  Sixty three members of the 100 Myr old open cluster M47 (NGC 2422) have been
detected at 24 micron with Spitzer. The Be star V 378 Pup shows an excess both
in the near-infrared and at 24 micron (K-[24] = 2.4 mag), probably due to
free-free emission from the gaseous envelope. Seven other early-type stars show
smaller excesses, K-[24] = 0.6-0.9. Among late-type stars, two show large
excesses: P922 - a K1V star with K-[24] = 1.08 pm 0.11 and P1121 - an F9V star
with K-[24] = 3.72 pm 0.02. P1121 is the first known main-sequence star showing
an excess comparable to that of beta Pic, which may indicate the presence of an
exceptionally massive debris disk. It is possible that a major planetesimal
collision has occurred in this system, consistent with the few hundred Myr time
scales estimated for the clearing of the Solar System.

Astrophysics