Coma Berenicids

Observing

This shower's duration extends from December 8 to January 23. The precise date of maximum is not known, but probably falls within the period of December 20-29, at which time the radiant is at α=165°, δ=+30°. The stream's activity is very weak, but numerous meteors have been photographed in the United States and the Soviet Union.

History

The discovery of this meteor shower came about as a result of stream searches among the photographic meteors detected during the Harvard Meteor Project of 1952-1954. First mention of this stream's existence was made by R. E. McCrosky and A. Posen in 1959. Their find was based on 6 photographic meteors which indicated a duration of January 13 to 23. In 1973, A. F. Cook, B.-A. Lindblad, B. G. Marsden, McCrosky, and Posen isolated seven photographic meteors from the same collection of Harvard meteors that indicated another stream with a duration of December 12 to 17, which they called the "December Leo Minorids." They commented that the "orbit bears a strong resemblance to that of the Coma Berenicids in January."

Indeed the orbits of both streams are so similar that their mutual existences cannot be due to mere chance. Unfortunately, a gap in the photographic records that spans the period of December 17 and 29 eliminates data that could have provided a vital link between these two streams. In addition, there have been no coordinated efforts to study this shower more completely since the stream's announcement---the only available observations being accidental prediscovery sightings made while observing other showers of December and January. The Author believes these "accidental" sightings not only provide proof that the two streams are one and the same, but probably point to a late December or early January maximum. A few of these observations are listed below.

  • During December 20-21, 1878, T. W. Backhouse (Sunderland, England) observed seven meteors from a radiant located at RA=157 deg, DEC=+35 deg.
  • On December 29, 1940, Professor Mohd. A. R. Khan (Begumpet, India) plotted 6 meteors from a radiant of RA=171 deg, DEC=+31 deg. Designated AMS radiant no. 4060, Khan's estimate of the radiant's reliability was given as "good".
  • On December 29.35, 1948, Jeremy H. Knowles (Marblehead, Massachusetts) plotted 4 meteors which seemed to originate from RA=170 deg, DEC=+22.5 deg. Designated AMS radiant no. 3036, Knowles estimated this as a "good" observation.

What makes this minor meteor stream especially interesting is the similarity of its orbit to the orbit of an "unconfirmed" comet that was reported in 1912-1913. The comet was officially designated 1913 I and was discovered in the early morning hours of December 30, 1912, by B. Lowe, an amateur astronomer in South Australia. Lowe managed to continue observations on January 2, 4, 5, and 9, before the comet entered morning twilight. However, an unfortunate positional error in Lowe's announcement telegram, which had been sent to Adelaide Observatory on January 7, caused searches made on January 8 and 11 to reveal nothing. Using four positions that could be derived from Lowe's rough observations, both A. C. D. Crommelin and M. Viljev were able to independently compute nearly identical orbits, except for a variation of 40 deg in the orbital inclination. [Recent calculations by the Author reveal Viljev's orbit to more precisely represent the observed positions.]

First mention of this curious relationship was made in 1954 by Fred L. Whipple. In an article showcasing 144 photographic meteor orbits obtained during 1936 to 1951, by Harvard College Observatory cameras, Whipple identified one meteor (designated 1918) with an orbit so similar to that of 1913 I, so as to make a comet-meteor association "fairly probable except for an uncertainty in the inclination of the comet's orbit." Whipple added that "if future meteor observations confirm the association, we may learn more about the orbit of Comet Lowe by meteor studies than we can glean from the direct observation." The suggestion that the Coma Berenicids were associated with comet Lowe was also suggested by McCrosky and Posen in 1959.

Beginning with the original 13 meteors isolated in the earlier computerized stream searches, the Author began examining other sources and soon compiled a database consisting of 23 photographic meteors. As a whole, these meteors indicate an orbital period of 72.4 years, but what is most striking is that this orbit seems to be composed of two fairly distinct filaments with periods of 27.3 years and 157.1 years. In addition, the orbital inclinations differ very little, while the perihelion distances vary by 0.1 AU and the argument of perihelion differs by 13 deg. A comparison is given in the "Orbit" section below.

Recent observations have been made by amateur astronomers in Western Australia, but the failure to detect the stream annually indicates either an irregular distribution of this stream's meteors or very weak annual activity which is occasionally detected only by very diligent surveys. During the period of 1969-1980, Michael Buhagiar (Perth, Western Australia) plotted 20,974 meteors for the purpose of compiling a list of southern hemisphere meteor radiants. On two occasions during those 12 years, he detected a radiant near Delta Leonis. Given a duration of December 20-23 and a maximum of December 21, the activity radiated from RA=167°, DEC=+27° with a maximum hourly rate of 2. The Western Australia Meteor Section, led by Jeff Wood, managed to detect activity from this radiant during January 5-6, 1980. A maximum ZHR of 6.44+/-3.22 was detected on January 6 from RA=171°, DEC=+24°.