Weighing the Non-transiting Hot Jupiter τ Boo b

We report the detection of the orbital velocity of non-transiting hot Jupiter τ Boo b. By employing high-resolution ground-based spectroscopy around 2.3 μm during one half-night, we are able to detect carbon monoxide absorption lines produced in the planet atmosphere, which shift significantly in wavelength during the course of the observations due to the orbital motion of the planet. This detection of the planetary signal results in the determination of the orbital inclination as being i = 47⁺⁷ _{- 6} deg and, furthermore, allows us to solve for the exact planetary mass, m _p = 5.6 ± 0.7 M _Jup. This clearly confirms the planetary nature of the non-transiting companion to τ Boo.