M. Wi¶niewski and A. Olech
Abstract.We present the visual and telescopic study of the Delphinid stream. The radiant of the shower is clearly visible both in visual and telescopic plots. The equatorial coordinates and the geocentric velocities are alpha=304, delta=+5, V=35km/s and alpha=301, delta=+7, V=45km/s for visual and telescopic observations, respectively. The activity profile shows maximum with ZHR=1.6+-0.3 at lambda=119.
Meteors radiating from Delphinus constellation were visualy observed around the end of the last century, (slow meteors, few subradiants). A shower with similar parameters was described by Abalakin (1981) and called gamma-Delphinids; (period of activity Jul 14-31; coordinates of the radiant alpha=310, delta=+19; geocentric velocity V=34.5km/s).
In 1990 July two Bulgarian meteor observers from Astorclub "Canopus" Plamen Stoychev and Yulian Markov, announced the discovery of "new" suspected shower with similar parameters. Their Zenithal Hourly Rates (ZHR) of the Delphinids were extremely high (about 20!). In 1996 Velkov (1996) presented data from 1990 to 1996 and supposed that there are two subradiants which he called the Northern and Southern Delphinids.
The first attempt to analyze Polish data with the goal of searching the Delphinids activity was performed by Olech, Jurek and Gajos (1999). From visual observations they obtained the coordinates of the radiant: alpha=303.5 and delta=+5.8. The maximum of activity was noted at lambda=119 with ZHR=1.7+-0.5
From 9 to 31 July of 1996, 1997 and 1998 Comets and Meteors Workshop (CMW) observers plotted on gnomonic star maps 3992 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. We used the CooReader software (Samuj³³o and Olech, 1999) to take equatorial coordinates of the begins and ends of these events from gnomonic maps and then with their velocities and times we put them into the RADIANT software (Arlt, 1992). Changing the geocentric velocity of the meteors V and the daily drift of the radiant we can obtain different density distributions of the probability area near suspected radiant. Choosing the best distribution we are able to estimate the values of V and the daily drift.
Fig.1. The density of probability map resulting from CMW visual observations. Assumed parameters are: V=35 km/s, lambda(max)=119, Delta lambda=1.0 deg and maximum distance is 60 deg. Number of the events is 3992.
During our calculations we remove meteors observed at a distance larger than 60 degrees from the radiant of the stream and excluded meteors with velocities smaller than 1 deg/s and greater than 26 deg/s. The assumed lambda is equal to 119 and daily drift of the radiant equal to Delta lambda=1 deg/day.
The best fit of a two dimensional Gaussian distribution we obtained for geocentric velocity V=35 km/s and coordinates of the radiant: alpha=304 and delta=+5. (Fig. 1) Velkov (1996) found a double radiant of Delphinids. One can see that our radiant can be connected with Velkov's Southern Delphinids with alpha=308.3 and delta=+12.2, and there is no trace of Northern Delphinids with alpha=309.1 and delta=+15.5 in our data.
Telescopic observations present a very useful tool for meteor investigations. Meteors are very often plotted witch a larger accuracy than in case of visual observations. It gives the possibility to study the structure and drift of the radiant. We also obtain information about magnitude distribution for fainter events. The main problem with telescopic observations is that this kind of watching meteors requires good equipment, experienced observers and a lot of patience.
The astronomical camps of CMW which we organize in each July allow us to collect many valuable telescopic observations. We use mostly 10X50, 20X60 and 7X35 binoculars and Russian AT-1 refractors with field of view as large as 11 deg. For plotting meteors we use A-type maps of International Meteor Organization (IMO), Uranometria 2000.0 and Milenium Star Atlas charts. We used the RADIANT software for the analysis of the paths of our telescopic meteors . Our sample contains 2533 meteors with known velocities. The best fit (with smallest chi^2 value) is obtained for the following parameters: alpha=301 and delta=+7 and geocentric velocity V=45 km/s (Fig. 2b) which is different than that obtained from visual observations. Also the coordinates of the radiant are slightly different tan these from visual data. The reason of these discrepancies may be a fact that due to the low elevation of the Delphinids' radiant at Polish latitudes we have small number of meteors observed below the radiant.
Comparing density intensity of probability maps receive from visual and telescopic observations presented on figure 1 and 2 we can see that coordinates of the radiant for visual observations is above coordinates of the radiant for telescopic observations. We think, that this difference is because we have only two telescopic fields below the radiant of the Delphinids.
Comparing the results obtained for different geocentric velocities we can see revealed influence of other showers like Pegasids for high geocentric velocities and alpha-Capricornids for low geocentric velocities (Fig 2a). It is very surprising because the alpha-Capricornids are known to be very bright and here we detect this stream with magnitude range between 6 and 9!
We also tried to calculate the activity profile of Delphinid shower. We assumed a population index r equal to 2.6 which is a typical value among meteor streams and zenith exponent gamma equal to 1.0 . For calculation we used data from 1996 and 1998. Data from years 1997 and 1999 are still under reduction. The result of our calculations is presented in Fig. 3. Meteors belonging to this small shower were detected from July 9 (lambda=112) to July 28 (lambda=126). The highest activity with ZHR = 1.6+-0.3 was detected at lambda=119 which corresponds to the night of July 21-22.
Fig.3. The activity profile of Delphinid shower. Data from 1996 and 1998.
We are going to observe this shower next year both visually and telescopically and we hope to obtain more results in future.
This work was supported by KBN grant number 2~P03D~004~17 to A. Olech. We are also grateful to IMO for financial support.
Abalakin V.K., 1981, Astronomical Calendar - Invariable Part, Nauka, Moscow, in Russian Arlt, R., 1992, WGN, 20, 62
Olech A., Jurek M., Gajos M., 1999, Proceedings of the International Meteor Conference, Star'a Lesn'a, Slovakia, p. 58
Samuj³³o, M., Olech,
A., 1999, Proceedings of the International Meteor Conference, Star'a
Lesn'a, Slovakia, p. 65 Velkov, V., 1996, Proceedings of IMC 1996,
Apeldoorn, p. 32