Delta Mensids

Observer's Synopsis

The duration of this stream extends from March 14-21. At maximum on March 18 (solar longitude=358 deg), an hourly rate of 1 to 2 meteors can be seen emanating from a radiant of RA=55 deg, DEC=-80 deg.

History

This shower was discovered during 1969, by observers operating the radio meteor system at Adelaide Observatory in Australia. In analyzing the data, G. Gartrell and W. G. Elford found two fairly distinct, but similar streams active while the system was in operation during the period March 16 to 22. The first stream, designated 3.04, possessed a radiant of RA=51 deg, DEC=-81 deg, while the second stream, designated 3.05, was located at RA=50 deg, DEC=-78 deg.
The orbits of these two streams were found to be nearly identical except for their semimajor axes---stream 3.04 had an average value of 2.13 AU, while stream 3.05 was determined as 10.0 AU. Gartrell and Elford indicated these streams provided a very important key to meteor stream formation, when they are compared to comet Pons of 1804 (C/1804 E1). As can be seen below, the orbits of all of these objects are very similar except in their values of the semimajor axes. The authors said the orbital similarities "give further evidence that the low eccentricity orbits could be the result of evolution rather than direct formation from low eccentricity comets." They added that if the orbit of comet C/1804 E1 is parabolic as indicated, then "only 170 years have been available for 3.04 to contract from [a semimajor axis greater than] 10 a.u. to the present value of 2.13 a.u."
No apparent records appear to exist concerning past observations of this shower. However, southern hemisphere observers have been making occasional observations of this stream during the 1970's and 1980's. According to Jeff Wood, director of the meteor section of the National Association of Planetary Observers (Australia), this shower has a duration spanning March 14 to 21. At maximum on March 18, 1 to 2 meteors per hour can be detected from an average radiant of RA=55 deg, DEC=-80 deg.

Orbit

Two orbits were determined for this stream at Adelaide during 1969. They were published in GE1975 and were designated 3.04 (average date March 18) and 3.05 (average date March 19). Stream 3.04 was based on 11 meteors, while 3.05 was based on 10 meteors.

AOP AN i q e a
3.04 347 178 55.3 0.98 0.53 2.13
3.05 346 178 58.3 0.98 0.87 10.00

The orbit of comet Pons (C/1804 E1) is listed in Brian G. Marsden's Catalog of Cometary Orbits (1995) as follows:

AOP AN i q e a
C/1804 E1 331.9 179.5 56.5 1.071 1.0 ---

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