Spitzer MIPS observations of stars in the β Pictoris moving group
We present Multiband Imaging Photometer for Spitzer (MIPS) observations at 24 and 70 μm for 30 stars, and at 160 μm for a subset of 12 stars, in the nearby (~30 pc), young (~12 Myr) β Pictoris moving group (BPMG). In several cases, the new MIPS measurements resolve source confusion and background contamination issues in the IRAS data for this sample. We find that 7 members have 24 μm excesses, implying a debris disk fraction of 23%, and that at least 11 have 70 μm excesses (disk fraction of ≥37%). Five disks are detected at 160 μm (out of a biased sample of 12 stars observed), with a range of 160/70 flux ratios. The disk fraction at 24 and 70 μm, and the size of the excesses measured at each wavelength, are both consistent with an "inside-out" infrared excess decrease with time, wherein the shorter wavelength excesses disappear before longer wavelength excesses, and consistent with the overall decrease of infrared excess frequency with stellar age, as seen in Spitzer studies of other young stellar groups. Assuming that the infrared excesses are entirely due to circumstellar disks, we characterize the disk properties using simple models and fractional infrared luminosities. Optically thick disks, seen in the younger TW Hya and η Cha associations, are entirely absent in the BPMG. Additional flux density measurements at 24 and 70 μm are reported for nine Tucana-Horologium association member stars. Since this is <20% of the association membership, limited analysis on the complete disk fraction of this association is possible.
Additional Information© 2008 The American Astronomical Society. Received 2007 July 18, accepted for publication 2008 March 6. L. M. R. wishes to acknowledge funding from the Spitzer Science Center to allow her to take a "science retreat" to work intensively on this paper. The authors wish to acknowledge the MIPS GTO team for allowing us to use the DAT to process the 160 m data. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL, Caltech. This research makes use of data archived and served by the NASA Star and Exoplanet Database(NStED) at the Infrared Processing and Analysis Center. NStED is jointly funded by the National Aeronautics and Space Administration (NASA) via Research Opportunities in Space Sciences grant 2003 TPF-FS, and by NASA's Michelson Science Center. NStED is developed in collaboration with the NASA/IPAC Infrared Science Archive (IRSA). This research has also made use of NASA's Astrophysics Data System (ADS) Abstract Service, and of the SIMBAD database, operated at CDS, Strasbourg, France. This research has also made use of data products from the Two Micron All-Sky Survey (2MASS), which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, funded by NASA and the National Science Foundation. These data were served by the NASA/IPAC Infrared Science Archive, which is operated by JPL, Caltech, under contract with NASA. The research described in this paper was partially carried out at JPL, Caltech, under contract with NASA.
Published - REBapj08.pdf