PhD positions

In the late stages of their evolution, low- to intermediate-mass stars (LIMS) are in a rapid transition from the Asymptotic Giant Branch (AGB) to the White Dwarf (WD) cooling track through the transient post-AGB and the Planetary Nebula (PNe) phases. During their ascent of the AGB, stars eject most of their initial mass. This ejecta (mainly in the form of gas, but with some contribution in the form of dust) is enriched in C, N and heavy elements as a result of internal nucleosynthesis and subsequent transport to the stellar surface. It forms the major source of these elements for their host galaxy. Although this evolution scheme is well established, there is little understanding from first principles of the different important physical processes that govern these evolutionary phases. More importantly, the evolution of any star, especially during the giant phases will be strongly affected if the star is in a binary system.

Three Ph.D. positions are therefore open in the framework of the STARLAB project (see also summary below) involving the Institut d'Astronomie of the Université libre de Bruxelles, the Royal Observatory of Belgium, and the Instituut voor Sterrenkunde of the Katholieke Universiteit Leuven, located within 25 kms of each other in central Belgium.

The goal of the STARLAB project is to improve our understanding of these key physical and chemical processes at work in single and binary low- and intermediate-mass stars. A first Ph.D. project is focused on abundance determinations in late-type stars as tracers for nucleosynthesis and mixing processes, another on binary-star interaction physics, and the third one on the study of the circumstellar environment of late-type mass-losing stars as tracers for the mass loss processes.

The Ph.D. students will be co-supervised by teams from a pair of the institutes and will receive joint Ph.D. degrees. A work plan has been established that implies extended stays at one and the other among the two supervising institutes. The net monthly salary is about 1900 EUR/month, including social security benefits. Contracts are for one year, renewable up to 4 years, depending on positive progress reviews. Candidates will participate in the teaching (in English, if the candidate is not French or Dutch speaking) or other functional work. The initial contract is under provision of acceptance in the Doctoral School programme of the universities at stake.

Starting date is September 1st, 2015. Deadline for applications is Sunday, June 28, midnight CET.

Profile: With this vacancy, we are searching for excellent and motivated PhD students with a master diploma in astrophysics, physics or mathematics.

For more information please contact Prof. Alain Jorissen at +32.2.6502834 or via email at

Application: You can apply by sending

  • a motivation letter,
  • at least one letter of reference,
  • a resume / curriculum vitae, including the final grades,
  • if possible, the grade transcript for individual courses,
  • and, if possible, the electronic version of the master thesis

to indicating which Ph.D. project is preferred (i, ii, or iii below).

Specifically, three Ph.D. positions are open with the following goals:

(i) to derive the surface abundances on the basis of high-resolution optical spectra of specific LIMS and confront them with nucleosynthesis predictions. The targets will be well-selected AGB and post-AGB stars in the Galaxy, the Magellanic Clouds and the Galactic Bulge. We will also derive isotopic ratios via molecular tracers, rather than elemental abundances via atomic lines. The determination of the atmospheric composition of evolved LIMS will provide strong diagnostics on the internal nuclear burning and mixing processes at play in the stellar interior. The goal will be to come to a better understanding of all nucleosynthetic and mixing processes which determine the chemical evolution of LIMS, from a comparison with predictions from stellar-evolution models.

Supervisors: H. Van Winckel (KUL), S. Van Eck (ULB)

(ii) to assess how the various classes of LIMS binaries fit within a global picture. Binary evolution is very complex and faces many problematic and critical issues, e.g. the mass transfer involving an AGB star. The binary stellar evolution code BINSTAR will be used to compute evolutionary sequences (with different initial masses, periods and eccentricities) for a representative selection of low- and intermediate-mass binaries (LIMBs). With this, the aim is to identify the binary-evolution channel leading to specific families of LIMBs like dusty-disc post-AGB systems, dwarf Ba stars and giant Ba stars, and to confront the abundance pattern at the surface of these LIMBs with those predicted by the BINSTAR code. Once the different evolutionary channels are disclosed, we plan to perform dedicated population synthesis calculations to investigate how representative every evolutionary channel is. This project is embedded in our long-term observational programme we deployed at the 1.2 Mercator telescope.

Supervisors: L. Siess (ULB), H. Van Winckel (KUL)

(iii) to study the circumstellar winds of LIMS at different spatial scales using mid-IR interferometry, Herschel and ALMA data. Mass loss is one of the most important characteristics of LIMS. Molecules and dust grains form close to the star, and are then expelled in a wind where dust and gas are momentum coupled and driven outwards by radiation pressure on the grains. Ultimately, gas and dust will be injected into the interstellar medium forming the building blocks for new stars and planets. The aim of this project is to elucidate the role of different physical and chemical mechanisms in driving the stellar winds. We therefore will use interferometry to study the dust condensation process close to the star, Herschel 60-200 micron spectra to study the dust density profile in the wind, and ALMA data on specific objects in our Galaxy and the Magellanic Clouds. The data will be analysed using sophisticated theoretical models to derive the thermodynamical and chemical structures of these winds.

Supervisors: L. Decin (KUL) and M. Groenewegen (ROB)