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    The Mid-Infrared Extinction Law In The Ophiuchus, Perseus, And Serpens Molecular Clouds

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    Date
    2009-01
    Author
    Chapman, Nicholas L.
    Mundy, Lee G.
    Lai, Shih-Ping
    Evans, Neal J.
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    Abstract
    We compute the mid-IR extinction law from 3.6 to 24 mu m in three molecular clouds-Ophiuchus, Perseus, and Serpens-by combining data from the "Cores to Disks" Spitzer Legacy Science program with deep JHK(s) imaging. Using a new technique, we are able to calculate the line-of-sight (LOS) extinction law toward each background star in our fields. With these LOS measurements, we create, for the first time, maps of the chi(2) deviation of the data from two extinction law models. Because our chi(2) maps have the same spatial resolution as our extinction maps, we can directly observe the changing extinction law as a function of the total column density. In the Spitzer Infrared Array Camera (IRAC) bands, 3.6-8 mu m, we see evidence for grain growth. Below A(Ks) = 0.5, our extinction law is well fitted by the Weingartner and Draine R(V) = 3.1 diffuse interstellar-medium dust model. As the extinction increases, our law gradually flattens, and for A(Ks) >= 1, the data are more consistent with the Weingartner and Draine R(V) = 5.5 model that uses larger maximum dust grain sizes. At 24 mu m, our extinction law is 2-4 times higher than the values predicted by theoretical dust models, but is more consistent with the observational results of Flaherty et al. Finally, from our chi(2) maps we identify a region in Perseus where the IRAC extinction law is anomalously high considering its column density. A steeper near-IR extinction law than the one we have assumed may partially explain the IRAC extinction law in this region.
    Department
    Astronomy
    Subject
    infrared: stars
    ism: clouds
    stars: formation
    spitzer c2d survey
    interstellar clouds
    nearby
    legacy
    dust
    mips
    irac
    glimpse
    stars
    astronomy & astrophysics
    URI
    http://hdl.handle.net/2152/34838
    xmlui.dri2xhtml.METS-1.0.item-citation
    Chapman, Nicholas L., Lee G. Mundy, Shih-Ping Lai, and Neal J. Evans II. "The mid-infrared extinction law in the Ophiuchus, Perseus, and Serpens molecular clouds." The Astrophysical Journal, Vol. 690, No. 1 (Jan., 2009): 496
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