Formation and Evolution of Planetary Systems (FEPS) Primordial Warm Dust Evolution From 3-3.pdf

THE ASTROPHYSICAL JOURNAL 639: 10 MARCH 2006 PART 2 MSWD PREPRINT: PRINTED 11/8/05 1 FORMATION AND EVOLUTION OF PLANETARY SYSTEMS (FEPS): PRIMORDIAL WARM DUST EVOLUTION FROM 3-30 MYR AROUND SUN-LIKE STARS Received 2005 Feb 28; accepted 2005 Nov 5; to be published 2006 March 10 M.D. SILVERSTONE1, M.R. MEYER1, E.E. MAMAJEK2, D. C. HINES3, L.A. HILLENBRAND4, J.?NAJITA5, I. PASCUCCI1, J. BOUWMAN6, J.S. KIM1, J.M. CARPENTER4, J.R.?STAUFFER7, D.E. BACKMAN8, A. MORO-MARTIN9, T. HENNING6, S. WOLF6, T.Y.?BROOKE7, D.L. PADGETT7 ABSTRACT We present data obtained with the Infrared Array Camera (IRAC) aboard the Spitzer Space Telescope (Spitzer) for a sample of 74 young (t 30 Myr old) Sun-like (0.7 M*/M? 1.5) stars. These are a sub-set of theobservations that comprise the Spitzer Legacy science program entitled the Formation and Evolution of Planetary Systems (FEPS). Using IRAC we study the fraction of young stars that exhibit 3.6-8.0μm infrared emission in excess of that expected from the stellar photosphere, as a function of age from 3-30 Myr. The most straightforward interpretation of such excess emission is the presence of hot (300-1000K) dust in the inner regions ( 3 AU) of a circumstellar disk. Five out of the 74 young stars show a strong infrared excess, four of which have estimated ages of 3-10 Myr. While we detect excesses from 5 optically thick disks, and photospheric emission from the remainder of our sample, we do not detect any excess emission from optically thin disks at these wavelengths. We compare our results with accretion disk fractions detected in previous studies, and use the ensemble results to place additional constraints on the dissipation timescales for optically-thick, primordial disks. Subject headings: circumstellar matter — infrared: stars — planetary systems: protoplanetary disks Accepted to the ApJ for publication in issue 10 March 2006, v. 639, part 2 1 Steward Observatory, The Univers