Tracing the evolution of protoplanetary disks

This thesis presents new insights of protoplanetary disk evolution. It focuses on the characterisation of several elements in the earliest phases of planet formation in protoplanetary disks: the connection between the SED and disk gaps (Chapters 2, 3 and 4), PAHs in the gas flows in disk gaps (Chapter 5) and dust processing of forsterite in evolving protoplanetary disks (Chapter 6).LKBF, Leiden observatoryUBL - phd migration 201

The 69 {μμ}m forsterite band in spectra of protoplanetary disks. Results from the Herschel DIGIT programme

Context. We have analysed far-infrared spectra of 32 circumstellar disks around Herbig Ae/Be and T Tauri stars obtained within the Herschel key programme Dust, Ice and Gas in Time (DIGIT). The spectra were taken with the Photodetector Array Camera and Spectrometer (PACS) on board the Herschel Space Observatory. In this paper we focus on the detection and analysis of the 69 {$μ$}m emission band of the crystalline silicate forsterite. Aims: This work aims at providing an overview of the 69 {$μ$}m forsterite bands present in the DIGIT sample. We use characteristics of the emission band (peak position and FWHM) to derive the dust temperature and to constrain the iron content of the crystalline silicates. With this information, constraints can be placed on the spatial distribution of the forsterite in the disk and the formation history of the crystalline grains. Methods: The 69 {$μ$}m forsterite emission feature is analysed in terms of position and shape to derive the temperature and composition of the dust by comparison to laboratory spectra of that band. The PACS spectra are combined with existing Spitzer IRS spectra and we compare the presence and strength of the 69 {$μ$}m band to the forsterite bands at shorter wavelengths. Results: A total of 32 disk sources have been observed. Out of these 32, 8 sources show a 69 {$μ$}m emission feature that can be attributed to forsterite. With the exception of the T Tauri star AS 205, all of the detections are for disks associated with Herbig Ae/Be stars. Most of the forsterite grains that give rise to the 69 {$μ$}m bands are found to be warm (~{}100-200 K) and iron-poor (less than ~{}2% iron). AB Aur is the only source where the emission cannot be fitted with iron-free forsterite requiring approximately 3-4% of iron. Conclusions: Our findings support the hypothesis that the forsterite grains form through an equilibrium condensation process at high temperatures. The large width of the emission band in some sources may indicate the presence of forsterite reservoirs at different temperatures. The connection between the strength of the 69 and 33 {$μ$}m bands shows that at least part of the emission in these two bands originates fom the same dust grains. We further find that any model that can explain the PACS and the Spitzer IRS observations must take the effects of a wavelength dependent optical depth into account. We find weak indications of a correlation of the detection rate of the 69 {$μ$}m band with the spectral type of the host stars in our sample. However, the sample size is too small to obtain a definitive result. Appendix A is available in electronic form at http://www.aanda.or

SEEDS Adaptive Optics Imaging of the Asymmetric Transition Disk Oph IRS 48 in Scattered Light

Stars and planetary system

Vergleich unterschiedlicher Brennverfahren fuer kleine schnellaufende Dieselmotoren

SIGLEAvailable from the library of Muenchen Technische Univ. (DE) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Polycyclic aromatic hydrocarbon ionization as a tracer of gas flows through protoplanetary disk gaps

Context. Planet-forming disks of gas and dust around young stars contain polycyclic aromatic hydrocarbons (PAHs). Aims. We aim to characterize how the charge state of PAHs can be used as a probe of flows of gas through protoplanetary gaps. In this context, our goal is to understand the PAH spectra of four transitional disks. In addition, we want to explain the observed correlation between PAH ionization (traced by the I6.2/I11.3 feature ratio) and the disk mass (traced by the 1.3 mm luminosity). Methods. We implement a model to calculate the charge state of PAHs in the Monte Carlo radiative transfer code MCMax. The emission spectra and ionization balance are calculated in the parameter space set by the properties of the star and the disk. Results. A benchmark modeling grid is presented that shows how PAH ionization and luminosity behave as a function of star and disk properties. The PAH ionization is most sensitive to ultraviolet (UV) radiation and the electron density. In optically thick disks, where the UV field is low and the electron density is high, PAHs are predominantly neutral. Ionized PAHs trace low-density optically thin disk regions where the UV field is high and the electron density is low. Such regions are characteristic of gas flows through the gaps of transitional disks. We demonstrate that fitting the PAH spectra of four transitional disks requires a contribution of ionized PAHs in “gas flows” through the gap. Conclusions. The PAH spectra of transitional disks can be understood as superpositions of neutral and ionized PAHs. For HD 97048, neutral PAHs in the optically thick disk dominate the spectrum. In the cases of HD 169142, HD 135344 B and Oph IRS 48, small amounts of ionized PAHs located in the “gas flows” through the gap are strong contributors to the total PAH luminosity. The observed trend in the sample of Herbig stars between the disk mass and PAH ionization may imply that lower-mass disks have larger gaps. Ionized PAHs in gas flows through these gaps contribute strongly to their spectra

Architecture and literature: Reflections, imaginations / Architectuur en literatuur: bespiegeling, verbeelding

ArchitectureArchitectur

The Star Formation History of RCW 36

Recent studies of massive-star forming regions indicate that they can contain multiple generations of young stars. These observations suggest that star formation in these regions is sequential and/or triggered by a previous generation of (massive) stars. Here we present new observations of the star forming region RCW 36 in the Vela Molecular Ridge, hosting a young cluster of massive stars embedded in a molecular cloud complex. In the periphery of the cluster several young stellar objects (YSOs) are detected which produce bipolar jets (HH 1042 and HH 1043) demonstrating that these objects are still actively accreting. The VLT/X-shooter spectrum of the jet structure of HH 1042 provides detailed information on the physical conditions and kinematical properties of the jet plasma. From this information the YSO's accretion history can be derived. Combining the photometric and spectroscopic observations of RCW 36 gives insight into the formation process of individual stars and the star formation history of this young massive-star forming region