Spitzer Space TelescopeObservations of G Dwarfs in the Pleiades: Circumstellar Debris Disks at 100 Myr Age

Fluxes and upper limits in the wavelength range from 3.6 to 70 microns fromthe Spitzer Space Telescope are provided for twenty solar-mass Pleiadesmembers. One of these stars shows a probable mid-IR excess and two others havepossible excesses, presumably due to circumstellar debris disks. For the starwith the largest, most secure excess flux at MIPS wavelengths, HII1101, wederive Log(L[dust]/L[Sun]) ~ -3.8 and an estimated debris disk mass of 4.2 x10^-5 M(Earth) for an assumed uniform dust grain size of 10 microns If thestars with detected excesses are interpreted as stars with relatively recent,large collision events producing a transient excess of small dust particles,the frequency of such disk transients is about ~ 10 % for our ~ 100 Myr,Pleiades G dwarf sample. For the stars without detected 24-70 micron excesses,the upper limits to their fluxes correspond to approximate 3 sigma upper limitsto their disk masses of 6 x 10^-6 M(Earth) using the MIPS 24 micron upperlimit, or 2 x 10^-4 M(Earth) using the MIPS 70 micron limit. These upper limitdisk masses (for "warm" and "cold" dust, respectively) are roughly consistent,but somewhat lower than, predictions of a heuristic model for the evolution ofan "average" solar-mass star's debris disk based on extrapolation backwards intime from current properties of the Sun's Kuiper belt.Comment: 32 postscript pages including 8 figues and 3 tables. To appear in the Astronomical Journa