The First Post-Kepler Brightness Dips of KIC 8462852

TL;DR

This study reports the first observed brightness dips of KIC 8462852 since 2013, indicating dust-related occultations with no spectral or polarization changes, and suggests non-grey extinction consistent with optically thin dust.

Contribution

First detection of brightness dips post-Kepler, with detailed multiband photometry supporting dust occultation models over thick material explanations.

Findings

Dips show differential reddening, indicating non-grey extinction.

No spectral or polarization changes during dips.

Data favor optically thin dust models.

Abstract

We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in October 2015, and a sequence of dipping began in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth. We distinguish four main 1-2.5% dips, named "Elsie," "Celeste," "Skara Brae," and "Angkor", which persist on timescales from several days to weeks. Our main results so far are: (i) there are no apparent changes of the stellar spectrum or polarization during the dips; (ii) the multiband photometry of the dips shows differential reddening favoring non-grey extinction. Therefore, our data are inconsistent with dip models that invoke optically thick material, but rather they are in-line with predictions for an occulter consisting primarily of ordinary dust, where much of the material must be optically thin with a size scale <<1um, and may also be consistent with models invoking variations intrinsic to the stellar photosphere. Notably, our data do not place constraints on the color of the longer-term "secular" dimming, which may be caused by independent processes, or probe different regimes of a single process.