Jan-Uwe Ness

Astronomer, Faculty Sentinel (Chair)


Main Research Fields

X-ray observations of Classical Nova outburst; Stellar Activity and Stellar Coronae

Nova explosions occur in accreting cataclysmic binary systems and are powered by explosive nuclear burning of hydrogen-rich material that has previously been accreted by the white dwarf primary. The explosion ejects material at high velocities which forms an optically thick envelope similar to a stellar atmosphere. The outflow of mass decreases with time, and as a consequence the opacity of the envelope changes. This allows successively deeper views into the outflow where it is hotter, shifting the peak of the observable spectrum to successively shorter wavelengths (=higher energies). After a few weeks to months (sometimes years), the envelope becomes bright in X-rays with a spectrum of an X-ray atmosphere. During this phase, the X-ray spectrum of the nova resembles those of the class of Super Soft X-ray Binary Sources (SSS).

A more detailed description of research interests can be found under http://januweness.eu/#research

Magnetically induced activity of cool stars

The outer atmosphere of the Sun is filled with tenuous plasma of kinetic temperatures ranging over a million degrees. During solar eclipses, straylight scattered by this plasma can be seen appearing like a crown around the sun. For this reason this plasma is called the Solar Corona. In X-rays, the corona is the prime emission source, and for other stars, any X-ray emission can thus be assumed to probe the stellar coronal plasma. During my PhD thesis, I have performed spectral analyses of X-ray emission lines in stellar coronae yielding plasma temperatures and densities from which the spatial extent can be derived assuming loop scaling laws.


  • See http://januweness.eu/#research
  • Classical Nova Outbursts
  • Super Soft X-ray Binary Sources
  • Supernova Ia progenitors
  • High-Resolution X-ray spectroscopy
  • Monitoring and spectral changes during stellar flares
  • Simultaneous Doppler Imaging and X-ray spectroscopy
  • X-ray emission in the Solar System
  • N-Body simulations of Interacting galaxies

Ongoing collaborations

  • University of Hamburg (Germany: J. H.M.M. Schmitt, C. Schneider)
  • Slovak University of Technology in Bratislava (A. Dobrotka)
  • Harvard University (CfA, USA: J.J. Drake)
  • Massachusets Institute for Technologies (MIT, USA: M. Guenther)
  • University of Leicester (UK: J. Osborne, K.L. Page, A. Beardmore)
  • University of Oxford (UK: C. Jordan)
  • Institut de Ciencies de l'Espai (M. Hernanz)
  • Universitat Politècnica de Catalunya.BarcelonaTech (G. Sala)
  • Liverpool John Moores University (UK: M. Bode)
  • Arizona State University (USA: S. Starrfield)
  • University College London, MSSL (UK: R. Schoenrich)
  • DAA, TIFR, Mumbai (India: K.P. Singh)
  • University of Wisconsin (USA) and Padova University (IT: M. Orio)


ORCID: 0000-0003-0440-7193

ADS filters:

Project/mission at ESA

ESA Athena Science Study Team

European XRISM Science Operations Centre

Chair of ESAC Science Faculty

Latest results


Spectral Time Map of XMM-Newton RGS spectrum of the Recurrent Nova V3890 Sgr (1962, 1990, 2019). The four panels share x/y axes as follows:

1) Top left: photon flux versus wavelength: Average spectrum (black line with blackbody approximation with red dotted line) and two spectra extracted from different time intervals (see below)

2) Top right: Colour code along photon flux axis used in:

3) Bottom left: Time (from top down) versus wavelength: Time resolved spectra, the colours correspond to photon fluxes as in top right panel. Horizontal dashed lines mark the time intervals over which the shaded spectra of same colour in the top left panel are integrated

4) Bottom right: Light curve turned around by 90 degrees with time along same axis as 3) and count rate horizontally. The shaded areas mark the time intervals over which the shaded spectra of same colour in the top left panel are integrated



Current Research

My work involves XMM-Newton, Chandra, and Swift X-ray and UV spectroscopy and monitoring observations of novae during the SSS phase. The X-ray spectra can be fitted with Blackbody curves, but they are a lot more complex. The high-resolution spectra contain deep absorption lines that are broadened and oftentimes significantly blue-shifted. The Swift monitoring light curves show extremely high degrees of variability, especially during the early SSS phase. The UV and X-ray brightness should be anticorrelated, but this is not always observed.

As a secondary topic I am interested in stellar coronae. The formation and heating of the Solar Corona to 1000 times the photospheric temperature is still an outstanding problem. One approach is to study the coronae around other stars in order to find systematic trends between coronal properties and stellar parameters. High-Resolution X-ray spectra taken with XMM-Newton RGS and Chandra LETGS/HETGS allow measurements of temperatures densities, and elemental abundances.


See my personal homepage at http://januweness.eu/#pers

Main Hobby: Church Organ

Here my YouTube Channel

Participation at 2021 Fete de la Musique, here the Playlist

Some highlight recordings, for full collection, see Selected Music Recordings

A) Spontaneous improvisations: I just played what came to mind. Getting a totally perfect improvisation is not so easy, as the mind sometimes wanders a bit far away, so some deficiencies will be noted. Giving names to improvisations is difficult, so I just label them with roman numbers. Below I give some comments describing a bit the character.

  • Impro I (2:26): Plenum, with flowing character

B) Concierto a Oña (Baroque Spanish-style Organ from 1766)

  1. Largo by G.F. Haendel (1685-1759)

C) Literature on various organs:

  1. Mattheus-Final, J.S. Bach, Orchestration de Ch. Widor (1844-1937); Played on Great Organ in Magdeburg Cathedral

D) Literature on Viscount Organ at home:

  1. Toccata and Fuge D-minor BWV 565 (J.S. Bach)
  2. Concerto II A minor BWV 593