You need slightly more than 4GB to compile graph-tool, unfortunately. If
you have around 6GB with swap, make sure there is nothing else consuming
much memory, and that the compilation is not being done in parallel
(i.e. do not use make -j2 or similar).

If you still cannot compile it, you can try using the clang compiler. It
is also available for ubuntu, and it should use only about half as much

I'll try this tonight.

It worked with nothing else memory-consuming running.

gcc 4.8.2
~3.5GB free memory, 2GB swap

Meanwhile the sysadmin installed the Debian package found in your repo, but its name was graph-tool, not python-graph-tool.

Thank you again for your help,