Brightness variations of the FUor-type eruptive star V346 Nor

Abstract

Decades after the beginning of its FU Orionis-type outburst, V346 Nor unexpectedly underwent a fading event of $\Delta K$ = 4.6 mag around 2010. We obtained near-infrared observations and re-analysed data from the VISTA/VVV survey to outline the brightness evolution. In our VLT/NaCO images, we discovered a halo of scattered light around V346~Nor with a size of about 0.04 arcsec (30 au). The VISTA data outlined a well-defined minimum in the light curve at late 2010/early 2011, and tentatively revealed a small-amplitude periodic modulation of 58 days. Our latest data points from 2016 demonstrate that the source is still brightening but has not reached the 2008 level yet. We used a simple accretion disk model with varying accretion rate and line-of-sight extinction to reproduce the observed near-infrared magnitudes and colors. We found that before 2008, the flux changes of V346 Nor were caused by a correlated change of extinction and accretion rate, while the minimum around 2010 was mostly due to decreasing accretion. The source reached a maximal accretion rate of $\approx 10^{-4}{M}_{\odot }$ yr${}^{-1}$ in 1992. A combination of accretion and extinction changes was already invoked in the literature to interpret the flux variations of certain embedded young eruptive stars.

7 pages, 4 figures, appendices. Accepted for publication in A&A Letters

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• V346 Nor: the post-outburst life of a peculiar young eruptive star
• Mass transport from the envelope to the disk of V346 Nor: a case study for the luminosity problem in an FUor-type young eruptive star
• Dissecting the different components of the modest accretion bursts of the very young protostar HOPS 373
• A multi-epoch, multi-wavelength study of the classical FUor V1515 Cyg approaching quiescence
• The outbursting protostar 2MASS~22352345+7517076 and its environment
• Grain growth in newly discovered young eruptive stars
• Polarimetric differential imaging with VLT/NACO. A comprehensive PDI pipeline for NACO data (PIPPIN)
• Molecular inventory of a young eruptive star's environment -- Case study of the classical FU Orionis star V1057 Cyg
• A study of the photometric and spectroscopic variations of the prototypical FU Orionis-type star V1057 Cyg