A Transient Transit Signature Associated with the Young Star RIK-210

TL;DR

This study reports transient, periodic dimming events in the young star RIK-210, likely caused by circumstellar or circumplanetary material, not stellar companions or active disks, revealing complex star-disk interactions.

Contribution

It introduces the first detailed analysis of transient, variable transit-like dimming events in a young star, exploring multiple potential origins beyond simple eclipsing bodies.

Findings

Dimming events are variable in depth, duration, and shape.

Events are periodic and synchronized with stellar rotation.

Dimming cannot be explained by stellar companions or active disks.

Abstract

We find transient, transit-like dimming events within the K2 time series photometry of the young star RIK-210 in the Upper Scorpius OB association. These dimming events are variable in depth, duration, and morphology. High spatial resolution imaging revealed the star is single, and radial velocity monitoring indicated that the dimming events can not be due to an eclipsing stellar or brown dwarf companion. Archival and follow-up photometry suggest the dimming events are transient in nature. The variable morphology of the dimming events suggests they are not due to a single, spherical body. The ingress of each dimming event is always shallower than egress, as one would expect for an orbiting body with a leading tail. The dimming events are periodic and synchronous with the stellar rotation. However, we argue it is unlikely the dimming events could be attributed to anything on the stellar surface based on the observed depths and durations. Variable obscuration by a protoplanetary disk is unlikely on the basis that the star is not actively accreting and lacks the infrared excess associated with an inner disk. Rather, we explore the possibilities that the dimming events are due to magnetospheric clouds, a transiting protoplanet surrounded by circumplanetary dust and debris, eccentric orbiting bodies undergoing periodic tidal disruption, or an extended field of dust or debris near the corotation radius.