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The young star V1331 Cyg received previous attention because it is surroundedby an optical, arc-like reflection nebula. V1331 Cyg is commonly considered tobe a candidate for an object that has undergone an FU-Ori (FUOR) the outbreakin the past. This in turn could lead to a time-varying appearance of the dustyarcs that may be revealed by multi-epoch imaging. In particular, a radialcolour analysis of the dust arcs can then be attempted to check whether radialgrain size distribution was modified by a previous FUOR wind. Second-epochimaging of V1331 Cyg was obtained by us in 2009 using the Hubble SpaceTelescope (HST). By comparing this to archival HST data from 2000, we studiedthe time evolution of the circumstellar nebulae. After a point spread functionsubtraction using model point spread functions, we used customised routines toperform a proper motion analysis. The nebula expansion was first derived bydeconvolving and correlating the two-epoch radial brightness profiles.Additional data from other facilities TLS, UKIDSS, SPITZER, and HERSCHEL werealso incorporated to improve our understanding of the star in terms ofenvironment, viewing angle, bipolar outflow length, and the FUOR phenomenon.The derived radial colour profiles do not indicate a spatial separation of thedust grain sizes. The HERSCHEL 160 micron images show for the time thermalemission from dust probably residing in the outer arc. By viewing V1331 Cygalmost pole-on, the length of the bipolar outflow exceeds previous estimates byfar. The outer arc expansion timescale is consistent with the implantation timeof the CO torus, which supports the hypothesis of an outburst that occurred afew thousand years ago. The azimuthal colour variation of the outer arc isprobably due to changes of the scattering angle, imposed by a tilt or helicalgeometry of the dust configuration.

Hubble imaging of V1331 Cygni: Proper motion study of its circumstellar structures