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178 Spectral Energy Distributions of the Young Stars with Disks in Serpens Serpens are coeval, this result supports the idea that disks around more massive stars evolve on faster timescales. Figure 7.6 shows the stellar luminosity related to the fractional disk luminosity for the sample in Serpens (black points), Taurus (red points), Upper Sco (blue points), and η Cha (green points). Horizontal dotted lines separate stellar luminosities of Herbig Ae/Be stars (earlier than F0), T Tauri stars (down to M7) and brown dwarfs (below M7), while the vertical lines roughly separate accreting from passive disks, as in Figure 7.3. It can be seen that the few Herbig Ae stars in Serpens follow the locus of L disk /L star established by the larger sample of Herbig Ae/Be stars by Meeus et al. (2001), not occupying either tail of the distribution. Figure 7.6 – Fractional disk luminosity (L disk /L star) versus the stellar luminosity (L star) derived for the objects in Serpens (black circles), compared to the objects in Taurus (gray squares), in Upper Sco (gray stars), and in η Cha (gray triangles). Besides the stellar and disk characteristics given in § 7.2, Oliveira et al. (2011) present the dust mineralogy and mean grain sizes in the surface of disks around the stars in Serpens, together with those disks in Taurus, Upper Sco and η Cha, obtained using the exact same procedure. Those results, combined with the analysis of their SEDs by Maud et al., allow the comparison of different disk and dust characteristics for all 4 regions. Figures 7.7, 7.8 and 7.9 relate the stellar and disk fractional luminosities and mass accretion rate, respectively, with the results from the B2C decomposition method (Olofsson et al. 2010) on the mineralogy of the dust in the upper layers of these disks. In those figures, the two upper panels show the mean mass-average grain size and the two lower panels show the mean crystallinity fraction of the dust. The two left panels are the results for the warm component close to the stars, while the right panels show the results for the cold components, further away and deeper into the disk. The low
Evolution of Dust in Protoplanetary Disks 179 Figure 7.7 – Dust mineralogy versus the stellar luminosity (L star) derived for the objects in Serpens (black circles), compared to the objects in Taurus (gray squares), in Upper Sco (gray stars), and in η Cha (gray triangles). number of Herbig Ae/Be stars and brown dwarfs in this sample do not allow a study across the stellar mass regime. No strong correlations are seen in either Figures 7.7, 7.8 or 7.9, pointing to no direct cause-effect relationships between either stellar or disk fractional luminosity and the dominant grain size or crystallinity fraction of the surface dust in a disk. The results from Figure 7.8 differ from those for Herbig Ae/Be stars (Meeus et al. 2001), which find a correlation between the mean grain size in the disk surface (as derived from the silicate features) and the geometry of the disk. Their study of a small number of disks (14 objects) argues that as the disk becomes flat (transitioning from group I into group II, and therefore decreasing L disk /L star , as they interpret), small dust grains are removed from the disk surface (by coagulation into bigger grains or blown away by the stellar radiation), which yields larger dominating grain sizes for flatter disks. Their results are supported by a less steep sub-mm slope for group II sources than for group I. Acke et al. (2004) studied the mm slope of a sample of 26 Herbig Ae/Be stars and found a correlation between this parameter and the geometry of the disk. It is important to note, however, that the mm data probe the entire dust population and do not say anything about the size of the dust in the disk surface, as is discussed here. Acke et al. (2004) suggest a geometry evolution from flared to selfshadowed with a concurrent evolution of the size of grains in the disk. Furthermore, similar results as those of Meeus et al. (2001) are found for T Tauri stars by Bouwman
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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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10 Introduction of them (e.g., β P
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12 Introduction responsible for dis
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14 Introduction Figure 1.4 - Eviden
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16 Introduction stars (due to spect
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18 Introduction the potential to ch
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20 Introduction Gorti, U., Dullemon
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2 Optical Characterization of a New
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Evolution of Dust in Protoplanetary
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52 YSOs in the Lupus Molecular Clou
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4 A Spitzer Survey of Protoplanetar
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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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