High resolution spectroscopy of the inner ring of SN 1987A

Abstract

We discuss high resolution VLT/UVES observations (FWHM ∼ 6 km s −1 ) from October 2002 (day ∼5700 past explosion) of the shock interaction of SN 1987A and its circumstellar ring. A large number of narrow emission lines from the unshocked ring, with ion stages from neutral up to Ne V and Fe VII, have been identified. A nebular analysis of the narrow lines from the unshocked gas indicates gas densities of (∼1.5−5.0) × 10 3 cm −3 and temperatures of ∼6.5 × 10 3 −2.4 × 10 4 K. This is consistent with the thermal widths of the lines. From the shocked component we observe a large range of ionization stages from neutral lines to [Fe XIV]. From a nebular analysis we find that the density in the low ionization region is 4 × 10 6 −10 7 cm can be seen probably arising from a small fraction of shocked high density clumps. We discuss these observations in the context of radiative shock models, which are qualitatively consistent with the observations. A fraction of the high ionization lines may originate in gas which has yet not had time to cool, explaining the difference in width between the low and high ionization lines. The maximum shock velocities seen in the optical lines are ∼510 km s −1 . We expect the maximum width of especially the low ionization lines to increase with time.

The outer rings of SN 1987A

“…The centre of the supernova-ring system is at +286.6 km s −1 according to Gröningsson et al (2008a) and +289 km s −1 according to Crotts & Heathcote (2000). If we use Gröningsson et al (2008a) as reference, because it partly uses the same data as we do, both areas 1 and 4 are redshifted compared to the supernova by roughly ∼6 and ∼4 km s −1 , respectively.…”

“…If we use Gröningsson et al (2008a) as reference, because it partly uses the same data as we do, both areas 1 and 4 are redshifted compared to the supernova by roughly ∼6 and ∼4 km s −1 , respectively. The redshift of the NOR point is easy to understand from Fig.…”

“…For a detailed description of the steps involved in the reductions we refer the reader to Gröningsson et al (2008a). For the time evolution of the fluxes an accurate absolute flux calibration is necessary.…”

“…For the time evolution of the fluxes an accurate absolute flux calibration is necessary. As discussed in Gröningsson et al (2006) and Gröningsson et al (2008a), we estimated the accuracy of the flux calibration by comparing the spectra of flux-calibrated spectro-photometric standard stars with their tabulated physical fluxes. In addition, we compared emission line fluxes from different exposures (and hence with different atmospheric seeing conditions) within the same epochs.…”

The 3-D structure of SN 1987A's inner ejecta

“…The outer ejecta of SN 1987A travelling at around 30 000 km s −1 have reached the outer ring a decade ago, and have become visible mostly in the reverse shocks generated by the collision with the ring material (McCray 2003;Gröningsson et al 2006Gröningsson et al , 2008bKjaer et al 2007;Zanardo et al 2010). The inner ejecta are still heated by the radioactive decays (mostly positrons from the 44 Ti decays; Fransson & Kozma 2002) and have expanded enough to be spatially resolved.…”