Paul Ledoux (8 August 1914 – 6 October 1988) was a Belgian
astrophysicist best known for his work on stellar stability and variability. With
Theodore Walraven, he co-authored a seminal work on stellar oscillations. In 1964 Ledoux was awarded the
Francqui Prize
The Francqui Prize is a prestigious Belgian scholarly and scientific prize named after Émile Francqui. Normally annually since 1933, the Francqui Foundation awards it in recognition of the achievements of a scholar or scientist, who at the star ...
for Exact Sciences, and was awarded the
Eddington Medal
The Eddington Medal is awarded by the Royal Astronomical Society for investigations of outstanding merit in theoretical astrophysics. It is named after Sir Arthur Eddington. First awarded in 1953, the frequency of the prize has varied over the ye ...
of the
Royal Astronomical Society
The Royal Astronomical Society (RAS) is a learned society and charitable organisation, charity that encourages and promotes the study of astronomy, planetary science, solar-system science, geophysics and closely related branches of science. Its ...
in 1972 for investigations into problems of
stellar stability and
variable stars
A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...
. He was awarded the
Janssen Medal of the French Academy of Sciences in 1976.
Ledoux criterion
In
stellar astrophysics, Ledoux's name is now associated with the criterion under which material in a star becomes unstable to convection in the presence of a gradient of chemical composition. In homogeneous material, the
Schwarzschild criterion shows that material is unstable to convection if the radiation field alone would establish a steeper temperature gradient steeper than the adiabatic (or isentropic) temperature gradient. However, Ledoux showed that a composition gradient stabilises or destabilises the material against convection.
In convectively-stable regions destabilised by the composition gradient, one expects ''thermohaline mixing''; in convectively-unstable regions that are stabilised, one expects double-diffusive mixing, known in stellar astrophysics as ''semiconvection''.
References
20th-century Belgian astronomers
1914 births
1988 deaths
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