\newcommand{\Msun}{{\rm M}_\odot}

<HEADER><TITLE>The Orbital Period Derivative of PSR~B1957+20</TITLE>

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<DL><DT><B>Session 69 -- Cataclysmic Variables and Pulsars</B>

<DT><I>Oral presentation, Thursday, 10:30-12:00, Dwinelle 155 Room</I>

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<H2>[69.04] The Orbital Period Derivative of PSR~B1957+20</H2>

<I>Andrew S. Fruchter (UC Berkeley), Zaven Arzoumian, Joseph H. Taylor (Princeton University)</I>

<P>The eclipsing pulsar B1957+20 is part of an extraordinary binary system.

The spin-down radiation of this 1.6 ms pulsar heats its $0.02\, \Msun$ companion to

optical temperatures, and an ionized evaporated wind off of the secondary's

surface

delays and absorbs the pulsar's radio signal.  Timing

observations undertaken between 1988 and 1991 revealed

a large orbital period derivative, corresponding to an orbital

lifetime of only $3\times10^7$ yrs, which is far less than is suggested

by the tenuousness of the

observed evaporate.  However, compact

binaries occasionally display non-secular orbital period derivatives

over timescales of years.  Here we report the results of an intensive

timing program designed to determine whether the pulsar is indeed

destroying its companion at this astounding rate.



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