Mid-infrared spectroscopy with MIRI on board the James Webb Space Telescope: Using detector interferometric fringes to detect spatially unresolved sources at KU Leuven

The Institute of Astronomy (IoA) of KU Leuven in Belgium is a young and vibrant research group of some 80 scientists, engineers, and administrative staff, including 7 full-time and 3 part-time professors. The institute is an expertise centre in stellar physics and astrophysical instrumentation, and is active in several international consortia and collaborations, involving telescopes at observatories worldwide and in space. Members of IoA have access to parallel computing facilities at the Flemish Supercomputer Centre. The IoA is responsible for the organisation of the Master in Astronomy & Astrophysics and the Advanced Master of Space Studies of the Faculty of Science, and operates the 1.2m Mercator telescope at the Roque de los Muchachos, La Palma Observatory, Canary Islands. The institute has a long tradition in instrumental, observational, and theoretical studies of stellar evolution.


  • The James Webb Space Telescope (JWST) is an international collaboration between the USA National Aeronautics and Space Administration NASA, the European Space Agency, and the Canadian Space Agency. JWST is planned for launch at the end of 2021. Using its four primary scientific instruments, including the mid-infrared instrument MIRI, and its massive primary mirror (6.5 meters in diameter) JWST will be able to peek further into the universe than any other mission before it. The instrument MIRI will be used to look at the first galaxies formed after the Big Bang, as well as young stars, circumstellar debris disks, and exoplanets, answering important questions about how these objects form and evolve over time. To do so MIRI will resolve the light coming from these sources in the 5 to 28 micron wavelength range. One of the ways it will do this is using a medium-resolution integral field spectrograph, also known as the MIRI MRS. Integral field spectroscopy allows to simultaneously extract the 2D spatial information and spectral information of a given source, and is becoming an increasingly popular technique in many fields in astronomy. The MRS was the second most requested mode of observation with JWST by the astronomical community, and will thus contribute to the advancement of infrared astronomy and our understanding of the universe in a major way. The KU Leuven Institute of Astronomy is involved very closely in the calibration efforts of the MRS and is committed in maximising the impact of MRS science.
  • One of the major systematic effects impacting the calibration of the MIRI MRS is caused by the coherent reflection of light inside the MRS detector layers. The layers behave as efficient Fabry-Pérot etalons and introduce a 30% sinusoidal modulation, termed fringing, on the MRS spectral baseline. Fringes are very sensitive to the illumination pattern on the detector, and although a lot of work has been invested in removing them from the MRS spectra empirically, it is theoretically possible to model and use the fringes in the spectral dimension to detect sources that are spatially unresolved. The goal of this PhD project is to 1) model the fringes on the detector based on MIRI ground-based point source observations, 2) develop a new method for detecting unresolved nearby companions using the MRS fringes, 3) investigate whether the flux of two unresolved nearby companions can be disentangled using a fringe forward model. The selected PhD candidate will participate in the JWST/MIRI commissioning phase during the first six months after launch, and will also be able to work on MIRI MRS Guaranteed Time Observations, acquired during the exciting first year of JWST operation in orbit. The candidate will join the MIRI European Consortium, under the supervision of Dr. Ioannis Argyriou, Dr. Bart Vandenbussche and Prof. Denis Defrère. (S)he will be part of the MIRI European Consortium and work as part of an international network of collaborators in Europe, the UK, and the US.


PhD applicants must hold a M.Sc. degree in physics, astrophysics or mathematics or else own an equivalent diploma. The degree must be dated at the latest one month before the position can be taken up. Expertise in signal processing, python programming, and astrophysics is an asset but not a requirement. Proficiency in English is required.


The selected PhD student will be offered a 2-year contract, once renewable with 2 more years after positive evaluation. The salary will be commensurate to the standard scale for PhD students at KU Leuven; it includes social and medical insurance as well as pension rights. The foreseen starting date is October 1st 2021 but can be negotiated. The successful PhD applicant will have to register at, and comply with, the regulations of the Arenberg Doctoral School of KU Leuven. Good command of the English language is a requirement. The successful PhD applicant will follow a doctoral programme including personal training in management, science communication, and teaching. As part of the doctoral requirements, the PhD student will have to take up a teaching task of at maximum 4 hours per week in one of the Bachelor (in Dutch) or Master (in English) programmes. PhD students at IoA are also required to perform at least one observing run of 10 nights per year at the Mercator Telescope for the pooled IoA long-term monitoring programmes.


To apply for this position, please follow the application tool and enclose

  • Full CV, with a publication list (if relevant) and contact details of two reference persons who would be prepared to send confidential recommendation letters;
  • A statement of interest (max. one page);
  • A summary of the research experience (max. 2 pages);
  • Full list of credits and grades of both BSc and MSc degrees (as well as their transcription to English if possible). If you haven’t finished your degree yet, just provide us with the partial list of already available credits and grades.
  • Further information on the position and on the project may be obtained by contacting the promotor Prof. Denis Defrère and the supervisor Dr. Ioannis Argyriou by email (denis.defrere@kuleuven.be / ioannis.argyriou@kuleuven.be ). You may also contact Dr. Clio Gielen for questions. tel.: +32 16 37 46 28, mail: clio.gielen@kuleuven.be.

You can apply for this job no later than May 15, 2021 via the online application tool

KU Leuven seeks to foster an environment where all talents can flourish, regardless of gender, age, cultural background, nationality or impairments. If you have any questions relating to accessibility or support, please contact us at diversiteit.HR@kuleuven.be.

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