Formation and Evolution of Planetary Systems: Properties of Debris Dust Around Solar-Type Stars

Abstract

We present Spitzer photometric (IRAC and MIPS) and spectroscopic (IRS low resolution) observations for 314 stars in the Formation and Evolution of Planetary Systems (FEPS) Legacy program. These data are used to investigate the properties and evolution of circumstellar dust around solar-type stars spanning ages from approximately 3 Myr to 3 Gyr. We identify 46 sources that exhibit excess infrared emission above the stellar photosphere at 24µm, and 21 sources with excesses at 70µm. Five sources with an infrared excess have characteristics of optically thick primordial disks, while the remaining sources have properties akin to debris systems. The fraction of systems exhibiting a 24µm excess greater than 10.2% above the photosphere is 15% for ages < 300 Myr and declines to 2.7% for older ages. The upper envelope to the 70µm fractional luminosity appears to decline over a similar age range. The characteristic temperature of the debris inferred from the IRS spectra range between 60 and 180 K, with evidence for the presence of cooler dust to account for the strength of the 70µm excess emission. No strong correlation is found between dust temperature and stellar age. Comparison of the observational data with disk models containing a powerlaw distribution of silicate grains suggest that the typical inner disk radius is > ∼ 10 AU. Although the interpretation is not unique, the lack of excess emission shortwards of 16µm and the relatively flat distribution of the 24µm excess for ages < ∼ 300 Myr is consistent with steady-state collisional models.

Insights into Planet Formation from Debris Disks

“…It was later shown that both the scatter seen in the observations and the decay in emission levels could be explained by the steady state erosion of extrasolar Kuiper belts (Wyatt et al 2007b); the level observed simply reflects the initial mass in the belt and its distance from the star, which was far enough that the emission was generally cold and so also explained the observations at 70 µm toward the same stars (Su et al 2006). The same issue affected the interpretation of Sun-like stars, since it was found that the emission spectrum for the majority of these stars was rising toward longer wavelengths implying that the 24 µm emission arises in a belt far enough from the star (> 10 au) to be explained by steady state processes (Carpenter et al 2009). That is, while recent giant impacts are not ruled out as the origin of the 24 µm emission, a steady state interpretation is more likely for most systems, and regardless the relatively cool temperature of the emission implies that this arises from a location outside that typically associated with the formation of terrestrial planets.…”

The debris disk – terrestrial planet connection

“…The observed statistics of debris disks show that 15-20% of solar-type stars have bright dust emission at 70 µm (Trilling et al 2008;Carpenter et al 2009). Our simulations show that debris disk systems generally represent dynamically calm environments that should have been conducive to efficient terrestrial accretion, and are therefore likely to contain systems of terrestrial planets.…”

Spectral energy distribution simulations of a possible ring structure around the young, red brown dwarf G 196-3 B

“…This is also the value accepted for describing debris discs in the solar system (Carpenter et al 2009). We imposed that the grains at the inner edge of the disc must be in radiative equilibrium with the central substellar object, and that the disc is spatially extended.…”