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C/2013 R1 (Lovejoy)


On Sep. 7, 2013 Terry Lovejoy succeeded in discovering a 14.0 mag comet on the border of the constellations Monoceros and Orion; he noted an apparent coma diameter of 0.5'. Additional observers of the comet reported a 3' coma of total magnitude 13.0 with a distinct central condensation and a fan-shaped 1' tail at p.a. 250°. The comet will pass its perihelion at the end of December 2013 and will pass Earth at a distance of only 0.40 AE on Nov. 20 (CBET 3649 / MPEC 2013-S08). In the days around perigee it should reach magnitude 7. However, the brightness will be distributed over a coma with a diameter of 10'. Thus the coma will show a rather low surface brightness. Until April 2014 the comet will pass through the constellations Monoceros, Canis Minor, Cancer, Leo Minor, Ursa Major, Canes Venatici, Bootes, Corona Borealis, Hercules, Ophiuchus and Serpens, being situated in the morning sky. Earth will cross the comet's orbital plane on Dec. 3.

During autumn 2013 the comet surprised the observers in a very positive manner. It became 1.5 mag brighter than expected, peaking at 5.0 mag around Nov. 25. Its evolution is well documented by 142 observations of 10 members of the German Comet Section and 545 international observations. These indicate a very continuous brightening prior to perihelion. Post-perihelion two periods have to be distinguished. During the first 55 days after perihelion the comet faded slowly, but thereafter much more rapidly. The appropriate formulae are as follows:

pre-perihelion: t < 0d: m = 7.1 mag + 5×log D + 12.2×log r
post-perihelion: t < +55d: m = 6.5 mag + 5×log D + 6.5×log r
post-perihelion: t > +55d: m = 5.8 mag + 5×log D + 12.5×log r

Heliocentric Magnitude versus r

Alternatively the post-perihelion evolution can be simulated rather well with the unusual formula m = 3.3 mag + 5×log D + 3.2×r.

Total Brightness and Coma Diameter

The apparent coma diameter increased slowly from 1.5' to 4' between mid-September and mid-October 2013. Thereafter the increase accelerated, which may, in part, be explained by the change in instrumentation. It reached 16' around Nov. 10 (perigee: 0.397 AU on Nov. 19). The apparent coma diameter decreased significantly slower. It measured 13' at the end of November, 9' during the Christmas days, 6' at the end of January 2014, 3.5' in mid-April and 1.5' at the start of June. The absolute coma diameter increased from 125.000 km at the start of the apparition to 225.000 km in mid-October and to 375.000 km on Nov. 10. During the days around perigee the derived absolute coma diameters indicate a shrinkage to 260.000 km. However, this could be due to a contrast problem, with the surface brightness of the outer coma regions only marginally above the sky background, which was brightened by the Moon between Nov. 15 and 27 (Full Moon was on Nov. 17). Thereafter, the derived absolute coma diameters increase again, reaching a maximum of 450.000 km in mid-January 2014. Until the start of March it shrunk quickly to 275.000 km, thereafter more slowly, reaching 160.000 km at the start of June.

Degree of condensation (Moving weighted 3-days-means)

The degree of condensation evolved symmetrical, pre- and post-perihelion. Until the start of December it increased from DC 1-2 to DC 6-7. This value was halted until mid-January. Thereafter it decreased, reaching DC 2-3 at the start of April and DC 1-2 in mid-May.

Tail Length

Between the start of November and mid-March 2014, the tail could be glimpsed visually, reaching a maximum length of 3.5° (5.5 Mio. km) during the first week of December. It was oriented toward West until mid-November, rotating towards North until mid-December, thereafter rotating back to West.

Position Angle of Tail

Andreas Kammerer

FGK observations


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