Autumn Arietids

Observing

The duration of this meteor shower extends from September 7 to October 27. Maximum occurs around October 8 (λ=194 deg) from α=32 deg, δ=+8 deg, with an hourly rate of 3-5. The radiant's daily motion is +0.90 deg in α and +0.35 deg in δ.

History

This shower is part of a cluster of radiants that is active in the Taurus-Aries region during the period of September through November. The complex nature of this region was first noted in 1928, when William F. Denning published the details of thirteen radiants. One of these radiants, the "Xi Arietids" was said to be active during September and October from an average radiant of RA=30.9 deg, DEC=+9.6 deg, while another radiant---the "Sigma Arietids"---was said to be active during October from RA=41.9 deg, DEC=+13.7 deg. At the time Denning was still a strong believer in the stationary radiant theory, but the currently known movement of the October Arietids would seem to link these two radiants.

F. W. Wright and Fred L. Whipple were the next people to isolate the October Arietids when, during a 1950 investigation of the photographic Taurid meteors, they found 8 photographic meteors which came from an average radiant of RA=+41.3 deg, DEC=+10.3 deg. The mean date of activity was October 20.22. This study involved 102 meteors photographed during the period of October 15-December 2, in the years 1896-1948. The authors expressed their opinion that the October Arietids might form a continuous stream with the southern Taurids, though they suggested further studies would be needed to clarify the situation.

The use of radar equipment came of age during the 1950's, but, despite numerous observations of the Taurids, the equipment was not yet sensitive enough to separate diffuse radiants close together. This changed in the early 1960's when two radio-echo studies detected the October Arietids: B. L. Kashcheyev and V. N. Lebedinets (Kharkov Polytechnical Institute) detected 18 meteors during October 10-21, 1960, from an average radiant of RA=40 deg, DEC=+15 deg and C. S. Nilsson (Adelaide Observatory, South Australia) detected 30 meteors during October 20-31, 1961, from an average radiant of RA=44.8 deg, DEC=+12.4 deg.

Nilsson may have also detected the October Arietids during the last days of September. He contemplated the matter after noting a similarity between a stream he designated 61.9.1 and the "Arietids" (designated 61.10.1). The stream was detected during September 22-29, from an average radiant of RA=18.1 deg, DEC=+4.9 deg. It was based on 19 meteors and is listed below with the October branch. Nilsson found the orbit of this stream to closely resemble the orbit of the June daytime shower called the Zeta Perseids. He added, "It is just possible that the two streams 9.1 and 10.1 are both part of a wide band of meteors, but consideration of the characteristics of the October Arietids and November Taurids does not encourage this view." The Author points out that the radio equipment at Adelaide was not operational during September 30 to October 19, 1961.

The two sessions of the Radio Meteor Project conducted during the 1960's at Havana, Illinois, also succeeded in detecting the October Arietids. Zdenek Sekanina said the 1961-1965 session revealed activity extending from September 11 to October 23. The date of the nodal passage was given as October 1.4 (solar longitude=187.8 deg), at which time the radiant was at RA=23.9, DEC=+8.8. From data compiled during the 1968-1969 session, Sekanina gave the duration as September 7 to October 22. The date of the nodal passage was given as October 11.5 (solar longitude=197.8 deg), while the average radiant was at RA=32.3 deg, DEC=+10.2 deg.

The October Arietids are a neglected shower among visual observers and, if not for the photographic and radar programs of the last 30 years, virtually nothing would be known of this stream. Most of this neglect is probably due to the Southern Taurid stream which moves through a region of the sky a few degrees to the southwest. This latter shower is also a larger producer of meteors, with rates typically near 10 per hour.

One of the most significant visual studies occurred while seven Russian astronomers observed the Orionids during October 17-21, 1973. Coordinated by G. N. Sizonov, the observations took place from the meteor station of Armavir middle school #18. Combined observations of the October Arietids revealed an average magnitude of 3.37, based on 43 magnitude estimates, and a maximum ZHR of 3.4. Sizonov showed the highest ZHR to have occurred on October 20 at which time the average distance between particles within the stream was 484 kilometers.

From analyzing the photographic meteors of both the October Arietids and the Southern Taurids, the Author has noted that the radiants of each stream remain fairly close together. At the time they both appear in mid-September, the October Arietids are 7 deg east of the Southern Taurids, while they are about 4 deg northeast at the end of October. Both streams also possess diffuse radiants, so that it is nearly impossible to visually separate one from the other. This analysis also revealed the October Arietid daily motion to be +0.90 deg in RA and +0.35 deg in DEC.