# Deep Long Asymmetric Occultation in EPIC 204376071

## TL;DR

A young M star exhibits a rare, deep occultation event likely caused by orbiting dust or transient dusty material, with implications for understanding circumstellar environments and transient phenomena.

## Contribution

This study reports the discovery of a unique deep occultation in a young M star and models potential dust-based causes, advancing knowledge of circumstellar dust structures.

## Key findings

- Deep occultation lasting 1 day observed in a young M star.
- Possible causes include orbiting dust or transient accretion events.
- Estimated dust mass required is at least 10^19 grams.

## Abstract

We have discovered a young M star of mass $0.16\,M_\odot$ and radius $0.63\,R_\odot$, likely in the Upper Sco Association, that exhibits only a single $80\%$ deep occultation of 1-day duration. The star has frequent flares and a low-amplitude rotational modulation, but is otherwise quiet over 160 days of cumulative observation during K2 Campaigns C2 and C15. We discuss how such a deep eclipse is not possible by one star crossing another in any binary or higher-order stellar system in which no mass transfer has occurred. The two possible explanations we are left with are (1) orbiting dust or small particles (e.g., a disk bound to a smaller orbiting body, or unbound dust that emanates from such a body); or (2) a transient accretion event of dusty material near the corotation radius of the star. In either case, the time between such occultation events must be longer than $\sim$80 days. We model a possible orbiting occulter both as a uniform elliptically shaped surface (e.g., an inclined circular disk) and as a `dust sheet' with a gradient of optical depth behind its leading edge. The required masses in such dust features are then $\gtrsim 3 \times 10^{19}$ g and $\gtrsim 10^{19}$ g, for the two cases, respectively.