Nova explosions & nucleosynthesis

Studying novae

This group is actively involved in the study of different models of novae, extragalactic novae (especially in the Andromeda galaxy), particle acceleration in novae and nova contribution in the origin of Galactic 7Li.


Observing X-rays to understand novae

White dwarfs are the last stages of stellar evolution of stars with masses smaller than 10 Msun approximately. When isolated they cool-down to invisibility, but when they are in close binary systems they can be "rejuvenated" by mass accretion from their companion star, and eventually explode as novae or thermonuclear supernovae. A nova explosion is a hydrogen thermonuclear runaway on top of the white dwarf, made of either carbon and oxygen (CO) or oxygen and neon (ONe). Mass is ejected at high velocities, but the white dwarf is not disrupted and a new explosion is expected to occur after thousands (103-105) of years.

Relatively recently, in 2007, it was predicted by this group for the first time that novae can be particle accelerators (for RS Oph in its 2006 explosion), and thus play a role on the origin of cosmic rays; accelerated protons and electrons will subsequently emit high-energy gamma rays (with energies larger than 100 MeV), through inverse Compton and/or pion decay processes. The Fermi satellite, launched in 2008, has in fact detected already several novae at such energies, confirming our theoretical expectations.

Focus

  • Models of novae including detailed nucleosynthesis and gamma ray emission; prediction of spectra in the MeV range, to be observed with current (INTEGRAL) and future gamma-ray satellites (e-ASTROGAM). We lead large international collaborations responsible for ToO (Target of Opportunity) INTEGRAL observation proposals.
  • Origin of Galactic 7Li and the nova contribution; approach through modeling and observations: 7Li in optical, 7Be in UV (co-Is of ESO proposals) and 7Be in 478 keV gamma-rays (PIs of INTEGRAL proposals)
  • Participation in observations of novae in outburst, searching for supersoft emission revealing residual nuclear burning on top of the white dwarf, with XMM-Newton, Swift/XRT, Chandra X-ray satellites. Same for post-outburst novae, to understand how accretion is reestablished after the explosion.
  • Particle acceleration in novae and its understanding through X-ray early observations (application to RS Oph and V745 Sco recurrent novae)
  • Study of extragalactic novae, especially in the Andromeda galaxy (M31). The large data base (optical and in X-rays) includes exciting objects, like M31-2008-12a, the nova with the shortest recurrence period (about 1 year), hosting an extremely massive white dwarf and thus being the best-known candidate to explode as a thermonuclear supernova.

 

Senior institute members involved

Meet the senior researchers who participate in this research line.

  • Margarita Hernanz

  • Jordi Isern


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