, M. Forestini
, P. Valiron
, L. M. Ziurys
, M.A. Anderson
, J. Cernicharo
, C. Kahane
IRAM, 300 rue de la piscine, F-38406 S
Martin d'Hères,
France
Laboratoire d'Astrophysique, Observatoire de Grenoble,
BP 53, F-38041 S
Martin d'Hères Cedex 09, France
Arizona State University, Dept. of Chemistry, Tempe, AZ 85287-1604, USA
Centro Astronomico de Yebes, IGN, E-19080 Guadalajara, Spain 
NC and
NC, as well as of a line at 234433 MHz, which could be
the J= 7--6 transition of
F (an alternate, although less likely identification would be the
J= 9--8 transition of NaF). The derived
:
:
isotopic abundance ratios (
) are consistent with the solar system values
(78.7:10.1:11.2). According to new calculations of evolutionary
models of 
and 
AGB stars, these ratios and the
previously measured N, O and Si isotopic ratios imply that the central
star had an initial mass 
and has
already experienced many 3
dredge-up events. From this, it
can be predicted that the 
/
isotopic ratio
lies between 0.01 and 0.08; in fact, the value derived in the case
U234433 arises from 
F is 
/
=
0.04.
Figure: Two spectra, observed toward IRC+10216 with the IRAM 30-m
telescope, and covering the frequencies of the J= 7--6 transitions
of 
F (top) and 
F (bottom). The
channel width is 1 MHz. The position and strength of the
F line hyperfine components are denoted by vertical
lines. U234433 lies only 0.9 MHz below the calculated frequency of
F (7--6) and could well be this line; an alternate, but
less likely identification is the J= 9--8 line of NaF, the rest
frequency of which is 234435.2 MHz.
Figure:
The N= 7--6 through N= 9--8 rotational lines of 
NC in
IRC+10216. The channel width is 1 MHz
The identification of the 
NC and 
NC lines
was made possible by ab-initio quantum mechanical calculations
of the molecule geometrical structure. It was confirmed through
millimeter-wave laboratory measurements. The quantum mechanical
calculations are briefly described and the laboratory results
presented in some detail. The rotation constants B, D, H and the
spin-rotation constant 
of 
NC and
NC, and the hyperfine constants b and eqQ of
NC are determined from a fit of laboratory and
astronomical data.
Accepted by Astronomy and Astrophysics
(For preprints, contact guelin@iram.fr)