IfA, University of Hawaii, U.S.A.
Observatoire de Paris-Meudon, France
Royal Observatory, Edinburgh, U.K. and Joint Astronomy Centre, Hawaii,
U.S.A.
Institut de Radio Astronomie Millimétrique, Grenoble, France
Observatoire de Bordeaux, France
Caltech, California, U.S.A
Uppsala Astronomiska Observatorium, Sweden
Onsala Space Observatory, Sweden
DLR, Institut für Planetenerkundung, Berlin, Germany 
OH, H 
CO, H S, CS, CH CN,
HNC) have been monitored as a function of heliocentric distance
( 
) from 7 AU pre-perihelion to 4 AU post-perihelion (Fig. 4). As comet
Hale-Bopp approached and receded from the Sun, these species displayed
different behaviours. Far from the Sun, the most volatile species were
found in general relatively more abundant in the coma. In comparison
to other species, HNC, H CO and CS showed a much steeper increase
of the production rate with decreasing . Less than 1.5 AU from
the Sun, the relative abundances were fairly stable and approached
those found in other comets near 1 AU.
The kinetic temperature of the coma, estimated from the relative intensities
of the CH OH and CO lines, increased with decreasing , from about
10 K at 7 AU to 110 K around perihelion. The expansion velocity of the gaseous
species, derived from the line shapes, also increased with a law close to
.
Figure: Production rates of the different molecular species as functions
of heliocentric distance
To appear in Proceedings of the First International Hale-Bopp Conference, Puerto De La Cruz (Tenerife), Spain, Feb. 2-5, 1998.