= Stellar radial-velocity semi-amplitude
{title2=$K$}
Half the peak-to-peak line-of-sight orbital <velocity> range of a <star> in a single-companion <Kepler orbit>. It equals $K=2\pi a_\star\sin i/[P\sqrt{1-e^2}]$, where $a_\star$ is the stellar barycentric <semi-major axis>, $P$ the <orbital period>, $i$ the sky-plane <orbital inclination>, and $e$ the <orbital eccentricity>. The <Doppler spectroscopy> formula follows from <Kepler's third law> for the relative <orbit>, $a^3=G(M_\star+M_p)P^2/(4\pi^2)$.
Back to article page
