A Spitzer MIPS Study of 2.5-2.0 M _⊙ Stars in Scorpius-Centaurus

Abstract

We have obtained Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS) 24 μm and 70 μm observations of 215 nearby, Hipparcos B- and A-type common proper-motion single and binary systems in the nearest OB association, Scorpius-Centaurus. Combining our MIPS observations with those of other ScoCen stars in the literature, we estimate 24 μm B+A-type disk fractions of 17/67 (25⁺⁶ _{- 5}%), 36/131 (27⁺⁴ _{- 4}%), and 23/95 (24⁺⁵ _{- 4}%) for Upper Scorpius (~11 Myr), Upper Centaurus Lupus (~15 Myr), and Lower Centaurus Crux (~17 Myr), respectively, somewhat smaller disk fractions than previously obtained for F- and G-type members. We confirm previous IRAS excess detections and present new discoveries of 51 protoplanetary and debris disk systems, with fractional infrared luminosities ranging from L _IR/L _* = 10^-6 to 10^-2 and grain temperatures ranging from T _gr = 40 to 300 K. In addition, we confirm that the 24 μm and 70 μm excesses (or fractional infrared luminosities) around B+A-type stars are smaller than those measured toward F+G-type stars and hypothesize that the observed disk property dependence on stellar mass may be the result of a higher stellar companion fraction around B- and A-type stars at 10-200 AU. Finally, we note that the majority of the ScoCen 24 μm excess sources also possess 12 μm excess, indicating that Earth-like planets may be forming via collisions in the terrestrial planet zone at ~10-100 Myr.