The mass outflows in T Tauri stars ( TTS ) are thought to be an effective mechanism to remove angular momentum during the pre-main-sequence contraction of a low-mass star .
The most powerful winds are observed at the FUor stage of stellar evolution .
V1331 Cyg has been considered as a TTS at the pre-FUor stage .
We analyse high-resolution spectra of V1331 Cyg collected in 1998–2007 and 20-d series of spectra taken in 2012 .
For the first time the photospheric spectrum of the star is detected and stellar parameters are derived : spectral type G7–K0 IV , mass 2.8 M _ { \odot } , radius 5 R _ { \odot } , v \sin i < 6 km s ^ { -1 } .
The photospheric spectrum is highly veiled , but the amount of veiling is not the same in different spectral lines , being lower in weak transitions and much higher in strong transitions .
The Fe ii 5018 , Mg i 5183 , K i 7699 and some other lines of metals are accompanied by a ‘ shell ’ absorption at radial velocity of about -240 km s ^ { -1 } .
We show that these absorptions form in the post-shock gas in the jet , i.e .
the star is seen though its jet .
The P Cyg profiles of H \alpha and H \beta indicate the terminal wind velocity of about 500 km s ^ { -1 } , which vary on time-scales from several days to years .
A model of the stellar wind is developed to interpret the observations .
The model is based on calculation of hydrogen spectral lines using the radiative transfer code torus .
The observed H \alpha and H \beta line profiles and their variability can be well reproduced with a stellar wind model , where the mass-loss rate and collimation ( opening angle ) of the wind are variable .
The changes of the opening angle may be induced by small variability in magetization of the inner disc wind .
The mass-loss rate is found to vary within ( 6 - 11 ) \times 10 ^ { -8 } M _ { \odot } \mathrm { yr } ^ { -1 } , with the accretion rate of 2.0 \times 10 ^ { -6 } M _ { \odot } \mathrm { yr } ^ { -1 } .