  We used FLAMES+GIRAFFE (Medusa mode) at the VLT to obtain moderately high
resolution spectra for 30 red horizontal branch (RHB) stars, 4 RR Lyrae
variables, and 17 blue horizontal branch (BHB) stars in the low-concentration,
moderately metal-rich globular cluster NGC6723 ([Fe/H]=-1.22+/-0.08 from our
present sample). The spectra were optimized to derive O and Na abundances. In
addition, we obtained abundances for other elements, including N, Fe, Mg, Ca,
Ni, and Ba. We used these data to discuss the evidence of a connection between
the distribution of stars along the horizontal branch (HB) and the multiple
populations that are typically present in globular clusters. We found that all
RHB and most (13 out of 17) BHB stars are O-rich, Na-poor, and N-poor; these
stars probably belong to the first stellar generation in this cluster. Only the
four warmest observed stars are (moderately) O-poor, Na-rich, and N-rich, and
they probably belong to the second generation. While our sample is not fully
representative of the whole HB population in NGC6723, our data suggest that in
this cluster only HB stars warmer than ~9000 K, that is one fourth of the
total, belong to the second generation, if at all. Since in many other clusters
this fraction is about two thirds, we conclude that the fraction of
first/second generation in globular clusters may be strongly variable. In
addition, the wide range in colour of chemically homogeneous first-generation
HB stars requires a considerable spread in mass loss (>0.10 Mo). The reason for
this spread is yet to be understood. Finally, we found a high Ba abundance,
with a statistically significant radial abundance gradient.
