Title:
------
Spatially resolved STIS spectroscopy of SN 1987A: evidence for shock 
interaction with circumstellar gas

Authors:
--------
G. Sonneborn, C. S. J. Pun, R. A. Kimble, T. R. Gull, P. Lundqvist, R. Mc Cray,
P. Plait, A. Boggess, C. W. Bowers, A. C. Danks, J. Grady, S. R. Heap,
S. Kraemer, D. Lindler, J. Loiacono, S. P. Maran, H. W. Moos, & B. E. Woodgate

Abstract:
---------
Visual and ultraviolet spatially resolved (0.1 arcsec) spectra of SN 1987A were
obtained on days 3715 and 3743 with the Space Telescope Imaging Spectrograph on 
the Hubble Space Telescope. Very broad Ly-alpha emission is detected with 
velocities extending to +/- 20,000 km s^{-1}, undoubtedly the result of 
high-velocity SN debris colliding with circumstellar gas. The Ly emission is 
located inside the inner circumstellar ring and appears to fill most of the 
surface area within 0.67 +/- 0.03 arcsec (0.14 pc at a distance of 50 kpc) of 
the ring's center. The observed flux in the Ly-alpha feature is 
(1.85 +/- 0.53)E{-13} erg cm^{-2} s^{-1} and (1.25 +/- 0.53)E{-12} erg cm^{-2} 
s^{-1} after correcting for extinction. The size of the central ring in 
forbidden lines of oxygen has a dependence on ionization potential. The ring's
radius in [O I], and [O III] along the major axis (PA 88 degrees) are 0.792 and
0.845 arcsec, respectively. A spatially unresolved blue-shifted emission 
feature was discovered in H-alpha (and other lines) on the inner ring at 
PA (31 +/- 8) degrees. The H-alpha emission extends to -250 km s^{-1} with no 
corresponding red-shifted emission. This suggests that a highly localized 
interaction is underway between high-velocity gas and material in or close to 
the near side of the inner ring. The dereddened flux from the SN debris is 
(1.5 +/- 0.53)E{-16} erg cm^{-2} s^{-1} A^{-1} in the range 1400-1700 A.

To appear in:
-------------
ApJ Letters, January 1998

(Paper available on request from G. Sonneborn.)