  One very important object for understanding the nature of red novae is V1309
Sco. Its pre-outburst observations showed that, before its red-nova eruption in
2008, it was a contact binary quickly evolving to the merger of the components.
It thus provided us with a direct evidence that the red novae result from
stellar mergers. We analyse the spectral energy distribution (SED) of the
object and its evolution with time. From various optical and infrared surveys
and observing programmes carried out with OGLE, HST, VVV, Gemini South, WISE,
Spitzer, and Herschel we constructed observed SED in 2010 and 2012. Some
limited data are also available for the red-nova progenitor in 2007. We analyse
the data with our model of a dusty envelope surrounding a central star. Dust
was present in the pre-outburst state of V1309 Sco. Its high temperature
(900-1000 K) suggests that this was a freshly formed dust in a presumable
mass-loss from the spiralling-in binary. Shortly after its 2008 eruption,
V1309~Sco became almost completely embedded in dust. The parameters
(temperature, dimensions) of the dusty envelope in 2010 and 2012 evidence that
we then observed matter lost by the object during the 2008 outburst. Its mass
is at least $10^{-3}\,M_\odot$. The object remains quite luminous, although
since its maximum brightness in September 2008, it has faded in luminosity by a
factor of ~50 (in 2012). Far infrared data from Herschel reveal presence of a
cold (~30 K) dust at a distance of a few thousand AU from the object. This
conclusion could be verified by submillimeter interferometric observations.
