Debris Disks around Sun‐like Stars

Abstract

We have observed nearly 200 FGK stars at 24 and 70 microns with the Spitzer Space Telescope. We identify excess infrared emission, including a number of cases where the observed flux is more than 10 times brighter than the predicted photospheric flux, and interpret these signatures as evidence of debris disks in those systems. We combine this sample of FGK stars with similar published results to produce a sample of more than 350 main sequence AFGKM stars. The incidence of debris disks is 4.2 +2.0 −1.1 % at 24 microns for a sample of 213 Sun-like (FG) stars and 16.4 +2.8 −2.9 % at 70 microns for 225 Sun-like (FG) stars. We find that the excess rates for A, F, G, and K stars are statistically indistinguishable, but with a suggestion of decreasing excess rate toward the later spectral types; this may be an age effect. The lack of strong trend among FGK stars of comparable ages is surprising, given the factor of 50 change in stellar luminosity across this spectral range. We also find that the incidence of debris disks declines very slowly beyond ages of 1 billion years.Subject headings: circumstellar matter -planetary systems: formation -infrared: stars IntroductionPlanetary system formation must be studied through various indirect means due to the relative faintness of distant planets and the long timescales over which planetary system -2evolution takes place. One powerful technique has advanced substantially in the era of the Spitzer Space Telescope: investigations of dusty debris disks around mature, main sequence stars. Debris disks arise from populations of planetesimals that remain from the era of planet formation; the analogs in our Solar System are the asteroid belt and the Kuiper Belt. Any system that possesses a debris disk necessarily has progressed toward forming a planetary system to some degree.The many small bodies that inhabit a debris disk can, on occasion, collide, producing a shower of fragments that grind each other down to dust particles. These dust grains can be heated by the central star to temperatures ∼100 K, where they can be detected at wavelengths of 10-100 microns. Data from the IRAS and ISO satellites were used to identify and characterize debris disks (e.g., Aumann et al. 1984;Decin et al. 2000;Spangler et al. 2001;Habing et al. 2001;Decin et al. 2003). The Multiband Imaging Photometer for Spitzer (MIPS; Rieke et al. (2004)) offers substantially improved sensitivities at 24 and 70 microns and therefore can be used to advance the study of debris disks and measure the fraction of stars that possess colliding swarms of remnant planetesimals.A number of these surveys have been carried out using MIPS. Rieke et al. (2005) and Su et al. (2006) observed hundreds of A stars and found that the number of A stars showing thermal infrared excess suggestive of collisionally-produced dust decreases as a function of stellar age, from 50% or more at ages just past the gas dissipation age of 10 Myr to 30% at 500 Myr. The excess rates are lower for older and lower mass stars. Bryden et al. (2006) found th...

EXPLORATIONS BEYOND THE SNOW LINE:SPITZER/IRS SPECTRA OF DEBRIS DISKS AROUND SOLAR-TYPE STARS

“…Figure 11 summarizes the rates of IR excess detection in IRS spectral surveys and compares them with MIPS photometric results. For two wavelengths in each instrument, the distribution (Bryden et al 2006;Beichman et al 2006b;Trilling et al 2008). For IRS spectra, 203 stars with spectral types F0-M0 are observed from 10 through 32 μm (from this survey and the stars in Table 6).…”

“…f Star has MIPS 24 and 70 μm data from Plavchan et al (2009). g Star has MIPS 24 and 70 μm data from Trilling et al (2008). h IRS data has been co-added with IRS data from the FGK or SIM/TPF program (see Table 3).…”

Circumstellar disks and planets

“…Spitzer surveys have established that 10-50% of young main sequence stars host a debris disks (Trilling et al, 2008;Meyer et al, 2008;Lestrade et al, 2009), confirming that the formation of planetesimals is a very common outcome of disk evolution, in line with the high proportion of detected exoplanets around nearby stars (Udry and Santos, 2007).…”

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.…”

“…The rough observational limit of the MIPS instrument on NASA's Spitzer Space Telescope is shown with the dashed line (Trilling et al 2008). All planetesimal particles were destroyed as of 45 Myr via either collision or ejection.…”