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

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.