Proceedings of the IMC, Pozna´ n, 2013 1 Lyrids – analyses of worldwide video data Roman Piffl 2 , Leonard Kornoˇ s 1 , Jakub Koukal 2 , and Juraj T´oth 1 1 Faculty of Mathematics, Physics and Informatics, Comenius University in Bratislava, Mlynsk´ a dolina, 842 48 Bratislava, Slovakia kornos@fmph.uniba.sk 2 CEMeNt - Central European Meteor Network In the paper, an analysis of 1616 mostly video orbits of Lyrids is presented. We confirmed an existence of a short and long-period part of the stream. However, the dispersion in semimajor axis and eccentricity is quite large. So based on a distribution in semimajor axis, the short-period part of Lyrids is divided into nine group. Moreover, the distribution suggests a fainter structure of the short-period part which might be caused by resonant effects with giant planets. 1 Introduction The Lyrids are a regular meteor shower active in April 16-26 with a maximum around April 21-22. Shower’s zenital hourly rates are mostly low, of 5 to 20 mete- ors. The Lyrids are connected to the comet C/1861 G1 Thatcher. In spite of that the Lyrids are known about 2500 years, the structure and evolution of the stream is not well understand. Together with a development of observational video tech- nique, new catalogues of meteor orbits are created. In contrast to photographic ones, video catalogues contain of about one order more meteor orbits. Considerably higher number of video Lyrids allows us to perform a more detail analysis. 2 TV data of Lyrids Based on available sources and personal communica- tion, 1616 orbits of Lyrids from seven catalogues have been collected (Table 1). The data come from the fol- lowing catalogues: CAMS, Cameras for Allsky Meteor Surveillance (Jenniskens et al., 2011), CMN, Croatian Meteor Network (Korlevi´ c et al., 2013), CVMO, Cata- logue of video meteor orbits (Koten et al., 2003), DMS, Dutch Meteor Society (Betlem et al., 1998), EDMOND, European viDeo MeteOr Network Database (Kornoˇ s et al., 2013), 17 photographic orbits from IAU MDC Cat- alogue (Lindblad et al., 2003) and SonotaCo Network (SonotaCo, 2009). A homogenization of data in each orbital element (q, a, e, I , w, W ), radiant position (Ra, Dec) and geocentric velocity (V g ) was made by using a 3-sigma criterion. Resulted data set contains 1412 orbits, in which 305 (21.6 %) are hyperbolic (e> 1) orbits, 154 long-periodic (P> 200 yrs) and 953 short-periodic (P< 200 yrs) orbits. The number of hyperbolic orbits is about two times greater than the number of long-periodic orbits. On the other hand, about two third of all collected data are short-periodic orbits. The hyperbolicity of orbits is very probably caused by an uncertainty of velocity determination (Hajdukov´a, 2008, 2013). Table 1 – Video Lyrids from different catalogues (see in text). N – number of orbits. Source N CAMS 251 CMN 113 CVMO 8 DMS 3 EDMOND 954 IAU MDC 17 SonotaCo 270 Total 1616 3 Structure of Lyrids In the first step, the orbits of Lyrids were divided into two groups, a short-period (a< 32 AU) and a long- period (a> 32 AU) one. The short-period part contains 942 orbits and the long-period part 165 orbits. The hyperbolic part was excluded from the next analysis. Applying an iterative method of Porubˇ can and Gavaj- dov´a (1994) and using the limiting value of D criterion of Southworth and Hawkins (1963), D SH < 0.08, we de- rived new mean orbits of short and long-periodic part of Lyrids. The mean orbits of both parts and also of the comet Thatcher are in Table 2. We found that 142 orbits (86 %) of long-periodic part fulfilled the D criterion. Followed mean orbit is almost the same as the orbit of the parent comet C/1861 G1 Thatcher. In the short-period part, only 585 orbits (62 %) sat- isfy the D criterion and also the dispersion in orbital parameters, mainly in semimajor axis and eccentricity, is large. So we decided to perform a new inspection. Based on a distribution in semimajor axis (Figure 1), all 942 short-periodic orbits can be divided into nine