On June 23, 2006 an asteroidal object of magnitude 17 was discovered near the border of the constellations Ophiuchus and Sagittarius, which was found to be cometary in the course of more detailed observations. Observations on the following day showed a round 6" coma with a distinct central condensation. Orbit calculations made shortly after the discovery indicated that the object is identical with comet P/Barnard 2 (1889c = 1889 III), which was reported as faint and very diffuse during its whole apparition. However, the observations of 1889 can only be linked to the ones of 2006 by assuming significant non-gravitational forces. In the meantime comet P/2006 M3 (Barnard), with a current period of 119.6 years, received the permanent designation 177P/Barnard. The current apparition is very favourable with a minimum Earth distance of only 0.35 AU in mid-June. It passed perihelion at the end of August, expected to reach magnitude 13-14, assuming an average brightness evolution (IAUC 8726, Comet's Mailing List). However, applying the brightness parameters of 1889 yields a maximum brightness of 8 mag. Thus it was speculated whether the comet will show a high activity parameter (n) or was still in a rather inactive state at discovery.
The analysis of 35 observations by 7 members of the German Comet Section and 240 international ones, indicates indeed a high activity parameter n. However, especially concerning the steep brightness increase during the first week, it seems plausible that the comet also turned to an active state. In every case the steep brightness increase during the first days in part is a result of estimates done with too big instruments which did not show the whole extent of the extremely diffuse coma. Therefore I have omitted the estimates of the first days when I derived the brightness parameters. Due to the very diffuse coma the estimates show a large scatter. Nevertheless the overall evolution cann be well described by the formula m = 9.0m + 5×log D + 23×log r, resulting in maximum brightness of 8.5 mag in mid-August.
Total Brightness and Coma diameter
Due to the extremely diffuse coma the scatter of the coma diameter is large too. Due to the mentioned instrument effects, the coma diameter during the first days of about 4' (50.000 km) was strongly under-estimated. Around July 22 estimates with adequate instruments yielded a coma diameter of 9' (160.000 km). During the following four weeks the apparent coma diameter increased further, reaching 14' (300.000 km) around Aug. 20. Thereafter it shrunk rapidly at first, reaching 9' (200.000 km) at the end of August, and considerably more slowly during the following weeks, reaching 3.5' (110.000 km) at the end of October. In binoculars the coma presented itself as very diffuse, with an almost unnoticeable brightening towards center. In a telescope the very diffuse coma could be well recognized, displaying a faint small knot of material at center. Until the start of October the degree of condensation was estimated between DC 2 and 3, declining to DC 1 during the second half of October.
Andreas Kammerer
