Debris Disks in NGC 2547

TL;DR

This study used Spitzer to survey 30 Myr-old NGC 2547, finding that inner planetary debris disks around solar-type stars clear out within 10 million years, while outer disks persist longer, indicating inside-out disk evolution.

Contribution

First comprehensive infrared survey of NGC 2547 revealing the rapid clearing of inner debris disks around solar-type stars by 30 Myr.

Findings

Less than 1% excess at 8 um among cluster members.

Approximately 40% of B-F stars show excess at 24 um.

Inner disks clear out within 10 Myr, outer disks last much longer.

Abstract

We have surveyed the 30 Myr-old cluster NGC 2547 for planetary debris disks using Spitzer. At 4.5-8 um we are sensitive to the photospheric level down to mid-M stars (0.2 Msol) and at 24 um to early-G stars (1.2 Msol). We find only two to four stars with excesses at 8 um out of ~400-500 cluster members, resulting in an excess fraction <~1 percent at this wavelength. By contrast, the excess fraction at 24 um is ~40 percent (for B-F types). Out of four late-type stars with excesses at 8 um two marginal ones are consistent with asteroid-like debris disks. Among stars with strong 8 um excesses one is possibly from a transitional disk, while another one can be a result of a catastrophic collision. Our survey demonstrates that the inner 0.1-1 AU parts of disks around solar-type stars clear out very thoroughly by 30 Myrs of age. Comparing with the much slower decay of excesses at 24 and 70 um, disks clear from the inside out, of order 10 Myr for the inner zones probed at 8 um compared with a hundred or more Myr for those probed with the two longer wavelengths.