PT Unknown
AU Scicluna, P
TI Radiative transfer modelling and observations of clumpy, dusty astrophysical environments
PY 2015
PU Christian-Albrechts-Universität zu Kiel
WP https://macau.uni-kiel.de/receive/diss_mods_00017537
LA en
DE Radiative transfer; cosmic dust; star formation; stellar evolution
AB This thesis explores selected aspects of cosmic dust through a series of case studies of different dusty environments, in particular those where the dust distribution is clumpy. Cosmic dust plays a key role in a number of physical processes: it allows stars to lose mass, adding heavy elements to the interstellar medium; it helps regulate the formation of sun–like stars; it allows the formation of complex molecules in space; and perhaps most importantly of all, it gets turned into planets, plants, and even people. However, it must be studied indirectly, through the detection of stellar photons that have interacted with interstellar dust, or by observing photons emitted by dust which is heated by stars. As a result, it is crucial to understand the interactions of photons with dust, and their propagation through dusty environments; this necessitates radiative transfer modelling.
This thesis explores the influence of the geometrical distribution of dust on observations of the extinction of starlight by dust, which is one of the main methods for constraining the properties of dust. Modelling work shows that geometrical effects in
clumpy environments compromise efforts to constrain dust properties in embedded or extragalactic environments, but that diffuse interstellar extinction measurements are unaffected.
It also considers the possibility that stars in a clumpy molecular cloud might interact with the dense clumps, which is found to be a surprisingly probable occurrence. This is shown to result in the possible accretion of a sufficient supply of material to
form a protoplanetary disc, opening the possibility of a second epoch of planet formation, with a diverse range of potential consequences for young planetary systems.
Results of simultaneous modelling of both components of the binary young–stellar–object VV Corona Australis are presented, which show that both discs have similar inclinations, but rather large scale heights. Based on the model results, an age of 3.5 Myr is derived for the system, and stellar masses of 1.7 M ; in combination with
near–infrared spectroscopy, this suggests an accretion rate of 4 × 10−8 M yr−1 for the primary.
Finally, the results of a high–contrast imaging and polarimetric study of the dusty mass–loss envelope of the nearby extreme red supergiant VY Canis Majoris are presented, along with a new radiative transfer model of the envelope. The radiative
transfer model reveals the presence of at least 6 × 10−3 M of dust, implying that the star has ejected at least 1 M in the last 1000 yr. Polarimetric imaging reveals the presence of dust grains ∼ 50 times larger than dust in the interstellar medium; grains
of this size are likely to survive the eventual supernova of VY CMa provided it does not occur within the next 5000–10000 yr. This suggests that pre–supernova mass loss can make a significant contribution to the dust content of galaxies in the early universe.
PI Kiel
ER