Aries-Triangulids

History

Unexpected meteor activity was independently observed on the night of September 12, 1993, and subsequently reported to the International Meteor Organization (IMO). The observations were made by long-time ALPO members Gary W. Kronk (Troy, Illinois) and George W. Gliba (Greenbelt, Maryland), with Kronk being assisted by Kurt Sleeter (Swansea, Illinois).

Kronk and Sleeter were observing deep sky objects from 4:00 to 5:15 UT and noted 11 meteors from the Aries-Triangulum region, including two which were seen through the telescope. The brightest meteor was estimated as magnitude 1, while all of the others were between magnitudes 3 and 4.5. There was no reasonable guess as to the actual amount of time spent watching for meteors, so no ZHR estimate could be made.

By 5:15 UT, Kronk and Sleeter began looking exclusively for meteors, and continued to observe until 6:15 UT. They unfortunately were severely hampered by clouds for over one-half hour, but still detected 5 meteors of which 3 were from the Aries-Triangulum region. The magnitudes were all between 3 and 4.

Gliba began observing meteors at 5:18 UT. He was located near Mathias, West Virginia, at a private observing site for members of the Westminster Astronomical Society in Maryland. He had just finished some extensive deep-sky observing and decided to put in some time looking for meteors. During the next two hours, under very clear skies, he observed 35 meteors, of which 11 seem to have radiated out of the Aries region. Of these eleven, one was magnitude -2, another magnitude 1, and the remaining were between magnitudes 3 and 5.

Kronk visually estimated the radiant as α=35°, δ=+30°, Sleeter plotted five of his observed meteors on a star chart and obtained a radiant of α=30°, δ=+30°, and Gliba estimated his radiant was near Gamma Arietis, which indicated a radiant near α=28°, δ= +19°. Kronk and Sleeter had the good fortune of observing a short-trailed meteor just 10 degrees south of Triangulum which generally confirmed the right ascension of the radiant and indicated a declination more northerly than Gliba's +19 deg, but Gliba noted his right ascension was more accurate than his declination because of the meteor distribution he observed. He suggested the radiant was diffuse and noted his radiant could subsequently be off by as much as 5° in any direction.

Taking the three radiants and adding high weights to the declinations of Kronk and Sleeter, and the right ascension of Sleeter and Gliba, the resulting average radiant was α=30°, δ=+29°. This radiant is less than 2° from Alpha Trianguli.

Gliba, Sleeter, and Kronk all reported the meteors were moving at slow to medium speeds. Kronk and Sleeter noted the meteors were much slower than Perseids, and comparable to the speeds seen for the Aquariids and Capricornids.

In an attempt to try and find other observers of this event, Kronk posted notices to several computer bulletin boards within 48 hours of the observations. He requested positive and negative observations of enhanced activity, with no radiant or general location in the sky given. In addition, Kronk also contacted Peter Brown (Coordinator of the North American IMO Section) and Robert Lunsford (Recorder of the ALPO Meteor Section). He gave them the complete details of his observations and asked them to send him any confirmatory reports. Over the course of the next three weeks, a few telephone discussions and numerous e-mail discussions uncovered more information.

Several observers in Europe indicated no unusual visual activity was seen during the period of 21:00 to 24:00 UT on September 11. However, between 0:00 and 2:00 UT on September 12, M. De Meyere (Deurle, Belgium) was operating a forward scatter radio meteor detector and registered enhanced activity that was 17% to 83% higher than during the same hours on all other dates during the period of September 1 to 15.

Among the many United States reports that were received, were a few which supplied some interesting details.

    Brandon Craig Rhodes (Windy Gap, a camp in North Carolina) had been looking at the stars with a friend and wrote:
      "I noticed that during the fifteen or twenty total minutes we spent looking up...we saw an unusually high number of meteors for an inter-shower period when one would expect only a few erratics an hour. We together saw about seven or eight meteors...in that period of time, suggesting an hourly rate of perhaps as high as 20 to 30 meteors.... I commented on the high frequency, but upon arrival home did not find that any shower was strongly active at that time."
    Tim Hager (New Milford, Connecticut) spent the entire night observing variable stars and conducting his routine photographic nova patrol program. He wrote:
      "I did notice an unusual number of meteors that night. So many in fact that I went inside to check to see if there were any minor showers active." He added, "Some seemed to radiate from the Perseus-Cassiopeia area. Now, I know that the Perseids are long over and the radiant has moved somewhere else by now but that's where two or 3 of the brighter ones seemed to radiate from."

    Although Hager's estimated radiant is about 30 degrees from that accepted above, his additional description of the three meteors pinpointing this radiant showed they were all moving east to west, either towards or through Cygnus some 50-70° away. Only slight alterations in the remembered paths would be needed to move the radiant closer to the Triangulum region.

    Paul Martz wrote:

      "I was camping with a friend who's vision is far superior to mine. We were in the southern Uinta mountains, about 200 miles ESE of Salt Lake City, Utah. My friend's limiting magnitude was around 5.0-6.0. He claimed to see much more activity than usual, mostly east to west. This was for observations done from 8:15pm (dusk) to 10pm MST (1:15 -3:00 GMT)."

Several additional observers reported meteors moving from east to west during observations in early evening hours. Considering the radiant did not reach the zenith until 2:31 a.m. (local time), the east to west movement at least suggests the radiant producing higher-than-normal activity was in the eastern half of the sky, which would include the Aries-Triangulum region.

It should be noted that other minor radiants were active at the time of the above observations, most of which could produce meteors with an east to west movement. Kronk and Sleeter noted a total of two Piscids and two sporadics, while Gliba saw six Piscids, one Gamma Aquariid, and 17 sporadics during 2 hours. These figures indicate that the observed activity levels of these radiants were about typical for the date of the observations, which might lend support to the possibility that any abnormal activity observed in an east to west direction would likely be from the same radiant observed by Kronk, Sleeter, and Gliba.

The question now most prevalent was whether this radiant had ever been observed in the past, and a search was conducted through previously published radiant observations which quickly revealed potential support.

A search through nearly 10000 visual radiants, reveals several likely candidates. In particular, there are several probable observations in the records of the American Meteor Society (AMS) during the period of 1934 to 1967. They are as follows:

Desig.DateRADECSolar Long.Observer
1683a1934, Sep. 10.034.0+31.0166.6Smith, Franklin W.
1683b1934, Sep. 11.033.0+27.0167.6Smith, Franklin W.
40511940, Sep. 8.026.0+19.0165.2Khan, Mohd. A. R.
30581940, Sep. 12.336.0+20.0169.4Anderson, Paul
45921945, Sep. 9.732.0+26.0166.6Komaki, Koziro
31111950, Sep. 6.230.0+23.0163.0Worley, Charles E.
31101950, Sep. 7.2*27.5+21.0164.0Worley, Charles E.
31861951, Sep. 9.326.0+32.5165.8Knowles, Jeremy H.
31921951, Sep. 10.826.0+27.0167.3Knowles, Jeremy H.
34131951, Sep. 13.327.0+24.0169.7Worley, Charles E.
34151951, Sep. 15.331.0+23.5171.6Worley, Charles E.
38881955, Sep. 13.329.5+20.0169.7Knowles, Jeremy H.
55071967, Sep. 11.8*25.0+29.0168.3Menzel, R.

*Means date was an average of two or more nights of observation.

Another strong group of radiants comes from C. Hoffmeister's 1948 book Meteorströme.

Desig.DateRADECSolar Long.Observer
7471915, Sep. 12.935+21169Hoffmeister
10751921, Sep. 9.034+17165.8Hoffmeister
12401923, Sep. 12.725+25168.9Hoffmeister
50861929, Sep. 9.633+34166.4Richter
22731934, Sep. 10.023+29166.6Hoffmeister
27161936, Sep. 10.537+29167.6Hoffmeister
41411937, Sep. 7.032+27164.0Hoffmeister

Interestingly, there are no traces of this radiant in the records of A. King, A. S. Herschel, E. Heis, and R. P. Greg. However, W. F. Denning included a radiant called the "Beta Triangulids" in his 1899 catalog, which he observed during the period of August 24 to September 14, 1872, from a radiant of α=34°, δ=+35°. Denning's supplement to that catalog was published in 1912 and included a radiant detected during September 3-17, 1885, from α=29°, δ=+36°, and a radiant detected during September 3-7, 1902, from α=30°, δ=+37°.

For the most part, Denning's radiants were typically higher in declination than those of the AMS and Hoffmeister, and were certainly of a greater duration. It should even be noted that Denning's 1902 radiant was the only radiant to average more than one meteor per night, which indicates the overall weakness of this data. Therefore it seems likely that the earliest recorded radiant from the Aries-Triangulum region would be that of Hoffmeister's in 1915.

Arguments might still be made by some meteor stream researchers that the strength of the pre-1993 support is too low to consider as confirmed, but there are key observations within the visual data that are indisputable. First on September 10, 1934, the radiant was observed by Smith in the United States and Hoffmeister in Germany. Second, in both 1940 and 1951, the radiant was detected independently by two AMS observers.

There is reason to put a high confidence upon the AMS data. First, the observers of the radiant in 1934, 1940, and 1951, were among the most prolific and experienced observers in the organization's history. Second, in the days of Charles P. Olivier, the AMS criteria for radiant determination was the intersection of four or more meteors within a circle of no more than 2.5 deg, which is more stringent than what some groups accept today.

When all of the apparent visual confirmations are considered, the average radiant derived from the 1993 observations appeared little changed and Kronk computed a series of hypothetical orbits. Although the meteors were obviously not moving at speeds indicative of a parabolic orbit, it was decided to start from there and then determine three elliptical orbits. The results were as follows:

ωΩiqePeriod
Parabola304.2169.5127.50.2211.0---
Ellipse #1321.5169.5117.40.1430.9292.83
Ellipse #2337.4169.593.70.0780.9221.00
Ellipse #3343.5169.542.50.0820.8820.586

No comets were found with orbits anywhere within the range defined by the parabola and ellipse #1. It is curious that comet Machholz (1988 XV) moved in an orbit nearly identical to ellipse #3, but the ellipse would be indicative of an Aten-class minor planet, while the comet's orbit was a parabola. Although comet Machholz' orbit was defined on less than a month's worth of precise positions, all attempts by Kronk to generate a short-period orbit drastically fails to represent the available positions as well as the parabola.

It was obvious that visual observations would do little to isolate the orbit. A search through other sources was needed. The next search was among nearly 7000 photographic meteors. Searches by radiant and orbit were made for the period of mid-August to the end of September, but absolutely no matches were made. This could offer additional support to the 1993 evidence that the stream meteors are primarily faint.

Next, the results of the various radio-echo surveys conducted during the 1950s, 1960s, and 1970s were checked, and two probable candidates were found. Z. Sekanina's 1969 survey revealed streams which he called the "Alpha Triangulids" and the "Alpha Arietids". The "Alpha Triangulids" were based on 13 radio-echo meteors which indicated an average radiant of RA=30.4°, DEC=+29.5°. The "Alpha Arietids" were based on six radio-echo meteor orbits which came from an average radiant of RA=32.6°, DEC=+21.8°. The resulting orbits were as follows:

ωΩiqePeriod
Alpha Triangulids345.9165.738.70.0870.8700.55
Alpha Arietids324.6165.8117.40.1430.9292.81

Since these streams were detected after the 1969 survey, Kronk decided to go to the raw data obtained by Sekanina, which amounted to nearly 40,000 orbits, and find all meteors detected during the period of 1962 to 1965, as well as 1969. It was hoped that if any members were found for the period of 1962 to 1965 their orbits could be combined with those detected in 1969 to more precisely determine the orbit. Unfortunately, where the solar longitude of the radiant's appearance in 1993 was 169.5°, Sekanina's surveys never operated while the radiant was above the horizon after λ=168.1°, or more than a day earlier than the potentially observed maximum in 1993, but as the visual radiants indicated a visibility of several days, it was assumed the radio-echo data would confirm this. A radiant ephemeris was computed for the period preceding a solar longitude of 169.5 deg, and the search was conducted for meteors seen during the first half of September, with a right ascension between 20° and 40°, and a declination between 10 deg and 40 deg.

The result of the initial search was the detection of 47 meteors. Among those were perhaps five potential streams. Both the "Alpha Triangulids" and "Alpha Arietids" were detected among this group, as well as three potential minor radiants which produced 4 meteors or less. The "Alpha Arietids" exclusively appeared in 1969, so that the above orbit could not be improved upon. The "Alpha Triangulids" produced meteors in 1962, 1963, and 1969 (the equipment did not operate between August 23 and September 21 during 1965, and no meteors were detected in 1964), which subsequently increased the overall number of radio meteors. However, it was then noted that a strong core of 9 meteors was apparent. The orbit of this core was as follows:

ωΩiqePeriod
Radio-echo344.1165.836.10.0970.8570.560

The average radiant for λ=165.8° was α=27.5°, δ=+28.8°, which was less than one degree from the extrapolated radiant of ellipse #3. Subsequently, if the probable radiant motion was added to this radiant the predicted position for a λ=169.5° would be about α=30.8°, δ=+30.3°.

Despite the evidence presented above, much still needs to be learned about this radiant. The only solid facts that seem to be indisputable from the above discussion is that the radiant probably produces annual activity and its perihelion distance is well within the orbit of Mercury.

The next possible date of maximum was September 12.5, 1994 (UT). The most extensive set of observations was made by Gliba and these revealed the stream was still active one year after the discovery. Gliba observed on the nights of September 10/11 and 11/12 and recorded the following hourly numbers from this radiant:

      September 10/11
    • 8:07-9:07 UT--4 meteors
      September 11/12
    • 4:17-5:17 UT--3 meteors
    • 5:17-6:17 UT--6 meteors
    • 6:17-7:17 UT--4 meteors
    • 7:17-8:17 UT--5 meteors

Sources: Denning, W. F., Memoirs of the Royal Astronomical Society, 53 (1899), p. 231. Denning, W. F., Monthly Notices of the Royal Astronomical Society, 72 (May 1912), p. 632. Olivier, Charles P., Flower Observatory Reprint, No. 58 (1942), p. 20. Olivier, Charles P., Flower Observatory Reprint, No. 63 (1943), p. 41. Hoffmeister, C., Meteorströme. Leipzig: Verlag Werden und Werken Weimar (1948), pp. 1-286. Olivier, Charles P., Flower Observatory Reprint, No. 84 (1951), pp. 1 and 26. Olivier, Charles P., Meteoritics, 1 (1954), pp. 260 and 272. Olivier, Charles P., Meteoritics, 1 (1955), p. 369. Olivier, Charles P., Flower and Cook Observatory Reprint, No. 131 (1961), p. 9. Olivier, Charles P., Flower and Cook Observatory Reprint, No. 149 (1964), pp. 12 and 14. Olivier, Charles P., Flower and Cook Observatory Reprint, No. 184 (1968), p. 12. Sekanina, Zdenek, Icarus, 27 (1976), p. 284. Sekanina, Zdenek, Personal Communication (March 19, 1985). Sekanina, Zdenek, Personal Communication (May 8, 1985). Murray, Carl, Personal Communication (July 1986). Gliba, George, Personal Communication (October 5, 1994).