Dippers and Dusty Disks Edges: A Unified Model

TL;DR

This paper presents a unified model explaining large flux dips in young stars caused by dusty circumstellar material, emphasizing the role of magnetospheric truncation and disk-star interactions.

Contribution

It introduces a comprehensive model linking dipper phenomena to magnetospheric truncation and disk orientation, unifying observations with physical theory.

Findings

Dips are caused by material near the star's corotation radius.

Disk temperatures at corotation are too low for dust sublimation.

Magnetospheric truncation explains the lifting of dusty material into the line of sight.

Abstract

We revisit the nature of large dips in flux from extinction by dusty circumstellar material that is observed by Kepler for many young stars in the Upper Sco and $\rho$ Oph star formation regions. These young, low-mass "dipper" stars are known to have low accretion rates and primarily host moderately evolved dusty circumstellar disks. Young low mass stars often exhibit rotating star spots that cause quasi-periodic photometric variations. We found no evidence for periods associated with the dips that are different from the star spot rotation period in spectrograms constructed from the light curves. The material causing the dips in most of these light curves must be approximately corotating with the star. We find that disk temperatures computed at the disk corotation radius are cool enough that dust should not sublime. Crude estimates for stellar magnetic field strengths and accretion rates are consistent with magnetospheric truncation near the corotation radius. Magnetospheric truncation models can explain why the dips are associated with material near corotation and how dusty material is lifted out of the midplane to obscure the star which would account for the large fraction of young low mass stars that are dippers. We propose that variations in disk orientation angle, stellar magnetic field dipole tilt axis, and disk accretion rate are underlying parameters accounting for differences in the dipper light curves.