ATEL #13945 ATEL #13945
Title: Rotation of Comet C/2020 F3 (NEOWISE)
Author: Michal Drahus (Jagiellonian University in Krakow), Piotr Guzik
(Jagiellonian University in Krakow), Andrew Stephens (Gemini Observatory),
Steve B. Howell (NASA Ames Research Center), Stanislaw Zola (Jagiellonian
University in Krakow), Mikolaj Sabat (Jagiellonian University in Krakow),
Daniel E. Reichart (University of North Carolina at Chapel Hill)The observed morphological evolution implies a rotation period of 7.58 +/- 0.03 hr with no obvious temporal changes or deviations from a simple rotation state over the reported time interval. This result is consistent with an earlier value of 7.5 +/- 2.3 hr reported by Masi 2020 (CBET 4816).
I decided to establish a correlation period of rotation - diameter of the nucleus, it is known that the greater the diameter the rotation of the comet nucleus is slower, and the smaller the diameter the rotation is faster, the average rotation period of many comets is approximately about 15 hours, based on Whipple's work.
In the case of comet C / 2020 F3 NEOWISE the P (rot) = 7.5 hours, analyzing other comets such as 6 P / D'Arrest, P (rot) = 7.2 h (Lowry, Weissman 2007), and a D (km) = 1.6 km (Ferrin 2009), results in a nuclear radius of Rn = 0.8 kms, another comet similar in the period of rotation to F3 NEOWISE is comet 46 P / Wirtanen, with D (km) = 0.9 kms (Fink V. et at. 1997), with a P (rot) = 7.6 h (Ferrin 2009), looking for articles with references, the most interesting is that of Sosa / Fernandez, who establish the following equation 1.0:
log D (km) = 1.5 - 0.13 * H ........... (Sosa & Fdez)
Checking this formula 1.0 I applied it to the previous results, and it was not a good fit, so I decided to apply a new personal adjustment, which is the following 1.1:
log D (km) = 1.3 - 0.13 * H ............... (Navarro)
finding a comet diameter of 0.94 kms, a value that is more in line with reality.
Another new formula that relates the activity index with the gas production rates is the following 1.2:
log Q (C2) / log Q (H2O) = - n ............... (Navarro)
Coefficient of variation of the rate of increase in brightness 1.3:
K = d (n) / d (r)
r heliocentric distance
n rate of increase in brightnes