A<i>SPITZER</i>INFRARED SPECTROGRAPH STUDY OF DEBRIS DISKS AROUND PLANET-HOST STARS

Abstract

Since giant planets scatter planetesimals within a few tidal radii of their\norbits, the locations of existing planetesimal belts indicate regions where\ngiant planet formation failed in bygone protostellar disks. Infrared\nobservations of circumstellar dust produced by colliding planetesimals are\ntherefore powerful probes of the formation histories of known planets. Here we\npresent new Spitzer IRS spectrophotometry of 111 Solar-type stars, including\n105 planet hosts. Our observations reveal 11 debris disks, including two\npreviously undetected debris disks orbiting HD 108874 and HD 130322. Combining\nour 32 micron spectrophotometry with previously published MIPS photometry, we\nfind that the majority of debris disks around planet hosts have temperatures in\nthe range 60 &lt; T &lt; 100 K. Assuming a dust temperature T = 70 K, which is\nrepresentative of the nine debris disks detected by both IRS and MIPS, we find\nthat debris rings surrounding Sunlike stars orbit between 15 and 240 AU,\ndepending on the mean particle size. Our observations imply that the planets\ndetected by radial-velocity searches formed within 240 AU of their parent\nstars. If any of the debris disks studied here have mostly large, blackbody\nemitting grains, their companion giant planets must have formed in a narrow\nregion between the ice line and 15 AU.\n