Pulsations in evolved massive stars

Advisor: Michaela Kraus (AI CAS)

Funding: basic scholarship; additional top-up funding for the first 2 years is granted. Top-up funding beyond that period depends on the outcome of future grant applications.

Website: http://stelweb.asu.cas.cz/~kraus/

Contact: michaela.kraus@asu.cas.cz

The Hertzsprung-Russell (HR) diagram is populated by numerous classes of pulsating stars. However, not for all of these classes the pulsation properties of the stars are properly known. This is especially true in the upper, luminous region of the HR diagram, which is populated by extreme stars with intense winds and mass ejection phases. These objects might provide suitable conditions for the excitation of strange-mode instabilities, which have proven to be ideal candidates for driving mass-loss in a similar amount as the line-driven winds of these objects. Understanding the pulsation properties of massive stars in extreme phases of their evolution is ultimate for a deeper comprehension of the total mass-loss of these objects and the origin and time evolution of density inhomogeneities developing in their winds.

This project aims at investigating the pulsation behavior of luminous super- and hypergiants and the link between pulsations and the occurrence of phases of enhanced mass-loss in these objects. For this purpose, combined data sets from satellites and ground-based facilities (for both spectroscopy and photometry) will be utilized, including observations with the Perek 2m-telescope at Ondřejov Observatory. The student will learn how to observe and process the data as well as how to process data from satellite missions. Furthermore, the student will utilize sophisticated tools from modern asteroseismology and from stellar wind modeling to analyze the data in order to derive pulsation patterns along with the stellar parameters. The observationally derived pulsation properties will be confronted with predictions from theoretical models, which will be computed based on the sets of derived stellar parameters using state-of-the-art stellar evolution codes with pulsations.

Figure description: Mid-infrared images of the evolved star IRAS 17163-3907 at three different wavelengths. The central star and two dusty detached shells, likely resulting from phases of pulsation-triggered mass eruptions, are clearly seen. Based on these images, the source is dubbed fried-egg nebula. This image is taken from Lagadec et al. (2011).


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