153P/Ikeya-Zhang and the comet of Hevelius

1. 153P/Ikeya-Zhang and the comet of Hevelius Mark R. Kidger Instituto de Astrofísica de Canarias

2. Why is 153P/Ikeya-Zhang important? • Before Comet Ikeya-Zhang the longest confirmed 2-return comet period was 35P/Herschel-Rigollet. • 155 years • Observed in 1788 and 1939 • 153P/Ikeya-Zhang has been the first confirmed case of a multi-return comet with P>200yrs. It may be many years before there is another. • The 1661-2002 linkage is secure. • There are proposed linkages to previous comets. • But there are some major unresolved problems with all of the previous known and suspected apparitions.

3. The comet of Hevelius (C/1661 C1) • Discovered on February 3rd 1661 in the morning sky with a 6º tail. • The comet was not discovered by Hevelius, but he carried out a study of it. • It faded rapidly and was last seen on March 28th. • Shortly after discovery Hevelius estimated it as “fainter than Altair” (around magnitude 1-1.5?) • It is assumed that his last observation on March 28th was made with the naked eye with the comet just visible. • Hevelius mentions multiple nuclei (unlikely) and a rapid decrease in condensation (plausible, because the DC decreased rapidly after perihelion in 2002).

4. Previous identifications • There has been a great effort to find previous apparitions of Ikeya-Zhang given that it is a bright comet of quite short period. • Comets are found by Nakano & by Waddington in 877 and/or 1273 that are possible previous apparitions.

5. The comet(s?) of 1273 • Ho’s comet catalogue lists a broom star seen by the Japanese (Feb. 5) in the evening sky and the Koreans (Feb. 17) in the morning sky. • The Chinese saw a “bluish white guest star with the appearance of loose cotton” in Auriga on Apr. 9th. • Ho lists the two as identical (Ho 439), although their position and movement seems incompatible with this. • Nakano links the former with 153P/Ikeya-Zhang (T = 1273 Feb. 4.8) based on the evening-morning shift.

6. The comet(s?) of 1273 • Waddington shows that the track of the Chinese comet is close to that of 153P. • Over 21 days it moved from the asterism 28////15 UMa through the bowl of the Plough to disappear near Arcturus (evening  morning sky). • The perihelion date is tightly constrained by these observations: • T=1273 Mar. 27.51 day • The latest orbit solution from 1661-2002 gives T =1272 Dec. 155 days with the known non-gravitational terms.

7. The comet(?) of 877 • The Japanese record a Guest Star in Pegasus that appeared on February 11th (Ho 307). • A comet was observed in the west from Europe for 15 days in March and a comet in China in June & July (Pingré 349) • A “Guest Star” (ko-hsing) was usually a nova, especially if no movement was recorded. A comet was a “hui-hsing” if tailed and a “po-hsing” if not. • Nakano links the Japanese and European observations with 153P.

8. The comet(?) of 877 • Yeomans states that the European comet was seen in Libra, in the south-west in the morning sky. • Nakano’s linkage puts the comet in eastern Cygnus, in the eastern sky at dawn! • Theoretically it was just visible at magnitude 3 at this time in the north-west at sunset from northern Europe, but very low in a very bright sky. • It looks very unlikely that it would have been observed in the evening sky, but would have been easy at dawn.

9. A Joker in the Pack: C/1532 R1 • Edmond Halley noticed that the orbits of C/1532 R1 and C/1661 C1 are also very similar. • Initially the preferred identification of C/2002 C1 was C/1532 R1.

10. The 1661 mystery • 1661 was a very favourable apparition: the best of the 4 returns. • The comet should have had excellent evening visibility before perihelion, but was NOT observed.

11. Why did Hevelius not see it before? • Hevelius would have had two chances to discover the comet pre-perihelion in the evening sky if it was as bright as we believe: • In late December-early January around New Moon at magnitude 2.5-3 in a dark sky. • After the January 15th Full Moon around magnitude +0.5 in twilight. • Even assuming widespread bad weather, if the comet was as bright as thought it would have been seen by someone before perihelion.

12. Two alternative explanations • An outburst at perihelion • It is a common phenomenon in comets often associated with sudden aspect changes • Hevelius’s observations of multiple nuclei But: • Hevelius’s observations are not really credible. He could not even resolve Saturn’s rings clearly! • John Bortle suggested (2002, TA, 35, 298) that Hevelius did not see the comet because of a perihelion asymmetry. But: • Not really seen in Ikeya-Zhang’s light curve.

13. If we assume that “n” was constant after perihelion... Perihelion asymmetry Post-perihelion m0 increases slowly to peak at m0=5.4 at T+90days. Too little, too late to explain Hevelius’s observations.

14. The two comets of 1273 are completely incompatible. Could the Japanese/Korean date of observation be a transcription error, as in the 4BC “Star of Bethlehem” event? Chinese data

15. Given the Nakano linkage 877 and 1273 were rather poor apparitions. In 877 Comet Ikeya-Zhang would not have passed m1=3.5 and in 1273 m1=2.9. Waddington’s 1273 linkage is even worse!!!

16. Which linkage is correct? • Nakano uses the doubtful Japanese observation in Pegasus in 877 to fix the 877 perihelion passage and works forward to 1273. • Waddington uses the detailed Chinese observations from 1273. • The observational evidence makes the Waddington linkage appear more plausible. • The European observations in 877 and the Chinese data from 1273 are difficult to fit to Nakano’s linkage.

17. How bright was the comet of 1273? • The Chinese observation of colour suggests that the comet was very bright. • If the Waddington linkage is correct the comet would have been magnitude 1.5 and fading at discovery, even if it was as bright as Hevelius’s comet. • Probably too faint to show colour!! • We must assume that it was even brighter in 1273 than in 1661.

18. How to make sense of all this? • There is evidence of a systematic fade 1273  1661  2002. • What if C/1532 R1 and 153P/Ikeya-Zhang are fragments of a single comet that split in the 1st Century AD? • The very bright (m0= 1.8) comet of 1532 would be the principal nucleus. • The descending node of 153P is close to Jupiter’s orbit and permits very close encounters. A post-split encounter with Jupiter could separate the nuclei.

19. This scenario explains the similarity of orbits between C/1532 R1 and 153P. • As a secondary (and much smaller nucleus) a systematic fade with time would be expected. • There are many possible scenarios, but one would have a splitting during an apparition in 58AD, followed by an encounter with Jupiter in 458AD that separated the fragments in T.

20. A prediction If the splitting scenario is correct, C/1532 R1 should return around the end of this century. Prepare for a potentially very bright comet with an orbit similar to Ikeya-Zhang!!