A 17.5 mag comet was discovered by the LINEAR-team on May 19, 2005 in the constellation Cepheus. Comet C/2005 K2 (LINEAR) showed a very diffuse 8" coma with a small central condensation and a broad 1' tail in p.a. 255-275°. The comet approached earth, reaching a minimum distance of 0.64 AU on June 19 (expected maximum brightness: 14 mag) (IAUC 8533, MPEC 2005-L29).
On a CCD image Michael Jäger and Gerald Rhemann discerned the comet on May 25 at magnitude 13, showing a rather diffuse 2.5' coma. On May 29 the first visual observers estimated the comet to be of magnitude 12.5. Thereafter the evolution accelerated: on June 6 the comet was of magnitude 11.5, on June 7 of magnitude 10.5, on June 8 magnitude 10.0 and on June 9 magnitude 9.0. The coma diameter increased from 1.5' to 4'.
Then on June 12, a CCD image from Michael Jäger and Gerald Rhemann showed a fainter secondary condensation in the direction of the tail. Scrutinizing additional CCDs by other observers recognized this secondary nucleus as early as June 10 (Comets Mailing List, IAUC 8543).
According to Z. Sekanina the secondary nucleus separated already on Apr. 22, 2005 (uncertainty 2 days) from the main component. According to him this fragmentation of the nucleus facilitated the comet's discovery, but is not directly related to the flare-up around June 10. He suggested that the companion is a fragment with a limited lifespan, possibly less then 100 days (IAUC 8545).
During the first half of June the comet increased its brightness rapidly from 13 mag to 9.0 mag (around June 10). This maximum was hold for several days, only to drop rapidly afterwards. Unfortunately this fading was not observable any longer from mid-Europe since the comet had already dipped below the evening horizon. It remained unobservable from any place on Earth until the end of July. On a CCD image taken by M. Mattiazzo on the evening of Aug. 1, no object brighter than 16 mag was seen at the comet’s location. Thus the fragmentation of the nucleus was only the first stage in the process of the comet's disintegration!
Total Brightness and Coma diameter
Andreas Kammerer
