JEAN-PAUL ZAHN (1935 - 2015)
We were saddened to learn of the death of Jean-Paul Zahn, Emeritus astronomer at
the Paris Observatory.  Our esteemed friend and colleague passed away on July 15 2015.
Jean-Paul Zahn began his career in 1962 at the Institut d'Astrophysique de Paris in
the group of Evry Schatzman.  In 1966, he defended his dissertation there under the title
\The tidal in a close double star".  In this work, he described the properties of tides in a
close double star for the rst time.  In addition, he provided the rst description of the
physical mechanisms that act on the dynamic evolution of the system and the evolution
of stellar components.  In that same year, he was appointed to the position of Astronomer
at the Nice Observatory of which he was the Director from 1972 to 1981.
15
While Paul Couteau and Paul Muller, distinguished members of Commission 26 \Dou-
ble Stars", observed the visual double star with the 74 cm and 50 cm refractors, welcomed
Antoine Labeyrie whose rst two interferometer telescopes opened the way for modern
developments in the high angular resolution study of double stars.  As a physicist in the
eld of 
uid dynamics, the studies of Jean-Paul Zahn have made major contributions to
the theory of the internal structure of stars and stellar evolution.
Regarding binary stars, he studied in detail the physical phenomena induced by the
tidal such as non-adiabatic stellar oscillations generated by the periodic variation of the
gravitational  eld  (J.  P.  Zahn  ,  1970,  1975),  the  friction  phenomena  in  the  convective
envelope  and  the  evolution  of  a  binary  system  under  the  eect  of  including  the  tidal
circularization  of  the  orbit,  and  the  synchronization  of  stellar  rotation  and  associated
physical phenomena .
Jean-Paul Zahn was primarily a theoretician but he attached great importance to the
\theory-observation" interface.  He considered with great interest the spectroscopic and
high angular resolution observations that allow the precise determination of fundamental
stellar parameters necessary to test the internal structure of models of stellar evolution.
Jean-Paul Zahn was the Director of the Observatory of the Pic du Midi and Toulouse
from 1981 to 1988 before joining the Paris Observatory in 1993.
Among  his  numerous  national  and  international  responsibilities,  it  should  be  noted
that Jean-Paul Zahn was President of the IAU Commission 35, \Constitution of Stars",
from 1997-2000.
His enthusiasm and warm character will remain in our memories.
Daniel Bonneau
Honorary astronomer at C^ote d'Azur Obs