TPF-I SWG Report - Exoplanet Exploration Program - NASA

C HAPTER 3
Figure 3-3. Three possible geometries for the centers of T Tauri disks and synthetic images
of these models in scattered light. TPF-I could distinguish among these possibilities, shedding
light on the origin of close-in planets (Dejan Vinkovic, Princeton Univ.).
planetary systems mature, their central stars reach the main-sequence, and birth clusters and associations
disperse (Lada and Lada 2001; Adams et al. 2004). While in the standard model for the formation of lowmass
stars, they evolve gradually from accreting (Class 0 and I) protostars into Class II and III T Tauri
stars, in the modern clustered formation paradigm, catastrophic events such as dynamical interactions
with sibling stars (Reipurth 2000; Tan 2004), evaporation of envelopes and disks by the intense radiation
fields (Johnstone, Hollenbach, and Bally 1998), winds, and supernova explosions punctuate early stellar
and planetary system evolution (Hollenbach et al. 2000). Contrary to being hazardous, UV radiation in
from both the central protostar and nearby massive stars may actually promote the formation of
planetesimals by selectively removing light gases and small particles (Throop and Bally 2005).
Massive stars appear to be preferentially formed in ultra-dense proto-cluster environments where cluster -
stellar densities are higher than 10 5 stars per cubic parsec. Interstellar separations are frequently less than
a few thousand AU. Darwin/TPF-I 2- to 10- mas resolution in the thermal infrared will resolve a
projected interstellar separation of 10 to 50 AU at a distance of 5 kpc, enabling the cores of embedded
proto-clusters to be resolved, and their structure analyzed anywhere in the Galaxy. Does the high
multiplicity fraction of massive stars originate in the primordial fragmentation of the parent cloud core, or
does it develop later in the evolution of the cluster by means of stellar dynamical processes such as threebody
encounters
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