= R. Paul Butler
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<R. Paul Butler> develops precise stellar <radial velocity> measurements for detecting orbiting companions. With <Geoffrey W. Marcy>, he developed <iodine-cell Doppler calibration>, superimposing a dense reference spectrum on the same <light> entering a stellar <spectrograph>.
The reference lines constrain both the <wavelength> scale and the instrumental <point spread function> during the observation. Modeling them together with the shifted stellar <radiation spectrum> reduces errors caused by changes in the instrument. Their 1992 tests obtained a velocity scatter below $25\,\mathrm{m\,s^{-1}}$ over a year, providing a practical foundation for searches for low-<mass> companions.<Precision Radial Velocities with an Iodine Absorption Cell by Geoffrey W. Marcy and R. Paul Butler>[p. 270, abstract; introduction on differing optical paths and systematic errors]{ref}
\Image[https://commons.wikimedia.org/wiki/Special:Redirect/file/R._Paul_Butler.jpg?width=260]
{title=Portrait of <R. Paul Butler>}
{description=NASA Astrobiology Institute. Public domain (NASA). https://commons.wikimedia.org/wiki/Template:PD-USGov-NASA[Source usage terms], via Wikimedia Commons.}
{source=https://commons.wikimedia.org/wiki/File:R._Paul_Butler.jpg}
{width=260}
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