July Phoenicids

Observer's Synopsis

The duration of this shower extends from July 9-17. Maximum occurs on July 14 (solar longitude=112 deg), from a radiant of RA=32 deg, DEC=-48 deg. The maximum hourly rate reaches 30 for radio-echo observations, but is no greater than 1 visually. The radio-echo observations also reveal the radiant to be diffuse.

History

The first observation of this shower is attributed to A. A. Weiss (Adelaide Observatory, South Australia) because of his detection of a radiant at RA=31 deg, DEC=-44 deg during July 12-17, 1957. Weiss had been conducting a radio-echo survey in an attempt to locate active meteor showers visible in the Southern Hemisphere. He said the shower possessed "a marked asymmetry in activity across the stream, with a fairly sharp maximum at solar longitude=112 deg. The activity is patchy and the radiant tends to be diffuse."
An idea of this stream's activity was quickly obtained by Weiss as he proceeded to reexamine the radio-echo observations begun at Adelaide in 1953. In that first year's records, the July Phoenicids were recognized from observations made on July 9, 10, 13 and 16, and a radiant of RA=30 deg, DEC=-43 deg was determined. Weiss was also confident that observations had been made in 1954 and 1956 since increased activity had been noted around July 13, "which could be due to a radiant which transits near 08 hr. This is sufficiently close to the transit time of from 06.49 to 07.12 found from the radiant equipment to identify this activity also with the Phoenicid radiant." The shower was re-observed by Weiss in 1958, so that he concluded that the activity was annual, with a 15-day duration centered on July 14, at which time the activity reached a maximum radio-echo rate of 30 from a radiant of RA=32 deg, DEC=-48 deg.
Although Weiss showed the July Phoenicids to be an exceptional radar shower, naked-eye observations have shown it to be very weak. During the period of 1969-1980, Michael Buhagiar (Perth, Western Australia) observed 20,974 meteors. In 1981, he compiled them into a list which revealed 488 visual radiants. During the 12-year period of study, Buhagiar observed this shower on only two occasions. He gave the duration as July 11-15, while a maximum hourly rate of one came on July 14 from a radiant of RA=34 deg, DEC=-50 deg.
According to Jeff Wood, observations by the Western Australia Meteor Section have produced somewhat inconclusive results as to the activity of this stream. Members failed to detect any activity from the region in 1977, and the 1979-1980 observations failed to cover the shower's period of activity with observing gaps of July 2-19 in 1979, and July 7-18 in 1980.
The conclusion that might be reached concerning this meteor shower is that, although strong activity seems to be present in the radio-echo (and probably telescopic) range, visual activity is very low. Even though the Australian observations revealed rates of only one per hour, it should be noted that Robert A. Mackenzie (director of the British Meteor Society) gives the maximum ZHR of this shower as five. He agrees with the July 14 date of maximum, and gives the duration as July 3-18.

Orbit

Insufficient data has been gathered to allow the determination of the velocity and, hence, the orbit of this stream. The Author has therefore computed the following parabolic and elliptical orbits, the latter of which is based on an assumed semimajor axis of 2.0 (a good average for meteor streams).

AOP AN i q e a
25.5 292.0 86.1 0.967 1.0 ---
37.0 292.0 79.0 0.946 0.527 2.0

The Author notes a strong similarity between this parabolic orbit and the slightly hyperbolic orbit of comet Gale (1912 II). There is also a close similarity with comet Peltier-Whipple (1932 V), which has an orbital period of 291 years, although the biggest problem here is the ascending node. Jack D. Drummond (New Mexico State University) predicted that a shower from this latter comet would reach maximum on September 8 from RA=57 deg, DEC=-39 deg.

Comet AOP AN i q e a
1912 II 25.6 297.5 79.8 0.716 1.0 ---
1932 V 38.5 344.8 71.7 1.037 0.976 43.891

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