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Gas and dust disks around protostars are the precursors of planetary systems. Several mechanisms have been proposed to explain grain growth from μm-sized dust to pebbles and planetesimals, leading to transitional disks and planetary systems with debris disks. These theories need now to be confirmed by observations combined with laboratory measurements of light scattering by dust particles. The distribution of μm-sized grains in protoplanetary disk envelopes and in optically thin debris disks can be traced by optical and near-IR observations of scattered starlight. The angular dependence of the intensity (the phase function) and of the degree of linear polarization (DLP) of scattered light carry information about grain size, structure and composition. Large grains produce a narrow peak in forward scattering, but detecting it is difficult. At intermediate angles, the phase function also depends on grain composition and structure, implying that spherical shape, which shows a unique phase function, is a poor assumption. The phase function of the dust rings surrounding Fomalhaut and HR4796A increases with angle at side- and back-scattering, suggesting particles as large as 100 μm. Compact spherical particles of that size are however incompatible with the observed DLP. This suggests large fluffy aggregates made of μm-sized monomers. However, numerical and experimental simulations still fail at delivering the complete picture. The number of such challenging cases is growing, as high-contrast imaging polarimeters (e.g. VLT/SPHERE, Gemini/GPI) have delivered dozens of high-quality images in the past 5 years, and upcoming observatories (JWST, WFIRST, ELT) will continue to provide such data. In order to maximize the scientific return from these multi-wavelength photopolarimetric observations, and to feed models with physical parameters constraining planet formation theories, new laboratory measurements of the phase function and DLP of representative dust analogues are crucial.
The thesis project will be developed within the Cosmic Dust group of the Department of Solar System at IAA where we conduct a national project entitled Laboratory Experiments, ObservatioNs and modellIng of cometary Dust: A new Strategy (LEONIDAS). Studies extend from cometary tails, including exploitation of OSIRIS and Giada-Rosetta data and participation in upcoming missions such as Comet Interceptor, to the Zodiacal Cloud and other circumstellar disks. The work involves researchers from IAA and another Spanish institute (ICV-CSIC). The student will also benefit from our collaborations in Finland and the UK. The project will be carried out in a word-class laboratory facility (Cosmic Dust Laboratory, CODULAB) dedicated to measurements of scattering matrices of cosmic dust analogues and atmospheric aerosols using goniometric spectro-photopolarimetry techniques. Development of the PhD will see the student acquiring, reducing and analyzing new photopolarimetric data in the laboratory, as well as helping in the synthesis of circumstellar dust analogues and characterizing the samples using laser particle sizing and scanning electron microscopy, among others. Astronomical data consisting in scattered light and polarimetry images of circumstellar disks will be provided by our partners at the Institute of Planetology and Astrophysics of Grenoble (IPAG, France). The student, who will be co-advised by Dr. Julien Milli, will be instructed in analyzing astronomical observations using laboratory experimental data and comparing to results obtained using Mie theory as well as other approximations. This facilitates interpretation of physical properties of circumstellar dust, including characterization of size, structure and composition and will better constrain dust disk models. The student will make stays in centers with which we collaborate, will attend relevant astronomical schools and will participate each year in international astronomical meetings to present research results.
IAA is an equal opportunity institution. Applications to this program by female scientists are particularly encouraged.
Should you need any further information or assistance concerning the application, please contact the IAA at severoochoa[at]iaa.es