Alpha and Beta Centaurids

Observing

The duration of these meteor showers extends from February 2 to February 25. Maximum occurs around February 8. The Alpha Centaurids emanate from α=216°, δ=-60°, while the Beta Centaurids have a radiant of α=208°, δ=-58°. Despite the closeness of the radiants, they do have differences. The Alpha Centaurids have maximum hourly rates of 3, while the Beta Centaurids can reach hourly rates as high as 14. The Alpha Centaurids have an average magnitude of 2.45, while the Beta Centaurids are probably about 1.6.

History

This discovery of this shower should be attributed to M. Buhagiar (Western Australia), who obtained observations of both Centaurid radiants during 1969-1980. In his "Southern Hemisphere Meteor Stream List" of 1980, Buhagiar listed two radiants which reached maximum on February 7. "Radiant 290" was active during February 6-8, from α=206°, δ=-57°, while "radiant 299" was active during February 5-9, from α=214°, δ=-64°. Both radiants were referred to as "Beta Centaurids."

Although both radiants have continued to be observed following the publication of Buhagiar's meteor stream list, observers have rarely distinguished between the two radiants during the same year.

During 1979, members of the Western Australia Meteor Section (WAMS) managed to observe the "Alpha Centaurids" during February 2-18. At maximum on February 7, the radiant is at α=216°, δ=-59°. During 1980, the same group observed members of the "Alpha Centaurids" during February 2-24. They noted that maximum came on February 8, from α=209°, δ=-58°. The 1979 radiant obviously represents the true Alpha Centaurids, while the 1980 radiant is the Beta Centaurids.

Although it is possible that C. Hoffmeister observed this shower (α=210°, δ=-57°) on 1938 February 2, while in South Africa, the observational history of this stream essentially began in 1969, so that the characteristics of each shower are hard to determine. Nevertheless, some interesting details should be noted. First of all, the Alpha Centaurids are apparently a consistent shower, with Buhagiar assigning an hourly rate of 3, and WAMS observers detecting high rates of 2 (ZHR calculated as 8.56+/-4.94) in 1979. The Beta Centaurids are apparently variable in activity, according to Buhagiar, with his 1969-1980 observations revealing high rates of 10 meteors per hour. WAMS observers obtained maximum rates of 11-14 per hour (ZHR calculated as 28.48+/-4.88) during a one-hour interval on 1980 February 8/9.

Characteristics of the Centaurid meteors have also been gathered in recent years. During 1979, 20 Alpha Centaurids revealed an average magnitude of 2.45, while, during 1980, 169 Beta Centaurids revealed an average magnitude of 1.6 (the latter number is an approximation by the Author based on a table published in the October 1980 issue of Meteor News).

The Alpha Centaurids may have been detected by radar at Adelaide Observatory during 1969. G. Gartrell and W. G. Elford operated the radar system during February 10-17. Two meteors were noted from a radiant of α=223°, δ=-61°, with the date of nodal passage being determined as February 15. Assuming these meteors are members of the Alpha Centaurids, then this stream orbit has an inclination near 105°, and a semimajor axis near 2.5 AU. This identification would also indicate that the radiant's daily motion is very close to +1° in α. The movement in δ can not be determined from the available observations.