TPF-I SWG Report - Exoplanet Exploration Program - NASA

G ENERAL A STROPHYSICS
Figure 3-4. A computer simulation showing how a protoplanetary disk surrounding a young star
begins, in a relatively short time, to fragment and form gas giant planets with stable orbits
(Courtesy of Lucio Mayer, ETH Zürich).
Thermal IR interferometry will resolve the acceleration region where stellar winds are produced in premain-sequence
stars, Wolf-Rayet stars, and giants. Many such systems are in multiple systems where
phenomena associated with wind–wind interactions can be directly imaged. Interferometric spectroimaging
of highly ionized species will provide unique diagnostics of these systems that will complement
radio-wavelength observations.
Darwin/TPF-I will resolve forming super-star clusters and starbursts in our Galaxy and in nearby
galaxies. Milli-arcsecond angular resolution will enable TPF-I to peer inside clusters to determine the
volume density of stars and to directly test formation models for the most massive stars in such systems,
even when the clusters are still highly embedded and their stars are still accreting. Do massive stars sink
rapidly to the cluster center due to on-going accretion and dynamical friction Do massive stars always
form by accretion, or do stellar interactions and mergers contribute The multiplicity fraction of massive
stars as a function of location within a cluster, and as a function of cluster age, will provide clues.
TPF-I/Darwin will have the capability to resolve the structure of circumstellar and planet-forming disks,
and to trace the shadows cast by the “dust walls” formed at the disk inner edge (Figure 3-3), spiral waves,
gaps created by forming giant planets, and the compositional variations resulting from condensation
sequences (Figure 3-4). The inner radii associated with the evaporation of various ices (such as water,
ammonia, and methanol) should be detectable by their characteristic spectral bands. Polarization
measurements will enable the measurement of magnetic field geometries by their power to align dust
grains. These observations will produce direct tests of planetary system formation models to distinguish
between competing paradigms, such as core-accretion and formation via gravitational instability.
The ionization and shock fronts produced by ionizing radiation will be resolved and diagnosed by the
analysis of spectral-line ratios. The highest resolution observations should resolve the inner regions
where jets and disk winds are launched, thereby providing direct tests of outflow generation models. Are
jets formed by ordinary stellar winds, the magnetic X-points where stellar magnetospheres interact with
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