Circumstellar dust of stars of different evolutionary stages

Jurkić, Tomislav (2012) Circumstellar dust of stars of different evolutionary stages. Doctoral thesis, Faculty of Science > Department of Physics.

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Abstract

Circumstellar dust represents an important constituent of the circumstellar medium that dominates infrared spectra. Proper understanding of the stellar evolution and interaction between stellar environment and star’s atmosphere cannot be achieved without knowing dust geometry and dust properties, which were determined around stars in two extreme evolutionary phases. DUSTY numerical code was used to model the spectra, colour indices and visibilities in order to find dust geometry and its properties, such as sublimation temperature, grain size, dust distribution, optical depth and mass loss rate. Spectral energy distribution (SED) of symbiotic Mira RR Tel was reconstructed from available observations during and outside obscuration epochs. Long-term changes in dust properties around seven symbiotic Miras were determined by modelling temporal variations of colour indices. The properties of stellar environments of T Tauri and Herbig Ae/Be stars were found from analysis of the near-IR interferometric visibilities and of the spectra in 40 young objects. We proposed a new model-independent method of scaling visibilities to compare the near-IR sizes of young stars. Pulsation properties of RR Tel were found by PDM method. Model of the circumstellar environment and its dynamical behaviour in RR Tel were established. It consists of the optically thin circumstellar dust envelope and optically thick dust region outside the line of sight. Increase in optical depth caused by the newly condensed dust in sublimation region and higher mass loss can explain obscuration events in RR Tel. This leads to the formation of compact dust shell, shielded from the influence of the hot component. Circumstellar dust shells are also present in other symbiotic Miras whose obscuration events are caused by increased optical depth. Changes in the dust properties inside pulsation cycle are caused by interaction between the dust and Mira itself. We have compared scaled near-IR visibilities of young stars and found significant clustering between low- and high- luminosity (L > 1000 L⊙) stars that implies similar circumstellar properties in each of the two groups. Low-luminosity Herbig Ae/Be and T Tauri stars show larger near-IR sizes than their high-luminosity counterparts. Visibilities and SEDs of young stars can be explained with optically thin circumstellar dust envelopes whose properties and optical depths are similar, as well as their inner radius determined by the sublimation. Dust envelope cannot explain high-luminosity objects, where hot gas in accretion disk is probably responsible for the near-IR excess. Similarities in dust properties and geometry between stars of different evolutionary phases imply similar processes governing envelope evolution and dust formation, growth and destruction.

Item Type: Thesis (Doctoral thesis)
Keywords: circumstellar matter ; radiative transfer ; binary stars ; symbiotic stars ; stars: AGB ; Pre-main sequence ; instrumentation: infrared ; interferometers
Supervisor: Kotnik-Karuza, Dubravka
Date: 12 October 2012
Number of Pages: 0
Subjects: NATURAL SCIENCES > Physics
Divisions: Faculty of Science > Department of Physics
Depositing User: Gordana Stubičan Ladešić
Date Deposited: 21 Dec 2013 22:44
Last Modified: 05 Jan 2018 14:57
URI: http://digre.pmf.unizg.hr/id/eprint/32

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