Brightness variations of the FUor-type eruptive star V346 Normae

Abstract

Decades after the beginning of its FU Orionis-type outburst, V346 Nor unexpectedly underwent a fading event of ∆K = 4.6 mag around 2010. We obtained near-infrared observations and re-analyzed 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 (30 au). The VISTA data outlined a well-defined minimum in the light curve in 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 yet reached the 2008 level. 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 the flux changes of V346 Nor before 2008 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 highest accretion rate of ≈10 −4 M yr −1 in 1992. A combination of accretion and extinction changes has been invoked in the literature to interpret the flux variations of certain embedded young eruptive stars.

V346 Nor: The Post-outburst Life of a Peculiar Young Eruptive Star

“…The K-band photometry of V346 Nor in Fig. 1 shows that its light curve is also special: after almost 30 years in the bright outburst state, it displayed a sudden fading with a deep minimum around 2010-11, which we attributed to a significant drop in the accretion rate (Kraus et al 2016;Kóspál et al 2017a).…”

“…On each observing night we typically obtained 5 images in the I band, and 5-10 images in the J, H, and K s bands. More information on the instrument, data reduction, and photometry can be found in Kóspál et al (2017a), where the results for the first two epochs are also presented. These numbers, together with our subsequent monitoring are given in Tab.…”

“…V346 Nor fell into the nonlinear regime. The correction method is described in detail in Appendix A of Kóspál et al (2017a). The J and H photometry, as well as the K s band results after the non-linearity correction are given in Tab.…”

“…In order to compare quantitatively the 2013-2015 flux levels with the outburst phase, we computed the average magnitudes for the period 1998-2004, when the source was still at maximal brightness, using the photometric data collected by Kóspál et al (2017a). The results are I = 13.59 mag, J = 9.80 mag, H = 8.64 mag, K = 7.34 mag, and L = 4.98 mag.…”

“…V346 Nor is a FUor in the southern hemisphere, which went into outburst around 1980 (Kóspál et al 2017a, and references therein). It is located in the Sa 187 molecular cloud at a distance of 700 pc.…”