant-mass planets found associated with ultracool dwarfs. The presence of a Saturn-like planet on a circular orbit 0.3 au from a 0.06−0.08 M ⊙ star represents a challenge to planet formation theory. This is the first astrometric detection of a planet at radio wavelengths.