Eta-Virginids: another asteroidal meteoroid stream
Eta-Virginids is a less-known meteor shower active in March. We investigated the meteoroids of this shower using fireball data from the European Fireball Network supplemented by video data of faint meteors. We first derived the criteria for assigning meteors to this shower. A fragmentation model was then applied to selected shower fireballs with good deceleration data and light curves. Meteoroid fragmentation strengths and bulk densities were derived and compared with three other showers. We have confirmed the four year periodicity in the activity of eta-Virginids and their presence in the 3:1 mean motion resonance with Jupiter. The orbital period of four years was directly measured for the fireballs. Fainter meteors showed somewhat longer periods but the shower is poor in faint meteors. No member fainter than magnitude +1 was observed instrumentally. The physical properties of meteoroids are different from cometary streams and are similar to the Geminids. The limiting fragmentation strength of 0.5 MPa and typical bulk density of cm-sized meteoroids of 1500 kg/m3 suggest that the parent body is a carbonaceous asteroid. Besides Geminids, eta-Virginids is another stream of asteroidal origin. Some small meteoroids have densities around 2500 kg/m3. Three asteroids of the sizes between 40 - 120 meters have been found to have similar orbits but their relation to eta-Virginids remains uncertain.