4 PHD positions at the Instituut voor Sterrenkunde, K.U.Leuven, Belgium

4 PHD positions at the Instituut voor Sterrenkunde, K.U.Leuven, Belgium

The Instituut voor Sterrenkunde (IvS) of the Katholieke Universiteit Leuven, Belgium is a young and active research group of some 50 scientists, engineers and administrative staff (http://www.ster.kuleuven.be). The institute is involved in several international networks and research projects, involving telescopes at international observatories and space missions. The institute is also responsible for the organization of the Master in Astronomy & Astrophysics of the Faculty of Science at Leuven University and the Advanced Master of Space Studies.

With these vacancies, we are searching for motivated PhD students to join the IvS-team.

1. Binary stellar evolution and the hot subdwarf stars
2. Post-AGB stars of the LMC, SMC and Galactic Bulge
3. The circumstellar environment of evolved stars as traced by molecules
4. Study of mass flows from evolved stars with Herschel

The candidate

• has a Master diploma in Astrophysics, Physics or Mathematics.
• has good knowledge of the English language.

Tasks

• The PhD student shall perform research in the framework of the defined PhD project.
• The PhD student shall take up a teaching assistance task of 4 hours per week in the Bachelor of Physics (Dutch) or in the Master of Astronomy & Astrophysics (English)
• The PhD student shall perform at least one observing run of two weeks per year for the pooled IvS programmes at the Mercator telescope of La Palma (Spain) as part of his/her PhD education and as part of this specific PhD project.

Contract

• Following the usual procedure at Leuven University, the initial contract runs over two years and will be prolonged with another two years after positive evaluation. The position starts preferentially on the 1st of September 2011.
• Salary is according to the university regulations for PhD positions (roughly 1600 Euro per month net tax-free salary, depending on age and experience).

Applications and contact

Send curriculum vitae and a 1-page motivation letter, in PDF format, to

1.    Binary stellar evolution and the hot subdwarf stars
       Dr. Roy Oestensen: Roy.Oestensen@ster.kuleuven.be
                       or
       Prof. Dr. Hans Van Winckel: Hans.Vanwinckel@ster.kuleuven.be
 
2.    Post-AGB stars of the LMC, SMC and Galactic Bulge
       Dr. Joris Blommaert: Joris.Blommaert@ster.kuleuven.be
                                       or
       Prof. Dr. Hans Van Winckel: Hans.Vanwinckel@ster.kuleuven.be
 
3.    The circumstellar environment of evolved stars as traced by molecules
       Prof. Dr. Leen Decin: Leen.Decin@ster.kuleuven.be
 
4.    Study of mass flows from evolved stars with Herschel
       Prof. Dr. Christoffel Waelkens: Christoffel.Waelkens@ster.kuleuven.be

The candidates also must arrange for two letters of recommendation to be sent electronically to the same email address. Please also apply for the PhD position of your choice via the Leuven Arenberg Doctoral School using this link: http://phd.kuleuven.be/set/voorstellen_departement?departement=50000437#detail

Candidates who wish to apply for more than one position do not need to send in multiple applications but are requested to indicate it in their letter of motivation.

The application and recommendation letter deadline is 1st of July 2011. Only complete applications will be considered.

Binary stellar evolution and the hot subdwarf stars

Project description

With this vacancy, we are searching for a motivated PhD student to work on our project to use the properties of hot subdwarf stars to constrain poorly understood binary evolution channels. One of the most important issues regarding the final evolution of stars is the impact of binarity. A rich zoo of peculiar, evolved objects are born from interaction between the loosely bound envelope of a giant, and the gravitational pull of a companion. Subdwarf B (sdB) stars are core-helium burning stars whose hydrogen envelope have been stripped off through interaction with a companion during the first red giant phase. Theory predicts that the majority of sdBs form through stable mass transfer leading to long period binaries. To date almost 100 short-period sdB binary systems have been found, but these are predicted to be the outcome of unstable mass transfer resulting in common envelope ejection, and not a single long-period system resulting from stable mass transfer has been established. Han et al.(2002, 2003) made a thorough binary population synthesis study of the hot subdwarfs, and predicting that the period distribution of the long-period systems should have a strong peak just above 100 days. We are now collecting high-resolution spectroscopy of a sample of such systems in order to test these predictions. Combining results from observations with binary population synthesis models and Monte-Carlo simulations will reveal whether the current prescription for stable mass transfer is accurate or not.

Post AGB stars of the LMC, SMC and Galactic Bulge

Project description

With this vacancy, we are searching for a motivated PhD student to work on our project to use the recently identified extra-galactic and Bulge population of post-Asymptotic Giant Branch stars (post-AGB) to constrain the AGB nucleosynthesis.

The final evolution of low- and intermediate-mass stars is a rapid transition from the Asymptotic Giant Branch (AGB) over the post-AGB transit towards the Planetary Nebula Phase (PN), before the stellar remnant cools down as a White Dwarf (WD). Although this scheme may be generally acknowledged, there is no understanding from first principles of different important physical processes that govern these evolutionary phases. The main shortcomings are related to the lack of understanding of the mass-loss mechanisms and mass-loss evolution along the AGB ascent, the subsequent shaping processes of the circumstellar shells and the lack of fundamental understanding of the internal chemical evolution of these stars.

In this project, we want to focus on this last item. More in particular on the poorly understood AGB 3rd dredge-up phenomenon, during which products of the internal nucleosynthesis are brought to the surface of the star. AGB stars are important contributors to the cosmic abundances of carbon, nitrogen as well as the heavy elements past the iron peak. Post-AGB photospheres bear witness to the total AGB chemical changes.

We propose to exploit our newly identified large sample of post-AGB stars in the Large and Small Magellanic clouds as well as in the Galactic Bulge, to study the slow-neutron capture production and associated 3rd-dredge-up processes. Our sample covers a range in luminosity and metallicity and has magnitudes such that high-resolution spectra will allow us to determine the abundances of a wide range of elements, from CNO up to the heaviest s-process elements. These abundances will be modeled using state-of-the-art chemical stellar evolution models.

Only a combination of high-quality data of a well defined sample of post-AGB stars and a detailed theoretical modelling, can make significant progress in our understanding of the dredge-up processes and the associated s-process nucleosynthesis of solar like stars. This is the final goal of this project.

The circumstellar environment of evolved stars as traced by molecules

Project description

The project is embedded in a larger theoretical and observational effort at the IvS to study in detail the late stages of evolution of low and intermediate mass stars.

Evolved stars are important sources for the enrichment of the interstellar medium due to their dense outflows. These outflows are variable on many timescales and their physics and chemistry are not well understood. Presently, the IvS is at the unique position to use guaranteed time observations of both the HIFI and PACS instrument onboard the Herschel Space Observatory (launched May 2009) to study with unprecedented detail the role of different molecules and dust species in the stellar winds of evolved stars. E.g., HERSCHEL gives us for the first time a full inventory of water both in the gas phase and in the form of solid water ice. Water plays a pivotal role in the physics and chemistry of the molecular envelopes that surround AGB stars. From September 2011 onward, the first (cycle 0) ALMA interferometric observations will be obtained. ALMA will provide the astronomical community with a unique instrument in terms of sensitivity and spatial resolution.

The goal of the present PhD project is to study the role of different molecules (H2O, CO, HCN, … and their isotopologues) and dust species in the chemical and thermodynamical structure of the envelopes of stars with a wide range in stellar wind properties. Deriving the isotope ratios will shed light on the role of nucleosynthesis and different dredge-up processes in the stellar core/atmosphere. From the ALMA observations, one can study the dust condensation regions and trace the dust distribution. Depending on the interest of the successful candidate, this PhD project can either have a more theoretical or a more observational accent.

The Herschel HIFI and PACS data, and the planned ALMA observations, will be complemented with already obtained ground-based high-resolution sub-millimeter single-dish and interferometric data of several molecules excited in the stellar wind of AGB stars.

Study of mass flows from evolved stars with Herschel

Project description

The final evolutionary stages of stars are largely determined by ejection of mass from the stellar envelope. The mechanisms at work are thought to be understood in broad terms, but several major aspects remain elusive. Among those is the role of different kind of instabilities, which cause the mass outflows to be variable in time. It has now also become clear that the interaction of mass outflows with the pre-existing interstellar medium on the one hand substantially complicate the interpretation of observational data, but on the other hand provide a new tool to study the interstellar medium.

The project focuses on the interpretation of images and spectra obtained with the Herschel satellite of the mass outflows from evolved stars (AGB stars and massive supergiants). The aims are to reconstruct the mass-loss history of these objects and to understand the interaction of the outflows with the interstellar medium. Tools are the analysis of the Herschel data in the framework of the Herschel key program on evolved stars (MESS) and hydrodynamical simulations to be developed.