Non-gray, Month-long Brightening of KIC 8462852 in the Immediate Aftermath of a Deep Dip

Abstract

We present an analysis of the results of long-term multi-band photometric monitoring of the enigmatic star, KIC 8462852. Observations in the $B$, $g^{\prime }$, $V$, $r^{\prime }$ and $I_C$ passbands have been acquired at University College London Observatory (UCLO) between May 2017 and September 2018. We interrogate the wavelength dependence of the $\sim$month-long dimming and brightening exhibited by the target star over an 85-day interval, immediately following a days-long $\sim 5$ per cent drop in brightness on Julian Date (JD) 2458203. Between JD 2458215--300 we measure brightness variations which correspond to relative extinctions of $A_B/A_V=1.39\pm 0.27$, $A_{g^{\prime }}/A_V=1.16\pm 0.11$, $A_{r^{\prime }}/A_V=0.80\pm 0.25$ and $A_{Ic}/A_V=0.49\pm 0.19$, from which we infer an Angström absorption coefficient of $1.33\pm 0.43$ ($R_V\simeq 3.2_{-1.0}^{+2.6}$). As with the days-long `dips', the wavelength dependence of the longer-term brightness variations must also be associated with extinction arising from a dust distribution containing a substantial fraction of sub-micron-sized grains. This implies some common mechanism is responsible for the star's variability over both these short and longer timescales.

arXiv comment8 pages, 3 figures

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