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R. C. Iping, G. Sonneborn (NASA GSFC)
O VI 1032, 1038 A emission from the circumstellar pre-explosion gas around SN 1987A has been detected in spectra obtained by the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. FUSE observes in the wavelength range 900-1185 A at a spectral resolution of 15-20 km/sec. O VI is the highest ionization state yet detected in line emission from the SN 1987A circumstellar material. The O VI emission line profiles are narrow, with FWHM <35 km/sec, and have a heliocentric radial velocity of +280 km/sec. This places the emitting gas at rest relative to the supernova. Spectra obtained in Oct. 2000 and Sept. 2001 have essentially the same O VI fluxes. Simultaneous spectra obtained in the other FUSE apertures, positioned about 100 arcsec from SN 1987A, show nothing at the O VI wavelengths, eliminating diffuse emission in the LMC as a possible source of the O VI feature.
We present an analysis of the interstellar absorption lines in FUSE spectra of the two early B-type companion stars of SN 1987A, Star 2 and Star 3. Stars 2 and 3 are 2.9 and 1.7 arcsec, respectively, from the position of the former Sk -69 202. They are separated by 4.5 arcsec, or about 1.1 pc in the LMC. Spectra of Star 3 were taken through 1.25x20 arcsec and 4x20 arcsec apertures; Star 2 was observed only through the 4x20 arcsec aperture. The lines of sight have interstellar Milky Way and LMC features, including molecular hydrogen and O VI. The interstellar O VI 1032 A profile and some other features are not the same on the two lines of sight. Analysis of the O VI profiles show that the LMC O VI absorption is present only at heliocentric velocities less than about +260 km/sec. This supports the analysis of the O VI emission from SN 1987A , particularly the conclusion that ISM absorption does not interfere with the O VI 1032 emission line profile. The interstellar line profiles show that intervening absorption has a negligible effect on the shape of the O VI emission.
This work has been supported in part by NASA grant NAG5-11137 to Catholic University of America.
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.