These images
are different enhancements of a 500 second exposure of
Comet C/1996 B2 (Hyakutake) taken
on March 11, 1996 (11:40 UT) through a narrowband H2O+ filter (central
wavelength 6200A, FWHM of 15A). The initial image was taken by Dr. Walt
Harris from
the Space Astronomy Lab of the
University of Wisconsin using the 3.5m
WIYN
telescope on
Kitt Peak with a 2048x2048 CCD chip with a plate scale of 0.2"/pixel, and was reduced by Dr. Beatrice
Mueller from NOAO.
These images were taken at the 3.5m
WIYN telescope during queue-mode
observing, for the collaborative project between Dr. Walt Harris
(Wisconsin) and
Dr. Beatrice Mueller (NOAO).
There is one image from
each of the nights of Tuesday March 19th and Wednesday March 20th.
These frames show a much smoother tail coming from the head of the comet,
as compared to the March 11th image (see above)
probably due to increased, no longer patchy, activity. Different
physical components making up the comet are represented by different colors
in these false color composites: the dusty material is shown as red,
water and ice are shown as green, and carbon emission (basically, soot)
is shown as blue. Color gradients therefore show the different
distributions of these components due to their varying densities and
level of activity. The image from March 20th has more exaggerated
color gradients than the picture from the day before: this probably
does not reflect a physical difference, simply the way the picture
was created.
The comet is moving very rapidly across the sky, and stars appear as
faint streaks in only one color: by the time the image of the next comet
component is taken, the stars from the previous field are already out
of the frame. There are also some colored "flecks" visible: these are
due to random events triggering the very sensitive CDD detector and are
quite spurious. These `cosmic rays' are usually edited out of images
before final use, but that rather time-consuming step has not yet been
performed. The reductions of these images were done by
Dr. Nigel Sharp at NOAO.
Here we show two observations from the
WIYN telescope from the nights
of Sunday March 24th and Tuesday March 26th (UT of observation 25/03/96
12:10 and 27/03/96 11:35). These images show the nucleus of Comet
Hyakutake, revealing apparent `chunks' moving back along the tail, as
well as a strong `fan-like' structure in the coma, mostly in front of
the nucleus. The frames are paired, with the earlier observation to
the left, and are presented in black and white and in
false color. The images were then enhanced, by dividing
by a smoothed model in order to show the structures more clearly, and
the result is also shown in false color. These observations
were made by Dr. Walter Harris from the Space Astronomy Laboratory (SAL)
at the
University of Wisconsin, Dr. Kent
Honeycutt from
Indiana University, and
Dr. Beatrice Mueller from NOAO.
These observations were only possible because of special non-sidereal
tracking software written especially for this observation by
Jeff Percival (also of SAL).
Conditions on
Kitt Peak were better for the
first observation, which
shows smaller scale structure which is more blurred in the later data,
but the feature in the tail is clearly moving out behind the nucleus,
and the structure in the `fan' also changes with time.
These images were created from observations made on the night of
Monday March 25th, 1996. The first frame
is a composite of two, two-minute
exposures using a blue continuum filter (4875/38 Angstroms), and shows
similar structure to other images taken of Comet Hyakutake and available
at this site. This picture is shown using a similar false color scheme.
The second frame, however, is a summation of three, two-minute exposures
taken using a filter (at 3919/199 Angstroms) that isolates emission
coming from a bright set of CN lines (the cyanogen molecular complex).
Two pictures are shown derived from this frame, firstly a false color
representation of the summed image, and secondly
a false color version of
the image after enhancement by dividing by a
smoothed model of the image. A shaded 3D plot is
also shown of the summed image.
The images comprising the first frame were taken before and after the observations making up the second frame, so that the differences are not simply a change in time but represent a definite difference in the comet's structure between different molecular species. In the CN frame, a bright structure is observed extending in the anti-sunward direction from the comet, appearing as an arc crossing the tail with a faint conical feature reaching as far as the nucleus itself. The conical structure is only detectable in bright resonant emission lines from neutral gas such as CN or OH. For example, there no trailing features apparent in the continuum filter image, which looks mainly at dust. The shape of this feature is most reminiscent of a 3-dimensional analog to a ship's wake, and that may indeed be what it is, although considerable study is still required before we will know for sure the causes of this structure or its composition.
These observations were performed at the 3.5m WIYN telescope by Dr. Walter Harris from the Space Astronomy Laboratory (SAL) at the University of Wisconsin and Dr. Kent Honeycutt from Indiana University with the assistance of Alex Macdonald ( NOAO).
Note: All image enhancements were done by Dr. Nigel Sharp (520-318-8273) at NOAO.
