Physical observations of 1996 PW and 1997 SE5: Extinct comets or D-type asteroids?

The minor planets 1996 PW and 1997 SE5 are two of the few known asteroids w ith orbital elements typical of long-period and Jupiter-family comets and a s such represent strong candidates for extinct cometary nuclei. We obtained filter photometry of 1996 PW and filter photometry and medium-resolution C CD spectroscopy of 1997 SE5 during their discovery apparitions. We also obs erved a suite of D-type asteroids as possible spectral analogs of cometary nuclei. Both 1996 PW and 1997 SE5 have moderately red, featureless spectra typical of the D-type asteroids, cometary nuclei, and other extinct cometar y candidates. The photometry for 1997 SE5 was fit by a triple-peaked lightc urve with a period of 9.050 +/- 0.005 h and an amplitude of 0.4 magnitude, suggesting a relatively complex and elongated shape. With this work, 1997 S E5 and 1996 PW join the ranks of 3552 Don Quixote and 944 Hildago as establ ished candidates for extinct comet nuclei. (C) 2000 Academic Press.