Non-grey dimming events of KIC 8462852 from GTC spectrophotometry

TL;DR

This study presents ground-based spectrophotometry of KIC 8462852's dimming events, revealing wavelength-dependent dimming consistent with small dust particles, and discusses implications for dust properties and replenishment timescales.

Contribution

First spectrophotometric analysis of KIC 8462852's dimming events showing wavelength-dependent absorption consistent with small dust particles.

Findings

Dimming is deeper in blue wavelengths than in red.

Absorption coefficient compatible with tiny dust particles (0.0015 to 0.15 μm).

Dust particles must be replenished on timescales of days.

Abstract

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 \AA ngstr\"om absorption coefficient of $2.19\pm0.45$, which is compatible with absorption by optically thin dust with particle sizes on the order of 0.0015 to 0.15 $\mu$m. 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.