Outburst history

Observations by Juan Antonio Henríquez Santana (MPC J51) show that a major outburst of Comet 17P/Holmes has taken place. Photometry taken during the night of 2007 October 23/24 show that the comet is some 9 magnitudes brighter than on 2007 Oct 22 in a 10" aperture and that the comet was brightening by approximately 0.5 magnitudes/h in a 10" aperture over the course of 6 hours. The outburst has been confirmed by Gustavo Muler at MPC J47 and by Ramón Naves and Montse Campàs at MPC 213.

17P/Holmes had an outburst to approximately magnitude 4 in 1892, but has since been very faint and was lost from 1906 to 1964.

Measured R magnitudes in a 10” square aperture are as follows:

2007 Oct 24.067, 8.4

2007 Oct 24.100, 8.0

2007 Oct 24.136, 7.3

Images taken by Gustavo Muler on October 22 show normal brightness. This outburst is evidently still in a very early phase and the bright, inner coma is almost stellar. Almost all the light is concentrated in the inner 20”. A preliminary pair of “before” and “after” images can be found at http://astrosurf.com/comets/cometas/17p/imagenes/17p.html. An animation of the 6 hours of photometry showing a brightness increase of approximately 3 magnitudes will be available in a few hours.

Further analysis for observations by J. A. Henriquez Santana (Tenerife) during the rise to maximum show that an abrupt increase in rate of brightening occurred on Oct. 24.077 from 0.36 magnitudes per hour to 0.48 magnitudes per hour based on 148 R measures in a 10” square aperture made between Oct. 24.000 and Oct. 24.139. When extrapolated backwards the rate of brightening suggests that the outburst initiated at approximately Oct. 23.0. Photometric measures by Gustavo Muler (Lanzarote) around this time show a small brightening: Oct. 22.989, 16.51; 23.003, 16.41; 23.018, 16.39 respectively in a 10” square aperture, while the respective magnitudes in the 20” aperture were 15.77, 15.78 and 15.79. These measures are consistent with marking the initiation of the photometric outburst. Careful examination of Muler’s images does not show any evidence of an anomally that might be due to the onset of activity, although a short, faint tail is detected in PA 236.

[Note: as per IAUC 8886, observations were obtained by Henriquez over more than 6 hours, but the first 2.5 hours of data have had to be discarded for analysis as the central condensation was saturated in the images.]

Prediction
Just out of pure curiosity, it is worth pointing out that the 1892 outburst came 5 months after perihelion (just like the 2007 outburst). The descriptions of the comet are almost identical in 2007 to those in 1892/93 so, making a long range punt, if the symmetry between 1892/93 and 2007 continues, I would recommend paying careful attention to the comet around January 4th 2008, however faint it may be before that date.

The story of the discovery of the outburst (in Czech)": http://ian.cz/detart_fr.php?id=2640