| 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. |
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