**The Alpha Cygnids in 1995-1999**

Dominik Stelmach and Arkadiusz Olech

Warsaw University Observatory

Al. Ujazdowskie 4, 00-478 Warszawa, Poland

e-mail:

stelmach@antares.astrouw.edu.pl

olech@sirius.astrouw.edu.pl

Abstract

We present the telescopic and visual study of the Alpha Cygnid shower. Based on observations made in 1995-1999 by the members of Polish Comets and Meteors Workshop (CMW) we estimated the equatorial coordinates of radiant as alpha=295.3 deg. and delta=+49.6 deg (from visual observations) and alpha=295.3 deg and delta=+49.6 deg (from telescopic observations). We noted maximum activity at lambda =114.8 +/- 0.5 with ZHR=2.4 +/- 0.1.

HISTORY

The Alpha Cygnids shower was discovered by W.F.Denning (1919). In 1885-1918 he observed 50 fast and medium fast meteors radiating from close vicinity of Deneb (Alpha Cyg).

We have rather poor information about the activity of Alpha Cygnids after work of Denning (1919). This concerns not only visual observations but also photographic ones, because we have information about only one possible Alpha Cygnid photographed in Dushanbe on July 12, 1961. The radiant of this event was alpha=304.5 deg. delta=+48.7 deg., and its geocentric velocity V=41.0 km/s (Babadzhanov and Kramer, 1961).

In the comprehensive study of visual meteor showers undertaken by Dutch Meteor Society (DMS) and the North Australia Planetary Observers, Meteor Section (NAPO-MS) in 1981-1991 and described by Jenniskens (1994) one can read about a minor stream called Omicron Cygnids. During 98 hours of effective time of observations, 8 observers noted 72 possible members of that shower. From this data, Jenniskens (1994) estimated the following parameters of the Omicron Cygnids: equatorial coordinates of the radiant during the maximum of activity: alpha=305 deg. delta=+47 deg., drift of the radiant (in units deg./day) Delta_alpha=+0.6 Delta_delta$=+0.2, the maximum of activity is at lambda(1950)=116.0 deg., population index r=2.7, maximum Zenithal Hourly Rates (ZHRs) equal to 2.5 +\- 0.8, the entry velocity is V=37.0 km/s, and the activity period is from lambda=105 deg. to lambda=127 deg.

The next approach to investigate Alpha Cygnids was made by Olech et al (1999a). Based on 785 hours and 41 minutes of effective time of visual observations and 757 possible mateors from the Alpha Cygnids shower and 4569 sporadic events, they obtained the activity period of the Alpha Cygnids from around June 30 to July 31 with a clear maximum near July 18 (lambda=116.5 deg.). Maximum ZHRs are equal to 3.6 +\- 1.2. The coordinates of the radiant during the night of maximum are alpha=302.5 deg. and delta=+46.3 deg., the entry velocity was V=41 km/s and the population index was r=2.55+\-0.14. The number of plotted meteors in this study was 2758.

This study was quickly followed up by the next paper of Olech et al (1999b) who analyzed the Alpha Cygnids from years 1995-1998. The number of events plotted and entered into the RADIANT software (Arlt, 1992) was already 4187. Increase of the sample by a factor of 1.5 gave slightly different coordinates of the radiant: alpha=305.2 deg. and delta=+45.1 deg. The other parameters of the stream were almost the same as before. Olech et al (1999b) presented also the activity of Alpha Cygnids in 1998 and it was in good agreement with the activity profile given by Olech et al (1999a).

**OBSERVATIONS OF THE CMW**

The results given by Olech et al (1999b) were obtained using material presented by Olech et al (1999a) (758 hours 41 minutes of visual observations obtained in years 1995-1997) and additional preliminary data obtained in July 1998 (about 200 hours of effective time). Now, our sample is significantly larger because we used all data obtained in 1998 (420 hours) and 360 hours obtained by the participants of our Astronomical Camp in Ostrowik in 1999.

Also our telescopic sample is larger because we analyze 2137 meteors observed by 20 observers during 209 hours (see Table 1 in Olech and Jurek 1999). All the equatorial coordinates of the meteors were obtained using the CooReader software (Samuj³³o and Olech, 1999).

**RESULTS**

**Radiant of Alpha Cygnids**

We have not entered the visual meteors of 1999 into the RADIANT software yet and our sample still contains 4187 meteors resulting in the above mentioned radiant coordinates of the Alpha Cygnids at alpha=305 deg, delta=45 deg. The resulting picture of the radiant is presented in Fig. 1.

**Fig. 1:**The radiant of the Alpha Cygnids resulting from CMW visual data. Assumed parameters are: V=41 km/s, lambda max = 116 deg, Delta_alpha = +0.6 deg, Delta_delta = +0.2 deg. The number of meteors is 4187.

Fortunally, our telescopic sample is now significantly larger than in the previous years. We processed it using the following parameters: V=40 km/s and lambda(max)=116 deg., Delta_alpha=0.6 deg. Delta_delta=0.2 deg., the maximum distance of meteors from the region of ineterst of 50 deg. and the speed factor (SSF) equal to 3 which gives the angular velocity between 1 and 3 deg./sec for meteors of A-class velocity, 4-6 deg./sec for B, 7-9 deg./sec for C, 10-12 deg./sec for D, 13-15 deg./sec for E, and 16-18 deg./sec for F-velocity events. The resulting picture of the radiant of the Alpha Cygnids shower is shown in Fig.2a. The radiant are similar to the above and equal to alpha=295.3 deg., delta=+49.6 deg. We also changed the SSF to 4. The result is shown in Fig.2b. The radiant looks more compact and its coordinates are alpha=294.5 deg., delta=+54.6 deg.

**Fig. 2:**The radiant of the Alpha Cygnids resulting from CMW telescopic data. The assumed parameters are: V=40 km/s, lambda max = 116 deg, Delta_alpha = +0.6 deg, Delta_delta = +0.2 deg. The number of meteors is 2137. Left: speed-scale factor is equal to 3; Right: speed-scale factor is equal to 4.

Activity profile

Using the value of the population index r=2.61 +\- 0.23 obtained by Olech et al (1999a) and a zenith exponent of gamma=1.0 we can compute the ZHR. The activity profile obtained by Olech et al (1999a) from 1995-1997 is presented in Figure 3. The maximum with ZHR=3.6 +\- 1.2 is found for lambda=116.5 deg. It is also possible that the true maximum is somewhere in the vicinity of that point because we obtained ZHR = 2.9 +\- 0.4 for lambda=114.5 deg. and ZHR=3.1 +\- 0.6 for lambda=118.5 deg.

**Fig. 3:**The activity profile of the Alpha Cygnids during 1995-1997 from Olech et al. (1999a). The solid line represents the fit given i equation (1) with lambda_max=116.5 deg., ZHR_max=3.6 and B=0.045

In Figure 4 we present the activity profile from 1998-1999. The amount of observations used for this profile is 800 hours which is larger than for 1995-1997. The clear maximum with ZHR=2.3+\-0.2 was detected at lambda=114.3+\-0.6 deg.

**Fig. 4:**The activity profile of the Alpha Cygnids during 1998-1999.

We decided to use all our data from years 1995-1999 to compute the final activity profile for these years. The result is presented in Figure 5. The solid line corresponds to the fit given by equation:

^{-B*|lambda-lambda_max| }

**Fig. 5:**The activity profile of the Alpha Cygnids during 1995-1999. The solid line represents the fit given i equation (1) with lambda_max=114.8 deg., ZHR_max=2.4 and B=0.026.

The maximum with ZHR_max=2.4 +\- 0.1 is found at lambda = 114.8+\-0.5 deg. The B parameter is equal to 0.026 +\- 0.003. At the beginning of the activity period, ZHRs are around 1 strongly suggesting that the actual activity period is longer and the first meteors from Alpha Cygnid shower were observed during the last days of June. On the other hand, at the end of the activity, ZHRs drop to near 0, and we conclude that there is no activity of the shower during the first days of August.

Despite of making many photographic exposures we have still no photographic confirmation of this shower. On the other hand, the latest video results seem to show a clear radiant near coordinates obtained from our visual observations (Molau 2000, this issue).

**Acknowledgments**: This work was supported by KBN grant number 2
P03D 004 17 to A. Olech. We are also grateful to IMO for supporting our
participation in the IMC.

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