Our data are derived from 10-inch photographic plates taken with the 48-inch Palomar Schmidt Telescope (Hickson 1977). The emulsions employed were Kodak 127-02 or Kodak 098-04, both used with 2 mm Schott RG-1 glass filter, which corresponds to the red photographic F-band of Oemler (1974). Plates were calibrated using the Palomar spot sensitometer.
Fields containing the clusters originally selected by Hickson (1977), as well as
some additional Abell clusters
well visible on the plates, were scanned in transparency mode using a PDS
1010G micro-densitometer in Rome, producing a digital image for each cluster
field having pixel sizes ranging from 10 to 25 
m, according to the noise
level of the plate and cluster distance.
The signal to noise ratio is 
for a few objects brighter
than 12 mag, about 25 for 
14 mag and falls to about 5
for 
mag.
Objects are automatically detected and
magnitude values are computed in many circular apertures,
thus producing a magnitude profile from which
objects are automatically classified as point-like or diffuse.
Total magnitudes 
are computed from the flux integrated in an aperture
whose radius is R1=1.5r1, where r1 is the first momentum
of the intensity distribution (see T92).
With the above definition, total magnitudes correspond on average
to the magnitude 
computed in a circular aperture determined by
the isophote 
mag 
, with the advantage that r1 is less
noisy than the corresponding isophotal radius (see Flin et al. 1995).
Magnitude zero points are taken
from the literature as indicated in Sect. 3.
For comparison we give also the magnitude computed in a fixed aperture of 5
pixels radius. The corresponding value of the radius in arcsec is given in
Table 1 (click here) for each cluster.
The ellipticity and the orientation of each object are computed from the second-order momenta of the intensity distribution.
In each field a reference set of about 10 (properly distributed) stars
belonging to the Guide Star Catalog of STScI (GSC), has been selected. Then,
the right ascension 
and declination 
referred to 2000 have
been computed from the rectangular scanning coordinates, using the COORDS
utility from the IRAF package. The resulting and
show a rms deviation smaller than 2 arcsec from GSC coordinates.
Density images of the clusters have been computed with a different method with respect to the two previous papers. The new algorithm applies an adaptive filter which operates a smoothing of the number density distribution using a Gaussian kernel with density dependent variance, as described in Pisani (1993), see also Merritt & Tremaine (1994). Density images were computed using all galaxies brighter than m3+2 for the clusters A76, A157, A2028, A2052 and A2657 while for the remaining 10 clusters we adopted m3+3 as limiting magnitude. Isodensity maps of each cluster field are shown in Figs. 1 (click here)b to 15 (click here)b.
For comparison we have computed also the isodensity images of each cluster with the algorithm adopted in Papers I and II. It appears that the new method provides smoother isopleths without loss of spatial resolution. As an example we show in Figs. 16 (click here) the isodensity map of the irregular cluster A407, computed with the algorithm of Papers I and II.
|
Abell # | N | z |  |  |  |
| A76 | 1 | 0.0416 | 00 36 50 | +06 27 00 | 8.4 |
| A157 | 0.103 | 6.7 | |||
| A407 | 1 | 0.0463 | 02 58 44 | +35 38 23 | 6.7 |
| A505 | 1 | 0.0543 | 04 51 12 | +80 06 09 | 7.4 |
| A671 | 1 | 0.0502 | 08 25 27 | +30 36 02 | 7.4 |
| A779 | 1 | 0.0230 | 09 16 46 | +33 57 29 | 7.4 |
| A1700 | 0.119 | 5.0 | |||
| A2028 | 1 | 0.0776 | 15 07 01 | +07 44 17 | 6.7 |
| A2040 | 3 | 0.0456 | 15 10 20 | +07 37 42 | 6.7 |
| A2052 | 1 | 0.0348 | 15 14 12 | +07 12 26 | 6.7 |
| A2063 | 1 | 0.0337 | 15 20 39 | +08 47 14 | 6.7 |
| A2065 | 18 | 0.0722 | 15 20 18 | +27 53 49 | 6.7 |
| A2593 | 1 | 0.0421 | 6.7 | ||
| A2657 | 1 | 0.0414 | 23 42 25 | +08 55 02 | 8.4 |
| A2670 | 1 | 0.0761 | 23 51 40 | -10 41 43 | 6.7 |
|
|
the redshift has been estimated from
the z-m10 relation