Królikowska M., Dybczynski P.A. (2019). Discovery statistics and 1/a distribution of long-period comets detected during 1801–2017. Monthly Notices of the Royal Astronomical Society, 484, 3463-3475, doi: 10.1093/mnras/stz025.

Abstrakt / Abstract: For the last two decades, we have been observing a huge increase in discoveries of long-period comets (LPCs), especially those with large perihelion distances. We collected data for a full sample of LPCs discovered during 1801–2017, including their osculating orbits, discovery moments (to study the discovery distances) and original semimajor axes (to study the number ratio of large-perihelion to small-perihelion LPCs in the function of original 1/a and to construct the precise distribution of original 1/a). To minimize the influence of parabolic comets on these distributions, we determined definitive orbits (which include eccentricities) for more than 20 LPCs previously classified as parabolic comets. We show that the percentage of large-perihelion comets is significantly higher within Oort-spike comets than in a group of LPCs with a<10000 au; this ratio of large-perihelion to small-perihelion comets for both groups has grown systematically since 1970. The different shape of the Oort spike for small-perihelion and large-perihelion LPCs is also discussed. A spectacular decrease of the ratio of large-perihelion to small-perihelion LPCs with the shortening of semimajor axis within the range 5000–100 au is also noticed. Analysing discovery circumstances, we found that Oort-spike comets are discovered statistically at larger geocentric and heliocentric distances than the remaining LPCs. This difference in the percentage of large-perihelion comets in both groups of LPCs is probably a direct consequence of the well-known comet fading process, due to ageing of the surface during consecutive perihelion passages, and/or reflects different actual q distributions.