SNBinaries · Close binary progenitors and ejected donor remnants of supernovae type Ia

Close binary progenitors and ejected donor remnants of supernovae type Ia

Observations in the last decades indicate that our universe is not only expanding, but that this expansion accelerates. To explain this expansion, cosmologists introduced the concept of dark energy. The properties of this dark energy are basically unknown, despite the fact that it largely dominates the energy budget of the Universe. Deriving those properties is therefore one of the key unsolved problems in modern astronomy. The analysis of supernovae type Ia (SN Ia) is widely used as a tool to achieve that goal. SN Ia are very bright stellar explosions. The characteristic decay of their apparent brightness has been found to be related to their absolute luminosities. If the absolute luminosity of a source is known, its distance can be determined. Astronomers call such rather rare objects standard candles. SN Ia can be used to measure the largest distances in the universe. However, the progenitors of SN Ia explosions are still unknown and this might affect the applicability of SN Ia as standard candles. To investigate this it is not only necessary to unambiguously identify the progenitor population, but also to characterize its fundamental properties as detailed as possible. The observed properties of SN Ia are best explained by the explosion of a white dwarf. White dwarfs are the end stages of stellar evolution for most stars. Extreme conditions are necessary to trigger the explosion of a white dwarf, which can only be reached, when matter is transferred by a companion star. Recently, close, eclipsing binaries consisting of white dwarfs and compact helium stars (hot subdwarfs, sdO/B) have been identified as important progenitor candidates. The detonation of accreted helium at the surface of the white dwarf is expected to trigger the SN Ia explosion. Because those binaries stars have very close orbits, the helium star companions are ejected after the SN Ia explosion with the most extreme velocities known in our Galaxy. This so-called helium double-detonation scenario therefore provides the unique opportunity to study both the progenitor sample and the sample of the ejected companions in detail. During this Marie Curie fellowship we want to use public data of time-domain surveys to identify the progenitors and ejected companions. Based on photometric and spectroscopic analyses, we want to characterise representative samples of them. These fundamental samples can be used in the future to reconstruct the formation and evolution of the progenitor systems and determine the effects when using SN Ia as cosmic distance indicators.

Data: CORDIS, © European Union