An Analysis of the Ion Tail of C/2004 Q2 (Machholz)
Jeff van Kerkhove1, Zhong Yi Lin2, Wing-Huen Ip2
1University of Rochester (Rochester, NY, USA), 2National Central University (Jhongli City, Taiwan)
Abstract
We have reduced and processed CO+ and H2O+ filter images of the comet
C/2004 Q2 (Machholz) between its perigee and perihelion in January
2005. Many of these images display folding ray phenomena, which are
believed to be related to solar wind. This poster discusses the
determination of the ray folding rates, speculating whether or not there is
a correlation to changes in the solar wind velocity. The results suggest
there very well could be a correlation, though a more thorough analysis
must be carried out first to improve the method’s validity.
Background
Comets are a class of small Solar System bodies that can generally be
thought of as dusty iceballs. That are composed of water, CO, CO2, with trace
quantities of organic molecules. For much of its existence, the comet is a icy
nucleus. Though when it gets close enough to the Sun, the volatile materials
start to sublimate, forming a diffuse coma around the nucleus. Radiation
pressure and solar winds are then presumed to push the loose particles away,
forming streaming dust and ion tails. Our study focuses on C/2004 Q2
(Machholz), a comet that passed quite close (0.35AU) to the Earth in January
2005.
Results
We observe the folding ray phenomenon (ion rays folding in toward the comet’s
antisolar axis) in these images over time. Degroote 2007 suggests a
connection between these folding rays and solar winds. They believe such
changes are caused by peaks in proton flux density, which is followed by an
increase in solar wind velocity. So, if the solar wind velocity increases, shouldn’t
there be a complimentary increase in the ion ray folding rate?
Coma-subtracted images (top
row has CO+ filtered images,
bottom row has H2O+ images)
To test this, we consider the proton flux spike on January 21, which imparts an
increase in wind velocity soon after. It takes about 3 days for these winds to
reach the comet. Thus, the changes from the spike should be evident between
January 24 and 25.
SoHO data-the middle graph
represents proton flux density
with respect to time, while the
top graph show solar wind
velocities with respect to time.
Note the proton flux peaks
(blue circles) are followed by
spikes in solar wind speed (red
circles).
From the folding rate calculation made, we did notice a distinct change in the
folding rates from January 24th to the 25th. However, it is difficult to draw
definitive conclusions due to the relatively large error of such measurements.
Thus, future work should be devoted to improving the validity of folding rate
measurements.
Data/Methods
Our images were taken using LOT (Lulin One-meter Telescope) at Lulin
Observatory in central Taiwan. We then reduced the data by subtracting zero
and dark frames from raw images, and dividing by flat fields in CO+ and H2O+
filters. These filters were used, as they are the most abundant ions found in
the ion tail. The images are then centered, rotated, and trimmed to a standard
size. We then subtract the comet’s coma from each image using a ring
masking method to better view ion ray folding phenomena. The rates of folding
can be calculated by measuring the change in the position of the ray’s edge
between frames.
Analysis/Conclusions
Folding rate velocities (for H2O+ filtered
images) with respect to Julian date. (The leftmost
plot shows all 5 observation dates, below are data from January 24, 25)
Carroll, Bradley, and Dale Ostlie. An Introduction to Modern Astrophysics. 2nd. New York: Pearson, 2007.
DeGroote, P., Bodewits, D., & Reyniers, M. 2008, A&A 477, L41-L44.
Fernandez, Julio Angel. Comets: Nature, Dynamics, Origin, and their Cosmological Relevance. Dordrecht,
Netherlands: Springer, 2004.
Ip, W.-H. 2004, Comets II, 605.
Lin, Zhong Yi. "A Study of Cometary Comae of Split Comets." Diss. National Central University, 2007.
Lin, Z. Y., Weiler, M., Rauer, H. & Ip, W. H. 2007, A&A 469, 771-776.
Acknowledgments
I would like to thank SUNY Oswego and National Central University for
organizing this program, as well as the National Science Foundation (Office of
International Science and Engineering, grant number 1065093), for funding my
work.