A continuum frame (i.e., dust) was taken on Sunday March 24th at UT 05:10 by Beatrice Mueller (observing time courtesy of Marc Postman (STScI) and Tod Lauer (NOAO)) using the 4m telescope on Kitt Peak. The false color image is 11.7 arc minutes on a side and shows varying intensity. The black and white image is the central 4 arc minutes of the same frame. The reductions and color enhancements of this image were done by Dr. Nigel Sharp (520-318-8273) at NOAO.
This picture shows two sequences from the nights of March 22nd, 23rd and 24th (going from left to right) using images taken at the 4m telescope on Kitt Peak. The upper row were made in the C2 (carbon molecule) emission line, and the lower frames are continuum images (mostly dust). The comet nucleus, and the tail close to the nucleus, both show a developing strong asymmetry. Each square is two arc minutes on a side. The images were taken by Beatrice Mueller (NOAO) (observing time courtesy of Marc Postman (STScI) and Tod Lauer (NOAO); the reductions were done by Beatrice Mueller.
This is part of a high resolution (0.2 Å) echelle spectrum of the OH 0-0 band in comet C/1996 B2 (Hyakutake), obtained with the 4m telescope at Kitt Peak on March 25, 1996, by R. Meier, L. M. Woodney, M. F. A'Hearn, and D. Wellnitz (Department of Astronomy, University of Maryland).
The OH is produced by photodissociation of water, which is by far the most abundant molecule in comets (about 80%). The OH 0-0 band is in the near ultraviolet wavelength range which is heavily attenuated by our atmosphere, and this renders the molecule very difficult to observe with ground-based telescopes. The entire series of lines seen here is caused by fluorescence transitions between the ground state and the first electronically excited state of OH. The designation "0-0 band" means that the vibrational state of the OH remains zero during the transition (the O and H atoms are vibrating relative to each other). The specific individual lines are due to simultaneous changes in the rotational state of OH, and are clearly separated because the rotational frequency can only change by discrete amounts. Every molecule has its own set of characteristic line positions which enable us to identify molecules unambiguously. The relative strengths of the different lines provide information not only about the abundance of a particular molecule, but also about the extent to which the molecule is experiencing collisions with other molecules, and about the relative speed between the comet and the Sun. This last is important because the solar light which ultimately causes all of the observed transitions is Doppler shifted to a greater or lesser degree by the relative speed between the comet and the Sun (this is known as the Swings effect). The observing project which obtained these data is actually primarily interested in the 0-0 bands of NH and CH, both of which have also been observed. The scientists were particularly looking for possible emission lines from ND and CD, which are molecules containing the heavier isotope deuterium (D) instead of the common hydrogen (H) atom. They were also looking for lines from so far undetected species.