Variability of the Infrared Excess of Extreme Debris Disks

TL;DR

This study investigates the rapid variability of infrared excess in extreme debris disks around solar-like stars aged 30-130 million years, suggesting violent collisions may be more common than previously thought.

Contribution

It presents the first evidence of short-term infrared excess variability in debris disks, indicating rapid evolution possibly due to large collisions among planetesimals.

Findings

Infrared excess varies on timescales of a few years.

Variability occurs despite stars being optically stable.

Rapid evolution suggests frequent large collisions.

Abstract

Debris disks with extremely large infrared excesses (fractional luminosities $> 10^{-2}$) are rare. Those with ages between 30 and 130 Myr are of interest because their evolution has progressed well beyond that of protoplanetary disks (which dissipate with a timescale of order 3 Myr), yet they represent a period when dynamical models suggest that terrestrial planet building may still be progressing through large, violent collisions that could yield large amounts of debris and large infrared excesses. For example, our Moon was formed through a violent collision of two large proto-planets during this age range. We report two disks around the solar-like stars ID8 and HD 23514 in this age range where the 24 {\mu}m infrared excesses vary on timescales of a few years, even though the stars are not variable in the optical. Variations this rapid are difficult to understand if the debris is produced by collisional cascades, as it is for most debris disks. It is possible that the debris in these two systems arises in part from condensates from silicate-rich vapor produced in a series of violent collisions among relatively large bodies. If their evolution is rapid, the rate of detection of extreme excesses would indicate that major collisions may be relatively common in this age range.