The CHEERS Project

Where and when did chemical elements like oxygen and iron form in the Universe? And how do they get mixed into interstellar matter and form stars and planets? These are the driving questions behind the CHEERS project, the CHEmical Enrichment RGS Sample.

One of the best ways to study chemical enrichment on the scale of the universe is to look at the X-ray emission of the gas in clusters of galaxies. In their X-ray spectra we can detect features of nitrogen, oxygen, neon, magnesium, silicon, sulphur, argon, calcium, chromium, manganese, iron and nickel. These elements are the most abundant in the universe apart from hydrogen and helium. We can not only detect these elements, but we can also measure their abundance.

The CHEERS project started with the acceptance of a very large observing program with ESA's X-ray observatory XMM-Newton. We obtained 1.6 million seconds of exposure time (about 19 days) on a total of 11 clusters of galaxies. Together with data from the XMM-Newton archive we compiled a sample of 44 clusters with good quality RGS spectra.

Since we obtained the data, we have studied the 44 clusters in many different aspects. The list of published scientific papers can be found here. The papers do not only report results on the chemical enrichment, but also discuss turbulence in the hot gas and its thermal properties.

Image courtesy Ciro Pinto.

The image above shows all the X-ray images of the clusters in the CHEERS sample. (Image courtesy: Ciro Pinto).

The work has been done in an international collaboration. The members of the collaboration are listed on the right.

About the PI

Jelle de Plaa studied Astrophysics at Utrecht University from 1998-2002 and did his PhD at SRON from 2002-2007 (see Thesis). In the years between 2007 and 2009 he worked as a post-doc at Delft Technical University. Since 2009, he is back at SRON and currently employed as Senior Software Design Engineer in the Astrophysics programme.


  • September 10-11, 2013, Utrecht
  • March 24-25, 2014, Bonn
  • July 15-16, 2014, Utrecht
  • March 11-12, 2015, Bonn


SRON Netherlands Institute for Space Research
Jelle de Plaa
Sorbonnelaan 2
3584 CA Utrecht