Non-grey dimming events of KIC 8462852 from GTC spectrophotometry

Plot of the measured depths Dn in the five wavelengths indicated, versus the depths Dw, averaged over all bands, for the 14 pointings with GTC that were taken at several dimming events of the star KIC 8462852.
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D. Nespral
T. Boyajian
2018 A&A 610 L12

We report ground-based spectrophotometry of KIC 8462852, during its first dimming events since the end of the Kepler mission. The dimmings show a clear colour-signature, and are deeper in visual blue wavelengths than in red ones. The flux loss' wavelength dependency can be described with an Ångström absorption coefficient of 2.19±0.45, which is compatible with absorption by optically thin dust with particle sizes on the order of 0.0015 to 0.15 μm. These particles would be smaller than is required to be resistant against blow-out by radiation pressure when close to the star. During occultation events, these particles must be replenished on time-scales of days. If dust is indeed the source of KIC 8462852's dimming events, deeper dimming events should show more neutral colours, as is expected from optically thick absorbers.