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Preparation to the cosmological analyses with the legacy survey of space and time (LSST) of the Vera Rubin Observatory (VRO): Characterization of the atmospheric absorption (H/F)

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    First Stage Researcher (R1)
    07/05/2021 23:59 - Europe/Brussels
    France › MONTPELLIER


The LUPM is an UMR (Unité Mixte de Recherche) located on the campus of the Faculty of Sciences (FdS) of Montpellier. Two CNRS institutes supervises the LUPM: INSU for astrophysics and IN2P3 for high energy particle physics. The proposed phd subject on astroparticles, astrophysics and cosmology deals with the three research teams of the LUPM, with experimental, theoretical and multidisciplinary contributions:
(i) The LSST is a major project of IN2P3. Cosmology with LSST, proposed as the finality of the thesis, is part of the continuity of the major astroparticle projects of the LUPM such as Fermi and HESS for the research of dark matter.
(ii) The new proposed photometric calibration will be of an unprecedented precision. It will allow advances in stellar astrophysics developed in particular at LUPM.
(iii) The proposed characterization of the atmosphere is directly linked to the activities of the LIDAR developed in the laboratory for the international experiments HESS and now CTA. Collaborations are planned with the “Maison de la Télédétection” with which the project leaders are already discussing nanostatellite-type projects dedicated to earth observation in collaboration with the University of Sciences and Techniques of Hanoi (USTH).
(iv) Finally, the themes addressed are directly linked to the teachings of the “Cosmos Field and Particles” and “Astrophysics” masters of the FS.

For any additional question please contact eric.nuss@umontpellier.fr and bertrand.plez@umontpellier.fr.
• Location: Astro-particles, Astrophysics and Cosmology group at LUPM, Montpellier University, France.
• Starting October 1st, 2021, or as soon as possible after this date.
• Duration: 3 years, standard duration for a french PhD.

Key Requirements:
Ideally, the successful applicant:
• will hold a masters degree (or equivalent) in physics with knowledge in the related field of research: detector physics, astrophysics, cosmology, astro-particle physics, ...
• will have experience in data acquisition and analysis, and programming as python, C++, ...
• should also have excellent English or French written and oral skills,
• as well as good team-working abilities.
Additional qualifications:
• experience with Linux operating systems,
• experience working with laboratory equipment and electronics, data acquisition,
• experience with statistical analysis of large data set.

Why should you apply?
• working in an international, creative and highly motivated environment,
• cutting-edge research topics with high application potential,
• Working in a multidisciplinary research team,
• with a stimulating and friendly supervising and mentoring environment,
• unique research facilities,
• training and development possibilities (seminars, workshops, conferences, ...),
• software and physics skills training.

• assembling, testing, characterizing and operating an experimental setup for testing infrared cameras for astrophysics,
• data and image analysis,
• atmospheric modelling and correlation between thermal infrared sky measurements and stellar optical photometry,
• cooperation with other research institutions on developing a subsystem for the photometric calibration of the LSST, taking part in data acquisition and analysis,
• publication of scientific papers, presenting their work at international meetings, workshops and conferences, visits and collaboration with other institutions, taking part in writing reports.
• implication of your results on LSST cosmology

Please include the following information with your application:
• contact details and personal data,
• copy of the highest degree,
• language skills,
• contact details for 2 or 3 references. Your academic referees should send us recommendation letters directly via email.

In addition, please include the following documents:
• cover letter describing your motivation and interest for the project,
• Curriculum, including degrees and other completed courses, work experience

Description of the project, context and motivations:
The Legacy Survey of Space and Time (LSST) will observe from 2023 and for 10 years the entire sky of the southern hemisphere with unprecedented precision [1,2,3].
This makes it possible, for example, to detect a large number of supernovae up to great distances and thus to characterize dark matter and energy. This major scientific objective of modern cosmology is nevertheless dependent on the possibility of performing photometric measurements with an accuracy of around 0.1%, while the best current measurements are of the order of 1%. Few teams in the world are engaged on this difficult and original road. For 5 years our team from LUPM (Univers et Particules laboratory in Montpellier) has been collaborating with teams from LPNHE and IJCLab (Paris), CPPM (Marseille) and OHP [4], in order to develop a method and instrumentation to meet this challenge. An American team from Harvard specializing in measuring instrumental transmission from telescopes joined us recently.

The idea, called “StarDice” [5], consists in using a light source that we observe with the same telescope as the stars whose flux we want to measure with precision. This makes it possible to calibrate very exactly the effect of the measurement chain and to determine the absolute flux of the stars measured. The ground source consists of a series of LEDs of different colors stabilized at better than 0.03% [5] that we observe as artificial stars. The standard stars thus measured by StarDice will then serve as calibrators for the LSST.

In 2019 we were able to show that the concept allows a photometric calibration of stars observed at the % level, thanks to a prototype system which operated in real conditions [6], which was the objective set for this first phase. This work, which was at the center of a thesis carried out at LPNHE [7], in particular highlighted that, beyond the necessary technical improvements, it is crucial to better characterize the atmosphere and its vertical and horizontal transmission. In particular, perturbations are caused by fine cirrus clouds which may remain invisible to conventional detection systems but which disturb stellar flux measurements beyond what is tolerable.
Following this success, we moved at the end of 2019 to phase 2 of the project, aiming at the nominal characterization of standard star photometry, which must be effective as soon as possible after the start of the LSST in 2021.

The final version of the system is therefore currently under development and being installed: a larger diameter telescope, new camera and filters, robotic piloting system ...
With these new performances, the main difficulty residing in the precise estimation of the vertical atmospheric absorption, between the instrument and the measured stars, and horizontal, between the instrument and the LEDs, becomes all the more crucial. We have therefore initiated interdisciplinary work with researchers from LATMOS (Paris) and OHP, where there are many instruments for measuring the atmosphere. Our team at LUPM is in charge of implementing a new infrared measurement instrumentation of the atmosphere which will allow the precise measurement of absorption linked to cirrus clouds. This original method will constitute the first part of the thesis work that we propose. The domes of the University of Montpellier and their equipment constitute a unique opportunity to carry out this work. The thesis will continue with an in-depth characterization of the atmosphere making the link between atmospheric and climatic science and astronomical photometric calibration. The method consists in repeatedly measuring the flux of stars stable over time and the flux of the calibration source (LEDs).
These observations, made over a large number of observation nights, are used to determine the temporal variations in atmospheric transmission. However, this does not make it possible to achieve the target precision of 0.1%. To do this, knowledge of certain atmospheric variables such as pressure and temperature on the ground, the quantity of precipitable water vapor, aerosols, and absorption by cirrus clouds must be integrated into the parameter adjustment method. This is an open question since it involves improving by a factor of ten the performance of models currently used in atmospheric sciences. This work is at the heart of the second part of the thesis. The final objective is to produce a standard photometric measurement of stars with the precision required for LSST, i.e. a factor 5 to 10 times better than what is currently achieved by the few teams working on the subject, in particular on the Hubble Space Telescope [6].
This work will have a major impact on the scientific return of the LSST both in cosmology and in other themes such as stellar astrophysics which are the final part of the thesis.

[1] https://www.lsst.org/
[2] https://arxiv.org/abs/0805.2366
[3] https://arxiv.org/abs/0912.0201
[4] http://www.obs-hp.fr/welcome.shtml
[5] N. Regnault et al., A&A 581, A45, 2015
[6] M. Betoule et al., https://astronomy2018.univie.ac.at/abstractsFM12/#FM12abstr10
[7] F.Hazenberg PhD thesis (in French), "Calibration photométrique des supernovae de type Ia pour la caractérisation de l'énergie noire avec l'expérience StarDICE" : http://www.theses.fr/2019SORUS142
[8] R.C. Bohlin et al., AJ 158, 211, 2019

More Information

Required Research Experiences


Offer Requirements

    Physics: Master Degree or equivalent
    FRENCH: Basic
Work location(s)
1 position(s) available at
Laboratoire univers et particules de Montpellier

EURAXESS offer ID: 630145
Posting organisation offer ID: 20871


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