R.H. McNaught rediscovered comet P/Hartley-IRAS (1983 v) near the borders of the constellations Horologium and Triangulum Australe, on images taken Nov. 3 and 5, 2004. Comet P/2004 V2 (Hartley-IRAS) was of magnitude 18, only slightly more diffuse than the stars nearby and without a tail. The correction to the predicted perihelion date was -4.8d (IAUC 8428). The comet will pass perihelion in June 2005, at which time it will become visible from mid-Europe. During the following weeks it will become circumpolar. Any prediction of the peak brightness is uncertain, because it showed a very extraordinary evolution during its last (and until now only) apparition. If the behaviour would be similar, it could reach magnitude 8, otherwise it will not become brighter than about 11 mag. In the meantime this comet received its permanent number: 161P/Hartley-IRAS.
The current apparition of this comet proceeded rather unspectacular and disappointing. With a maximum brightness of only about 11.0 mag it remained two magnitudes fainter than expected. In addition, a brightness surge as in 1983 did not occur. And because the comet remained very diffuse without a central condensation, it was an object for larger instruments, and even with these it was barely recognizable if the sky was not pitch black. Thus it is no surprise that only 13 reports by 4 members of the German Comet Section were received. 80 reports from international observers could be added for the analysis. These indicate a brightness evolution according to the formula
m = 9.4m + 5×log D + 5.5×log r
yielding a maximum brightness of 10.8 mag in the first days of July. The apparent coma diameter increased from 1.0' to its maximum of 3.0' at the end of July, thereafter declining to about 2.5' in the first days of September. The absolute coma diameter measured 90.000 km at first, increasing to 220.000 km until the end of July where it remained at least until the beginning of November. The DC-value was constant at DC 2-3 to DC 3. No visual tail sightings were reported.
Total Brightness and Coma diameter
Andreas Kammerer
