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WaterStars, from observation to experiments on water in space | Closing date: 2021-10-01 Contact: Fabrice Herpin |
Understanding the excitation of water in evolved stars implies knowing the collision rates for pure rotational transitions within the first four excited vibrational states (v1=1, v2=1, 2 and v3=1) as well as the rotational transitions between the ground state and these excited states. The first objective is therefore to obtain these collision rates. The second is to include these in an advanced radiative transfer code to reproduce the ALMA observations (ATOMIUM consortium). | ▸ more | Scientific subject: Water is the third most abundant molecule in the interstellar medium. It has been observed in various objects, but it is only in the extended atmosphere of the envelope of O-rich evolved stars that the very rich spectrum of rotational, vibrational and ro-vibrational transitions of water is observed, and sometimes in surprisingly excited energy states. To understand the excitation of water in these environments, it is necessary to model the excitation of water not only by the radiation from the central star and by radiative coupling with the background radiation, but also by collisions with its most abundant partners (H2, He, H, e-). This implies knowing the collision rates for pure rotational transitions within the first four excited vibrational states (v1=1, v2=1, 2 and v3=1) as well as the rotational transitions between the ground state and these excited states. The first objective is therefore to obtain these collision rates. The second is to include these in an advanced radiative transfer code to reproduce the ALMA observations (ATOMIUM consortium, (https://fys.kuleuven.be/ster/research-projects/aerosol/atomium/atomium) and interpret them. The crossed molecular beam experiment in Bordeaux allows the study of inelastic collisions down to very low collision energies, where quantum effects may be observed. The experimental studies will be used to validate theoretical methods in order to provide reliable data to astrophysicists. The first objective of the thesis will be to extend our first experimental studies on H2O and D2O + H2 to vibrationally excited water molecules. To model the emission of water lines from highly excited levels we will use a radiative transfer code published by Gray, Baudry et al (2016). The next step will be to include the results of the experimental or theoretical work done at the ISM, i.e. to incorporate the new collision rates, and to extend the code to the first four vibrational levels of water in an attempt to model all the lines observed in ATOMIUM.
Additional information: The Ph.D. student will work mainly at ISM, together with Fabrice Herpin (LAB) and Astrid Bergeat (ISM) and other WATERSTARS team members, in close collaboration with the ATOMIUM team. More information on the Laboratoire d?Astrophysique de Bordeaux and Institut des Sciences Moléculaires can be found at https://astrophy.u-bordeaux.fr and http://www.ism.u-bordeaux.fr, respectively. The 3-year paid thesis contract requires a Master's degree in Astronomy, Physics or Physical Chemistry (or equivalent), obtained before the start of the contract. The start date of the thesis will be between 1 October 2021 and 1 March 2022. Applications should include a brief description of research interests and a summary of previous experience relevant to the subject, a CV, copies of Master's and Bachelor's degrees, Master's certificates or transcripts and internships, as well as contact details of the Master's supervisor and internship supervisors. Applications are open until the vacancy is filled and should be sent to Fabrice Herpin (fabrice.herpin @ u-bordeaux.fr) or Astrid Bergeat (astrid.bergeat @ u-bordeaux.fr). A complete description of the position can be found at https://www.ism.u-bordeaux.fr/spip.php?article354
Skills required: Practical experience with spectroscopy, experimental kinetic techniques, use of lasers, programming language, radiative transfer calculations or analysis of observational data will be considered a merit.
Funding details: secured financing (ANR Ph-D fellowship)
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