Department of Physics

Department News

Dr. Nikta Amiri to present on May 3

Apr 27, 2012

Speaker: Dr. Nikta Amiri
Date: May 3, 2012 (Thursday)
Time: 4:00 pm
Room: 205 Currens Hall

Developing Asymmetries in AGB Stars: Occurrence, Morphology, and Polarization of Circumstellar Masers


Intermediate mass stars die extraordinary deaths, ejecting a significant amount of their mass into the interstellar medium, when they make a sudden transition (~1000 years) towards much hotter temperatures (>30,000 K) as compact white dwarfs. Such a heavy mass loss is important in astrophysics as it significantly affects the stellar evolution and influences the chemical composition of the Galaxy. The late stages of the evolution of Asymptotic Giant Branch (AGB) stars and in particular the formation of aspherical PNe is poorly understood. It is not clear why AGB stars exhibit significant asymmetric mass loss at the end of their evolution. The discovery of collimated jets in the stellar environment has opened up a new window to study this fascinating piece of stellar evolution in more detail. Magnetic fields have been proposed as possible agents for forming the striking asymmetries we observe in PNe. Using high resolution radio interferometers, I studied astrophysical masers which occur in the circumstellar envelopes of AGB stars. The results of my work have shown that the circumstellar envelopes of evolved stars show signs of aspherical expansion, traced by maser emission at various distances from the central evolved stars. Furthermore, the observations indicate significant magnetic field strengths, which imply that magnetic fields can have an important role in collimating the jets and shaping the circumstellar environment of dying stars.
About the speaker:
Nikta Amiri earned her PhD in Astronomy and Astrophysics from Leiden University in the Netherlands in October 2011. Her thesis topic was "Developing Asymmetries in AGB stars: Occurrence, Morphology, and Polarization of Circumstellar Masers".

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