Time-resolved photometry of the young dipper RX J1604.3-2130A: Unveiling the structure and mass transport through the innermost disk

TL;DR

This study uses time-resolved photometry to investigate the structure and matter transport in the inner disk of the young star RX J1604.3-2130A, revealing complex disk dynamics, dust properties, and accretion variability.

Contribution

It provides detailed constraints on the inner disk structure and mass transport mechanisms in a young dipper star, highlighting the role of inclined, irregular disks and variable accretion.

Findings

Inner disk contains slightly processed dust grains near the sublimation radius.

Eclipses show quasi-periodic behavior with drifting phase and variable depth.

Inner disk mass is a few percent of a Ceres mass, replenished on weekly timescales.

Abstract

RX~J1604.3-2130A is a young, dipper-type, variable star in the Upper Scorpius association, suspected to have an inclined inner disk with respect to its face-on outer disk. We study the eclipses to constrain the inner disk properties.We use time-resolved photometry from the Rapid Eye Mount telescope and Kepler2 data to study the multi-wavelength variability, and archival optical and IR data to track accretion, rotation, and changes in disk structure. The observations reveal details of the structure and matter transport through the inner disk. The eclipses show 5d quasi-periodicity, with the phase drifting in time and some periods showing increased/decreased eclipse depth and frequency. Dips are consistent with extinction by slightly processed dust grains in an inclined, irregularly-shaped inner disk locked to the star through two relatively stable accretion structures. The grains are located near the dust sublimation radius ($\sim$0.06 au) at the corotation radius, and can explain the shadows observed in the outer disk. The total mass (gas and dust) required to produce the eclipses and shadows is a few % of a Ceres mass. Such amount of mass is accreted/replenished by accretion in days to weeks, which explains the variability from period to period. Spitzer and WISE variability reveal variations in the dust content in the innermost disk on a few years timescale, which is consistent with small imbalances (compared to the stellar accretion rate) in the matter transport from the outer to the inner disk. A decrease in the accretion rate is observed at the times of less eclipsing variability and low mid-IR fluxes, confirming this picture. The v$sini$=16km/s confirms that the star cannot be aligned with the outer disk, but is likely close to equator-on and to be aligned with the inner disk. This anomalous orientation is a challenge for standard theories of protoplanetary disk formation.