New Debris Disks around Nearby Main-sequence Stars: Impact on the Direct Detection of Planets

Using the MIPS instrument on Spitzer, we have searched for infrared excesses around a sample of 82 stars, mostly F, G, andKmain-sequence field stars, alongwith a small number of nearbyM stars. These stars were selected for their suitability for future observations by a variety of planet-finding techniques. These observations provide information on the asteroidal and cometary material orbiting these stars, data that can be correlated with any planets that may eventually be found.We have found significant excess 70 m emission toward 12 stars. Combined with an earlier study, we find an overall 70 m excess detection rate of 13% 3%for mature cool stars. Unlike the trend for planets to be found preferentially toward stars with highmetallicity, the incidence of debris disks is uncorrelatedwithmetallicity. By newly identifying four of these stars as havingweak 24 mexcesses (fluxes 10% above the stellar photosphere), we confirm a trend found in earlier studies wherein a weak 24 m excess is associatedwith a strong 70 m excess. Interestingly, we find no evidence for debris disks around 23 stars cooler than K1, a result that is bolstered by a lack of excess around any of the 38K1YM6 stars in two companion surveys. Onemotivation for this study is the fact that strong zodiacal emission can make it hard or impossible to detect planets directly with future observatories such as the Terrestrial Planet Finder (TPF ). The observations reported here exclude a few stars with very high levels of emission, >1000 times the emission of our zodiacal cloud, from direct planet searches. For the remainder of the sample, we set relatively high limits on dust emission from asteroid belt counterparts. Subject headinggs: circumstellar matter — infrared: stars — Kuiper Belt