Julien H. Girard
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    • Nature Index (Migrant Astronomer)
    • 2010 Messenger
    • Ella es Astronoma
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European Southern Observatory (ESO)

Alonso de Cordova 3107
Vitacura
Santiago. Chile

Ground2Space

a blog by Julien H. Girard
News
Recent papers

Webb telescope captures its first direct images of carbon dioxide outside solar system

21/3/2025

 
So happy and proud of what William Balmer (PhD student at The Johns Hopkins University and in our group at the Space Telescope Science Institute) has managed to do with the JWST/NIRCam Coronagraphy mode. To achieve this incredible image, we had to push performance to the max, using the long wavelength bar (or wedge) occulter at its narrowest end to be able to recover planet e (the closest one) and also be able to get those new colors, only available from space.

Kellen Lawson (Postdoc NASA Goddard Space Flight Center) has managed to deconvolve coronagraphic images with a spatially varying (and complex) point spread function (PSF, the optical "response" of the telescope+instrument), an ill-posed problem but that's how we can see all 4 exoplanets simultaneously in this imaged.

This is a young, scaled up version of our solar system, one of the bonafide exoplanetary systems in our field of high contrast imaging and spectroscopy.

The outreach team at STScI has done a wonderful job too!

https://hub.jhu.edu/2025/03/17/webb-telescope-carbon-dioxide-exoplanet/​



JWST-TST High Contrast: Living on the Wedge, or, NIRCam Bar Coronagraphy Reveals CO$_2$ in the HR 8799 and 51 Eri Exoplanets' Atmospheres
Score: 25 = category weight 1 × (3×title count 6 + abstract count 7)
William O. Balmer, Jens Kammerer, Laurent Pueyo, Marshall D. Perrin, Julien H. Girard, Jarron M. Leisenring, Kellen Lawson, Henry Dennen, Roeland P. van der Marel, Charles A. Beichman, Geoffrey Bryden, Jorge Llop-Sayson, Jeff A. Valenti, Joshua D. Lothringer, Nikole K. Lewis, Mathilde M\^alin, Isabel Rebollido, Emily Rickman, Kielan K. W. Hoch, Rémi Soummer, Mark Clampin, C. Matt Mountain
https://arxiv.org/abs/2503.13608
High-contrast observations with JWST can reveal key composition and vertical mixing dependent absorption features in the spectra of directly imaged planets across the 3-5 $\mu$m wavelength range. We present novel coronagraphic images of the HR 8799 and 51 Eri planetary systems using the NIRCam Long Wavelength Bar in an offset "narrow" position. These observations have revealed the four known gas giant planets encircling HR 8799, even at spatial separations challenging for a 6.5 m telescope in the mid-infrared, including the first ever detection of HR 8799 e at 4.6 $\mu$m. The chosen filters constrain the strength of CO, CH4, and CO2 absorption in each planet's photosphere. The planets display a diversity of 3-5 $\mu$m colors that could be due to differences in composition and ultimately be used to trace their formation history. They also show stronger CO2 absorption than expected from solar metallicity models, indicating that they are metal enriched. We detected 51 Eri b at 4.1 $\mu$m and not at longer wavelengths, which, given the planet's temperature, is indicative of out-of-equilibrium carbon chemistry and an enhanced metallicity. Updated orbits fit to the new measurement of 51 Eri b validate previous studies that find a preference for high eccentricities ($e{=}0.57_{-0.09}^{+0.03}$), which likely indicates some dynamical processing in the system's past. These results present an exciting opportunity to model the atmospheres and formation histories of these planets in more detail in the near future, and are complementary to future higher-resolution, continuum-subtracted JWST spectroscopy.

July 18, 2022

18/7/2022

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Picture
I was invited to present the JWST/NIRCam Instrument at the SPIE 2022 Conference (in Montréal, Canada) Monday Plenary in front of over > 1,000 colleagues, engineers and astronomers from all over the world. This is a moment captured by Alan Watson. In this slide, I am showing the coronagraphic contrast curves that we obtained (at 3.35µm wavelength) just a few days before and the detection of the white dwarf companion HD 1141714 B, 10,000 times fainter than the central star and at just a 0.5" (arcsecond) angular separation, making this observing mode "science ready". This was a big highlight in my career and my first professional trip since the covid19 pandemic started!
The talk was recorded and is linked at the bottom of this page.
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We did it!!!!

14/7/2022

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The NIRCam Coronagraphy mode was the last, the 17th JWST mode to be declared ready for science. That happened on July 10th, Sunday, 1 day before @POTUS showed the deep field "SMAC" image. I can tell you it was crazy for me as we got the data only 4 days before and had... pressure!
Picture
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Astrometry with long baseline optical interferometry (direct photons) lead to the mass measurement of an exoplanet, β Pictoris c from the motion of its bigger "sister" β Pictoris b!

24/9/2021

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This is so cool, mind blowing 🤯: Exoplanet science is maturing with disruptive novel instruments like GRAVITY and the great ExoGRAVITY effort and generous collaboration led by Sylvestre Lacour. 

Urbain Le Verrier predicted the existence of Neptune using mathematics. Here, we achieved the mass measurement of an exoplanet, β Pictoris c from the motion of its bigger "sister" β Pictoris b!
Optical/NIR interferometry is saved and has now a long future at ESO and beyond, on the ground and in space!
I am so happy to be an insignificant part of this. In 2001 I tested integrated optics components as part of my master's internship between IPAG (then LAOG) and CEA/LETI. Then, there were H-band optimized 3-beam recombiners aimed at the IOTA interferometer in Arizona. The ~same technology is used in GRAVITY to recombine 4 telescope beams by pairs.
​The mass of Beta Pictoris c from Beta Pictoris b orbital motion.
S. Lacour, J. J. Wang, L. Rodet, M. Nowak, J. Shangguan, H. Beust, A.-M. Lagrange, R. Abuter, A. Amorim, R. Asensio-Torres, M. Benisty, J.-P. Berger, S. Blunt, A. Boccaletti, A. Bohn, M.-L. Bolzer, M. Bonnefoy, H. Bonnet, G. Bourdarot, W. Brandner, F. Cantalloube, P. Caselli, B. Charnay, G. Chauvin, E. Choquet, V. Christiaens, Y. Clénet, V. Coudé du Foresto, A. Cridland, R. Dembet, J. Dexter, P. T. de Zeeuw, A. Drescher, G. Duvert, A. Eckart, F. Eisenhauer, F. Gao, P. Garcia, R. Garcia Lopez, E. Gendron, R. Genzel, S. Gillessen, J. H. Girard, X. Haubois, G. Heißel, Th. Henning, S. Hinkley, S. Hippler, M. Horrobin, M. Houllé, Z. Hubert, L. Jocou, J. Kammerer, M. Keppler, P. Kervella, L. Kreidberg, V. Lapeyrère, J.-B. Le Bouquin, P. Léna, D. Lutz, A.-L. Maire, et al. (38 additional authors not shown)
http://arxiv.org/abs/2109.10671
We aim to demonstrate that the presence and mass of an Exoplanet can now be effectively derived from the astrometry of another Exoplanet. We combined previous astrometry of ββ Pictoris b with a new set of observations from the GRAVITY interferometer. The orbital motion of ββ Pictoris b is fit using Markov chain Monte Carlo simulations in Jacobi coordinates. The inner planet, ββ Pictoris c, was also reobserved at a separation of 96\,mas, confirming the previous orbital estimations. From the astrometry of planet b only, we can (i) detect the presence of ββ Pictoris c and (ii) constrain its mass to 10.04+4.53−3.10MJup10.04−3.10+4.53MJup. If one adds the astrometry of ββ Pictoris c, the mass is narrowed down to 9.15+1.08−1.06MJup9.15−1.06+1.08MJup. The inclusion of radial velocity measurements does not affect the orbital parameters significantly, but it does slightly decrease the mass estimate to 8.89+0.75−0.75MJup8.89−0.75+0.75MJup. With a semimajor axis of 2.68±0.022.68±0.02\,au, a period of 1221±151221±15 days, and an eccentricity of 0.32±0.020.32±0.02, the orbital parameters of ββ Pictoris c are now constrained as precisely as those of ββ Pictoris b. The orbital configuration is compatible with a high-order mean-motion resonance (7:1). The impact of the resonance on the planets' dynamics would then be negligible with respect to the secular perturbations, which might have played an important role in the eccentricity excitation of the outer planet.
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  • About
    • Nature Index (Migrant Astronomer)
    • 2010 Messenger
    • Ella es Astronoma
  • CV
  • Publications
  • Contact/Travel
  • Photography
    • oldies
    • black & white
    • astronomers
    • Ella es Astronoma
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  • astronomers