We have discovered a young M star of mass 0.16 M⊙ and radius 0.63 R⊙, 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 ∼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 ≳ 3 × 1019 g and ≳ 1019 g, for the two cases, respectively.
- Stars: binaries (including multiple): close
- Stars: binaries: eclipsing
- Stars: binaries: general