THE EXPANSION OF THE OUTER CIRCUMSTELLAR SHELL OF P-CYGNI

The expansion of a faint, outer irregular shell to the circumstellar n ebulosity of the luminous blue variable P Cygni has been measured with the Manchester Echelle Spectrometer combined with the high-altitude S an Pedro Martir 2.1-m UNAM telescope. This is the first ever measureme nt of the expansion velocity of such a historic remnant of a luminous blue variable star eruption. The faintness of the outer shell and the high brightness and close proximity of the star make it a particularly difficult observation. The high optical luminosity of the spectromete r and the clarity of the sky have combined to permit a successful meas urement. A radial expansion velocity of 185 +/- 10 km s(-1) is implied , which suggests an age of 2100 +/- 200 yr for this 1.6 arcmin diamete r outer shell, if we assume a distance of 1.8 kpc to P Cygni.