Licentiate Thesis: Detecting circumstellar dust surrounding type Ia supernovae and its implications on cosmology
by
Raphael Ferretti(Stockholm University, Department of Physics)
→
Europe/Stockholm
FB51
FB51
Description
Type Ia supernovae have been of great value to our understanding of cosmology. With the use
of supernovae, the accelerating expansion of the universe was first discovered and they are to
date of great importance in constraining cosmological parameters. Today the accuracy at
which one can determine cosmological parameters with supernovae is no longer limited by
small sample numbers, but rather systematic errors in our understanding of the explosions.
One such systematic error is the effect dust has on the observed supernovae. In particular,
peculiar extinction laws due to dust have recently become apparent. A possible explanation to
the unusual extinction laws would be the presence of circumstellar dust. Among other
methods to search for circumstellar matter around type Ia supernovae, is the analysis of highresolution
spectra. Gas in the vicinity of supernovae is expected to be ionised by early
ultraviolet radiation, which should cause narrow absorption lines to change detectably. Today
a small number of supernovae with varying sodium D absorption have been found, but no
cases can be conclusively attributed to photoionisation. Furthermore, recent results show that
most time-series of high-resolution spectra do not cover the relevant time frame during which
photoionisation is expected to occur. Future observation must aim at obtaining earlier spectra
to test for circumstellar matter.
