The Late Stages of Protoplanetary Disk Evolution: A Millimeter Survey of Upper Scorpius

TL;DR

This study conducts a millimeter survey of 37 stars in the 5-million-year-old Upper Scorpius OB association, revealing evolved disks with reduced dust mass and indicating that primordial disk depletion is largely complete at this stage.

Contribution

It provides new millimeter observations of disks in Upper Scorpius, showing significant disk evolution and the end of giant planet formation around most stars.

Findings

Detected disks around four low- and solar-mass stars and one debris disk.

Disks show significant evolution with decreased detection fraction at this age.

Primordial disks are largely depleted, ending giant planet formation around higher mass stars.

Abstract

We present deep 1.2 millimeter photometry of 37 stars in the young (5 Myr) Upper Scorpius OB association, sensitive to ~4 x 10^-3 Mjup of cool millimeter dust. Disks around four low- and solar-mass stars are detected, as well as one debris disk around an intermediate mass star, with dust masses ranging from 3.6 x 10^-3 -- 1.0 x 10^-1 Mjup. The source with the most massive disk exhibits a transition-disk spectral energy distribution. Combining our results with previous studies, we find the millimeter-detection fraction of Class II sources has significantly decreased from younger ages, and comparison with near-infrared and Halpha measurements indicates the present disks have undergone significant evolution in composition or structure at all radii. The disks of Upper Scorpius represent the tail-end of the depletion of primordial disks; while a few near-solar mass stars may still sustain giant planet formation, this process has finished around higher mass stars