THE MID-INFRARED EXTINCTION LAW IN THE OPHIUCHUS, PERSEUS, AND SERPENS MOLECULAR CLOUDS

Journal Article · Thu Jan 01 04:00:00 EST 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/690/1/496· OSTI ID:21565478

Chapman, Nicholas L; Mundy, Lee G ^[1]; Lai, Shih-Ping ^[2]; Evans, II, Neal J ^[3]

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1. Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
2. Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu 30043, Taiwan (China)
3. Department of Astronomy, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712 (United States)

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{sub 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}{sup 2} deviation of the data from two extinction law models. Because our {chi}{sup 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{sub K{sub s}}= 0.5, our extinction law is well fitted by the Weingartner and Draine R{sub V} = 3.1 diffuse interstellar-medium dust model. As the extinction increases, our law gradually flattens, and for A{sub K{sub s}}{>=}1, the data are more consistent with the Weingartner and Draine R{sub 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}{sup 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.

• OSTI ID: 21565478
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 690; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CLOUDS
DUSTS
ELECTROMAGNETIC RADIATION
EVOLUTION
GRAIN GROWTH
GRAIN SIZE
INFRARED RADIATION
MICROSTRUCTURE
RADIATIONS
SIZE
STAR EVOLUTION
STARS