Follow‑up imaging observations of comet 2I/Borisov

Follow‑up imaging observations of the first detected interstellar comet 2I/Borisov are presented, which were carried out with the Schmidt‑Teleskop‑Kamera at the University Observatory Jena in 11 observing epochs in October and November 2019. The orbital solution of the comet, derived from the obtained astrometric measurements, confirms its highly eccentric (e = 3.3570 ± 0.0006) and inclined (i = 44.0524 ± 0.0004°) orbit, that proves the interstellar origin of the comet. According to our best‑fitting orbital solution, comet 2I/Borisov reaches its perihelion on 2019 Dec 8 (q = 2.0066 au) and its closest encounter with Earth on 2019 Dec 28 (Δmin = 1.9368 au). The distance corrected brightness of the nucleus of the comet clearly exhibits a linear correlation with its phase angle. The slope of this correlation indicates the activity of the comet, which is also detected in deep imaging data, taken in five observing epochs, showing the coma and the tail of the comet. During our observing campaign the coma of comet 2I/Borisov exhibits on average a diameter of (4.57 ± 0.38) · 104 km, and the length of the tail of the comet measures (1.52 ± 0.12) · 105 km, assuming an anti‑solar orientation.