Andrea Chiavassa Ph.D. in Astrophysics

"Everything you can imaging is real" Pablo Picasso

Research

Computation of 3D simulations of cool stars with CO5BOLD (Freytag et al. 2002, Astronomische Nachrichten, 213-219) for star-in-a-box model (global model) and with Stagger-code (Nordlund, Stein et Asplund, Living Reviews in Solar Physics 2009, vol. 6, no. 2) for box-in-a-star (local model).

New generation of Red Supergiant simualtions to unveil the mass-loss mechanism

High numerical resolution / non-grey / grid of new stellar paramters

Click on the image to see a movie of the bolometric emerging intensity of the highest resolution simulation. Chiavassa, Freytag, Masseron & Plez 2011, A&A (ADS link)

Voyage over the surface of a supergiant. Click on the images to start the videos !!!!!!

3D Radiative Transfer code OPTIM3D (Chiavassa et al. 2009, A&A, ADS link) using three dimensional simulations in the star-in-a-box configuration (CO5BOLD) as input:

1) spectral synthesis --> to constrain the atmospheric dynamics, photometry, stellar parameters, abundances
2) intensity maps --> to constrain the granulation structure size, the limb darkening, the characterization of the hosted planets


Click on the image to see the convetion in the Hband. The Images have been computed with OPTIM3D for the IONIC - filter mountend at IOTA telescope	Click on the image to see the convetion in the Kband. The Images have been computed with OPTIM3D for the K222-continuum FLUOR filter wavelength 2.2 micron


Click on the image to see the convetion in TiO band at 6100-6600 A. The Images have been computed with OPTIM3D	Click on the image to see the convetion in CaI-H line. The Images have been computed with OPTIM3D


Click on the image to see the convetion with an instrumental convolution to the PSF of a 42 meters telescope in the optical region (GAIA G-band). These images can be qualitatively compared to the observations (image reconstruction). Done with OPTIM3D The simulation scaled to a distance of about 174.3 pc and an apparent diameter of 44.5 mas	Click on the image to see the convetion with an instrumental convolution to the PSF of a 42 meters telescope in the H band (IONIC filter). These images can be qualitatively compared to the observations (image reconstruction). Done with OPTIM3D The simulation scaled to a distance of about 174.3 pc and an apparent diameter of 44.5 mas


Click on the image to see the convetion at different wavelengths. Importance of the high spectral resolution in interferometry (H band) -> different features with respect to wavelength (computed with OPTIM3D)	Click on the image to see the velocity field in the red supergiants'atmospheres at 1.6 micron (computed with OPTIM3D)

Creating observables (visibility, closure phases, image reconstruction as a function of wavelengths and filters) to compare with interferometric observations at different wavelengths (VLTI-Amber/Midi/MATISSE/PIONER, CHARA, IOTA,...).

Data redution with VLTI-AMBER

Measurement and characterization of the convective pattern (granule size, surface contrast, timescales) of red supergiant stars.

Image reconstruction

Determination of the 1D - 3D models corrections on abundances, stellar parameters and velocity field at high resolution (top). Large spectral range computation for flux distributions, colors filters (red curves) and comparison to the observations (bottom)

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3D Radiative Transfer code OPTIM3D (Chiavassa et al. 2009, A&A, ADS link) using three dimensional simulations in the box-in-a-star configuration (Stagger-code, Nordlund, Stein et Asplund, Living Reviews in Solar Physics 2009, vol. 6, no. 2) as input:


Intensity maps computed at disk center and µ = 0.8, 0.6, 0.4 for a metal-poor K Giant simulation and integrated over the range 3500-9800 ˚A. The panels have individual scaling.	Determinations on the interferometric observables, limb darkening, characterization of the granulation pattern, and impact on hosted planet detection (Chiavassa et al. 2010, A&A, ADS link )


Determination of the 1D - 3D models corrections. Large spectral range computation for flux distributions, colors filters (red curves) and comparison to the observations for all the cool stellar types (Evolved giants, K-Dwarf, Sun, Main sequence stars) and with different metallicity	Determinations on the interferometric observables, limb darkening, characterization of the granulation pattern, and impact on hosted planet detection for main sequence stars (Chiavassa et al. 2012, A&A, in press)

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Visualisaztion

Visualizaiton of 3D data with VAPOR (Visualization and Analysis Platform for Ocean, Atmosphere, and Solar Researchers). Volume rendering of Temperature, Mach number, ratio of turbulent pressure/gaz pressure (movie done for one snapshot of a simulation)

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Publications and Works
Publications
Ph.D.
Talks
Other stuff

Summary:
10 Referred papers (8 as first author) + 1 close to submission + 1 referred proceeding

5 press releases + 1 television documentary

3 invited conferences + 15 proceedings

>>>>> Referred Papers <<<<<

A. Chiavassa, L. Bigot, P. Kervella, A. Matter, B. Lopez, R. Collet, Z. Magic, M. Asplund
Three-dimensional interferometric, spectrometric, and planetary views of Procyon

Astronomy & Astrophysics 2012, in press
ADS link

A. Chiavassa, B. Freytag, T. Masseron, B. Plez
Radiative hydrodynamics simulations of red supergiant stars. IV gray versus non-gray opacities

Astronomy & Astrophysics 2011, Volume 535, id.A22
ADS link

P. Kervella, G. Perrin, A. Chiavassa, S. T. Ridgway, J. Cami, X. Haubois and T. Verhoelst
The close circumstellar environment of Betelgeuse - II. Diffraction-limited spectro-imaging from 7.76 to 19.50 µm with VLT/VISIR

Astronomy & Astrophysics 2011, Volume 531, id.A117
ADS link

A. Chiavassa, E. Pasquato, A. Jorissen, S. Sacuto, C. Babusiaux, B. Freytag, H.-G. Ludwig, P. Cruzalebes, Y. Rabbia, A. Spang, and O. Chesneau
Radiative hydrodynamics simulations of red supergiant stars. III. Spectro-photocentric variability, photometric variability, and consequences on Gaia measurements

Astronomy & Astrophysics 2011, Volume 528, id.A120
ADS link

J.-P. Berger, F. Malbet, F. Baron, A. Chiavassa et al.
Imaging the heart of astrophysical objects with optical long-baseline interferometry

Astronomy & Astrophysics Review 2012, in press

A. Chiavassa, R. Collet, L. Casagrande, and M. Asplund
Three-dimensional hydrodynamical simulations of red giant stars: semi-global models for the interpretation of interferometric observations

Astronomy & Astrophysics 2010, Volume 524, id.A93
ADS link

A. Chiavassa, X. Haubois, J. S. Young et al.
Radiative hydrodynamics simulations of red supergiant stars: II. simulations of convection

Astronomy & Astrophysics 2010, Volume 515, id.A12
ADS link

A. Chiavassa, S. Lacour, F. Millour, et al.
VLTI/AMBER spectro-interferometric imaging of VX Sgr’s inhomogenous outer atmosphere

Astronomy & Astrophysics 2010, Volume 511, id.A51
ADS link

A. Chiavassa, B. Plez, E. Josselin, B. Freytag
Radiative hydrodynamics simulations of red supergiant stars: I. interpretation of interferometric observations

Astronomy & Astrophysics 2009, Volume 506, Issue 3, pp.1351-1365
ADS link

A. Chiavassa, C. Ceccarelli, A.G.G.M. Tielens, E. Caux, S. Maret
The 90-110 micron dust feature in low to intermediate mass protostars: calcite?

Astronomy & Astrophysics 2005, Volume 432, pp.547-557
ADS link

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>>>>> Conference Papers <<<<<

A. Chiavassa, L. Bigot, F. Thévenin, R. Collet, G. Jasniewicz, Z. Magic, M. Asplund
3D hydrodynamical model atmospheres: a tool to correct radial velocities and parallaxes for Gaia

Referred proceedings - GREAT-ESF Stellar atmospheres in the Gaia era Workshop: Quantitative Spectroscopy and Comparative Spectrum Modelling. Bruxelle, June 2011

P. Kervella, G. Perrin, A. Chiavassa, et al.
The surface and close circumstellar evironment of Betelgeuse

Proceedings - SF2A (Société Française d'Astronomie et d'Astrophysique) in Paris, France, June 2011

A. Chiavassa, E. Pasquato, A. Jorissen, et al.
Photocentric variability of Red Supergiant Stars and consequences on Gaia measurements

Proceedings - SF2A (Société Française d'Astronomie et d'Astrophysique) in Marseille, France, 21- 24 June 2010
ADS link

A. Chiavassa, E. Pasquato, A. Jorissen, et al.
Photocentric and photometric variability of Red Supergiant stars

Proceedings - Workshop "Why Galaxies Care About AGB Stars II", Vienna 16-20 August 2010
ADS link

S. Sacuto, A. Jorissen, P. Cruzalebes, E. Pasquato, A. Chiavassa, et al.
Interferometric constraints on Surface Brightness Asymmetries in Long-Period Variable stars. A threat to accurate Gaia parallaxes

Proceedings - Workshop "Why Galaxies Care About AGB Stars II", Vienna 16-20 August 2010
ADS link

F. Patru, A. Chiavassa, D. Mourard, N. Tarmoul
Direct imaging with a hypertelescope of red supergiant stellar surfaces

Proceedings of the SPIE 2010
ADS link

F. Malbet, W. Cotton, G. Duvert, P. Lawson, A. Chiavassa et al.
The 2010 Interferometric Imaging Beauty Contest

Proceedings of the SPIE 2010
ADS link

M. Creech-Eakmana, J. Young, C. Haniff, D. Busher, M. Elvis, A. Chiavassa, M. Schartmann
Imaging simulations of selected science with the Magdalena Ridge Observatory Interferometer

Proceedings of the SPIE 2010
ADS link

A. Chiavassa, B. Plez, E. Josselin, B. Freytag
Atmospheric Dynamics of Red Supergiant Stars and applications to Interferometry

Proceedings - Presented at the SF2A (Société Française d'Astronomie et d'Astrophysique) in Grenoble, France, 2- 6 July 2007
ADS link

A. Chiavassa
Atmospheric Dynamics of Red Supergiant Stars and Interferometry

Proceedings - Presented at the Workshop on Perspectives in Radiative Transfer and Interferometry in Chateau de Pizay, France, 14 - 16 May 2007
ADS link

A. Chiavassa, B. Plez, E. Josselin, B. Freytag
Line formation in 3D radiation hydrodynamics simulations of red supergiants

Proceedings - Presented at the SF2A (Société Française d'Astronomie et d'Astrophysique) in Paris, France, 26 - 30 June 2006
ADS link

A. Chiavassa, B. Plez, E. Josselin, B. Freytag
Radiative transfer in snapshot of 3D radiative hydrodynamics models of red supergiant

Proceedings - Presented at the GRETA workshop in Frejus, France, May 2005
ADS link

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>>>>> Collaboration with the science case working group on VSI (VLTI Spectro-Imager) and Matisse (Multi AperTure mid-Infrared Spectroscopic Experiment) for iamge recontruction. These are VLTI 2nd generation instrument under study <<<<<

J. V. Garcia Paulo, J.P. Berger, A. Marconi, A. Krivov, A. Chiavassa, et al.
Science case for 1 mas spectro-imagining in the near-infrared Optical and Infrared Interferometry

Edited by Schöller, Markus; Danchi, William C.; Delplancke, Françoise. Proceedings of the SPIE 2008, Volume 7013, pp. 70134N-70134N-14
link

Malbet, F. et al.
VSI: the VLTI spectro-imager

Optical and Infrared Interferometry. Edited by Schöller, Markus; Danchi, William C.; Delplancke, Françoise. Proceedings of the SPIE 2008, Volume 7013, pp. 701329-701329-12
link

Filho Mercedes, E. et al.
Phase closure image reconstruction for future VLTI instrumentation

Optical and Infrared Interferometry. Edited by Schöller, Markus; Danchi, William C.; Delplancke, Françoise. Proceedings of the SPIE 2008, Volume 7013, pp. 70133Z-70133Z-10
link

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>>>>> Ph.D. Thesis (defended 4th June 2008) <<<<<

Atmospheric Dynamics of red supergiant stars - Power Point presentation

PHD Thesis

Remerciment and first page (3.1 Mb)

Contents (276 Kb)

Introduction (2.6 Mb)

3D radiative hydrodynamical models with CO5BOLD (8 Mb)

3D radiative transfer code OPTIM3D (10.6 Mb)

Characteristics of Red Supergiants simulations (15.3 Mb)

Velocity fields in RSGs (9.6 Mb)

Spectral synthesis (5.7 Mb)

Introduction to interferometry (1.4 Mb)

Intensity maps and interferometry (33.2 Mb)

Exploratory attempt for a non-grey treatment of opacities with CO5BOLD (192 Kb)

Conclusions and perspectives (180 Kb)

Appendix (publications, images, visibility-phase IDL code, 3D visualization code) (34.2 Mb)

WHOLE PHD THESIS PDF File (122 Mb)

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>>>>> Invited Talks <<<<<

A. Chiavassa
Seminar at the "Collège de France"

Paris, 16 Mars 2011
link

A. Chiavassa
Convection signatures and characterization in late type stars

Presented at the Workshop on Interferometry Imaging WII09. Goutelas, France, 26-29 May 2009 link

A. Chiavassa
Atmospheric Dynamics of Red Supergiant Stars and applications to Interferometric

Presented at the SF2A (Société Française d'Astronomie et d'Astrophysique) in Grenoble, France, 2 - 6 July 2007

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>>>>> Contributed Talks <<<<<

A. Chiavassa
Interpretation of interferometric observations with 3D radiative hydrodynamics simulations of cool stars

Presented at the ESO Workshop on The Origin and Fate of the Sun: Evolution of Solar-mass Stars Observed with High Angular Resolution in Garching, Germany, 2-5 March 2010

A. Chiavassa
Atmospheric Dynamics of Red Supergiant Stars and Interferometry

Presented at the Workshop on Perspectives in Radiative Transfer and Interferometry in Chateau de Pizay, France, 14 - 16 May 2007

A. Chiavassa, B. Plez, E. Josselin, B. Freytag
Line formation in 3D radiation hydrodynamics simulations of red supergiants

Presented at the SF2A (Société Française d'Astronomie et d'Astrophysique) in Paris, France, 26 - 30 June 2006

A. Chiavassa, B. Plez, E. Josselin, B. Freytag
Line formation in CO5BOLD simulation of red supergiant

Presented at the CO5BOLD workshop in Freiburg, Germany, June 2006

A. Chiavassa, B. Plez, E. Josselin, B. Freytag
Radiative transfer in snapshots of 3D radiative-hydrodynamical models of red supergiants: spectra and images

Presented at the GRETA workshop in Frejus, France, May 2005

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>>>>> Other Works <<<<<

Master Graduation thesis
Mineralogia delle polveri nelle prime fasi della formazione di stelle di tipo solare

link

Curriculum Vitae

Download my Curriculum Vitae in English here

Name : Andrea
Surname : Chiavassa
Birthday : 08 January 1979
Birthplace : Savigliano, Italy

Professional Address : Institut d'Astronomie et d'Astrophysique Université Libre de Bruxelles CP226 Boulevard du Triomphe B-1050 Brussels Belgium
Tel : (+32) 2 650 5917
Fax : (+32) 2 650 4226

Professional E-mail : achiavas@ulb.ac.be
Private E-mail : andreew@alice.it

Languages :
Italian - native speaker
French - excellent
English - excellent
German - basic
Spanish - some notions

Current Position : Fellowship at Institut d'Astronomie et d'Astrophysique de Bruxelles with Prof. Alain Jorissen

Research Topic : 3D Chemical abundances in peculiar stars and Gaia predictions for cool stars

Academic experiences :

September 2008 - September 2010: Fellowship at Max Planck Institut for Astrophysics, Garching with Prof. Martin Asplund. Research topic: 3D modelling of convection in stellar atmosphere of cool stars. Interferometric and spectroscopic observables for red supergiant, K-giant and AGB stars.

PhD student (october 2004 - june 2008) at GRAAL, Montpellier, France. Development of a 3D radiative transfer code for radiation hydrodynamics simulations of red supergiants. Comparison of theoretical results with spectroscopic and interferometric observations. Determination of the convection pattern on red supergiant stars.

Master Degree final project ("Laurea in Astrofisica e Fisica Cosmica") at the Laboratoire d'Astrophysique de Grenoble (LAOG), France, under the supervision of Cecilia Ceccarelli (2004, 8 months ERASMUS exchange project) - The 90-110 micron dust feature in low to intermediate mass protostars

Bachelor final project ("Laurea in Fisica") at the University of Turin under the supervision of Gianni Navarra (Mars to June 2002) - Study of the high voltage circuit of photomultipliers of the Pierre Auger Observatory

Teaching and Diffusion of Scientific Knowledge :

Physics : Mechanics and Thermodynamics (univerisity level 2011, Belgium) - 36h

Informatics : Word, Excel and Power Point (univerisity level 2006, France) - 20h

Astrophysics : univerisity level (France, 2005) - 3h

Participation to the animations for the Year of Physics 2005 (Montpellier, France), (high school and primary school) - 60 hours

Several participations to public animations of astronomy (about 2-3 conferences per year)

Scientific interests : Radiative Transfer, Radiative Hydrodynamics, Surface convection, Spectroscopy, Interferometry, astrometry, planets, interstellar medium

Computer and Programming Skills :

MacOsX, Linux, Unix, Windows operating systems administration

Programming in Fortran95 e Fortran 77, IDL, Shell Scripts, Yorick Astronomical software : Supermongo, synthetic spectrum calculation, CO5BOLD photosphere models calculations

Others : LaTeX2e, Word, Excel, Power Point

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How to contact Me

Andrea Chiavassa

Where:

Institut d'Astronomie et d'Astrophysique
Université libre de Bruxelles - Campus Plaine
Bâtiment NO
CP 226
Boulevard du Triomphe
B-1050 Bruxelles

Mail : achiavas.at.ulb.ac.be
Telephone : 0032 2 650 5917
Fax : 0032 2 650 4226

Click on the image to access to Google Maps.