a) RGB bump and metallicity
The compilation of metallicity estimates tabulated in
Alcaíno et al.
(1994) shows that M 79 belongs to moderately metal deficient clusters;
the scatter of metallicity values exceeds 0.3 dex. Having reliable
photometry of sufficiently numerous red giants, we can apply the
indirect method of metallicity estimates used in our earlier studies
and by other authors. It is based upon the relation between the
position of the RGB "bump'' and the cluster metallicity
(Kravtsov
1989; Fusi Pecci et al. 1990). The luminosity function (LF) of the
RGB is shown by the solid line in Fig. 4 (click here); the bump is indicated with
an arrow. The discussed detail of the LF is not as evident in our data
as it is in the LF by Ferraro et al. (probably due to our smaller
sample), but its position is practically identical in both LFs. The
most obvious manifestation of the bump in our data is a "step'' in
the RGB LF at V=15.6. Taking into account the LFs from both papers,
we evaluate the bump position as 
, the error estimate
reflecting some ambiguity in the location of the bump. To determine
the metallicity of M 79, we used the analytic formula from
Sarajedini
& Forrester (1995). It relates the difference of V magnitudes
between the bump and the HB to the cluster metallicity in the scale of
Zinn & West (1984). For 
, 
. Substituting this value into Eq. (1) of
Sarajedini & Forrester (1995), we find for M 79 the metallicity
value [Fe/H] 
. This is within the range of earlier
published values based on different methods.
Figure 4: The luminosity function of the RGB (solid line) and of the
AGB (dashed line) for the globular cluster M 79. The arrow indicates
the position of the "bump''
b) Asymptotic giant branch
The AGB is the least studied of all sequences in globular-cluster CMDs above the turnoff. Even in its lower, denser populated part, this sequence is usually represented by an insufficient number of stars. Reliable separation of AGB stars from RGB stars critically depends upon photometric accuracy.
The accuracy of our photometry makes it possible to isolate AGB stars from
RGB stars with sufficient reliability, at least for V in the range from
to 
. The resulting LF of the AGB (dashes) is plotted in
Fig. 4 (click here),
together with the LF for the RGB. Note that the CMD from Ferraro et al.
shows three clumps of AGB stars, corresponding to the three maxima of
our LF, at 
, 
, and 
.