Jan-Uwe Ness

Astronomer

 

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).


Keywords

  • Classical Nova Outbursts
  • Super Soft X-ray Binary Sources
  • Single-degenerate Supernova Ia progenitors
  • High-Resolution X-ray spectroscopy
  • Monitoring and spectral changes during stellar flares
  • Simultaneous Doppler Imaging and X-ray spectroscopy

Ongoing collaborations

  • University of Hamburg (Germany: P. Hauschildt, D. van Rossum, J. H.M.M. Schmitt, C. Schmidt)
  • Slovak University of Technology in Bratislava (A. Dobrotka)
  • Harvard University (CfA, USA: J.J. Drake, M. Guenther)
  • University of Leicester (UK: J. Osborne)
  • University of Oxford (UK: C. Jordan)
  • Institut de Ciencies de l'Espai (M. Hernanz, M. Henze)
  • Universitat Politècnica de Catalunya.BarcelonaTech (G. Sala)
  • Liverpool John Moores University (UK: M. Bode)
  • Arizona State University (USA: S. Starrfield)
  • West Chester University (USA: G. Schwarz)
  • Japan Aerospace Exploration Agency (JAXA: M. Tsujimoto)

Publications

Publications

Project/mission at ESA

XMM-Newton

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.