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Star and planet formation

Circumstellar disks play an essential role in the star formation process. Not all the gas from which stars form can be directly accreted by the central object, but is partly forced by its angular momentum to a flattened structure, the circumstellar disk. In this disk the angular momentum is reduced and finally the gas is ionised at the inner rim of the disc and tranferred via magnetic funnels to the surface of the forming star. Disks are, however, not only important as mass reservoir. They are also the sites where planets form from the gas and the admixed dust. 

Although the importance of circumstellar disks is well established, our understanding of them is still limited. One open question is, whether the disks are homogeneously dispersed or the inner parts vanish more rapidly due to the interaction with the central star. To answer this question, we use photometric measurements covering a wide range of wavelengths, because the temperature of a disk decreases with the distance from the central star. For example, in the near-infrared we mainly see the inner rim of the disk, while the mid-infrared radiation also comes from the region where planets form.

Since these inner regions of the circumstellar disks are of special importance, we observe them spatially resolved. This is only possible due the availability of the "Very Large Telescope Interferometer" (VLTI) of the "European Southern Observatory" (ESO). Its telescopes with 8.2 m primary mirrors can be interferometrically combined. Auxiliary telescopes with a diameter of 1.8 m are also offered. The achieved spatial resolution is comparable to the resolution of a telescope with a primary mirror with a diameter of up to 200 m. Since in addition the observations are spectroscopically resolved, the interferometric measurements also trace the evolution of silicate dust. The spectra of the different parts of the disk reveal larger particles in those regions that are stronger exposed to the radiation of the central star. This dust processing is a first important step toward the formation of planets. 

Another important topic of our work are young binary stars. These can be used to determine with the help of Keplers third law the mass of the stars. This is particularly valuable for stellar evolutionary models that are still not well calibrated for young stars. Binary stars are also important because of the fact that both stars are of the same age and have been formed from the same material. Observations, however, reveal that the circumstellar disks of the components have different lifetimes. This can be explained by the individual stars, but also by the interactions of the stars with the disks.


Mag.rer.nat. Paul Beck Phone:+43 (0)316 380 - 5263

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