Astron. Astrophys. Suppl. Ser. 135, 291-297 (1999)
  Alpha Cygnids - a possible July minor meteor shower  

Arkadiusz Olech1,2, Marcin Gajos1,2, Michał Jurek2

1Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
2Comets and Meteors Workshop, ul. Sokolicz 3/59, 01-508 Warszawa, Poland

Abstract. We present a comprehensive study of a possible α-Cygnid meteor shower. Based on visual and telescopic observations made by Polish observers we estimate basic parameters of the stream. Activity of α-Cygnids lasts from around June 30 to July 31 with clear maximum near July 18 (solar longitude λo=116.5o ). Maximal Zenithal Hourly Rates (ZHRs) are equal to 3.6±1.2 . The structure of the radiant analyzed by radiant software is most compact for geocentric velocity of the events equal to 41 km/s, and for the drift of the radiant (in units o/day) equal to Δα=+0.6 Δδ=+0.2 . Center of the radiant for the moment of maximum is α=302.5o δ=+46.3o .We derive population index r equal to 2.55±0.14 from magnitude distribution of 738 possible members of the stream. Comparing the velocity distributions of 754 possible α-Cygnids and 4339 sporadic events by χ2 and Kolmogorov-Smirnov tests we conclude that both distributions are different with probability very close to 1.0.

Telescopic observations strictly confirm the results obtained from visual observations. The smallest values of χ2 parameter we obtained for the geocentric velocity equal to 40 km/s and for the drift of the radiant (in units o/day) equal to Δα=+0.6 Δδ=+0.2 . The center of the radiant for moment of maximum is α=304.9o δ=+46.2o.

In spite of making many photographic exposures we still have no photographic or video confirmation of the existence of this stream.

1. Introduction

The first informations about meteors from radiant near α Cygni come from W.F. Denning (Denning 1919). In years 1885-1918 he observed 50 meteors radiating from the close vicinity of Deneb. He did not know the activity period of the stream so he noted meteors during the whole year. It is clearly visible from his Table 2 that majority of meteors were noted during July nights. Almost all events observed in this month were classified as rapid.

During next years one can find the different parameters describing α-Cygnids stream in the astronomical literature. Polish meteor publications were giving activity period between June 16th and July 31st. No clear maximum of activity was found (Kosinski 1990).

Photographic data are also poor. Only one possible member was captured in Dushanbe on 1961 July 12. The radiant of this event was α=304.5o δ=+49.7o and geocentric velocity V=41.0 km/s (Babadzhanov & Kramer 1965).

Table 1. List of visual CMW observers
Observer 1995 1996 1997
teff Nalfa Nsp teff Nalfa Nsp teff Nalfa Nsp
Maciej Reszelski56h51m4027827h22m35181 11h58m18114
Arkadiusz Olech32h45m3525716h55m19129 31h31m39234
Tomasz Fajfer---31h30m3313439h30m52 341
Konrad Szaruga---11h28m68450h16m85257
Marcin Gajos26h00m121446h18m43810h40m 1183
Krzysztof Socha17h00m211036h54m438 18h16m12142
Maciej Kwinta4h00m0138h10m01326h50m9 157
Krzysztof Wtorek5h42m53210h00m1467 12h55m1245
Łukasz Sanocki14h30m17625h46m821 8h04m527
Tomasz Dziubiński15h47m16353h30m520 6h00m325
Jarosław Dygos------24h30m16157
Gracjan Maciejewski------21h15m891
Andrzej Skoczewski------20h23m2885
Artur Szaruga------19h55m1471
Wojciech Jonderko---4h15m01115h24m767
Marcin Konopka------18h39m17181
Michał Jurek---9h31m9807h39m953
Tomasz Żywczak------16h38m1043
Maria Woźniak13h45m1843------
Tomasz Ramza---6h30m5495h59m132
Łukasz Pospieszny---9h44m4623h31m1 18
Piotr Grzywacz11h30m2155------
Robert Szczerba---5h00m6216h20m1100
Krzysztof Kamiński------8h47m660
Łukasz Raurowicz---1h07m236h16m644
Tadeusz Sobczak------6h10m2046
Rafał Kopacki---5h30m845---
Michał Marek---4h00m650h30m14
Elżbieta Brembor4h00m85------
Ireneusz Sławiński---3h00m012---
Krzysztof Gdula---2h30m211---
Marek Piotrowski------2h25m214
Paweł Trybus------2h00m010
Paweł Musialski---1h3017---
Paweł Gembara1h00m010------
Total202h50m1931037180h30m1711031 402h21m3932501

Table 2. List of telescopic CMW observers
Observer 1995 1996 1997
teff Nalfa Nsp teff Nalfa Nsp teff Nalfa Nsp
Tomasz Dziubiński4h51m7204h40m531 9h31m1251
Michał Jurek1h56m133h31m1135h27m2 16
Konrad Szaruga1h21m353h58m6345h19m9 39
Marcin Gajos1h49m1102h42m4174h31m5 27
Jarosław Dygos---4h09m1104h09m110
Tomasz Fajfer2^05m292h00m294h05m4 18
Marcin Konopka---3h31m1133h31m113
Wojciech Jonderko---1h23m001h23m00
Łukasz Pospieszny---1h11m131h11m13
Rafał Kopacki1h00m03---1h00m03
Krzysztof Wtorek1h00m03---1h00m03
Maciej Reszelski---0h59m460h59m46
Michał Kopczak0h53m11---0h53m11
Andrzej Skoczewski---0h44m040h44m04
Total14h55m155428h32m2613943h27m41 193

In the comprehensive work undertaken by Dutch Meteor Society (DMS) and North Australian Planetary Observers - Meteor Section (NAPO-MS) in years 1981-1991 and described in detail by Jenniskens (1994) one can read about weak stream called ο-Cygnids. During 98 hours of effective time of observations 8 observers noted 72 possible members of that stream. From this data Jenniskens (1994) estimated the following parameters of the stream:

  • equatorial coordinates of the radiant during the maximum of activity: α=305o δ=+47o ,
  • drift of the radiant (in units o/day): Δα=+0.6 Δδ=+0.2 ,
  • maximum of activity: λo(1950.0)=116.0o±0.5o ,
  • population index r=2.7 , where r is defined as:

    and N(m) is the number of meteors with magnitude m corrected for probabilities of perception given by Koschack and Rendtel (1990),
  • Maximal Zenithal Hourly Rates (ZHRs) are equal to 2.5±0.8 , where ZHR is defined as:
    where Nh is the observed number of meteors per hour (corrected for clouds coverage), LM is the limiting magnitude in the field of view, H is an altitude of the radiant of the stream, and γ is a zenith exponent factor,
  • geocentric velocity: V=37 km/s.
From the Fig. 11 in paper by Jenniskens (1994) it is clearly visible that activity of ο-Cygnids lasts from λo≈105o to λo≈127o i.e. from around July 5th to July 27th.

2. Observations

2.1. Visual observations

July is a good month for meteor observers in Poland. Polish observers associated in Comets and Meteors Workshop (CMW) are mostly young people studying at secondary schools or universities. July is the first month of summer holidays. The warm nights, a lot of free time, good weather conditions strongly encourage to observations. Finally about 60-80% of whole year observations made by CMW members are collected in July and August. All above facts and rapidly growing interest in meteor observations in Poland during the last few years allowed us to investigate the activity of the stream called α-Cygnids or ο-Cygnids. Each July in years 1995-1997 many meteor observers watched the sky using visual, telescopic and photographic techniques. In order to obtain most reliable results we had to remove observations made incorrectly or in poor conditions. Using our standard methods (Olech & Woźniak 1996, Olech 1997) we required that:

  • mean limiting magnitude (LM) in the field of view should be at least 5.0 mag,
  • cloud coverage correction factor F should be smaller than 1.7,
  • the radiant of the stream should be above 20o over horizon (in Polish latitudes during whole July this condition is always satisfied),
  • center of the field of view should be at altitude higher than 40o .
Finally we obtained 785h41m of effective time of visual observations. During this time a group of 35 CMW members noted 757 possible meteors from α-Cygnid stream and 4569 sporadic meteors. The more detailed statistics with names of CMW observers is given in Table 1.

2.2. Telescopic observations

Telescopic observations present a very useful tool for meteor investigators. Meteors are very often plotted with larger accuracy than in case of visual observations. It gives the possibility to study the structure and drift of the radiant. We also obtain informations about magnitude distribution for fainter events. The main problem with telescopic observations is that this kind of watching meteors requires good equipment (preferably binoculars with large field of view mounted on tripod), experienced observers and a lot of patience.

Fortunately July is usually the time in which we organize an Astronomical Camp of CMW, which takes place at the Observational Station of Warsaw University Observatory in Ostrowik. The number of participants is always around 15, so we organize two four persons groups observing visually, one or two persons working with a few cameras pointed at different directions, and three-four persons observing telescopicaly different fields located 10o-40o from supposed radiant of α-Cygnids. We used mostly 7x50 , 10x50 and 20x60 binoculars and Russian AT-1 refractors ( 5x50 , field of view as large as 11o ). For plotting meteors we use A-type maps of International Meteor Organization (IMO) or Uranometria 2000.0 charts. Of course other observers which do not participate in the camp observe α-Cygnids both visually and telescopicaly at their locations.

Finally 14 our observers obtained 43h27m of telescopic observations with 234 meteors detected. The number of possible α-Cygnids equals to 41. Table 2 summarizes our telescopic observations.

Table 3. Magnitude distribution for 1995-1997 α-Cygnids
Year≤-5-4-3-2-101234567 Tot.
1995003.51.54532.572.535231420 193
1996000.53.547.5132545.5422550 171
1997030.52.5618.53265.59381.55318.5 0374
Tot.034.57.5143177.5163173.5146.592 25.50738

Table 4. Magnitude distribution for 1995-1997 sporadics
Year≤-5-4-3-2-101234567 Tot.
1995014.561662.5139.5252.5268.517387.5 1601027
1996004.5103272.5123.5197.5239202.5132 17.501031
1997516112567.5123274.5405.5547.5577.5 348.586.50.52488
Tot.5172041115.5258537.5855.51055953568 1200.54546

Table 5. Magnitude distribution for 1996-1997 telescopic α-Cygnids

Table 6. Magnitude distribution for 1996-1997 telescopics poradics

3. Results

3.1. Radiant of α-Cygnids

During July of 1995, 1996 and 1997 CMW observers plotted on gnomonic star maps 2748 paths of meteor events. For each of them the angular velocity was estimated. We used 0-5 scale with 0 corresponding to stationary meteor, 1 to very slow event, 2 to slow, 3 to medium, 4 to fast and 5 to very fast meteor. Equatorial coordinates of the begins and ends of these events and their velocities were put into the radiant software (Arlt 1992). This software as an input also requires the geocentric velocity of the meteors V and the daily drift of the radiant. Changing both these values we can obtain different density distributions of the probability area near suspected radiant. Choosing the best distribution (this one with smallest χ2 parameter) we are able to estimate the values of V and the daily drift. The systematic errors play a role, which are difficult to handle and estimate of the accuracy of the obtained value of V is difficult but the errors are at minimum ±5 km/s. For more details see Arlt (1993).

Before analyzing our sample we decided to analyze also the meteors observed by Denning (1919). However we selected only meteors observed by him during July nights. Number of these events accounted to 20. We performed our calculation using parameters of the stream given by Jenniskens (1994) i.e. V=37 km/s, &lambdao(max)=116o , Δα=+0.6 and Δδ=+0.2 . Results as probability function distribution of the presence of radiant are presented in Fig. 1. The best fit of the two dimensional Gaussian surface to the density of probability map gives coordinates of the radiant equal to α=312.4o and δ=+48.4o . The accuracy of this estimate is certainly low due to small number of events observed by Denning (1919).

Fig.1. The radiant of α-Cygnids resulting from Denning's (1919) observations. Assumed parameters are: V=37 km/s, λo(max)=116o , Δα=+0.6o and Δδ=+0.2o . Number of the events is 20.

Fortunately, the sample collected by CMW observers in years 1995-1997 is significantly larger. It allows us to derive a few valuable conclusions. First we calculate our sample (2748 meteors including possible member of the stream, sporadics and meteors from other showers) using parameters given by Jenniskens (1994). During calculation we remove meteors observed at distance larger than 85o from the radiant of the stream. The prominence of the α-Cygnid radiant on the resulting picture is striking. The best fit gives coordinates of the radiant as α=302.0o and δ=+46.1o . Nevertheless we obtain better results i.e. more compact shape of the radiant using geocentric velocity V=41 km/s and the drift of the radiant Δα=+0.6 , Δδ=+0.2 . The resulting radiant picture for the above parameters is displayed in Fig. 2. The final coordinates of the radiant of α-Cygnid stream are α=302.5o and δ=+46.3o , which do not differ significantly from coordinates obtained for parameters given by Jenniskens (1994).

We also used the radiant software for the analysis of the paths of our telescopic meteors. Our sample contains 234 meteors with known paths and velocities. The resulting density distribution from telescopic observations is displayed in Fig. 3. The best fit (with smallest χ2 value) is obtained for the following parameters: geocentric velocity V=40 km/s, the daily drift of the radiant Δα=+0.6o and Δδ=+0.2o . The coordinates of the center of the radiant are α=304.9o and δ=+46.2o . One can see that the position of the radiant obtained from telescopic observations differ from the position obtained from visual data by only 1.7o . Taking into account that radii of the majority of radiants vary between 2o and 7o both our results are strictly consistent. It is also clear that our parameters are in very good agreement with the data of the one photographed meteor (Babadzhanov & Kramer 1965).

Fig.2. The radiant of α-Cygnids resulting from CMW visual data. Assumed parameters are: V=41 km/s, λo(max)=116o , Δα=+0.6o and Δδ=+0.2o . Number of the events is 2748.

Fig.3. The radiant of α-Cygnids resulting from CMW telescopic data. Used parameters are: V=40 km/s, λo(max)=116o , Δα=+0.6o and Δδ=+0.2o . Number of the events is 234.

3.2. Population index r

In years 1995-1997 the CMW observers made as many as 738 and 4546 estimates of the brightness of meteor events from α-Cygnids and sporadics, respectively. The distribution of this quantity is presented in Tables 3 and 4.

Such a large amount of magnitude estimates for α-Cygnids encouraged us to compute the value of the population index r defined in equation (1). We obtained r=2.55±0.14 which is a typical value among meteor streams. Jenniskens (1994) obtained similar result with r equal to 2.7. The population index obtained from magnitudes of our 4546 sporadics is equal to r=2.61±0.23 .

Also the telescopic observers estimated the magnitudes of meteor events. The magnitude distributions for 1996 and 1997 α-Cygnids and sporadics are presented in Tables 5 and 6.

3.3. Activity profile

Knowing the value of r we can compute ZHR using the formula given in (3). According to the results of Koschack (1994) and Bellot (1995) who showed that for visual observations with radiant altitudes higher than 20o the zenith exponent factor γ≈1.0 , we adopted γ=1.0 . The resulting activity profile of α-Cygnids in years 1995-1997 is exhibited in Fig. 4. The activity of the stream lasts from λo≈100o (June 30) to λo≈130o (July 31). It seems to be slightly wider than the result of Jenniskens (1994) who noted meteors from α-Cygnid stream in interval λo=105-127o . The accuracy of the ZHR estimates by Jenniskens (1994) was low due to the small number of his observations, therefore we prefer our result.

Our Fig. 4 one exhibits a clear maximum of activity at λo≈116.5o with ZHR}=3.6±1.2 . The error of this estimate is large but points in the vicinity of the maximum have smaller errors and their moments and ZHRs are λo=114.5o with ZHR}=2.9±0.4 and λo=118.5o with ZHR}=3.1±0.6

Fig.4. The activity profile of α-Cygnids during 1995-1997. The solid line represent the fit given in equation (4).

The moment of the maximum and its ZHR is in very good agreement with result of Jenniskens (1994) who obtained &lambdao(max)=116.0±0.5o with ZHRmax}=2.5±0.8 .

Jenniskens (1994) found also that the activity profiles of meteor streams are well represented by the following equation:

For α-Cygnids he found B=0.13±0.03 . As we have already written our activity profile is much broader and thus our value of B is smaller and equal to 0.045±0.005 . In Fig. 4 the solid line represents fit given in equation (4) with ZHRmax=3.6 , &lambdao(max)=116.5o and B=0.045 .

3.4. Velocity distribution

The CMW observers estimated also the angular velocity of the events. The 0-5 scale (defined in Sec. 3.1 of this paper) was used. Finally we obtained 754 estimates of the angular velocity for α-Cygnids and 4339 estimates for sporadics. The velocity distribution from visual observations is presented in Tables 7-8.

Table 7. Velocity distribution for 1995-1997 α-Cygnids.

Table 8. Velocity distribution for 1995-1997 sporadics

We used the above distributions to find another proof for existence of the α-Cygnid stream. We compared empirical velocity distributions of α-Cygnids and sporadics using Kolmogorov-Smirnov and χ2 tests. We obtained that with the probability larger than 0.999 both distributions are different. Such a large probability is certainly caused by the clear enhancement of meteors with velocity 3 and 4 in α-Cygnid velocity distribution. This result is also with good agreement with the value of geocentric velocity obtained from radiant analysis of our visual and telescopic data. The meteors with velocity V=40-41 km/s given by radiant software at mean distance from the radiant of the stream appear mainly with velocities 3 and 4 in 0-5 scale.

The velocity of meteor events was also estimated by our telescopic observers. They used A - F scale with A corresponding to the angular velocity 2o/sec and F to over 25o/sec . Finally we obtained 41 estimates of the angular velocity for telescopic α-Cygnids and 192 velocity estimates for telescopic sporadics. Both distributions are presented in Tables 9-10.

For telescopic observations the distance from the radiant is generally well defined. Usually it is worthwhile to analyze the mean angular velocity as a function of distance from the radiant. Unfortunately due to the small number of our telescopic α-Cygnids which were observed in as many as 10 fields such an analysis is impossible yet.

Table 9.Velocity distribution for 1996-1997 telescopic α-Cygnids

Table 10.Velocity distribution for 1996-1997 telescopic sporadics

4. Discussion

We presented here the results of visual and telescopic observations of α-Cygnid stream made by CMW observers in years 1995-1997. This stream is not included in the IMO List of Visual Meteor Showers (Rendtel et al 1995) due to the lack of photographic, video and radio data confirming its presence. The only continuous (not visual) surveys are the Harvard Super Schmidt Program of the 1952-54 period and the Harvard Radar Project in the 1960's. Both have gaps in coverage due to weather or instrument irregularities. Unfortunately the α-Cygnids seem to fall in such gaps. McCrosky and Posen (1961) presented the orbital elements of 2529 meteors photographed simultaneously from two camera stations of the Harvard Meteor Project. The mean number of meteors captured in periods January-June and August-December is 221 events per month. The number of meteors photographed in July is only 102. It is over two times smaller than in other months and certainly it is the reason of lacking the meteors from α-Cygnid stream in that project. The similar situation occurred during the Harvard Radar Project. However recent radio results obtained by Michael Boschat from Dalhousie University in Canada (Boschat 1998) showed clear enhancement of radio echoes in days 1998 July 19-20.

Analysis of 2748 paths of meteor events observed in July 1995, 1996 and 1997 allowed us to obtain the basic properties of the stream. The geocentric velocity of the α-Cygnid events is V=41 km/s and daily drift of the radiant Δα=+0.6o , Δδ=+0.2o . The coordinates the center of the radiant of α-Cygnid stream are α=302.5o and δ=+46.3o .

We performed similar analysis for 234 telescopic meteors plotted also by CMW observers. Obtained parameters of the stream are in very good agreement with results derived from visual data.

Our results are also consistent with visual observations by Denning (1919) and Jenniskens (1994) and photographic results obtained by Babadzhanov & Kramer (1965).

From magnitude distribution of 738 α-Cygnids we obtained the population index r equal to 2.55±0.14 which is in good agreement with previously obtained value r=2.7 (Jenniskens 1994).

The velocity distributions of 754 α-Cygnids and 4339 sporadics are different with probability higher than 0.999 which gives another proof for reality of the α-Cygnid stream.

From visual observations made by CMW members in years 1995-1997 we obtained the clear activity profile of the α-Cygnid stream. Meteors belonging to this shower were detected from June 30 to July 31 with clear maximum near July 18 ( λo=116.5o ). The maximal ZHRs reached the level 3.6±1.2 . These results are in very good agreement with results presented by Jenniskens (1994) who obtained λo(max)=116.0±0.5o and ZHRmax}=2.5±0.8 .

In spite of making many photographic exposures we still have no photographic confirmation of this stream. To confirm of disprove our results further visual, telescopic and particularly video and photographic observations are clearly needed.

Acknowledgements We would like to thank to all observers who sent us their observations. We are especially grateful to Prof. Jerzy Madej for helpful discussions, reading and commenting on the manuscript and also to Dr. Jacek Chołoniewski for many helpful hints. This work was supported by KBN grants 2 P03D 020 11 and 2 P03D 002 15 to A. Olech.


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© 2001 Pracownia Komet i Meteorów.