January 2019

Preparing an outreach talk on the dark sector, I found that it could be nice to show an animated plot of the expansion of the universe. So I have requested half a million galaxies form the latest SDSS data release (here is a link to the sdss server)

G.ra, G.dec,
s.z, s.zerr
FROM Galaxy as G
JOIN SpecObjAll AS s ON g.specObjID = s.specObjID
JOIN ZooSpec AS zns ON G.objid = zns.objid
WHERE g.clean=1and ( g.flags & (dbo.fPhotoFlags('SATURATED'))) =0

which I convert in cartesian coordinates using astropy, and then plotting positions as a function of time, taken H0=70 km/s/Mpc ( to obtain






October 2018

Last week was held the fourth LSST-DESC Calibration workshop.

On the last day, Eli Rykoff showed a slide that most strikingly summarize the challenge that measuring the variability of the atmospheric transparency, at the milimagnitude level from the monitoring of its constituents, represents :

Eli Rykoff - Slide 2 - LSST/DESC Calibration Workshop 5 October, 2018

So, we just need to monitor...

The precipitable water vapor at 0.2 mm,

the aerosol optical depth at 0.0005

and the Ozone at 8 dobsons.

Mm.  May be ok for the Ozone, thinkable for the water. But to say the least, the Aerosols are going to be tough to nail at this level of precision :(



June 2018

Following remotly LSST@Europe third meeting, I saw for the first time a living Hertzsprung-Russell diagram with variable stars from Gaia DR2. The speaker nicely linked his video on youtube :

I find quite fascinating to realize how diverse and animated stars are. 





May 2018

We just had our third LSST/DESC Calibration Workshop, which took place this year in Paris.

Among the nice new things I learnt, one was the 3 mili-magnitude residuals between the Gaia and DES photometry, as you can see from Eli Rykoff slide ;)

DES VS Gaia photometry : A preliminary map of the residuals




September 2017

A few days ago, I attended Rémi Le Breton PhD defense at Jussieu. I was impressed by the results he obtained with his optoelectronic tests of LSST sensors : The measurement of pixels' spatial correlation was improved by two order of magnitude in the last two years !



June 2017

I was last week in Lyon to participate to an LSST Workshop.

LSST Lyon June 2017

As I learned many things, I must say that my most surprising finding happended at the meeting's dinner when I discovered that none of my US collegues knew what the english word for 'Papille' was.

What a surprise ?!





May 2017

I recently attended a seminary by Adam Riess about the determination of the Hubble constant and the tension that manifests with the Lambda-CDM model.

Harvard-Smithonian, seminary by Adam Riess
Harvard-Smithonian, seminary by Adam Riess










It drove me to read the paper that it was based on : A 2.4% Determination of the Local Value of the Hubble Constant ( As I found it excellent, I tried to give a snapshot at it : expanding-universe

February 2017

I participated in a workshop hosted by Harvard to discuss the calibration of the LSST : It looks like we have what the French would call "ceinture et bretelles" ... Which is great when it comes to metrology.

lsst site
Cartoon of the science telescope (left) along with the calibration telescope (right) that is being built right now in Chile


January 2017

I visited the Laboratoire de Physique Corpusculaire in Clermont-Ferrand and gave a seminar on the status of the "brighter-fatter" effect and how to deal with it when using wide field imagers.

bf effect
Electrostatic within CCDs : the trajectories of incoming charges are deflected by the charges already collected within the pixels.


December 2016

I went at Brookhaven National Laboratory in Long Island to participate to the 3rd Precision Astronomy with Fully Depleted CCDs meeting. There was many interesting talks that are available here, in particular, observation of a possible "brighter-fatter" like effect in CMOS devices ...

Happy Physicists


November 2016

On a trip to CTIO  to collect images from the .9-meter telescope so as to study the atmosphere there, I had a chance to take a tour at DECam under the dome of the 4-meter telescope.

CTIO 4-m telescope
CTIO : Picture of the 4-m telescope taken from the .9-m telescope while the dome opens so as to thermalize the enclosure before night observations resume.

The DECam imager sitting on top of the CTIO-Blanco 4-meter telescope and its equatorial mounting