Abstract: The AUD (#197) entry in the IAUMDC working list of meteor showers is confusing. The first reference orbit listed for AUD, AUD0, is a Harvard radar observation but very weak, slightly above the detection level. The second entry, AUD1, is a CAMS video observation and a conglomerate of two meteor shower activities; one should be named as ZDR that had been properly suggested by former researchers and the second one could be named AXD (August ξ-Draconids, preliminary name). ZDR (#73) in the IAUMDC list cannot be confirmed by other video observations. ZDR (#73) and AUD (#197) should be removed from the IAUMDC list or renamed by other more suitable names.
The August Draconids (AUD#197) shower has been first found by Sekanina in the Harvard radar observations, but it may be another different stream activity than the later ‘AUD’ records. The IAUMDC lists two other AUD observations though these are possibly misled by the activity of the CDC (Cygnid-Draconid Complex, see Koseki, 2014b), especially by the AXD and ZDR showers (see Section 4 in detail).
ZDR in the IAUMDC list seems to be false. The author pointed out that ZDR is badly treated in the IAUMDC working list; the name of ZDR is not correctly used by Jenniskens (2006, page 721). He also commented that the ZDR shower is equal to the θ-Herculids. The first line of his ZDR entry suggests it is based on the source ‘BA’ but ‘BA’ is not listed in his book. Meanwhile, Koseki (2014b) pointed out that one of the members of the Cygnid-Draconid Complex coincides with the ZDR proposed by Terentjeva (1966) and Lindblad (1971).
It is necessary to clear out what is active during the activity period and in the area of ‘AUD’. We use the 2018 January 13 20h35m17s version of the IAUMDC meteor shower database. Meanwhile, the shower list has been changed suddenly without written explanations.
2 AUD (#197) in the Harvard radar observations
The first orbit reference for the AUD (#197) in the IAUMDC shower list is the Harvard radar observation in 1968–69 (Sekanina, 1976, see Table 1). Sekanina reported other series of radar observations in 1961–65 (Sekanina, 1973) and we refer to these simply as 61–65 and 68-69 observations hereafter. We had better checked the observations in detail at first. Figure 1 shows the radar radiant distribution with the reference meteor showers.
Table 1 – The summary data of AUD (#197) entries. 0197AUD02 is omitted because it is similar to 0197AUD01.
Larger circles, which are closer to the core of the stream, seem to be concentrated on the center, but it is an apparent effect. It is necessary to check whether this concentration means a real shower activity by the D(M,N) distribution; DSH values (Southworth and Hawkins, 1963) calculated between the mean orbit M and the individual orbits N. We calculate DSH values between the AUD0 (#197) orbit and all the Harvard radar meteors and show the result in Figure 2. The shape is very different from video data; major showers are buried in a monotonous profile contrary to the complex profiles with sharp peaks (see Koseki, 2020a). Meteor showers observed by radar look different compared to video ones. Radar showers cannot be detected by video and vice versa (Koseki, 2014a). We should exclude the prejudice that a meteor shower can be observed by all observational techniques.
Figure 3 shows the distribution on a logarithmic scale with the supposed sporadic distribution (dashed line). We should not consider all the meteors below the DSH limit, such as DSH < 0.2, as belonging to the meteor shower. There are even sporadic meteors with DSH < 0.1 naturally, because sporadic meteors are distributed randomly. We can estimate the real number of AUD meteors by the difference between the straight line and the dashed line in Figure 3. The numbers of supposed AUD are slightly above 0 within the range of DSH smaller than 0.2. Its activity may be very weak (Figure 4). Though Sekanina reported AUD by 68–69 observations (Sekanina, 1976), it is interesting whether AUD can be detected in the 61–65 observations. Figure 5 is the result of the 61–65 observations after processing the data in the same way as the 68–69 data and the AUD shower activity cannot be not certified from this 61–65 dataset.
We can find several possible AUD radiants with D(M,N) < 0.2, and their distribution along with λʘ seems interesting (Figure 6). These meteors make clear peaks around λʘ = 140° both in the 61–65 and the 68–69 observations. The 68–69 peak is much higher than that of 61–65. But these peaks are false; Harvard radar observations were intermittent (Figure 7). Both observation series intended to observe the Perseids and the observations were operated around the Perseid maximum. It is natural that the larger the total number of observations, the more D(M,N) < 0.2 meteors. It is unfortunate for us that there are no or very few observations between λʘ = 145~150 when the ZDR (not the IAUMDC’s ZDR, see following sections) reaches its maximum. We cannot confirm the AUD nor the ZDR activity in the Harvard radar observation series; we will continue the study of the AUD and the ZDR in the following sections.
3 AUD (#197) in CAMS
The second entry of the AUD shower in the IAUMDC list is from CAMS, AUD1 (Table 1). But, AUD1 seems different from AUD0. Figure 8 gives the radiant distribution around AUD0 based on CAMS data; the plotting method is the same as in Figure 1. There are more D(M,N) < 0.2 radiants than in Figure 1. It is obvious that video meteors, which are brighter, are numerous in this field. This does not mean that the AUD0 activity is confirmed by CAMS observations. Many D(M,N) < 0.2 radiants belong to other showers (Figure 9 and Table 2). Figure 10 shows that CAMS did not catch the AUD0 activity. The number of D(M,N) < 0.2 meteors is obviously below the supposed sporadic distribution (dashed line). The geocentric velocity of AUD1 is some 4 km/s higher than AUD0. AUD1 is not equal or equivalent to AUD0; AUD1 seems to be another shower with brighter video meteors.
Table 2 – The IAUMDC showers that appear in Figure 9, (x, y) represents the position in Figure 9.
|Code||λʘ||λ – λʘ||β||vg||x||y|
Figure 11 shows all AUD1 meteors classified in the CAMS catalogue and we can see that the distribution curiously bends. Figure 12 reveals the cause for this unnaturalness. KCG is below left of the center and its distribution is elongated but not bent. CAMS’ AUD spreads from the center to right upward and left downward suggesting two elongated extents. Figure 13 strengthens the supposition that AUD1 consists of two shower activities; one reaching its maximum at λʘ = 140° and another around λʘ = 150°. We try to confirm these two components in the next section.
4 Recent observations on the CDC (Cygnid-Draconid Complex)
The author suggested at least four independent meteor shower activities in the Cygnus-Draco area in August (Koseki, 2014b) and confirmed these by three more recent video data sets; SonotaCo net, EDMOND and CAMS (Koseki, 2020b). These four shower activities have mistaken observers by their complexity. GDR (#184) crosses the KCG (#012) radiant path, the AXD (August ξ Draconids, preliminary name) runs parallel to the KCG and the early ZDR (#073) (not AUD (#197), see next section) activity overlaps with late AXD activity (Figure 14).
AXD was named KCG3 in the first paper (Koseki, 2014b) and marked as a steady shower activity and more active than the KCG in regular years (Table 3). AXD is located about 5 degrees west of the KCG and, therefore, not only visual observers but also video observers tend to misidentify AXD meteors as KCG.
Table 3 – The numbers of shower meteors classified in the SonotaCo net observations (Koseki, 2020b).
Table 4 – The comparison between four CDC shower activities from earlier results (Koseki, 2014). The upper lines are the earlier results, the lower lines are the result for this study.
|Code||λʘ||λ – λʘ||β||α||δ||vg||e||q||i||ω||Ω|
It is worthy to note the difference in the shower classification between the three video datasets; we can visualize the difference by comparing the activity profiles and the radiant distributions according to their own classification. Figure 15 represents the radiant distributions of the KCG and the AUD by CAMS. Compared with Figure 14 it is obvious that CAMS classified AXD meteors as AUD and clearly distinguished AXD from KCG. Figure 16 shows that CAMS extended the KCG activity to early July (λʘ < 95°) and the KCG in CAMS overflow Figure 15 leftwards below. SonotaCo net included AXD meteors as KCG but separated them from AUD (Figure 17). KCG seems strikingly more active than AUD in SonotaCo net (Figure 18) but this is caused because CAMS missed enhanced KCG activity while SonotaCo net had it twice. EDMOND inherits the definition of SonotaCo net and the results are similar to it (Figure 19 and 20); the sharp peak at λʘ = 126° is clearly due to the GDR activity.
It would have been better to search for the shower identification in the usual way rather than to use the classifications done by the networks in their own way. The author investigated the above mentioned four CDC shower activities (Koseki, 2020b) using his first study as the starting points (Koseki, 2014b). We use the mean radiant points and collect shower meteors by several iterations taking the radiant drift into consideration. The search periods are limited in time in order to exclude duplications in the shower identification (see Figure 14): GDR 119.6° < λʘ < 129.6°, KCG 130° < λʘ < 154°, AXD 135° < λʘ < 145°, ZDR 150° < λʘ < 160°. The summaries of the results are given in Table 4 and Figure 21. Both investigations are based on different methods but they are in good agreements. It is necessary to be careful that the activity profiles are limited according to the above-mentioned search periods. The hump in the profile of the GDR around λʘ = 140° is caused by another meteor shower activity, such as the AXD, which occurs on the path of the estimated radiant drift.
5 ζ-Draconids in photographic meteors
The name of ζ-Draconids owes to Denning (1899) and was reminded to us by Terentjeva (1966) and Lindblad (1971). Lindblad reexamined it later (Lindblad, 1995). Figure 22 shows his four shower activities with the radiant drift estimated from EDMOND observations. It is clear their ζ-Draconids coincide with our ZDR. This is why we call this activity not AUD but ZDR.
We notice that the AXD shower activity is not mentioned by Lindblad (1995). 3 zeta Draconid meteors, 2 kappa Cygnids and 5 August Lyrids in Figure 22 might represent the AXD shower. It is very interesting that the KCG are divided into two activities: alpha Lyrids and kappa Cygnids. Lindblad studied shower activities by using a computerized discrimination criterion with DSH < 0.10. This level is obviously too small though it is suitable for short lived shower activities and for high precision meteors. Three out of the four activities, KCG, AXD and ZDR, are more than twenty days active (Figure 21) and the radiant areas are elongated even if we take the radiant drift into consideration. Many D-criteria assume that the position of the perihelion axis does not move and data are distributed spherically in the D space. In Figure 22 we can visually see the elongated radiant distribution and the radiant drift, but in case of an analysis on the basis of D-criteria we cannot handle such nature. When we use only one of the search methods, D-criteria or radiant distribution, we would obtain apparent and false results.
The entry for ZDR (#073) in the IAUMDC working list of meteor showers is problematic, because it was connected with θ-Herculids in the first IAU list (Jenniskens, 2006) and later this initial ZDR has been replaced by recent video data. The present ZDR in the IAUMDC list is quite different from the first one and from the θ-Herculids, and, moreover, we cannot find any trace of it (Figure 23 and 24). It is only based on single station video meteors.
This study confirms the author’s former results; we can confirm two meteor shower activities in the neighborhood of the KCG: ZDR and AXD (Table 4). AUD in CAMS consists of two shower activities, AXD and ZDR, and does not relate to AUD0. AUD in the IAUMDC list should be classified as ‘working’. The present ZDR in the IAUMDC list should be removed or renamed, because the ZDR stream has been known as a different meteor shower activity by several observers and researchers, Denning, Terentjeva and Lindblad, before the present ZDR were included in the IAUMDC list.
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