Observational Constraints on The Evolution of Dust in ...

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60 YSOs in the Lupus Molecular Clouds IRAC and MIPS bands (at 3.6, 4.5, 5.8, 8.0, 24 and 70 µm, respectively) are also available online 1 (Evans et al. 2003). For each object, its photometric data and corresponding NextGen model atmosphere are used (matching its spectral type and the gravitational acceleration for a pre-main-sequence star). The observed photometric data are corrected for extinction at all wavelengths from the object’s visual extinction (A V ), using the extinction law by Weingartner & Draine (2001) with R V = 5.5. Subsequently, the NextGen atmosphere is scaled to the extinction corrected photometric data at a given band. The scaling band used is either the z WFI or J band, depending on the availability of the photometry and the quality of the fit. In Table 3.2, the extinction values and normalization bands are presented for all fitted objects. Figure 3.7 shows the constructed SEDs for 41 out of 54 objects. Here, the solid black line is the NextGen model atmosphere, the open squares are the observed photometry while filled circles show the extinction corrected data. SEDs could not be produced for 13 out of the 54 spectrally classified objects. Either not enough infrared (both 2MASS as Spitzer) photometry is available, or the different photometric data (optical, 2MASS and Spitzer) did not match well with each other. A wide variety of SEDs can be seen in Figure 3.7. Consequently, a wide variety in disk types is inferred. The infrared spectral index slope can be used as a characteristic to distinguish between Class I, II and III objects, as defined by Lada. For the 39 objects with available data in K and MIPS1, the slope can be calculated as: α 2−24µm = (λF λ) 24µm − (λF λ ) 2µm λ 24µm − λ 2µm These values are shown in Table 3.2. One object has α 2−24µm consistent with a Class I source (α > 0) and 15 consistent with Class III sources (α < −2), the majority of them are Class II, disk sources. Additionally, object #67 is a confirmed cold disk, as studied by Merín et al. (2010). Cold disks are disks with large inner dust holes (i.e. lack of warm dust). Objects # 27, 79 and 80 have SEDs consistent with inner dust holes. Although confirmation of their nature as cold disks requires SED modelling that is out of the scope of this work, 4 out of 41 objects with SEDs in Figure 3.7 amount to ∼10% of cold disks in the sample, which is consistent with the range of 4 – 12% of cold disk frequency derived by Merín et al. (2010). 3.5.1 Luminosities Stellar and disk luminosities can be derived for the objects for which SEDs could be plotted. Stellar luminosity is calculated with the formula: L ∗ = 4πD 2 ∫ F λ dλ 1 htpp://ssc.spitzer.caltech.edu/spitzerdataarchives/
Evolution of Dust in Protoplanetary Disks 61 Figure 3.7 – SEDs of all the objects. The thick black curve is the model atmosphere of a star at its given temperature. The open points are the observed optical, 2MASS and Spitzer data. The closed points are the extinction corrected data. Notice the wide variety in SEDs (and thus disk shapes).
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Observational <str
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Promotiecommissie Promotor: Co-Prom
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Cover Artwork: Roderik Overzier
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viii Chapter 3. YSOs in the Lupus M
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x Publications 217 Acknowledgments
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2 Introduction planets may eventual
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4 Introduction Figure 1.1 - Illustr
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6 Introduction 1.3.1.1 Disk Observa
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8 Introduction 1.3.1.3 Processes Af
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A. Background Sources 111 Table 4.3
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A. Background Sources 113 Figure A.
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118 Discovery of a Dusty Planetary
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128 From Protoplanetary Disks to Pl
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220 Thesis Acknowledgments Liesbeth
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