  We report the discovery of a wide pair (93 arcsec angular separation) of
extremely cool ($T_{eff}<4000$ K) white dwarfs with a very large common proper
motion ($\sim1.9$ arcsec/yr). The objects were discovered in a high proper
motion survey in the poorly investigated southern sky region with
$\delta<-60^{\circ}$ using SuperCOSMOS Sky Survey (SSS) data. Both objects,
SSSPM J2231-7514 and SSSPM J2231-7515, show featureless optical spectra. Fits
of black-body models to the spectra yield effective temperatures of 3810 K and
3600 K, respectively for the bright (V=16.60) and faint (V=16.87) component.
Both degenerates are much brighter than other recent discoveries of cool white
dwarfs with comparable effective temperatures and/or $B_J-R$ colours.
Therefore, they should be relatively nearby objects. The comparison with other
cool white dwarfs and a photometric distance determination yield distance
estimates between 9 pc and 14 pc. The latter seems to be more realistic, since
the good agreement of the proper motion of both components within the errors of
about 8 mas/yr and the angular separation between the two stars support a
distance of about 15 pc with relatively small masses of the components. With
smaller distance we should be able to measure a differential proper motion due
to orbital motion if the orbital plane is not strongly inclined and the present
orbital velocity vector is not close to the line of sight. The space velocity
based on that distance and assumptions on radial velocity makes the new pair of
extremely cool white dwarfs some of the probably oldest members of the Galactic
disk population, although the possibility that these objects are part of a
Galactic halo dark matter component can also not yet be ruled out.
