Events & Seminars

SĂ©minaire de Lucas Einig & Pierre Palud

Jeudi 18 janvier 2024 Ă  15h, salle J.F. Denisse de l’Observatoire de Paris

Efficient deep learning approaches to denoise radio astronomy line cubes and emulate astrophysical models by Lucas Einig (IRAM & Gipsa lab)

Surveys of the atomic and molecular gas produce huge position-position-velocity data cubes over wide fields of view with varying signal-to-noise ratios (SNRs). Besides, inferring the physicals conditions of the interstellar medium from these data requires complex and often slow astrophysical codes. The overall challenge is to reduce the amount of human supervision required to analyze and interpret these data. I will describe two applications of deep learning to tackle this challenge.

1/ I will first introduce a self-supervised denoising method adapted to molecular line data cubes (Einig et al. 2023) based on autoencoder neural networks. This method allows to recover the low SNR emission without affecting the signals with high SNR and surpasses current state of the art denoising tools based on multiple Gaussian fitting of line profiles.

2/ I will present a supervised method to derive fast and light neural-network based emulations of a model from a grid of precomputed outputs (Palud et al. 2023), using the Meudon PDR code as a template. This approach outperforms usual methods in terms of accuracy, memory space and calculation time.

Inferring physical conditions with a Bayesian approach and spatial regularization by Pierre Palud (laboratoire CRIStAL Centrale Lille & LERMA)

New facilities at the IRAM, ALMA and the JWST now produce large hyper spectral cubes containing large fields of view with high spatial resolution and the intensity of multiple lines.
One key use of these rich datasets consists in estimating maps of the physical conditions of these regions (e.g., pressure, intensity of incident radiation field, etc.).
The statistical methods that are common in interstellar medium studies often fail to produce physically exploitable maps due for instance to great variations of signal-to-noise-ratio within the cube.
In this presentation, we present a new state-of-the art statistical tool to perform this inversion.
It relies on a physically based spatial regularization to provide smooth maps of physical parameters, and on a Bayesian approach to quantify the uncertainties associated to the estimation.

Séminaire de Helgi Hrodmarsson, Marion Zanesse & Dominique Bocklée-Morvan

Lundi 09 Octobre Ă  14h30 – Salle de confĂ©rence au château de l’Observatoire de Meudon

Photodissociation and Photoionization in Space: Recent updates to the Leiden VUV Cross Section Database par Helgi Hrodmarsson (LISA)

OH as a probe of the warm water cycle in planet-forming disks observed with JWST par Marion Zanesse (IAS)

Observations comĂ©taires avec JWST: analyse de l’Ă©mission prompte de OH observĂ©e avec MIRI par Dominique Bockelee-Morvan (LESIA)

Abstract du séminaire de Helgi Hrodmarsson

VUV photons are important drivers of chemical processes in space. Thus, it is important to accurately characterize and constrain photorates in different radiation fields. This is done by utilizing photodissociation and photoionization cross sections of individual atoms and molecules which have been available in the Leiden VUV Photodissocation and Photoionization cross section database.[1] Experimental and theoretical advances in the past decade or so have allowed multiple new cross sections to be obtained, particularly photoionization cross sections of radicals. The database is hereby updated by including these more recent cross sections and is also expanded with several astronomically relevant species.[2] The cross sections have been used to calculate photodissociation and photoionization rates in several different radiation fields as well as from cosmic ray induced VUV fluxes. The reduction of rates in shielded regions has also been calculated as a function of dust, molecular and atomic hydrogen, atomic carbon, and self-shielding column densities. The relative importance of these shielding types is molecule/atom dependent, as well as the assumed dust absorbance. All the data are publicly available from the Leiden VUV cross section database.1The Leiden VUV cross section database has been updated with 14 new astrophysically relevant molecular species and 16 updates to previous entries. During this presentation I will give a brief introduction to cross sections, particularly the measurements of photoionization cross sections of radicals as well as photoabsorption and photodissociation cross sections which have been measured at the VUV beamline DESIRS at Synchrotron SOLEIL


[2] H. R. Hrodmarsson & E. F. van Dishoeck (2023), A&A, 675, A25.

SĂ©minaire d’Emmanuel Dartois et de Francois Dulieu

Lundi 22 Mai 14h30 – Salle Denisse (atelier) Ă  l’Observatoire de Paris

Influence of grain growth on ices spectroscopic profiles – Modelling for dense cores and disks

par Emmanuel Dartois (ISMO)

Interstellar dust grain growth in dense clouds and protoplanetary disks, even moderate, affects the observed interstellar ice profiles as soon as a significant fraction of dust grains is in the size range close to the wave vector at the considered wavelength. The continuum baseline correction made prior to analysing ice profiles influences the subsequent analysis and hence the estimated ice composition, typically obtained by band fitting using thin film ice mixture spectra. We explore the effect of grain growth on the spectroscopic profiles of ice mantle constituents, focusing particularly on carbon dioxide, with the aim of understanding how it can affect interstellar ice mantle spectral analysis and interpretation. Using the Discrete Dipole Approximation for Scattering and Absorption of Light, the mass absorption coefficients of several distributions of grains – composed of ellipsoidal silicate cores with water and carbon dioxide ice mantles – are calculated. A few models also include amorphous carbon in the core and pure carbon monoxide in the ice mantle. We explore the evolution of the size distribution starting in the dense core phase in order to simulate the first steps of grain growth up to three microns in size. The resulting mass absorption coefficients are injected into RADMC-3D radiative transfer models of spherical dense core and protoplanetary disk templates to retrieve the observable spectral energy distributions. Calculations are performed using the full scattering capabilities of the radiative transfer code. We then focus on the particularly relevant calculated profile of the carbon dioxide ice band at 4.27 μm. The carbon dioxide antisymmetric stretching mode profile is a meaningful indicator of grain growth. The observed profile toward dense cores with the Infrared space observatory and Akari satellites already showed profiles possibly indicative of moderate grain growth. The observation of true protoplanetary disks at high inclination with the JWST should present distorted profiles that will allow constraints to be placed on the extent of dust growth. The more evolved the dust size distribution, the more the extraction of the ice mantle composition will require both understanding and taking into account grain growth.

Que deviennent les atomes H et O qui interagissent avec les grains de poussière interstellaires ?

par Francois Dulieu (LERMA)

Environ un pourcent de la matière baryonique de notre univers local est sous forme de poussière interstellaire qui influence grandement le cycle de formation des étoiles et des planètes. Les grains de poussière ont en effet des propriétés radiatives singulières, mais également une rétroaction sur la phase gazeuse, ne serait-ce qu’en déplétant de cette dernière les éléments les plus lourds, lors des phases de refroidissement et de condensation, ou au contraire en libérant les molécules dans les phases de réchauffement.
Lors de ce séminaire je présenterai nos derniers résultats concernant l’interaction des atomes hydrogène et d’oxygène interagissant avec des molécules de coronène, utilisés comme archétypes de la poussière carbonée. Nous montrerons le rôle catalytique très puissant de ces très petites poussières pour convertir H en H2, et ce sur une grande plage de température (10-250K). Nous évaluerons la possibilité d’insérer les atomes d’oxygène dans les plans carbonés, et verrons enfin si, quand H et O sont combinés, l’insertion dans les grains ou la croissance des films moléculaires (glace d’eau) est favorisée.

François Dulieu, Emanuele Congiu, Saoud Baouche, et al. – LERMA CY Cergy Paris UniversitĂ©…

SĂ©minaire d’Asuncion Fuente & Alex Raga

Mardi 29 novembre – Salle du Conseil de l’Observatoire de Paris

A sulfur journey from molecular clouds to protoplanetary disks by Asuncion Fuente (OAN, Spain)
Sulfur is the tenth most abundant element in the Universe and is known to play a significant role in biological systems. Moreover, some sulfur compounds have been proposed as necessary catalysts to form amino acids in the interstellar medium. However, while the carbon and oxygen budgets have been extensively studied, sulfur is the only element whose gas-phase abundance is still uncertain by several orders of magnitude, hindering the usage of elemental sulfur abundance as a reliable tool to probe planet formation. This lack of information is due to the scarcity of observations and the still large uncertainties in the sulfur chemical network. This conference shows the state-of-the-art of the knowledge of sulfur chemistry in the interstellar medium, following sulfur evolution from  molecular clouds to proto-planetary disks.

Collisions of Herbig-Haro jets with dense obstacles by Alejandro Raga (ICN-UNAM, Mexico)
Low and intermediate mass young stellar objects (YSOs) have strong ejections in the form of collimated, bipolar jets. These so-called HH (Herbig-Haro) jets show structures that result from variabilities in the ejection, and from interactions between the jet and the surrounding (possibly structured) environment. Regions with many YSOs typically show jets deflected by collisions with other jets or with dense environmental cloudlets. In the field of jet/cloud collisions, the HH 110 jet is « the king”. This deflected jet has inspired the febrile mind of theorists, who have used it as an excuse for studying both analytic and numerical models of jet/cloud collisions. The problems of constant and time-variable jets « skipping » on the surface of the dense cloud and eventually drilling holes into the clouds have been studied. Recently, we have worked on the problem in which the cloud has a relative motion with respect to the jet source, leading to important changes in the dynamics of the jet/cloud interaction. This last work was in reparation for the observations of HH objects that were going to be made with the new James Webb Space Telescpe (JWST). A few days ago, the JWST obtained its first image of the HH 110 jet/cloud collision system. How does this image look? what does it tell us about this flow ? do the previous models survive the new observations? I am not sure about the answers to these questions, but I hope to have some answers for the date of this seminar.

SĂ©minaire de Thomas Bisbas

Jeudi 16 Juin 2022 – Salle de l’atelier de l’Observatoire de Paris

Title: The carbon cycle emission as a diagnostic tool for the interstellar medium state

Abstract: Carbon is one of the most abundant elements in the Universe and present to both local and distant galaxies. It can be found in three forms, known as the « carbon cycle »: ionized (C+), atomic (C), and molecular in the form of carbon monoxide (CO). Its chemical state is determined by the environmental parameters of the interstellar medium. Consequently, we can use the emission lines of the carbon cycle to estimate these environmental parameters, which ultimately shape the density distribution of the interstellar gas in galaxies. Through numerical modelling and comparison with observational data, I will discuss how each of the aforementioned line emissions can be used as a diagnostic of the chemical and dynamical state of the interstellar medium.

JournĂ©es de l’API Univers Froid

Mardi 24 mai – Salle des sĂ©minaires de l’IAP

Misha Haywood (GEPI)MIS, Ă©toiles jeunes et structure galactique 14h00
Philippe Salomé (LERMA)Radio Recombination Lines with NenuFAR14h15
Sylvie Cabrit (LERMA)Chocs & rétro-action14h30
Thibaut Paumard (LESIA)CubeFit : spectroscopie 3D régularisée du disque circumnucléaire Galactique14h45
Rosine Lallement (GEPI)MIS 3D15h00
Laurent Pagani (LERMA)COMs dans Orion KL & structure 3D de L13415h15
Franck Le Petit (LERMA)Modélisation des régions de photo-dissociation15h50
Emeric Bron (LERMA)Orion B & Machine Learning16h05
Xavier Michaut (LERMA)ExpĂ©riences de laboratoire – Jussieu16h20
François Dulieu (LERMA)ExpĂ©riences de laboratoire – Cergy : Interactions gaz-surface froides (sans apport Ă©nergie)16h35
Dominique Bockelée (LESIA)Comètes: perspectives JWST et radio16h50
Raphaël Moreno (LESIA)Atmosphères17h05

Double séminaire de Javier Goicoechea & Nicolas Biver

Jeudi 5 mai 2022 – 14h – Salle de confĂ©rence du château Ă  Meudon

  • Javier Goicoechea (CSIC Madrid) sur « Following the Sulfur trail in UV-illuminated molecular clouds” (14h)
  • Nicolas Biver (LESIA) sur  Â«Â Molecular composition and diversity of cometary atmospheres” (~ 15h30)

Tutoriel proposal ALMA

Mercredi 13 avril 2022 – 14h – Salle Danjon

Organisateurs : Raphaël Moreno, Philippe Salomé, Sylvie Cabrit