Low NH3/H2O ratio in comet C/2020 F3 (NEOWISE) at 0.7 au from the Sun

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Table 4

OH observations at NRT: line intensities and spectral characteristics.

UT date (yyyy/mm/dd)	Δ (au)	r_h (au)	υ_h (km s⁻¹)	i ⁽¹⁾	i ⁽²⁾	T_bg (K)	Area⁽³⁾ (mJy km s⁻¹ )	Δυ⁽⁴⁾ (km s⁻¹ )	(km s⁻¹)	(10²⁹ mol s⁻¹)	(10²⁹ mol s⁻¹)
				(Des)	(Sch)					(Des)	(Sch)
2020/07/02.46	1.19	0.30	−7.2	−0.31	−0.37	3.4	−30 ± 13	–	–	18.6 ± 4.8	22.0 ± 4.8
2020/07/18.54	0.72	0.53	38.5	0.20	0.28	3.1	526 ± 32	−0.41 ± 0.14	–	21.4 ± 3.8⁽⁶⁾	8.47 ± 1.17⁽⁶⁾
2020/07/19.55	0.71	0.55	38.7	0.22	0.30	3.1	379 ± 32	−0.13 ± 0.16	–	6.03 ± 0.93 ⁽⁶⁾	3.69 ± 0.48⁽⁶⁾
2020/07/20.56	0.70	0.57	38.8	0.23	0.30	3.1	491 ± 35	−0.33 ± 0.13	–	8.81 ± 1 .62⁽⁶⁾	5.14 ± 0.69⁽⁶⁾
2020/07/23.60	0.69	0.64	38.6	0.21	0.29	3.1	402 ± 20	−0.07 ± 0.09	–	5.13 ± 0.53⁽⁶⁾	3.00 ± 0.23⁽⁶⁾
2020/07/24.61	0.70	0.66	38.5	0.20	0.28	3.1	414 ± 23	−0.12 ± 0.09	2.25 ± 0.14	4.62 ± 0.38	3.41 ± 0.25
2020/07/26.63	0.71	0.71	38.2	0.17	0.25	3.1	359 ± 19	+0.05 ± 0.10	–	5.15 ± 0.59⁽⁶⁾	2.71 ± 0.23⁽⁶⁾
2020/07/27.63	0.72	0.73	38.0	0.15	0.23	3.1	279 ± 19	−0.10 ± 0.11	–	3.79 ± 0.47⁽⁶⁾	2.02 ± 0.20⁽⁶⁾

2020/06/01–2020/06/12	1.58	0.79	−37.5	−0.24	−0.26	3.4	−115 ± 5	−0.09 ± 0.06	2.44 ± 0.08	2.32 ± 0.12	2.10 ± 0.11
2020/06/14–2020/06/24	1.47	0.52	−37.7	−0.25	−0.26	3.5	−165±5	−0.20 ± 0.07	2.79 ± 0.11	8.00 ± 0.49	7.32 ± 0.50
2020/07/02–2020/07/03	1.18	0.30	−4.8	−0.23	−0.28	3.4	−49 ± 10	–	–	–	-
2020/07/18–2020/07/20	0.71	0.55	38.6	0.21	0.29	3.1	459 ± 19	−0.28 ± 0.08	2.72 ± 0.12	10.0 ± 1.1	5.30 ± 0.37
2020/07/23–2020/07/24	0.69	0.65	38.6	0.21	0.29	3.1	409 ± 14	−0.09 ± 0.06	2.35 ± 0.10	5.03 ± 0.34	3.03 ± 0.17
2020/07/26–2020/07/27	0.72	0.72	38.1	0.16	0.24	3.1	322 ± 13	−0.02 ± 0.08	1.94 ± 0.05	4.62 ± 0.41	2.40 ± 0.15

Notes. ⁽¹⁾Maser inversion from Despois et al. (1981) and corresponding inferred OH production rate. ⁽²⁾Maser inversion from Schleicher & A’Hearn (1988) and corresponding inferred OH production rate. ⁽³⁾Weighted average of the 1667 and 1665 MHz lines converted to the 1667 MHz intensity scale, assuming the statistical ratio of 1.8.⁽⁴⁾ Velocity offset from a Gaussian fit. ⁽⁵⁾Half lower bases of the fitted trapezia (Figs. 2 and 4). ⁽⁶⁾Trapezium fitting was not performed for this date. The assumed υ_p value is that deduced from the r_h evolution of υ_p measured from the 2–3 day averages over the 18–27 July 2020 period.

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