SN 1987A’s Circumstellar Envelope. II. Kinematics of the Three Rings and the Diffuse Nebula

We present several different measurements of the velocities of structureswithin the circumstellar envelope of SN 1987A, including the inner, equatorialring (ER), outer rings (ORs), and the diffuse nebulosity at radii < 5 pc, basedon CTIO 4m and HST data. A comparison of STIS and WFPC2 [N II]6583 loci for therings show that the ER is expanding in radius at 10.5+-0.3 km/s, with thenorthern OR expanding along the line of sight at about 26 km/s, and for thesouthern OR, about 23 km/s. Similar results are found with CTIO 4m data.Accounting for inclination, the best fit to all data show both ORs with anexpansion from the SN of 26 km/s. The ratio of the ER to OR velocities isnearly equal to the ratio of ER to OR radii, so the rings are roughlyhomologous, all having kinematic ages corresponding to about 20,000 yr beforethe SN explosion. This makes previously reported, large compositionaldifferences between the ER and ORs difficult to understand. Additionally, agrid of longslit 4m/echelle spectra centered on the SN shows two velocitycomponents over a region roughly coextensive with the outer circumstellarenvelope extending about 5 pc (20 arcsec) from the SN. One component isblueshifted and the other redshifted from the SN centroid by about 10 km/seach. These features may represent a bipolar flow expanding from the SN, inwhich the ORs are propelled 10-15 km/s faster than that of the surroundingenvelope into which they propogate. The kinematic timescale for the entirenebula is at least about 350,000 yr. The kinematics of these various structuresconstrain possible models for the evolution of the progenitor and its formationof a mass loss nebula.Comment: 25 pages AASTeX text plus 12 figures. ApJ, in pres