Contact

Laboratoire Lagrange
UMR 7293
Observatoire de la Cote d'Azur
Université de Nice Sophia-Antipolis
Bd de l'Observatoire
CS 34229 - 06304 Nice Cedex 4
France
andrea.chiavassa@oca.eu

Logo Lagrange



Ph.D. subject available in Nice on exoplanet atmospheres at high spectral resolution. Please contact me.

Andrea Chiavassa, Dr. in Astrophysics


fotoid



"Everything you can imaging is real" Pablo Picasso



Research





Computation of 3D simulations of cool stars with CO5BOLD (Freytag et al. 2012, Journal of Computational Physics, 231) 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/PIONIER, CHARA, IOTA,...).

Data redution with VLTI-AMBER

Measurement and characterization of the convective pattern (granule size, surface contrast, timescales) of red supergiant stars, K giants, sub-giants and solar type 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, link ; Chiavassa et al. 2014, A&A, link )
Determnation of the impact of granulation in planetary transit detection and characterisation (Chiavassa et al. 2015, A&A, link )


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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

My list of publications (20 February 2018)

44 Referred papers (14 as first author), 44 proceedings, a Chapter for a book, Gaia Techinical notes, Matisse Science note and E-ELT HIRES science case
1877 citations, H index 18
6 press releases plus 2 contributions to television documentary and movie
7 invited conferences
ADS link to referred publications
ADS link to not referred publications


Refereed articles

2018

  • The Stagger-grid: A grid of 3D stellar atmosphere models VII. Synthetic stellar spectra and broad-band photometry
    A. Chiavassa, L. Casagrande, R. Collet, Z. Magic, L. Bigot, F. Thevenin, M. Asplund
    Astronomy & Astrophysics
    ADS link
  • The convective photosphere of the red supergiant CE Tau. I. VLTI/PIONIER H-band interferometric imaging
    M. Montargès, R. Norris, A. Chiavassa, B. Tessore, A. Lèbre, F. Baron
    Astronomy & Astrophysics
    ADS link
  • Accurate effective temperatures of the metal-poor benchmark stars HD 140283, HD 122563 and HD 103095 from CHARA interferometry
    I. Karovicova, T. R. White, T. Nordlander et al.
    MNRAS
    ADS link

2017

  • Large granulation cells on the surface of the giant star π1 Gruis
    C. Paladini, F. Baron, A. Jorissen, J.-B. Le Bouquin, B. Freytag, S. Van Eck, M. Wittkowski, J. Hron, A. Chiavassa, et al.
    Nature
    Nature link
  • Tomography of cool giant and supergiant star atmospheres. I. Validation of the method
    K. Kravchenko, S. Van Eck, A. Chiavassa, A. Jorissen, B. Freytag, B. Plez
    Astronomy & Astrophysics
    ADS link
  • Multi-epoch VLTI-PIONIER imaging of the supergiant V766 Cen: Image of the close companion in front of the primary
    M. Wittkowski, F. J. Abellan, B. Arroyo-Torres, A. Chiavassa et al.
    Astronomy & Astrophysics
    ADS link
  • The mass function of GX 339-4 from spectroscopic observations of its donor star
    M. Heida, P.G. Jonker, M.A.P. Torres, A. Chiavassa
    Astrophysical Journal
    ADS link
  • The convective surface of the red supergiant Antares. VLTI/PIONIER interferometry in the near infrared
    Montargès, M., A. Chiavassa, Kervella, P.; Ridgway, S. T.; Perrin, G.; Le Bouquin, J.-B.; Lacour, S.
    Astronomy & Astrophysics
    ADS link
  • Asymmetries on red giant branch surfaces from CHARA/MIRC optical interferometry
    A. Chiavassa, Norris, R., Montargès, M., Ligi, R., Fossati, L., Bigot, L., Baron, F., Kervella, P., Monnier, J. D., Mourard, D., Nardetto, N., Perrin, G., Schaefer, G. H., ten Brummelaar, T. A., Magic, Z., Collet, R., Asplund, M.
    Astronomy & Astrophysics
    ADS link
  • Measuring stellar granulation during planet transits
    A. Chiavassa, Caldas, A., Selsis, F., Leconte, J., Von Paris, P., Bordé, P., Magic, Z., Collet, R., Asplund, M.
    Astronomy & Astrophysics
    ADS link
  • Gaia Data Release 1. Testing the parallaxes with local Cepheids and RR Lyrae stars
    Gaia Collaboration
    Astronomy & Astrophysics
    ADS link
  • Gaia Data Release 1. Open cluster astrometry: performance, limitations, and future prospects
    Astronomy & Astrophysics
    ADS link

2016

  • VLTI/AMBER spectro-interferometry of the late-type supergiants V766 Cen (=HR 5171 A), sigma Oph, BM Sco, and HD 206859
    M. Wittkowski, B. Arroyo-Torres, J. M. Marcaide, F. J. Abellan, F. J. A. Chiavassa, J. C. Guirado,
    Astronomy & Astrophysics
    ADS link
  • The Gaia mission
    Gaia Collaboration
    Astronomy & Astrophysics
    ADS link
  • Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
    Gaia Collaboration
    Astronomy & Astrophysics
    ADS link
  • Discovery of a complex linearly polarized spectrum of Betelgeuse dominated by depolarization of the continuum
    Aurière, M., Ariste López, A., Mathias, P., Lèbre, A., Josselin, E., Montargès, M., Petit, P., A. Chiavassa, et al.
    Astronomy & Astrophysics
    ADS link
  • The close circumstellar environment of Betelgeuse. IV. VLTI/PIONIER interferometric monitoring of the photosphere
    Montargès, M., Kervella, P., Perrin, G., A. Chiavassa, et al.
    Astronomy & Astrophysics
    ADS link
  • Near-infrared spectro-interferometry of Mira variables and comparisons to 1D dynamic model atmospheres and 3D convection simulations
    Wittkowski, M., A. Chiavassa, Freytag, B., Scholz, M., Hoefner, S., Karovicova, I., Whitelock, P. A.
    Astronomy & Astrophysics
    ADS link
  • The close circumstellar environment of Betelgeuse - III. SPHERE/ZIMPOL visible polarimetry of the inner envelope and photospheres
    Kervella, P., Lagadec, E., Montargès, M., Ridgway, S. T., A. Chiavassa, Haubois, X., Schmid, H.-M., Langlois, M., Gallenne, A., Perrin, G.
    Astronomy & Astrophysics
    ADS link

2015

  • A new view on exoplanet transits: Transit of Venus described using three-dimensional solar atmosphere Stagger-grid simulations
    A. Chiavassa, C. Pere, M. Faurobert, G. Ricort, P. Tanga, Z. Magic, R. Collet, M. Asplund
    Astronomy & Astrophysics
    ADS link
  • What causes the large extensions of red-supergiant atmospheres? Comparisons of interferometric observations with 1-D hydrostatic, 3-D convection, and 1-D pulsating model atmospheres
    B. Arroyo-Torres, M. Wittkowski, A. Chiavassa, M. Scholz, B. Freytag, J. M. Marcaide, P. H. Hauschildt, P. R. Wood, F. J. Abellan
    Astronomy & Astrophysics
    ADS link
  • The Stagger-grid: A grid of 3D stellar atmosphere models - IV. Limb darkening coefficients
    Z. Magic A. Chiavassa, R. Collet, M. Asplund
    Astronomy & Astrophysics
    ADS link
  • Benchmark stars for Gaia: fundamental properties of the Population II star HD140283 from interferometric, spectroscopic and photometric data
    O. Creevey, F. Thévenin, P. Berio, U. Heiter, K. von Braun, D. Mourard, L. Bigot, T. S. Boyajian, P. Kervella, P. Morel, B. Pichon, A. Chiavassa et al. Astronomy & Astrophysics
    ADS link
  • Departure from centrosymmetry of red giants and supergiants measured with VLTI/AMBER
    P. Cruzalèbes, A. Jorissen, A. Chiavassa, C. Paladini, Y. Rabbia, A. Spang
    Mon. Not. R. Astron. Soc.
    ADS link

2014

  • On the characterization of transiting exoplanets and magnetic spots with optical interferometry
    Ligi, R.; Mourard, D.; Lagrange, A.-M.; Perraut, K.; A. Chiavassa
    Astronomy & Astrophysics
    ADS link
  • Planet transit and stellar granulation detection with interferometry
    A. Chiavassa, R. Ligi, Z. Magic, R. Collet, M. Asplund, D. Mourard
    Astronomy & Astrophysics
    ADS link
  • Properties of the CO and H2O MOLsphere of the red supergiant Betelgeuse from VLTI/AMBER observations
    Montargès M., Kervella P., Perrin G., Ohnaka K., A. Chiavassa, Ridgway S. T, Lacour S.
    Astronomy & Astrophysics
    ADS link
  • An edge-on translucent dust disk around the nearest AGB star, L2 Puppis
    P. Kervella, M. Montargès, S. T. Ridgway, G. Perrin, O. Chesneau, S. Lacour, A. Chiavassa, X. Haubois, and A. Gallenne
    Astronomy & Astrophysics
    ADS link
  • Measuring deviation from centrosymmetry for a source brightness distribution observed by spectro-interferometry
    P. Cruzalèbes, A. Jorissen, Y. Rabbia, A. Chiavassa, C. Paladini, S. Sacuto, C. Siopis, G. Sadowski, A. Spang, O. Chesneau
    Mon. Not. R. Astron. Soc.
    ADS link

2013

  • The Stagger-grid: A Grid of 3D Stellar Atmosphere Models - I. Methods and General Properties
    Z. Magic, R. Collet, M. Asplund, R. Trampedach, W. Hayek, A. Chiavassa, R. F. Stein, Å. Nordlund
    Astronomy & Astrophysics
    ADS link
  • Fundamental parameters of 16 late-type stars derived from their angular diameter measured with VLTI/AMBER
    P. Cruzalèbes, A. Jorissen, Y. Rabbia, S. Sacuto, A. Chiavassa, Pasquato E., Plez B., Eriksson K, A. Spang, O. Chesneau
    Mon. Not. R. Astron. Soc.
    ADS link
  • SPIDAST: a new modular software to process spectro-interferometric measurements
    P. Cruzalèbes, Y. Rabbia, A. Jorissen, A. Spang, S. Sacuto, E. Pasquato, A. Chiavassa, et al.
    Mon. Not. R. Astron. Soc.
    ADS link
  • The temperatures of red supergiants
    B. Davies, R.-P. Kudritzki, B. Plez, S. Trager, A. Lancon, Z. Gazak, M. Bergemann, C. Evans, A. Chiavassa
    Astrophysical Journal
    ADS link

2012

  • Three-dimensional interferometric, spectrometric, and planetary views of Procyon
    A. Chiavassa, L. Bigot, P. Kervella, A. Matter, B. Lopez, R. Collet, Z. Magic, M. Asplund
    Astronomy & Astrophysics
    ADS link
  • Fundamental properties of the Population II fiducial stars HD 122563 and Gmb 1830 from CHARA interferometric observations
    O. L. Creevey, F. Thévenin, T. S. Boyajian, P. Kervella, A. Chiavassa, L. Bigot et al.
    Astronomy & Astrophysics
    ADS link
  • Imaging the heart of astrophysical objects with optical long-baseline interferometry
    J.-P. Berger, F. Malbet, F. Baron, A. Chiavassa et al.
    Astronomy & Astrophysics Annual Review
    ADS link

2011

  • Radiative hydrodynamics simulations of red supergiant stars. IV gray versus non-gray opacities
    A. Chiavassa, B. Freytag, T. Masseron, B. Plez
    Astronomy & Astrophysics
    ADS link
  • Radiative hydrodynamics simulations of red supergiant stars. III. Spectro-photocentric variability, photometric variability, and consequences on Gaia measurements
    A. Chiavassa, E. Pasquato, A. Jorissen, S. Sacuto, C. Babusiaux, B. Freytag, H.-G. Ludwig, P. Cruzalebes, Y. Rabbia, A. Spang, and O. Chesneau
    Astronomy & Astrophysics
    ADS link
  • 3D hydrodynamical model atmospheres: a tool to correct radial velocities and parallaxes for Gaia
    A. Chiavassa, L. Bigot, F. Thevenin, R. Collet, G. Jasniewicz, Z. Magic, M. Asplund
    Journal of Physics: Conference Series
    ADS link
  • The close circumstellar environment of Betelgeuse - II. Diffraction-limited spectro-imaging from 7.76 to 19.50 µm with VLT/VISIR
    P. Kervella, G. Perrin, A. Chiavassa, S. T. Ridgway, J. Cami, X. Haubois and T. Verhoelst
    Astronomy & Astrophysics
    ADS link

2010

  • Three-dimensional hydrodynamical simulations of red giant stars: semi-global models for the interpretation of interferometric observations
    A. Chiavassa, R. Collet, L. Casagrande, and M. Asplund
    Astronomy & Astrophysics
    ADS link
  • Radiative hydrodynamics simulations of red supergiant stars: II. simulations of convection on Betelgeuse match interferometric observations
    A. Chiavassa, X. Haubois, J. S. Young et al.
    Astronomy & Astrophysics
    ADS link
  • VLTI/AMBER spectro-interferometric imaging of VX Sgr’s inhomogenous outer atmosphere
    A. Chiavassa, S. Lacour, F. Millour, et al.
    Astronomy & Astrophysics
    ADS link

2009

  • Radiative hydrodynamics simulations of red supergiant stars: I. interpretation of interferometric observations
    A. Chiavassa, B. Plez, E. Josselin, B. Freytag
    Astronomy & Astrophysics
    ADS link

2005

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


Ph.D. Thesis - Atmospheric Dynamics of red supergiant stars

  • Exploratory attempt for a non-grey treatment of opacities with CO5BOLD
    Download link
  • Appendix (publications, images, visibility-phase IDL code, 3D visualization code)
    Download link

Curriculum Vitae

                       


Download my Full Curriculum Vitae in English here Download my 1 page Curriculum Vitae in English here

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




Professional Address : Laboratoire Lagrange
UMR 7293
Observatoire de la Cote d'Azur
Université de Nice Sophia-Antipolis
Bd de l'Observatoire
B.P. 4229 - 06304 Nice Cedex 4
France
Tel : (+33) (0)492 00 3027


Professional E-mail : andrea.chiavassa@oca.eu
Private E-mail : andreew@alice.it


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


Current Position : Permanent position at CNRS (Centre national de la recherche scientifique)

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




Academic experiences :

October 2010 - Agoust 2012: 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.

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)






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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Red Supergiant Workshop: 28-29 september 2015


RSG-ESO

Workshop objectives:

Red supergiant stars contribute extensively to the chemical and dust enrichment of the Galaxies, and ultimately the Universe. These stars combine violent convective motions, low surface gravity, magnetic field, and high luminosities to trigger strong stellar winds. However, the mass loss mechanism is still poorly known. New observations combining monitoring interferometry/spectro-polarimetry as well as imagery brought new insights on the regions very close to the photosphere where the mass loss ejection take place.

Workshop format:

The idea is to enhance the discussion, we require informal presentations of maximum 30 minutes with room for questions and exchanges. Adequate time for round table discussions are also in program.

Where:

SALLE NEF - Batiment CION
Observatoire de la Cote d'Azur
Bd de l'Observatoire
06304 Nice
France
Click here to access to Google Maps for the address.

Preliminary program:


Monday 28 September:
11.00 - 12.00: The point on the observations. Interferometry (Miguel Montargès), Radio (Alizee Duthu)
12.00 - 13.30: Lunch at the observatory
13.30 - 15.00: The point on the observations. Imagery with VLT (Eric Lagadec), Spectropolarimetrie (Philippe Mathias and Arturo Lopez Ariste), spectroscopy (Eric Josselin)
15.00 - 17.00: Discussion on future observations

Tuesday 29 September:
9.00 - 12.00: The point on the modelisation. The observables provided with 3D models (Andrea Chiavassa, Kateryna Kravchenko, and Bernd Freytag), stellar evolution (Jose Groh)
12.00 - 13.30: Lunch at the observatory
13.30 - 17.00: Discussion on link theory/observations and future collaborations/fundibg applications
N.B. Coffee will be provided in the room at anytime during the workshop

Participants:


Andrea Chiavassa - Observatore de la Cote d'Azur
Eric Lagadec - Observatore de la Cote d'Azur
Pierre Cruzalèbes - Observatore de la Cote d'Azur
Pierre Kervella - LESIA Paris (video conference)
Guy Perrin - LESIA Paris
Miguel Montargès - IRAM Grenoble
Eric Josselin - LUPM Montpellier
Agnès Lebre - LUPM Montpellier
Julien Morin - LUPM Montpellier (video conference)
Benjamin Tessore - LUPM Montpellier
Alizee Duthu - Observatoire de Bordeaux
José Groh - Observatoire de Geneve
Arturo Lopez Ariste - IRAP Toulouse
Michel Auriere - IRAP Toulouse (video conference)
Philippe Mathias - IRAP Toulouse
Pascal Petit - IRAP Toulouse (video conference)
Bernd Freytag - Uppsala (to be confirmed)
Kateryna Kravchenko - ULB Bruxelles
Sophie Van Eck - ULB Bruxelles

How to contact Me



Andrea Chiavassa


Andrea Chiavassa

Where:

Laboratoire Lagrange
UMR 7293
Observatoire de la Cote d'Azur
Batiment CION
Bd de l'Observatoire
B.P. 4229 - 06304 Nice Cedex 4
France

Obs map
Click on the image to access to Google Maps.