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C/2017 E4 (Lovejoy)

On Mar. 9, 2017 the Australian amateur Terry Lovejoy discovered a comet in the southwestern part of Sagittarius. He estimated the brightness of comet C/2017 E4 (Lovejoy) to be about 15.0 mag, showing an apparent coma of more than 1'. Follow-up observations showed a coma up to 2.8' in diameter with a total magnitude of 11.8 mag and a central condensation, in which a false nucleus of magnitude 14.5 could be discerned. The comet will pass perihelion on Apr. 23, 2017 at a distance of only 0.40 AU (IAUC 4373). During the weeks near perihelion it will be in conjunction with the Sun, well above the Ecliptic at first, but closing in to the Ecliptic during the following weeks, which will result in decreasing elongations. Thus it won't be an easily observable object. From mid-European locations it should be visible in the morning sky between Mar. 20 and the end of April, however at altitudes of less than 20°. During this period it will travel through the constellations Aries, Aquarius, Pegasus and Andromeda, expected to increase from magnitude 10.5 to magnitude 8.5 until mid-April, then start to fade, expected to reach 9.0 mag at the end of May.

The comet showed a rather steep brightness development during the first four weeks of its apparition, according to 95 observations from 31 observers. However, 15 days prior to perihelion (on Apr. 8) the activity suddenly ceased. The brightness deviated from the predictions in a growing manner, with the coma growing more and more diffuse, not showing a false nucleus any more. Thus, maximum brightness of 6.2 mag was reached on Apr. 8. The brightness development can be well described by the formulae

t < -15d: m = 11.7 mag + 5×log D + 23×log r
t > -15d: m = 10.0 mag + 5×log D + 0.18×(t-T)

Total Brightness and Coma Diameter

During the first four weeks the coma diameter increased equally fast from short of 1' (30.000 km) in mid-March to almost 8' (225.000 km) in early April, only to decrease to 2' (90.000 km) by Apr. 23. Whereas the coma condensed rapidly during the fast brightening phase from DC 3-4 to DC 7, it decreased rapidly after Apr. 8, reaching DC 2-3 on Apr. 23. Visually a tail was reported between Apr. 1 and 23 with a maximum length of 25' (600.000 km). It pointed westward at first and towards northwest at the end of its visual apparition.

Andreas Kammerer

FGK observations