Properties of the SN 1987A Circumstellar Ring and the Distance to the Large Magellanic Cloud

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• Gilmozzi, R.
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• Macchetto, F.
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• Adorf, H. -M.
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• Kirshner, R. P.

Abstract

We have determined the distance to SN 1987A by comparing the angular size of its circumstellar ring, measured from an HST image obtained in a narrow [O III] 5007 A filter, with its absolute size derived from an analysis of the light curves of narrow UV lines (N V λ1240, N IV] λ1486, N III] λ1750, and C III] λ1909) measured with IUE. Our analysis confirms that the observed elliptical structure is indeed a circular ring seen at an inclination of <i> = 42.8^deg^ + 2.6^deg^ and provides a determination of its absolute diameter of (1.27 +/- 0.07) x 10^18^ cm. Its ratio to the angular diameter of 1.66''+/- 0.03'' (Jakobsen et al.) gives an accurate determination of the distance to SN 1987A, i.e., d(1987A) = 51.2 +/- 3.1 kpc. Estimating the relative position of SN 1987A within the Large Magellanic Cloud on the basis of radial velocity data, the distance to the center of the LMC turns out to be 50.1 +/- 3.1 kpc and its distance modulus 18.50 +/- 0.13. This value agrees very well with the determinations obtained from light-curve analyses of variable stars.