Context : We present the first high spatial resolution monitoring of the dust forming nova V1280 Sco performed with the Very Large Telescope Interferometer ( VLTI ) .

Aims : These observations aim at improving the distance determination of such events and constraining the mechanisms leading to very efficient dust formation under the harsh physical conditions encountered in novae ejecta .

Methods : Spectra and visibilities were regularly obtained from the onset of the dust formation 23 days after discovery ( or 11 days after maximum ) till day 145 , using the beam-combiner instruments AMBER ( near-IR ) and MIDI ( mid-IR ) .
These interferometric observations are complemented by near-infrared data from the 1.2m Mt .
Abu Infrared Observatory , India .
The observations are first interpreted with simple uniform and Gaussian models but more complex models , involving a second shell , are necessary to explain the data obtained from t=110d after outburst .
This behavior is in accordance with the light curve of V1280 Sco which exhibits a secondary peak around t=106d , followed by a new steep decline , suggesting a new dust forming event .
Spherical dust shell models generated with the DUSTY code are also used to investigate the parameters of the main dust shell .

Results : Using uniform disk and Gaussian models , these observations allow us to determine an apparent linear expansion rate for the dust shell of 0.35 \pm 0.03 mas day ^ { -1 } and the approximate time of ejection of the matter in which dust formed as t _ { ejec } = 10.5 \pm 7 d , i.e .
close to the maximum brightness .
This information , combined with the expansion velocity of 500 \pm 100km.s ^ { -1 } , implies a distance estimate of 1.6 \pm 0.4kpc .
The sparse uv coverage does not allow to get clear indications of deviation from spherical symmetry .
The dust envelope parameters were determined .
The dust mass generated was typically 2-8 10 ^ { -9 } M _ { \odot } day ^ { -1 } , with a probable peak in production at about 20 days after the detection of dust and another peak shortly after t=110d , when the amount of dust in the shell was estimated as 2.2 10 ^ { -7 } M _ { \odot } .
Considering that the dust forming event lasted at least 200-250d , the mass of the ejected material is likely to have exceeded 10 ^ { -4 } M _ { \odot } .
The conditions for the formation of multiple shells of dust are also discussed .

Conclusions :