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

  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!


  CRIRES remote commissioning

Home office setup for remote commissioning.

Together with colleages in Uppsala and Germany, Italy, Chile, we’ve been building the CRIRES+ instrument for the Very Large Telescope in Chile. The project has been around a decade in the making.

But finally, we are “commissioning” the instrument now. This means we test all the functions, make sure the instrument works as it should, and check that performances are good. If all works well, then we can happily offer the instrument to the community.

Normally for this kind of work, our team would travel to the observatory and help with the observations. With the Covid situation, most of us are now doing this work remotely, from home. The people at the observatory simply share their screens with us so that we can see what they observe in real time!


  Swim season

Brunnsviken seen from Sjöstugan.

With the warm days, swim season is upon us in Stockholm! I went swimming every day since last Saturday, it is glorious. The water in the sea was still quite cold, around 13-14 degrees. In Brunnsviken though, it is perfect at around 18-19 degrees !

nature hobby photo

  Hops growing

One hop plant

The hops planted early May are growing fast and seriously climbing that pole.

brewing hops gardening photo

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