= 51 Pegasi b
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<51 Pegasi b> is the giant <exoplanet> whose 1995 discovery established a planet around a <Sun>-like <star>. It is a <hot Jupiter>: its roughly 4.23-day <orbital period> and about 0.05 <astronomical unit> separation differ markedly from Jupiter's distant orbit. Earlier confirmed <exoplanets> had already been found around a <pulsar>; the host category is part of this discovery's significance.<A Jupiter-mass companion to a solar-type star by Michel Mayor and Didier Queloz>[1995, abstract and orbital solution]{ref}
<Michel Mayor> and <Didier Queloz> used the <ELODIE spectrograph> to measure periodic <Doppler shifts> in the host star's spectrum. The star's motion around the shared centre of mass produces alternating approaching and receding velocities even though the planet is unresolved. For a nearly circular orbit and a planet much less massive than its host,
$$
K\simeq\left(\frac{2\pi G}{P}\right)^{1/3}\frac{M_p\sin i}{M_*^{2/3}}.
$$
The measured velocity amplitude and period therefore constrain $M_p\sin i$, originally about half Jupiter's <mass>, rather than independently determining inclination and true mass. Checking spectral-line changes also helps distinguish orbital motion from changing stellar line profiles.<A Jupiter-mass companion to a solar-type star by Michel Mayor and Didier Queloz>[Instrument, radial-velocity curve and discussion of alternative stellar explanations]{ref}
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