Southern May Ophiuchids

Observing

This ecliptic stream exhibits a long duration extending from April 21 to June 4. Maximum occurs between May 13 and 18 from an average radiant of RA=252°, DECL=-23°.

History

The first observations of activity from the Southern May Ophiuchids were made by two members of the American Meteor Society (AMS). Ronald A. McIntosh (Auckland, New Zealand), a long-time Southern Hemisphere member of the AMS, plotted nine meteors from a radiant of RA=249.5°, DECL=-26° on May 15, 1926, while G. W. Ridley (Alameda, California, USA) plotted three meteors from a radiant of RA=249°, DECL=-26.5° on May 18, 1931.

The 1930's marked the true beginnings of notable activity from this stream, with the bulk of the observations coming from Cuno Hoffmeister and other German observers. In his book Meteorströme, Hoffmeister lists nine radiants for the year 1933 alone which appear to represent activity from this stream. The observations covered the period of May 19 to June 2 (λ=58.1-72.3°). These observations indicate the radiant is rather diffuse, but there is a definite tendency for it to move eastward at a rate of about one degree daily. These observations do not show a clear trend as to whether the declination moves to the north or south. Additional radiants were given for 1936 and 1937.

The first apparent recognition of this stream as a potential annual producer of meteors was in 1935, when Ronald A. McIntosh's paper "An Index to Southern Meteor Showers" was published. Although a strong indication of the shower was not present, four fairly similar radiants were listed which could all refer to the Southern May Ophiuchids. Radiant 157 was based on four previously observed radiants and was given a duration of May 6-15. The average radiant position was given as RA=246°, DECL=-26°. Radiant number 159 was said to be active during May 17-24. It was based on two previously observed radiants and possessed an average position of RA=248°, DECL=-22.5°. Radiant 161 was based on only one previously observed radiant. It was said to be active on May 15 from RA=249.5°, DECL=-25°. Radiant 170 was based on three previously observed radiants and was given a duration of May 19-22. The average radiant position was RA=258°, DECL=-23°.

The Southern May Ophiuchids were well represented in the 1952-1954 Harvard Meteor Project. From a list of 2529 photographic meteors published in MP1961, the Author has isolated seven meteors (two of which had precise orbits computed in JW1961) which appear to be probable members of this stream. The indicated duration is May 5 to June 4, and the date of nodal passage is May 17 (λ=55.4°). The average radiant position was at RA=251.6°, DECL=-24.8°.

The 1960's were a decade when the true extent of the Southern May Ophiuchid stream was finally realized. Details were obtained during both sessions of the Radio Meteor Project. From the 1961-1965 data, Zdenek Sekanina established the duration as May 3-June 4. The nodal passage was determined as May 13.0 (λ=51.8°), at which time the radiant was RA=250.1°, DECL=-22.4°. From the 1968-1969 session, the duration was determined as April 21-June 3, while the date of the nodal passage was given as May 18.5 (λ=57.1°). The average radiant was given as RA=254.0°, DECL=-25.0°.

Recent observations of activity from this stream have been obtained by members of the Western Australia Meteor Section. According to the group's director, Jeff Wood, the Southern May Ophiuchids were detected in 1979 during the period of May 17-26 (they were referred to as the "Theta Ophiuchids"). A maximum ZHR of 2.27+/-0.55 was detected on May 19 from an average radiant of RA=254°, DECL=-25°. Possible activity was also detected in 1980 when meteors were observed during May 23-24 from an average radiant of RA=256°, DECL=-22°. The shower was labelled the "Xi Ophiuchids." A maximum ZHR of 1.78+/-0.07 was observed on May 23.