Three tails of comet Hale-Bopp

Abstract

We report on the imaging detection of the sodium tail of comet Hale-Bopp using large field-ofview, multi-wavelength observations from the McDonald Observatory in March 1997. We subtract off-band images from sodium-filter images to obtain the atomic sodium tail, and we find it to be more extended in width than either the dust or ion tails. The cross-tail integrated brightness of the sodium tail increases with distance from the nucleus for at least 8 million km. The direction of the sodium tail in our data is different from the ion tail, the dust tail, and the sodium tails imaged at different times by other observers. To account for these characteristics, there must be an extended source of sodium atoms tail ward of the comet nucleus. We propose that the sodium tail in March 1997 was produced by the release of sodium atoms from grains in the dust tail.