Expect posts about science, nonsense, brewing, and other interests.

  Summer reads

It’s been a while
Summer is in full swing
Holidays came and went by

During my holidays, I visited the bookshop for the first time in … too long, and got some nice books to read. Some books that I wanted, some that I randomly browsed and seemed interesting (the magic of going into the bookshop after all).

I started with Grey is the Color of Hope, the gulag memoirs of Irina Ratushinskaya (Ирина Ратушинская). A tough book, as expected, but excellent and somewhat lighter than I thought. The english translation is unequal sometimes.

I followed with Solaris, the 1961 sci-fi novel from Stanisław Lem which inspired, among other, the Solaris movie directed by Andrei Tarkovsky. I know Tarkovsky’s work from Stalker, and wanted to read Solaris before watching the movie. The book is very interesting, and definitely can give a great movie by Tarkovsky, given the general atmosphere and the overall mystery. I disliked some parts, but that’s OK!

random culture

  PNPS logo

A few design iterations for the new PNPS logo

Creating logos - as well as posters or websites - is something I find interesting and rewarding. When the French “National program of stellar physics” (PNPS, for Programme national de physique stellaire) opened a competition for a new logo, I submitted a proposal straight away.

They somehow ended up selecting my contribution :-), and after a few design iterations, the new logotype was introduced yesterday, together with a brand new website.

The picture above show some of these iterations, I think the process is quite typical. Starting from a very geometric and minimal design (using the colours of the old logotype), the design gains in complexity after a consensus had to be reached with board members requesting more physics included.

In the published version, there are stars - at different evolutionary stages (Sun-like star, red giant, hot star), stellar multiplicity, exoplanets, magnetic fields, a brown dwarf, and a disk (at least that what I see, you are welcome to see more than this).


  Holidays / analog pictures

A wineyard in Bélesta under the snow. Winter 2021 The Canigou mountain. Winter 2021 Water lilies in Victoriahuset, Stockholm botanical garden. Summer 2021.

It is now summer holidays for me after the Midsommar celebration here in Sweden. I got my latest photographic film developed, some photos above. I used the old Praktica MTL 3 camera with a russian Helios M44-2 lens. The film itself is interesting, it’s an Ilford SFX 200 with increased sensitivity in the red.


  First polarized spectra with CRIRES+

Circularly polarized spectra of the star Gam Eql, from CRIRES+ and SPIRou

In 2013, I started working on the CRIRES+ instrument for the Very Large Telescope, and particularly its polarimeter which we’ve built and tested in Uppsala before integrating it with the rest of the instrument. The whole goal of this system is to get polarized spectra of stars, to study, among other things, their magnetic fields.

Well, today, we just computed the first polarized spectra coming from that instrument, with observations we took earlier this month. The spectrum is of a polarized standard star Gam Equ, and the data looks reasonable when compared with data of the same star taken with a similar instrument, SPIRou.

There are of course many things to fix and to improve, but this is a great closure before the summer holidays 🎉.

work astronomy crires

  The devil (or the good god) is in the detail

Today I realized that no matter how much you dig into a topic, there are always interesting things to learn and surprises to be had.

The concrete example is this: My first research project ever, a 2-month research internship at Uppsala University, was to analyze spectropolarimetric data of a star and infer properties of its magnetic field. I had little time to dig into details. So I learned about polarization a bit, I learned about stellar spectra a bit, I learned about stars a bit, and about topographic imaging. This was a lot of fun and motivated me to continue into astronomy, eventually taking up a PhD with the same supervisor at Uppsala University.

During the PhD, I worked more on spectropolarimetry. I also helped build a spectropolarimeter for the CRIRES+ instrument. I got to learn about the instrument itself, how we can get the polarized spectra from the stellar light. I dug into the realms of instrument electronics, hardware, the optics, the control software, the mechanics. In the end, I thought I had a good idea how things work in the instrument (I was a bit wrong).

Now, during my postdoc, we commission the instrument at last at the telescope! It’s time to test many things I had little idea about: the way the observation blocks are handled, observing templates, FITS header management, and quality control. It was also time to test the data reduction pipeline on on spectropolarimetric observations. I got to dig into the equations of Stokes parameter demodulation, and see all the kinks and clever details in the software implementation.

The bottom line is: I found interesting things, strokes of genius, clever implementations, and also seemingly absurd things at all levels. I would actually not mind keep going deeper into the instrument business, e.g learning more about the manufacturing of polarization gratings (which are still a mystery to me), or into the pipeline-writing business.

random work


Nothing today. Working all day, too tired to write!


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