THE DISTANCE TO THE LARGE MAGELLANIC CLOUD FROM SN-1987A

The LMC is near enough that any distance derived from observations of SN 1987A must be corrected for the displacement of the supernova from the center of mass. In handling what may be the most reliable extragalactic distance ever determined, Panagia et al. (1991) approximated the LMC to be a sphere, in effect allowing the distance modulus to be between 18.40 and 18.69. In this model, estimation of the distance to the center of mass requires very accurate knowledge of the depth of the supernova within the galaxy, which is unachievable. In fact, it is known that the LMC is a disk galaxy with a well-defined orientation. The thickness of the young component relative to the scale length can be stringently constrained through comparison with the edge-on counterpart NGC 55. It is shown that the center of mass of the LMC is (0.03 +/- 0.03) mag nearer than the supernova. The uncertainty represents the entirety of the effect of allowing SN 1987A to be at any depth within the layer confining 99% of the light of the young disk. Thus, based upon SN 1987A, the heliocentric distance modulus for the LMC is 18.52 +/- 0.13, with negligible uncertainty due to the depth correction.