Strong detection of OH 18-cm emission from Comet C/2020 F3 (NEOWISE)
ATel #13968; Allison Smith (Arecibo Observatory/UCF), PK Manoharan (Arecibo Observatory/UCF), Anna McGilvray (Arecibo Observatory/UCF), Benetge Perera (Arecibo Observatory/UCF), Anish Roshi (Arecibo Observatory/UCF), Sravani Vaddi (Arecibo Observatory/UCF)
on 25 Aug 2020; 21:29 UT
Distributed as an Instant Email Notice Comets
Credential Certification: Benetge Perera (bhakthiperera@gmail.com)
We report radio spectroscopic observations of OH 18-cm emission from Comet C/2020 F3 (NEOWISE) performed during Director's Discretionary Time (Project code A3470) with the Arecibo Observatory. These observations took place on 2020 July 31.781 UT while the comet was at a heliocentric distance of approximately 0.82 AU. Near 1.6 GHz, the Arecibo beam size is ~3 arcminutes, and we observed a single position centered on the comet nucleus for approximately 110 minutes, thereby achieving an initial RMS of order 1 mK. The spectral backend was configured such that the spectral resolution (before smoothing) was 0.7 kHz.
We detected clearly the OH 1665 and 1667 MHz main lines from these observations. The preliminary line parameters were as follows: the line at 1667 MHz was 115+/-3 mK in amplitude and the linewidth was 2.55+/-0.08 km/s. At 1665 MHz, the line amplitude was 57+/-3 mK with a linewidth of 2.31+/-0.14 km/s. The central velocity of the detections was 34.82+/-0.03 km/s, consistent with the expected radial velocity of the comet. The relative population of the OH levels also appear consistent with the theoretical LTE ratio of 9:5 at 1667 and 1665 MHz, respectively. The preliminary fit was completed with a single gaussian model, which may indicate the frequently observed asymmetry of emission lines manifested by the Greenstein Effect was not observed in this comet at this heliocentric distance.
