The Medium Redshift Clusters CL0017-20 and CL0500-24

We present magnitudes and redshifts of galaxies in the cluster of galaxies CL0017-20 and in the double cluster CL0500-24. Luminosity functions and velocity distributions have been derived. CL0017-20 possesses a virial mass of $2.9\times {10}^{14}$ M${}_{\odot }$ and a \vmag band luminosity of $2.3 \pm 0.5 \times 10^{12}$L$\odot$($M/L{\rm V} = 127$), much of it in a very compact core of size 113 kpc. Our new velocities and photometry of CL0500-24 confirm its double nature. Our group algorithm clearly detects two subconcentrations with masses 1.9 and $2.2\times {10}^{14}$ M${}_{\odot }$. Its total \vmag band luminosity amounts to $2.7\pm 0.8\times {10}^{12}$ L${}_{\odot }$ ($M\mathrm{/}{L}_{\mathrm{V}}$ of 157). Since the crossing and collapse times in both clusters are smaller than the age of the Universe, they appear bound and virialized. It is surprising that although $M\mathrm{/}L$ is small in these clusters, giant arcs have been detected in both.