The Incidence of Debris Disks at 24 {\mu}m and 670 Myr

TL;DR

This study uses Spitzer 24 μm data to measure debris disk incidence at 670 Myr among various stars, finding that debris disks are still relatively common and challenging existing decay rate theories.

Contribution

It provides the first detailed debris disk incidence rate at 670 Myr for different stellar types using improved data reduction techniques.

Findings

Debris disk incidence at 670 Myr is approximately 5.7%.

Disks are still common around solar-like stars at this age.

Decay rates of debris disks do not differ significantly between early-type and solar-like stars.

Abstract

We use Spitzer Space Telescope 24 {\mu}m data to search for debris disks among 122 AFGKM stars from the \sim 670 Myr clusters Hyades, Coma Ber, and Praesepe, utilizing a number of advances in data reduction and determining the intrinsic colors of main sequence stars. For our sample, the 1{\sigma} dispersion about the main sequence V-K, K-[24] locus is approximately 3.1%. We identify seven debris disks at 10% or more (\geq 3{\sigma} confidence level) above the expected K-[24] for purely photospheric emission. The incidence of excesses of 10% or greater in our sample at this age is 5.7 +3.1/-1.7%. Combining with results from the literature, the rate is 7.8 +4.2/-2.1% for early- type (B9 - F4) stars and 2.7 +3.3/-1.7% for solar-like (F5 - K9) stars. Our primary sample has strict criteria for inclusion to allow comparison with other work; when we relax these criteria, three additional debris disks are detected. They are all around stars of solar-like type and hence reinforce our conclusion that disks around such stars are still relatively common at 670 Myr and are similar to the rate around early-type stars. The apparently small difference in decay rates between early-type and solar-like stars is inconsistent with the first order theoretical predictions that the later type stellar disks would decay an order of magnitude more quickly than the earlier type ones.