Abundances and density structure of the inner circumstellar ring around SN 1987A

Details Abundances and density structure of the inner circumstellar ring around SN 1987A Abundances and density structure of the inner circumstellar ring around SN 1987A

2010-02-22

arxiv.org/abs/1002.4195v2

Astronomy and Astrophysics

Astrophysics

Solar and Stellar Astrophysics

17 pages, 8 figures, accepted for publication in ApJ

Scientific paper

We present optical spectroscopic data of the inner circumstellar ring around SN 1987A from the Anglo-Australian Telescope (AAT) and the Very Large Telescope (VLT) between ~1400 and ~5000 days post-explosion. We also assembled the available optical and near-infrared line fluxes from the literature between ~300 and ~2000 days. These line light curves were fitted with a photoionization model to determine the density structure and the elemental abundances for the inner ring. We found densities ranging from 1x10^3 to 3x10^4 atoms cm^-3 and a total mass of the ionized gas of ~0.058 Msun within the inner ring. Abundances inferred from the optical and near-infrared data were also complemented with estimates of Lundqvist & Fransson (1996) based on ultraviolet lines. This way we found an He/H-ratio (by number of atoms) of 0.17+-0.06 which is roughly 30% lower than previously estimated and twice the solar and the Large Magellanic Cloud (LMC) value. We found an N/O-ratio of 1.5+-0.7, and the total (C+N+O)/(H+He) abundance about 1.6 times its LMC value or roughly 0.6 times the most recent solar value. An iron abundance of 0.20+-0.11 times solar was found which is within the range of the estimates for the LMC. We also present late time (~5000 - 7500 days) line light curves of [O III], [Ne III], [Ne IV], [Ar III], [Ar IV], and [Fe VII] from observations with the VLT. We compared these with model fluxes and found that an additional 10^2 atoms cm^-3 component was required to explain the data of the highest ionization lines. Such low density gas is expected in the H II-region interior to the inner ring which likely extends also to larger radii at higher latitudes (out of the ring plane). At epochs later than ~5000 days our models underproduce the emission of most of these lines as expected due to the contribution from the interaction of the supernova ejecta with the ring.

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