2 The sample of "hyperbolic'' comets

In their catalogue Marsden & Williams (1997) listed 307 comets with periods longer than 200 yrs and with well-determined orbits, e.g. comets belonging to quality classes 1 or 2 originally defined by Marsden et al. (1978). In this sample, 29 comets have negative reciprocals of original semimajor axes: $(1/a)_{\rm ori} < 0$. Furthermore, 16 long-period comets with determined non-gravitational effects and unknown $(1/a)_{\rm ori}$ (in the MW Catalogue) were taken into account. It turned out, however, that only six of these 16 comets had negative $(1/a)_{\rm ori}$. Thus, our sample consists of 35 candidates that have hyperbolic incoming orbits. Since the original observations were not available for four comets of the sample (1849 G2 Goujon; 1959 O1 Bester-Hoffmeister; 1895 W1 Perrine; 1911 S3 Beljawsky) the present analysis includes 31 comets observed before 1997 (see Tables 1 and 2). This sample was appended by two "hyperbolic'' comets discovered after 1997.