The Astrophysical Journal
Szabó, Zs. M.; Kóspál, Á.; Ábrahám, P.; Park, S.; Siwak, M.; Green, J. D.; Moór, A.; Pál, A.; Acosta-Pulido, J. A.; Lee, J. -E.; Cseh, B.; Csörnyei, G.; Hanyecz, O.; Könyves-Tóth, R.; Krezinger, M.; Kriskovics, L.; Ordasi, A.; Sárneczky, K.; Seli, B.; Szakáts, R.; Szing, A.; Vida, K.
Among the low-mass pre-main sequence stars, a small group called FU Orionis-type objects (FUors) are notable for undergoing powerful accretion outbursts. V1057 Cyg, a classical example of an FUor, went into outburst around 1969-1970, after which it faded rapidly, making it the fastest-fading FUor known. Around 1995, a more rapid increase in fading occurred. Since that time, strong photometric modulations have been present. We present nearly 10 yr of source monitoring at Piszkéstető Observatory, complemented with optical/NIR photometry and spectroscopy from the Nordic Optical Telescope, Bohyunsan Optical Astronomy Observatory, Transiting Exoplanet Survey Satellite, and Stratospheric Observatory for Infrared Astronomy. Our light curves show continuation of significant quasi-periodic variability in brightness over the past decade. Our spectroscopic observations show strong wind features, shell features, and forbidden emission lines. All of these spectral lines vary with time. We also report the first detection of [S II], [N II], and [O III] lines in the star.