4. Detection probability
We check the data set for the time intervals of the mission in which -meteoroids could be detected applying the following criteria for -meteoroids. Because there is no information about the exact impact direction of the particles available we assume an impact perpendicular to the surface of the detector (i.e. anti-parallel to the sensor axis). We take the impact direction to vary for from the nominal direction perpendicular onto the detector. In comparison to the detection probability as a function of impact angle this would account for 50% of all detected particles in the case of an isotropic flux (Grün et al., 1992a). From the model calculation we assume a maximum angle of between the direction of the particle velocity and the radial direction in order to take into account that the flux of the particles still varies from the radial direction as mentioned before. According to this estimate the measured particles can be -meteoroids, if the angle between the Sun and the sensor axis is less than about at the time of the impact. Furthermore, from the model calculation identified -meteoroids particle velocities have to be larger than 20 km/s (at heliocentric distances greater than 1.8 AU, which is the case for the time intervals 2 and 3 in our study) and larger than 30 km/s closer to the Sun at heliocentric distances smaller than 1.6 AU (i.e. in the first time interval according to Fig. 2).
© European Southern Observatory (ESO) 1999
Online publication: November 26, 1998