Debris discs in the 27 Myr old open cluster IC4665

TL;DR

This study uses Spitzer imaging to analyze debris discs in the 27 Myr old open cluster IC 4665, finding a high frequency of debris discs among solar-type stars indicative of ongoing planet formation processes.

Contribution

First detailed survey of debris discs in IC 4665 using Spitzer, revealing the highest debris disc frequency in clusters of this age and providing insights into planetary system evolution.

Findings

42% of solar-type stars have debris discs at 24um

Most discs show steady-state collisional evolution, not transient events

No correlation between multiplicity and debris discs

Abstract

We present Spitzer IRAC and MIPS 24um imaging of members of the 27+/-5Myr old open cluster IC 4665. Models for the assembly of terrestrial planets through planetesimal collisions and mergers predict episodic dust debris discs at this epoch. We determine that 42(+18-13)% of the solar-type (F5-K5) cluster members have excess emission at 24um indicative of these debris discs, the highest frequency of the clusters studied with Spitzer to date. The majority of these discs have intermediate levels of excess (F_24/F_phot < 2), and no source is found to have extreme levels of excess indicative of a recent transient event as opposed to steady-state collisional evolution. We find no evidence of a link between multiplicity and 24um excess in this cluster sample. Only the early-type star TYC424-473-1 (T_eff~8420K) has significant near-infrared excess from 4.5um as measured with IRAC. Two solar-type targets have low significance 8um excess but no significant 24um excess. All other targets show no evidence for near-infrared excess which could indicate the presence of an optically thick primordial disc, demonstrating that the observed 24um excess arises from a debris disc.