  CONTEXT: V1309 Sco is the only certain noncompact stellar merger, due to its
indisputable preoutburst light curve matching that of a contact binary of
almost equal mass stars. Therefore, anything that can be deduced from the
existing observations serves as benchmark constraints for models. AIMS: We
present some observational evidences to guide future hydrodynamical simulations
and common envelope studies. METHODS: Using archive spectra taken at high and
mid spectral resolution during the V1309 Sco outburst and late decline,
together with the inferential methods we developed to study nova ejecta through
panchromatic high resolution spectroscopic follow ups, we constrain the
physical state, structure, dynamics and geometry of the transient originated in
the stellar merger. RESULTS: We found that the emitted spectra arise from two
distinct contributions: matter expelled during the 2008 outburst and
circumbinary gas produced during historic mass loss episodes. These two
components likely have orthogonal geometry with the 2008 mass loss displaying a
dust-laden bipolar ejecta produced by a time limited rapidly accelerating wind
and the circumbinary gas having a donut-like shape. A central source powers
them both, having produced a fluorescent light pulse, but we cannot precisely
determine the time it started or its spectral energy distribution. We can,
however, place its upper energy cutoff at about 54 eV and the bulk of its
emission at $<$20 eV. We also know that the central source turned off within
months from the outburst and before the ejecta turned optically thin.
