Interacting Binaries

Interacting binaries usually contain a compact object and a companion star. The companions are observed in various stages of evolution and have different masses. Here in Madison, building on a long tradition of studies of stellar nebulae and outflows, we have been very active in studying white dwarf close binaries. We are especially (but not only) interested in those undergoing nuclear burning in the hydrogen or helium rich envelope they accrete from  their secondary star.

When the white dwarf is “rejuvenated” by accretion it can undergo thermonuclear burning of hydrogen with the very rapid CNO cycle, that leads to a violent ejection of the accreted layers. Then the NOVA phenomenon follows, with the ejection of a mass as high as 1/10000 the solar mass in the interstellar medium in a very fast wind, at velocities of thousands of kilometers per second.

Some interacting white dwarf binaries accreting material at a very high rate may not eject all the accreted mass, or they may not undergo the nova outburst at all. In this case they are on the path towards a violent thermonuclear supernova, or type Ia supernova, responsible for nucleosynthesis of most iron in the universe. We are trying to identify which types of the white dwarf binaries really are on this supernova path.

The following topics are researched by Marina Orio.

White Dwarf Atmospheres

We study X-ray grating spectra of extremely hot, hydrogen burning whte dwarfs atmospheres. Using the X-ray grating spectra onboard the Chandra and XMM-Newton X-ray satellites, we investigate their winds of nebular ejecta. We hope to measure the temperature, mass and chemical composition of the white dwarfs in this stage – and thus understand whether they may become supernovae.

X-ray Binary Populations

We conduct surveys of the population of X-ray binaries in different galaxies of the local group, with the aim of correlating them with star formation and other galaxy characteristics. One important  aim is obtaining detailed statistics of white dwarf binaries that are undergoing hydrogen burning in an accreted shell, but it is not the only focus of this research that yields important results for different types of astronomical objects.