Starting September 1, 2010
Deadline for applications : June 1, 2010

T1: Measuring magnetic fields in proto-planetary discs: a high resolution search for polarized emission in the millimeter domain.

Magnetic fields are believed to play an essential role in the physics of accretion which controls the star and planetary system formation. Measuring them in the proto-planetary discs which surrounds young stars is a challenge which has never been achieved so far. Although the alignment mechanism remains a very debated question, magnetic field directions can be traced by measuring the polarized thermal emission from dust grains at mm wavelength. On the other hand, magnetic field strengths can be measured by the Zeeman effect in suitable molecules, like CN and C2H. For discs, the latter aspect remains out of reach of current instruments, and must await the giant interferometer ALMA to become operational. However, the advent of polarization capabilities at the IRAM Plateau de Bure interferometer now allows us to reach the required sensitivity level to measure the polarization of dust continuum emission in discs. The mm domain is ideal for such studies, better than the sub-mm domain as the polarization can be suppressed at higher frequencies because of the larger opacities. Furthermore, the Zeeman aspect is testable not in discs, but in massive dense cloud cores. In collaboration with V.Pietu (IRAM), astronomers at LAB have started to develop the required specific observing techniques and data analysis method, and selected a number of potential candidate sources.

The successful candidate will take the lead in the overall project, starting with continuum observations and data analysis. Aspects concerning the Zeeman effect will be studied from an observational strategy and data analysis point of view. The candidate must have experience in radio observations, either in interferometry or polarization.

The Orion Nebula is one of the most studied regions in the sky, and the closest region to the Sun for massive star formation. At the very center of the Orion protocluster, the Orion Kleinmann-Low nebula is an atypical region which harbours one of the most luminous embedded IR sources in such a region (105 Lsol). Several components (Hot Core, Compact and Extended Ridges), IR sources and radio sources are associated with Orion-KL. A unique feature is the high speed shocked gas escaping from the center, which looks like the result of an explosive event. In this complex region, thermal or shock-induced release of grain mantle ices have been proposed as a cause of the rich chemistry, including several species of possible prebiotic importance.
Radio interferometric observations have led to high resolution maps (~1-2"). From a set of spectral maps covering 2GHz, we have made a detailed analysis of methyl formate distribution and temperature. We propose to analyse the distribution of other complex molecules from the same set of data 1) to constrain chemical models of their formation through grain surface or gas phase processes, 2) to relate molecule properties to the young or still forming stars, 3) to elucidate the action on chemistry of the recent (~500-1000 yr) explosive event proposed to have taken place at the heart of the nebula.

This work will take place in the context of the preparation for ALMA and the first Herschel/HIFI observations, on which members of our team are working. An interesting coupling of interferometric and HIFI Orion KL observations is foreseen, for example for water and dimethyl ether which are detected in both sets of data. Background appreciated : radioastronomy, interferometry, molecular spectroscopy, star formation. A working knowledge of the Gildas software is a bonus.

T3: Herschel M33 extended survey. A study of molecular cloud and star formation in M33.

The first step in the formation of a star is the formation of a molecular cloud which will subsequently fragment and form pre-stellar cores which then collapse under their own gravity. The Herschel satellite was launched on May 14, 2009 and makes possible studies of the interstellar medium (ISM) at an unprecedented sensitivity and resolution both in line and continuum emission throughout the Far-IR and submm domain. The Herschel M33 Extended Survey (HerM33ES): star-formation interplay with the ISM-Key Project is a detailed study of the nearby, metal-poor spiral galaxy M33, ideally suited for a study with Herschel of the dependence of the star formation characteristics on the physical conditions across the spatially resolved galactic disk. The major gas cooling lines, notably [CII], H2O, [OI], [NII], and [NIII] will be measured as well as the dust spectral energy distribution, using all three instruments on-board Herschel: HIFI, PACS, and SPIRE. At a distance of 840kpc, the individual molecular and atomic clouds can be resolved. A complete description of the HerM33ES project can be found here. M33 is a small, blue, gas-rich, and chemically young spiral galaxy. As such, it represents a stepping-stone towards both nearby Dwarf Irregular galaxies, which have much lower chemical abundances, and distant objects which share most of these properties.

The Bordeaux part of the HerM33ES collaboration (40 members, 10 countries) leads the observations of CO and HI in M33 and the molecular cloud formation part of HerM33ES. The HI observations have been completed and reduced but contain immensely more information than has appeared in the publications. The CO observations are mostly complete but still in progress and the post-doc would be expected to participate in these observations using the IRAM telescope near Granada, Spain. Depending on the scientific interests of the post-doc, a broad spectrum of subjects can be treated with these data, ranging from the dynamics of the ISM to the diffuse emission and how it varies with galactocentric distance. Several fields have also been observed at high resolution with the IRAM interferometer on the Plateau de Bure, allowing a study of several molecular clouds at a scale similar to observations in our own galaxy. The detailed HerM33ES data, coupled with the high-resolution CO and HI observations, are intended to provide a well-resolved view of the atomic-molecular phase changes and their relation to star formation. During the postdoctoral position, ALMA will open for "a early science" observations and we plan to participate via observations of molecular clouds in M33 and/or other Local Group galaxies.

T4: Astrometry and spectroscopy of open clusters and young associations for probing the galactic disc in the perspective of Gaia.

Open clusters (OCs) are essential as building blocks of the galactic disc and tracers of its kinematics and chemistry. They also constrain stellar formation and evolution theories. The ESA satellite Gaia will revolutionize the topic, providing a comprehensive census of OCs up to 5kpc with accurate distances as well as memberships from proper motions. Our group is currently involved the determination of the physical properties of OCs and associations and also in studies of stellar kinematics and chemistry across the galactic disc. We are seeking a postdoctoral fellow to lead a research programme which will take advantage of our astrometric and spectroscopic observations of OCs and associations and prepare for the scientific exploitation of the Gaia catalogue. Themes interesting our team include: the determination of the detailed chemical composition of open clusters from high resolution spectroscopy, the age-metallicity relation and metallicity gradient in the galactic disc, and the age determination of stellar systems. The precise topics will be tailored to the inclinations and expertise of the successful applicant. The postholder will be expected to contribute to the scientific preparation of Gaia, in which the LAB is involved.