Chi and Omega Scorpiids

Observer's Synopsis

The Chi and Omega Scorpiids are closely related ecliptic streams. The former, or northern stream, possesses a typical long duration which extends from May 6 to July 2. Maximum activity is not well defined, but seems most likely to occur between May 28 and June 5, from an average radiant of RA=245 deg, DECL=-12 deg. The Omega Scorpiids form the southern component and are active during May 19 to July 11. Maximum occurs during June 3-6, from an average radiant of RA=243 deg, DECL=-22 deg. The daily motions of both radiants are very similar and amount to +0.9 deg in RA and -0.2 deg in DECL.

History

The first detection of the Chi Scorpiids should be credited to William F. Denning. During 1886 to 1912, he observed several meteors emanating from RA=252 deg, DECL=-10 deg, during June 2-4. These meteors were described as "very slow."
In 1935, R. A. McIntosh published his "An Index to Southern Meteor Showers." The Chi Scorpiids were listed as radiant number 147. They occurred during May 28 to June 11. McIntosh's compilation of 5 previously observed radiants indicated the radiant moved from RA=241 deg, DECL=-13 deg to RA=247 deg, DECL=-18 deg. Although this indicates a daily motion slightly exaggerated over the mathematically predicted motion of RA=+0.93 deg, DECL=-0.14 deg, the accumulated visual, photographic and radar data indicate the radiant is fairly diffuse---amounting to a diameter of nearly 8 deg---so that an accurate visual determination would be truly remarkable.
McIntosh's radiant list also included the Omega Scorpiids. Designated as radiant 146, it was the first time activity had been officially recognized from this stream. The shower was active during the period May 29 to June 11, and moved from RA=240 deg, DECL=-21 deg to RA=247 deg, DECL=-18 deg. Like the Chi Scorpiids, this shower's radiant should track southeasterly, but since it also possesses a fairly diffuse radiant, McIntosh's determination should not be taken at face value.
Observations of the Chi Scorpiids have been fairly continuous during the 20th century, with nearly every major meteor radiant compilation providing evidence. Radiants from some of the more prominent observers follow:

Chi Scorpiids

Date (UT) Designation RA (deg) DEC (deg) Observer
1933, May 26-27 258 244 -14 Ernst Opik
1932, May 31 99 244 -10 Ernst Opik
1930, June 8.76 --- 244.8 -14.3 V. Maltzev
1912, June 9.2 403 248 -14 C. Hoffmeister

Observations of the Omega Scorpiids have been somewhat sporadic during the 20th century, except among observers in the southern hemisphere. Thus, the shower is represented in several major works. Some of the radiants follow:

Omega Scorpiids

Date (UT) Designation RA (deg) DEC (deg) Observer
1933, May 23.8 3065 235 -26 C. Hoffmeister
1933, May 28.3 3235 241 -25 C. Hoffmeister
1937, June 3.3 3415 247 -26 C. Hoffmeister
1937, June 4.0 3429 240 -25 C. Hoffmeister
1937, June 5.3 3439 244 -22 C. Hoffmeister
1937, June 7.4 3466 249 -27 C. Hoffmeister
1937, June 7.1 3476 249 -29 C. Hoffmeister
1937, June 11.4 3526 255 -23 C. Hoffmeister
1937, June 13.5 3548 253 -25 C. Hoffmeister
1937, June 15.0 3569 257 -25 C. Hoffmeister

Taken as a whole, the Chi and Omega Scorpiids are very similar to the Ophiuchids (and even the Theta Ophiuchids) discussed earlier in this chapter---there are northern and southern components with orbits differing only in AOP and AN (this variance equals 180 deg for each of these orbital elements). Unlike the other ecliptic streams, both branches are equally strong and have been listed as showers in their own right.
Further notice of these northern and southern branches was taken by Bertil-Anders Lindblad in 1971, when he detected the Chi Scorpiid stream in a computer study of photographic meteors. He pointed out that the Chi Scorpiid stream possessed two branches, with the southern branch being identical to McIntosh's radiant number 146.
As indicated earlier, observations of the Omega Scorpiids are at their best from the southern hemisphere. According to Jeff Wood, director of the meteor section of the National Association of Planetary Observers, a shower referred to as the "Omega Scorpiids" is visible every year in Australia. Reaching maximum on June 4 from RA=240 deg, DECL=-22 deg, it is visible during May 24 to June 13. Wood claims the ZHR typically varies between 5 and 20.
Interestingly, despite the fact that both streams seem well represented in the literature, the Chi Scorpiids seem the most consistent, with their existence being well represented in visual, photographic and radar data. On the other hand, the Omega Scorpiids seem more sporadic in appearance. The visual observations listed earlier are primarily made in 1937, with few additional observations being at hand. Similarly, Lindblad's photographic meteor study revealed a very weak sample of only 3 meteors to base this stream's orbit on. Finally, no radar survey has delineated this stream (in either the northern or southern hemisphere), while its northern counterpart has been revealed on a couple of occasions.

Orbit

Based on 32 meteors detected during the Radio Meteor Project during 1969, Zdenek Sekanina determined the following orbit for the Chi Scorpiid stream:

AOP AN i q e a
261.4 72.9 4.1 0.663 0.687 2.116

From photographic meteors obtained from W1954, MP1961 and BK1967, the following orbits were obtained for the northern and southern branches of this stream. The Chi Scorpiids are based on 12 meteors, while the Omega Scorpiids are based on 3 meteors.

AOP AN i q e a
Chi 256.8 74.0 8.4 0.675 0.768 2.909
Omega 74.7 249.3 1.7 0.693 0.757 2.852

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