A. Hajduk

Radar observations of the Geminid meteoroid stream

Continuous radio-wave monitoring of the Geminid activity in December 1992 and 1993 by using a forward scatter (FS) bistatic radar over the Bologna-Lecce baseline (700 km) in Italy, reveals peculiar structural aspects of the stream in terms of signal amplitude-rate and duration-rate dependence. The observational results of the Geminid display obtained in the two consecutive years with differentiated peak levels of transmitted power, exhibit different time distributions of underdense meteors against the signal received power. Both sets of the data relative to the peak activity in December 12–14, show reflection properties of Geminids which are atypical if compared with echoes from cometary-type showers, with really high echo counts at mid-upper levels of the peak received power. An assymmetric curve of activity of the Geminids complex is evidenced, with the peak flux of smaller particles occurring earlier than that of larger ones.

Debris from comet Halley, comet's mass loss and age

SummaryLarge particles released from the nucleus of comet Halley, but undetected directly by space probes, seem to affect decisively the mass loss and mass determination of the comet, and consequently its aging. Simultaneous radar meteor observations in 1985–86 at the approaches of the comet emphasize the relatively larger proportion of long-duration echoes with respect to previous years.

Lyrids 1994 observed by a forward scatter system

Radio observations of the Lyrid meteor shower obtained by a forward scatter radio system (Bologna-Lecce) in 1994 are analysed and discussed. The shower maximum appeared at solar longitude 31.0°(1950.0) and a distinct displacement between the maxima of the short-duration (< 1s) and long-duration (≥ 1s) echoes is observed. The shower has displayed a high activity, but no exceptional burst similar to that one observed in 1982, was recorded. It has been shown that the shower activity continues down to the smallest particle size of which existence in a meteoroid stream means their recent origin.

Reanalysis of four NASA stratospheric particles

Four stratospheric contaminants catalogued in the Cosmic Dust Catalogs published by the NASA Johnson Space Center (JSC) in Houston were reanalysed. The results are compatible with those obtained in JSC, however additional features have occurred in our chemical analyses and their interpretation is also discussed.

Baseline effect on the forward-scatter radar reflections from meteor trains

SummaryThe influence of the baseline orientation on the rate of recorded meteor echoes has been shown from the observations carried out during the Lyrid meteor shower periods in 1992 and 1993 with receivers rectangularly displaced from the transmitting station in Bologna with a baseline length of about 700 km. It is shown that the maximum echo rate precedes or occurs later than the shower radiant culminates (at heights of 80°), favouring the 45° radiant elevation and similar angle between the radiant and the beam axis. The consequences of the measured effect on the meteor flux within the shower and sporadic radiant distribution is discussed.

Radio Geminid meteor shower of 1994

SummaryThe geminid meteor shower observed by a radio forward-scatter system on the baseline Bologna-Lecce (Italy) in 1994 is discussed. The 1994 Geminid shower exhibited a distinct maximum for overdense echoes of duration >1 s, with the peak rate on December 13, 21–22 UT at solar longitude 261.0° (equinox 1950.0). The maxima of echoes of longer duration (>8 s and >32 s) are shifted to solar longitude 261.3°.

The analysis of four cosmic dust particles

A set of four stratospheric particles was reanalysed. These particles registered in the NASA Cosmic Dust Catalogs (CDCs) were classified in the Houston Johnson Space Center (JSC) as the particles of cosmic origin (”C”). Present energy-dispersive X-ray (EDX) spectra confirmed previous classification and revealed additional features in the chemical composition of the cosmic dust particles.The particles are extremely fine-grained aggregates with bulk chondritic composition. Somewhat higher content of oxygen may indicate a presence of hydroxide containing minerals in their phase composition.

Sunrise and range distribution of meteors

SummaryThe influence of the sunrise effect on the ionization of the meteor zone has been found from the comparison of meteor echo range distributions obtained by the meteor radars at Springhill (120 000 echoes) and Budrio (7000 echoes) during the activity of the Geminids meteor shower. The position of the maximum of the echo range distribution corresponding to the motion of the shower radiant was found to be shifted to larger distances, as expected from the sunrise effect, independently of different antenna systems of the two equipments.

Observations of the Leonid Meteoroid Stream by a Multistation FS Radio System

Results of joint campaigns of the Leonid meteoroid stream performed throughout the 1995–1999 years by the BLM (Bologna-Lecce-Modra) forward scatter (FS) radar, are shown and compared with visual observations. In 1998 and 1999 at both the stations of Lecce and Modra, the total reflection time is shown to give a better indication of the Leonid activity. For the two years the trends of the reflection time and of the overdense echoes (T > 8 sec duration) exhibit multiple peaks just at the maximum of the shower activity. In 1999, strong evidence of a short and extremely intense activity at the nodal longitude of the parent comet (November 18, 02h UT), is deduced from the radio data. The Leonid display is shown to follow a Gaussian activity profile and the particle density/stream width relationship is found to match observations of IRAS dust trails of comparable short-period comets. The mass distribution exponent shows a representation of an extended component of larger particles (brighter Leonids) in 1996 and especially in 1998. Average mass and population indices of radio and visual data show a similar trend in the 1995–1999 period.

Determination of origin of NASA stratospheric particles

Paper presents a reanalysis of four stratospheric particles registered in the Cosmic Dust Catalogs (CDC). Two particles have been classifed in the NASA Johnson Space Centre (JSC) in Houston as natural, terrestrial contaminants and the origin of the other two particles was found questionable, probably cosmic. Present study has confirmed these conclusions; however some new additional features in the chemical analysis have been found which can finally determine the classification of the particles with unclear origin.