Physical Observations of 1996 PW and 1997 SE5: Extinct Comets or D-Type Asteroids?

Abstract The minor planets 1996 PW and 1997 SE5 are two of the few known asteroids with orbital elements typical of long-period and Jupiter-family comets and as such represent strong candidates for extinct cometary nuclei. We obtained filter photometry of 1996 PW and filter photometry and medium-resolution CCD spectroscopy of 1997 SE5 during their discovery apparitions. We also observed 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 cometary candidates. The photometry for 1997 SE5 was fit by a triple-peaked lightcurve 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 SE5 and 1996 PW join the ranks of 3552 Don Quixote and 944 Hildago as established candidates for extinct comet nuclei.

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