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GEN-F213-2 (GEN-SCI-034) www.onera.fr PROPOSITION DE POST-DOCTORAT Référence : PDOC-DOTA-2018-01 (à rappeler dans toute correspondance) Laboratoire d’accueil à l’ONERA : Domaine : PHYSIQUE Lieu (centre ONERA) : Chatillon Département : Département d’Optique et Techniques Associées Unité : Haute Résolution Angulaire Contacts : Thierry Fusco [email protected] 0662484836 Intitulé : Maximizing the Scientific Return of AO assisted 3D-Spectroscopy instruments Mots-clés : Post Processing, Adaptive optics, wide Field of View, 3-D spectroscopy, Laser guide stars, PSF reconstruction Contexte : Adaptive Optics (AO) aims at compensating the quickly varying aberrations induced by the earth's atmosphere, and restoring images at the diffraction limit of current large ground based telescopes. Most of the current AO systems, however, require a bright and/or close reference source, and as such are well-suited for observations of relatively bright compact objects. For instance, in the past 20-years, AO observations have brought major discoveries in the study of the massive black hole at the center of our Galaxy or the first images of exo-planets [ref-1,2], but only a handful number of major extra-galactic studies in cosmological fields, as they are usually lacking of bright enough reference stars [ref-3]. A new generation of AO systems, a.k.a. Wide Field AO (WFAO), is addressing this limitation by significantly increasing the field of view of the AO-corrected images, and/or the fraction of the sky that can benefit from such correction [ref-4]. Very recently, such capability has been brought to its apogee by coupling the ESO-operated Adaptive-Optics Facility (AOF) with the cutting-edge instrumentation of the MUSE integral-field (3D) spectrograph [ref-5]. This achievement only represents a first step! Within less than a decade the world will see a new generation of telescopes with diameters up to 39m. Called the Extremely Large Telescopes (ELTs), the scientific potential of these giants relies on integrated WFAO capabilities, fully operating from first light. To what is currently AOF+MUSE, the ESO HARMONI instrument [ref-6] will produce the most sensitive and highest angular resolution 3D cubes of the deep Universe. The success of scientific AO-assisted 3D spectroscopy programs depends on meeting highly challenging levels of accuracies. In order to disentangle the instrument contribution from the intrinsic and tiny signature of the astrophysical signal in the observed data, one requires a precise knowledge of the instrumental spectral response (so called Line Spread Function - LSF) and spatial response (so-called Point Spread Function - PSF). While the first one can usually be precisely calibrated, the PSF delivered by AO systems has an unfavourable reputation, based on its complex shape and its spatial, spectral and temporal variability [e.g. ref-7,8]. But what is the impact of a variable PSF, and to what level of accuracy should we know it? The answer obviously depends on the science cases considered, and a mis-knowledge of the actual PSF has been identified as a critical limitation by several authors. For instance, Kamann et al. [ref-9] show that reaching an accuracy of 5% to 10% on the PSF modeling allows recovering the spectrum of a 10-times fainter star in a close binary configuration. Accuracy down to the percent level allows the same analysis for 100-times fainter stars. For nuclear stellar clusters, Thatte et al. [ref-10] show how the stellar kinematic signatures of intermediate mass black holes can be misinterpreted

PROPOSITION DE POST-DOCTORAT - w3.onera.frw3.onera.fr/formationparlarecherche/sites/w3.onera.fr.formationpar... · To what is currently AOF+MUSE, ... how the stellar kinematic signatures

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GEN-F213-2 (GEN-SCI-034)

www.onera.fr

PROPOSITION DE POST-DOCTORAT

Référence : PDOC-DOTA-2018-01 (à rappeler dans toute correspondance)

Laboratoire d’accueil à l’ONERA :

Domaine : PHYSIQUE Lieu (centre ONERA) : Chatillon

Département : Département d’Optique et Techniques Associées

Unité : Haute Résolution Angulaire

Contacts : Thierry Fusco – [email protected] – 0662484836

Intitulé : Maximizing the Scientific Return of AO assisted 3D-Spectroscopy instruments

Mots-clés : Post Processing, Adaptive optics, wide Field of View, 3-D spectroscopy, Laser guide stars, PSF reconstruction

Contexte : Adaptive Optics (AO) aims at compensating the quickly varying aberrations induced by the earth's atmosphere, and restoring images at the diffraction limit of current large ground based telescopes. Most of the current AO systems, however, require a bright and/or close reference source, and as such are well-suited for observations of relatively bright compact objects. For instance, in the past 20-years, AO observations have brought major discoveries in the study of the massive black hole at the center of our Galaxy or the first images of exo-planets [ref-1,2], but only a handful number of major extra-galactic studies in cosmological fields, as they are usually lacking of bright enough reference stars [ref-3].

A new generation of AO systems, a.k.a. Wide Field AO (WFAO), is addressing this limitation by significantly increasing the field of view of the AO-corrected images, and/or the fraction of the sky that can benefit from such correction [ref-4]. Very recently, such capability has been brought to its apogee by coupling the ESO-operated Adaptive-Optics Facility (AOF) with the cutting-edge instrumentation of the MUSE integral-field (3D) spectrograph [ref-5].

This achievement only represents a first step! Within less than a decade the world will see a new generation of telescopes with diameters up to 39m. Called the Extremely Large Telescopes (ELTs), the scientific potential of these giants relies on integrated WFAO capabilities, fully operating from first light. To what is currently AOF+MUSE, the ESO HARMONI instrument [ref-6] will produce the most sensitive and highest angular resolution 3D cubes of the deep Universe.

The success of scientific AO-assisted 3D spectroscopy programs depends on meeting highly challenging levels of accuracies. In order to disentangle the instrument contribution from the intrinsic and tiny signature of the astrophysical signal in the observed data, one requires a precise knowledge of the instrumental spectral response (so called Line Spread Function - LSF) and spatial response (so-called Point Spread Function - PSF). While the first one can usually be precisely calibrated, the PSF delivered by AO systems has an unfavourable reputation, based on its complex shape and its spatial, spectral and temporal variability [e.g. ref-7,8].

But what is the impact of a variable PSF, and to what level of accuracy should we know it? The answer obviously depends on the science cases considered, and a mis-knowledge of the actual PSF has been identified as a critical limitation by several authors. For instance, Kamann et al. [ref-9] show that reaching an accuracy of 5% to 10% on the PSF modeling allows recovering the spectrum of a 10-times fainter star in a close binary configuration. Accuracy down to the percent level allows the same analysis for 100-times fainter stars. For nuclear stellar clusters, Thatte et al. [ref-10] show how the stellar kinematic signatures of intermediate mass black holes can be misinterpreted

GEN-F213-2 (GEN-SCI-034)

because of percent level inaccurate PSF models. For extragalactic science, Davies et al., Epinat et al. [ref-11,12] show that a 10% PSF mis-knowledge can bias the rotation curves extraction for high-z galaxies, and increase the error on the maximum velocity determination.

Having access to an accurate PSF model associated with each 3D-data cubes would represent a major leap toward optimizing the scientific return of current and future AO-assisted instruments.

However, post-processing of partially corrected AO data is an Achilles' heel since the reconstruction of the AO-PSF is an extremely complex task to accomplish. Different PSF estimations methods have been considered over the past years [e.g. ref 13-14], but the rare on-sky demonstrations of PSF reconstruction is a clear sign of the complexity of the whole process [e.g. ref 15].

Scientific Objectives: The goal of the project is precisely to propose, test, validate and distribute PSF estimation algorithms for AO-assisted 3D spectroscopy observations. We aim at an integrated approach where not only the PSF is provided, but the estimated PSF are coupled with dedicated reduction tools already available for the project. The optimization of the whole data-processing chain is carried with 3D-spectroscopy specialists. The scientific impact and critical feedback on the process is evaluated with astronomers, on dedicated science observations addressing a set of representative science needs.

Description du sujet : The subject, over the nominal 2 years (1+1) duration, will be divided in 3 main parts (or workpackages). This repartition (which follow a logical timeline) allows focusing on various level of maturity and risk levels.

WP1 – Delivering an operational tool for MUSE PSF-Reconstruction + AOF-WFM

The AOF can work with two modes; namely the WFM (Wide-Field Mode) providing partial AO-corrections over a 1 arcminute Field of View (FoV), and the NFM (Narrow-Field Mode) providing diffraction limited corrections over a 10 arcsec FoV. The AOF-WFM mode represents the first step that our program will tackle. The advantage of this mode is that the AO-correction level provided being modest, only first order terms have to be taken into account in the PSF modeling. In other words, analytical PSF profiles with only few degrees of freedom (e.g. Moffat or Lorentzian distribution) can already provide a good PSF approximation. The estimation of the PSF free parameters can then be linked to system and environment parameter estimation such as the turbulence strength or its vertical distribution. Indeed, based on early data obtained during the MUSE commissioning, we have shown that there is almost one to one error propagation between the turbulence strength estimation (r0) and the PSF parameters (e.g. EE, FWHM). Our group and collaborators (A. Guesalaga, C. Béchet) have been leading effort toward efficient and accurate atmospheric parameter estimation [ref-16], and the first milestone of WP1 will be to validate and turn to operational those tools for the AOF. From this bedrock, we will build and validate a PSF estimation tool based on precursor work developed with the main actors of this project [ref-17]. The second milestone of WP1 will be to incorporate the PSF information in state-of-the-art post-processing tools (e.g. GalPak3D – N. Bouché, B. Epinat [ref-18]), and critically assess the gain brought by the PSF knowledge on dedicated science programs. Identified science programs cover deep extra-galactic surveys (R.Bacon, B. Epinat), gravitational lensing (J. Richard) and dense stellar clusters (J. Vernet, N. Thatte). But as the PSFs will be made available to the whole MUSE community, we expect a larger impact and feedback from the science users. In conclusion WP1 is low-risk/high-gain step, which will set the operational tools for more ambitious developments in WP2 and WP3. The maturity, criticality and international exposure of the work to be done should ensure a high publication and reward rate.

WP2 – Extension of the method to MUSE + AOF-NFM

The main challenge for modeling the PSF provided by the AOF-NFM will be precisely accounted for all the second order effects that were neglected in WP1. In other words, part of the formalism developed in WP1 will have to be revisited, and simple PSF model will not stand anymore. This WP then plan for a full 3D PSF (both spatial and spectral) reconstruction. Our team has initiated some

GEN-F213-2 (GEN-SCI-034)

pioneer work toward this goal, and we have proposed several approaches based on the AO telemetry data [ref-19,20]. As a first milestone of WP2, we will benchmark the different approaches on numerical simulations, benefiting from a full End-2-End platform available at LAM. As a second milestone, the proposed tools will be tested using on-sky data acquired during the MUSE+AOF-NFM commissioning. We also anticipate the need for better atmospheric parameter estimation models, which will be extended from the ones tested in WP1.

WP3 – Toward ELT and HARMONI

The last step of the work will be to extrapolate the results to ELTs scales. By means of simulations, and based on the experience gained with the on-sky data, we will study how the new developed methods may be applied to WFAO system for ELTs. Our main target is HARMONI, which by many aspects provides a logical continuity of the AOF+MUSE work. The first milestone of WP3 will then be to develop the set of numerical simulations required to accurately reproduce the ELT+HARMONI instrument. The tools developed during WP2 will be extended to account for ELT specificities (e.g. segmented pupil) and coupled with a numerical model of the HARMONI instruments, provided by Oxford (N. Thatte, M. Tecza). This tool, once validated, will be used to test and propose efficient PSF modeling algorithms: this is our second milestone. Finally, as the third milestone of WP3, we will extensively use this integrated tool to prepare and better constrain the ambitious science cases of HARMONI. This activity will be developed in close collaboration with B. Neichel and T Fusco, who are respectively the HARMONI Co-I leadership, and is responsible for its AO system developments.

Fournitures et retombées attendues : The final objective of the post doc is to develop a set of data reduction and analysis tools for AO-assisted 3D-spectroscopic instruments. This objective is achieved through proof-of-concept PSF reconstruction using MUSE as host instrument and offered to its user community through the standard data-reduction pipeline. These tools are paving the way for the preparation of the ELT 1st light instruments.

Collaborations extérieures : Laboratoire d’astrophysique de Marseille (LAM), Centre de Recherche en Astrophysique de Lyon (CRAL), European Southern Observatory (ESO), Oxford University, Université de Porto

Bibliography :

1. « Ten years of VLT adaptive Optics » 11. Davies et al., 2007, ESO calibration workshop 2. Chauvin et al., 2017, A&A, accepted 12. Epinat et al., 2010, MNRAS, 401, 4 3. Damjanov et al., 2011, PASP, 123, 901 13. Véran et al., 1997, JOSAA, 14, 11 4. Neichel et al., 2014, MNRAS, 440, 2 14. Steinbring et al., 2005, PASP, 117, 834 5. « Cutting-edge Adaptive Optics Facility Sees First Light »

15. Jolissaint et al., 2012, AO4ELT2

6. Thatte et al., 2014, SPIE, 914725 16. Guesalaga et al., 2017, MNRAS, 465, 2 7. Fusco et al., 2000, A&As, 142, 149 17. Villecroze et al., 2012, SPIE, 84475EW 8. Zieleniewski et al., 2013, AO4ELT3 18. Bouché et al., 2015, AJ, 150,3 9. Kamann et al., 2013, A&A, 549, 71 19. Martin et al., 2016, JATIS, 2 10. Thatte et al., 2017, AO4ELT5 20. Béchet et al., 2017, AO4ELT5

Durée : 12 mois, éventuellement renouvelable une fois

Salaire net : environ 25 k€ annuel

PROFIL DU CANDIDAT

Formation : PhD in Physics, Compétences souhaitées :

Astronomy, instrumentation

Adaptive Optics, post processing