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(meteorobs) Xi Draconids

I tried to begin my thorough investigation of the Xi Draconids with a 
computation of parabolic and likely ellliptical orbits, but ran into a problem 
with my program. I am still working on a solution. However, I did decide to 
take a look at my various databases and see what I could find. The results are 
interesting.

There seems to be no existing observations of the Xi Draconids prior to 1931. I 
checked Denning's General Catalog (1899), as well as his various supplements 
published during the first couple of decades of this century. Other lists of 
radiants published prior to 1931 also fail to list any observations of a 
radiant near the head of Draco. 

The Xi Draconids seem to make an appearance in 1931 when it was independently 
seen in the United States and in Germany. Radiant 1649 of Hoffmeister's catalog 
of 5406 radiants was detected by Hoffmiester on June 6.5, 1931 (solar 
long.=74.8 degrees) with a radiant of RA=274 degrees, DEC=+55 degrees. 
Hoffmeister does not seem to have made observations for the next several days, 
but did resume observation on June 15. Radiant 1650 was detected on June 15.8 
(solar long.=83.7 degrees), at a position of RA=271 degrees, DEC=+61 degrees. 
In the United States, Carlton Abernathy detected a radiant on June 10.1, 1931 
(solar long.=78.3). His plot of 5 meteors revealed a radiant of RA=277.0 
degrees, DEC=+56.0 degrees. This radiant was number 2612 in the American Meteor 
Society catalog. 

There was no activity reported from the Xi Draconid region during 1932 and 
1933. Hoffmeister's catalog and the AMS catalog contain plenty of observed 
radiants, but no Xi Draconids. In addition, Opik conducted a survey of radiants 
during 1932 and 1933 and nothing was reported in this region. I personally 
think this is very interesting, but don't know what to make of it at this time. 

Hoffmeister gives three radiants for 1934: 1 by him and 2 others by 
Teichgraeber.  Radiant 2153 was seen on June 13.0, 1934 (solar long.=81.3) by 
Hoffmeister. The position was RA=267 degrees, DEC=+49 degrees. Radiant 4890 was 
seen by Teichgraeber on June 10.2 (solar long.=78.6 degrees). The position was 
RA=288 degrees, DEC=+52 degrees. Radiant 4894 was seen by Teichgraeber on June 
13.3 (solar long.=81.6 degrees).  The position was RA=276 degrees, DEC=+47 
degrees. 

Thereafter, the radiant only occasionally appears in the visual records. There 
were AMS observations in 1941 (radiant 3074), 1952 (radiant 3303), and 1968 
(radiant 5520). Two of the AMS radiants had notes that they might be related to 
AMS radiants 1009 and/or 1022. I unfortunately have a gap in my datebase and 
have no details on either of these two radiants. If these radiants are actually 
good candidates, this would be the only evidence of activity prior to 1931. 
Meanwhile, Hoffmeister lists another radiant as seen in 1936 (radiant 2626). 

Now for the fun stuff.

A search through over 4000 photographic meteor orbits revealed 7 potential 
candidates. These all appear in the list of 2529 double-station meteors 
published by McCrosky and Posen in 1961. Two of these orbits were given more 
precisely by Hawkins and Southworth, also in 1961. Even more interesting is 
that the meteors were all detected in 1953 and 1954, with 6 appearing in 1954. 
I am still working on an average orbit, but pre-atmospheric velocities appear 
to be between 30 and 40 kilometers per second, with a perihelion distance of 
1.01 AU, and an orbital inclination near 40 degrees. The photographic meteors 
were all detected during the period of June 2 to 11 (solar long.=71 to 80 
degrees), with two meteors seen on the latter date. 

The 39,000 radio-echo meteors are a promising source of information, although 
the actual orbits usually suffer because of a small apparent error in the 
determined velocities. Another problem is that there are gaps in the 
observations records because of times when the equipment was shut down. This 
latter problem affects the potential observations of the Xi Draconids as the 
equipment was not operational during June 7-17, 1962, June 7-16, 1963, June 
6-14, 1964, and June 7-15, 1969. During 1965, the equipment would at first 
glance seem to have remained operational every day during the period of June 
1-18, but closer examination revealed that during the period of June 7-18 it 
only operated for half a day--the wrong half for adequately detecting Xi 
Draconids. Despite all of these potential problems, there are a couple of dozen 
potential candidates for Xi Draconids--especially in 1969. The orbits seem to 
confirm the perihelion distance and inclination indicated by the photographic 
meteors (as well as other orbital elements). The problem here is that radiants 
shift with time, and since most of the candidates were detected within the 
period of June 2 to 6, I need to compute the likely radiant drift (once I get 
my program back up and running) to see which of the radio-echo meteors are 
likely candidates.

What does this all mean? My preliminary analysis of all of the information 
indicates the Xi Draconids began, or at least grew to a strength that first 
enabled their detection in 1931. They seem to be active from June 2 to 16, with 
possible activity as early as late May and possibly continuing to at least June 
21. The orbit's perihelion distance is about 1.01 AU, while the inclination is 
near 40 degrees. Maximum activity is difficult to track down, but might occur 
within a couple of degrees from a solar longitude of 80 degrees. This latter 
number would also represent the orbit's ascending node. 

That's it for now. There will be more later.

Gary W. Kronk