The incidence of mid-infrared excesses in G and K giants

TL;DR

This study investigates the frequency of mid-infrared excesses in G and K giant stars using large-scale infrared survey data, suggesting debris discs as a potential cause and analyzing dust lifetime mechanisms.

Contribution

It provides the first large-scale statistical analysis of mid-IR excesses in G/K giants, identifying their incidence and exploring possible origins.

Findings

Mid-IR excesses are present in approximately 0.18% of G/K giants.

The incidence rate aligns with dust lifetimes governed by Poynting-Robertson drag.

Debris discs are a plausible source of the observed excesses.

Abstract

Using photometric data from the 2MASS and GLIMPSE catalogues, I investigate the incidence of mid-infrared excesses (~10 microns) of G and K stars of luminosity class III. In order to obtain a large sample size, stars are selected using a near-IR colour-magnitude diagram. Sources which are candidates for showing mid-IR excess are carefully examined and modelled to determined whether they are likely to be G/K giants. It is found that mid-IR excesses are present at a level of (1.8 +/- 0.4) x 10^-3. While the origin of these excesses remains uncertain, it is plausible that they arise from debris discs around these stars. I note that the measured incidence is consistent with a scenario in which dust lifetimes in debris discs are determined by Poynting-Robertson drag rather than by collisions.