Spitzer Space Telescope observations 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 μ from the Spitzer Space Telescope are provided for 20 solar-mass Pleiades members. One of these stars shows a probable mid-IR excess, and two others have possible excesses, presumably due to circumstellar debris disks. For the star with the largest, most secure excess flux at MIPS (Multiband Imaging Photometer for Spitzer) wavelengths, HII 1101, we derive log (L_dust/L*) ∼ -3.8 and an estimated debris disk mass of 4.2 × 10^-5 M _⊕ for an assumed uniform dust grain size of 10 μm. If the stars with detected excesses are interpreted as stars with relatively recent, large collisional events producing a transient excess of small dust particles, the frequency of such disk transients is ∼10% for our ∼100 Myr, Pleiades G dwarf sample. For the stars without detected 24-70 μm excesses, the upper limits to their fluxes correspond to approximate 3 σ upper limits to their disk masses of 6 × 10^-6 M_⊕ using the MIPS 24 μm upper limit or 2 × 10^-4 M_⊕ using the MIPS 70 μm limit. These upper limit disk masses (for "warm" and "cold" dust, respectively) are roughly consistent with, but somewhat lower than, predictions of a heuristic model for the evolution of an "average" solar-mass star's debris disk based on extrapolation backward in time from current properties of the Sun's Kuiper Belt.