Interferometric observations of pre-main sequence disks - Caltech ...

More documents

Recommendations

Info

14 Scientific overview depleted inner disk. The mid-infrared part of the SED comes from disk regions at distances between ∼5 AU and∼50 AU, where the disk opacity and the thermal emission are dominated by the dust. The dust density is generally high enough that the disk is optically thick to its own emitted radiation from near to far infrared and the resulting SED is in first approximation the sum of many black bodies with different effective temperatures. A closer look at the physics of a reprocessing disk reveals however that the disk surface temperature is generally higher than the effective temperature Td (Calvet et al., 1991; Chiang and Goldreich, 1997). Dust grains in the surface layers are directly exposed to the stellar radiation and are hotter than dust grains in the disk interior which are heated only by the diffused infrared emission of the disk itself. As a consequence, the thermal emission from this surface layer produces emission features in good agreement with nearly all the TTS and HAe stars spectra (Meeus et al., 2001; Kessler-Silacci et al., 2006). The analysis of spectroscopic features, mainly in mid-infrared, give a lot of information of the dust composition and size and will be discussed in more detail in the next section. Finally, particularly interesting for the study of circumstellar disk is the range of long wavelengths, from sub-millimeter to radio, where the dust opacity can be approximated by a power law, kν∝λ −β (Beckwith and Sargent, 1991), and the disk is optically thin to its own thermal radiation (τν < ∼ 1). In this case, the observed flux Fν is directly related to the dust surface densityΣ(see Eq. 1.3 and Eq. 1.4) and both the disk mass and the parameterβcan be derived from observations at different wavelengths (Mannings and Sargent, 1997; Testi et al., 2001 and 2003; Natta et al., 2004). Millimeter interferome- ters allow to resolve spatially the continuum disks observations and both spatially and spectrally the molecular lines. Using CO vibrational transitions, it has been confirmed that in most of the observed TTS and HAe stars the gas is orbiting the central star with velocity patterns in good agreement with keplerian rotation. In this case, the gas velocity gives a direct measure of the mass of the central object, which is independent of the position of the star on the HR diagram and of the evolutionary tracks. Taking advantage
1.3 Grain growth and planetary formation 15 of varying opacity of the different transitions of CO and its isotopes, is possible to probe disk properties at different depth and calculate the relative CO abundance. For some nearby stars, the continuum observations show asymmetry in the radial dust distribution which can be caused by dynamical perturbations of unknown companions or giant planets (Pietú et al., 2005; Corder et al., 2005). All these points will be discussed in more detail in Chapter 7 which describes new millimeter observations of the HAe star HD 163296. 1.3 Grain growth and planetary formation Circumstellar disks around TTS and HAe are composed for about 99% of gas and for only 1% of solid dust grains. Nevertheless, as seen in the previous section, the dust component is responsible for the observed disk thermal emission, which remains a key diagnostic tool to detect disks and characterize their structure. Dust grains dominate the disk opacity, control the disk temperature and geometry, regulate the chemical reactions of molecular species as CO and H2O in the colder parts of disks, and are the building block for the formation of planetesimals and planets within disks. From the diffuse interstellar medium to Class I objects, dust grains are, and remain, a mixture of amorphous silicates and carbons, with a size distribution from∼ 0.01µm to∼ 0.2µm (Draine et al., 2003; Bianchi et al., 2003; Kessler-Salacci et al., 2005). The situation changes drastically in circumstellar disks in which they grow many order of magnitude in size forming kilometers-size body (planetesimals) and even planets. While the growth from sub-micron to micron sizes is probably driven by collisional aggregation in Brownian velocity fields (Blum, 2004), it is still under debate if the formation of meter size objects occurs through collisional aggregation (see the review of Dominik et al., 2006) or gravitational instabilities in the over-dense dust regions of the disk (Youdin and Shu, 2002; Rice et al., 2004 and 2006). Modelling the grain growth requires a complex analysis of the dust and gas coupling, dust sticking properties and velocity fields within the disk. While growing in mass, particles start to decouple from
Page 1: Università degli Studi di Milano F
Page 5 and 6: CONTENTS I Introduction 1 1 Scienti
Page 7 and 8: CONTENTS v 4.5 Comparison with prev
Page 9: Part I Introduction
Page 12 and 13: 4 Scientific overview the critical
Page 14 and 15: 6 Scientific overview Log νFν Log
Page 16 and 17: 8 Scientific overview are the subje
Page 18 and 19: 10 Scientific overview disk regions
Page 20 and 21: 12 Scientific overview Figure 1.2:
Page 24 and 25: 16 Scientific overview the gas and
Page 26 and 27: 18 Scientific overview Figure 1.3:
Page 28 and 29: 20 Scientific overview We propose a
Page 31 and 32: CHAPTER 2 2.1 A bit of history Intr
Page 33 and 34: 2.1 A bit of history 25 measure ste
Page 35 and 36: 2.2 Basic principle of astronomical
Page 37 and 38: 2.3 Optical versus millimeter inter
Page 43 and 44: 2.4 Introduction to modelling techn
Page 45: 2.4 Introduction to modelling techn
Page 49 and 50: CHAPTER 3 The shape of the inner ri
Page 51 and 52: 3.1 Introduction 43 Tauri stars (Ei
Page 53 and 54: 3.2 Model description 45 adapt the
Page 55 and 56: 3.2 Model description 47 log(δR/R
Page 57 and 58: 3.2 Model description 49 the pressu
Page 59 and 60: 3.3 Results 51 Photospherical heigh
Page 61 and 62: 3.3 Results 53 ever, is sufficientl
Page 63 and 64: 3.3 Results 55 Sec. 3.3.1 (see Fig.
Page 65 and 66: 3.4 Discussion 57 the value ofǫ, t
Page 67 and 68: 3.4 Discussion 59 sample of Fig. 3.
Page 69 and 70: 3.5 Summary and conclusions 61 R in
Page 71 and 72: 3.6 Appendix 63 However, the bright
Page 73:
3.6 Appendix 65 Figure 3.9: Left pa
Page 76 and 77:
68 Large dust grains in the inner r
Page 78 and 79:
Page 80 and 81:
Page 82 and 83:
Page 84 and 85:
Page 86 and 87:
Page 88 and 89:
Page 90 and 91:
Page 92 and 93:
Page 94 and 95:
Page 96 and 97:
Face-on disk image Baseline (m) V 2
Page 98 and 99:
V 2 1 0.8 0.6 0.4 0.2 0 0 50 100 15
Page 100 and 101:
V 2 1 0.8 0.6 0.4 0.2 0 0 50 100 15
Page 103 and 104:
CHAPTER 5 More on the “puffed-up
Page 105 and 106:
5.1 Fuzzy and sharp rims 97 opacity
Page 107 and 108:
5.2 New shapes for the rim 99 grain
Page 109 and 110:
5.3 New observational results 101 (
Page 111:
5.3 New observational results 103 w
Page 115 and 116:
CHAPTER 6 Constraining the wind lau
Page 117 and 118:
6.1 Introduction 109 λ Fλ (erg cm
Page 119 and 120:
6.2 Observations and data reduction
Page 121 and 122:
6.3 Results and discussions 113 V V
Page 123 and 124:
6.4 Conclusions 115 note however th
Page 125:
Part IV The structure of the outer
Page 128 and 129:
120 The keplerian disk of HD 163296
Page 130 and 131:
Page 132 and 133:
Page 134 and 135:
Page 136 and 137:
Page 138 and 139:
Page 140 and 141:
Page 142 and 143:
Page 144 and 145:
Page 146 and 147:
Page 148 and 149:
Page 150 and 151:
Page 152 and 153:
Page 154 and 155:
Page 157:
Part V Conclusions and future prosp
Page 160 and 161:
152 Summary and Conclusions ∼1 an
Page 162 and 163:
154 Summary and Conclusions disk in
Page 165 and 166:
CHAPTER 9 Future developments As my
Page 167 and 168:
9.1 Gas in the inner disk of Herbig
Page 169 and 170:
9.2 Probing planet formation throug
Page 171 and 172:
Page 173 and 174:
Page 175 and 176:
Page 177:
Published papers • Isella, A.; Te
Page 180 and 181:
172 BIBLIOGRAPHY [2000] Bodenheimer
Page 182 and 183:
174 BIBLIOGRAPHY [2004] Gail H.-P.,
Page 184 and 185:
176 BIBLIOGRAPHY Arizona Press, Tuc
Page 186 and 187:
178 BIBLIOGRAPHY [2001] Thompson A.
show all

Interferometric observations of pre-main sequence disks - Caltech ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?